// Package tui is the terminal interface: browse accounts, write the rules that
// tag transactions, and see where the money went.
package tui

import (
	"fmt"
	"slices"
	"sort"
	"strconv"
	"strings"
	"time"

	"github.com/charmbracelet/bubbles/spinner"
	"github.com/charmbracelet/bubbles/table"
	"github.com/charmbracelet/bubbles/textinput"
	tea "github.com/charmbracelet/bubbletea"
	"github.com/charmbracelet/lipgloss"

	"git.petrovv.com/nikola/money/internal/config"
	"git.petrovv.com/nikola/money/internal/glob"
	"git.petrovv.com/nikola/money/internal/importer"
	"git.petrovv.com/nikola/money/internal/model"
	"git.petrovv.com/nikola/money/internal/report"
	"git.petrovv.com/nikola/money/internal/rules"
	"git.petrovv.com/nikola/money/internal/store"
	"git.petrovv.com/nikola/money/internal/transfers"
)

type view int

const (
	viewAccounts view = iota
	viewTxns
	viewReport
	viewRules
	viewRuleList
	viewTransfers
	viewTransferList

	viewCount = 7
)

// confirmation is a pending destructive action awaiting a y/n answer.
// Deleting rewrites a file the user maintains by hand, so it is never done on
// a single keypress.
type confirmation int

const (
	confirmNone confirmation = iota
	confirmDeleteRule
	confirmPruneRules
	confirmDeleteTransfer
	confirmPruneTransfers
)

// previewSort is the order the rule builder lists descriptions in. The two
// answer different questions, which is why both are here rather than one being
// chosen for the user: by name is how a payee you are looking at is found, and
// by count is where the rule worth writing next is — one pattern that claims
// forty rows, rather than the first of forty patterns claiming one.
type previewSort int

const (
	sortByName previewSort = iota
	sortByCount
)

// input is the modal state: the transaction list is read-only until the user
// starts typing a search.
type input int

const (
	inputNone input = iota
	inputSearch
)

// Model is the root Bubble Tea model.
type Model struct {
	root     string
	db       *store.DB
	accounts []*config.Account
	engine   *rules.Engine
	links    *transfers.Engine

	view  view
	input input

	accountTable table.Model
	txnTable     table.Model
	reportTable  table.Model
	text         textinput.Model
	spinner      spinner.Model

	// importing is set while an import runs in the background, so the UI keeps
	// redrawing instead of freezing on a slow PDF.
	importing bool

	txns []model.Transaction // rows currently shown in txnTable

	// Rule builder: four inputs on the left, and a live preview on the right of
	// which descriptions the glob would catch.
	ruleGlob      textinput.Model
	ruleAccount   textinput.Model
	ruleTag       textinput.Model
	ruleNote      textinput.Model
	ruleFocus     int // which of the inputs has the cursor
	ruleTable     table.Model
	ruleReturn    view // the view to go back to on esc
	previewGroups []descGroup
	previewSort   previewSort
	ruleMatches   int // previewed descriptions the current glob matches
	// ruleCandidates is how many were in view before the glob filtered them,
	// which the count needs: the preview now shows only matches, so the rows on
	// screen can no longer say what they were chosen out of.
	ruleCandidates int
	// ruleDropped counts the descriptions an edit would let go of. It is only
	// ever non-zero while editing: a new rule has nothing to lose.
	ruleDropped int

	// Editing an existing rule reuses the builder rather than a second form:
	// the fields start filled in, and enter rewrites the rule where it sits
	// instead of appending. ruleEditPos is its file position, which the edit
	// must not change — that is what still breaks ties between equally specific
	// rules. ruleEditOrig is the rule as it was, so what the form does not show
	// (the type pattern) survives the round trip instead of being dropped.
	ruleEditing  bool
	ruleEditPos  int
	ruleEditOrig config.Rule

	// Rule list: every rule with the number of transactions it actually
	// claims, so dead ones can be found and removed.
	ruleListTable  table.Model
	ruleUsage      []int
	ruleListReturn view // the view to go back to on esc
	confirm        confirmation

	// Transfer builder: the two sides of a movement on the left, and on the
	// right the pairs it would form out of what is already imported, together
	// with the legs it would catch but leave unpaired.
	transferFrom      textinput.Model
	transferFromDesc  textinput.Model
	transferTo        textinput.Model
	transferToDesc    textinput.Model
	transferTolerance textinput.Model
	transferNote      textinput.Model
	transferFocus     int
	transferTable     table.Model
	transferReturn    view
	// allTxns is every transaction in the index, held so the preview can pair
	// across accounts without going back to the database on each keystroke.
	allTxns          []model.Transaction
	previewPairs     int
	previewUnmatched int
	// previewFees is what the draft's pairs would lose to fees. Every leaving
	// leg is on one account, so there is a single currency to render it in.
	previewFees      int64
	previewFeeDigits int

	// Transfer list: every definition with what it currently pairs.
	transferListTable  table.Model
	transferResult     transfers.Result
	transferListReturn view // the view to go back to on esc

	filter       store.Filter
	onlyUntagged bool

	// The report's time axis: the windows ←/→ steps along, and which one it is
	// on. It is built from the whole index rather than from the rows on screen,
	// so changing account or search does not move the axis under the cursor.
	reportPeriods []report.Period
	reportPeriod  int
	// reportOrder is how the breakdown is arranged. It is not part of the
	// filter: it changes the order of the rows, never which rows there are.
	reportOrder report.Order
	// indexEmpty is whether the index holds no transactions at all, which the
	// report's empty state has to tell apart from a period that happens to be
	// empty: one asks for an import, the other for another period.
	indexEmpty bool

	status string
	err    error
	width  int
	height int
}

var (
	titleStyle  = lipgloss.NewStyle().Bold(true).Padding(0, 1)
	statusStyle = lipgloss.NewStyle().Faint(true).Padding(0, 1)
	errStyle    = lipgloss.NewStyle().Bold(true).Foreground(lipgloss.Color("9")).Padding(0, 1)
	helpStyle   = lipgloss.NewStyle().Faint(true).Padding(0, 1)
	emptyStyle  = lipgloss.NewStyle().Padding(1, 2)

	labelStyle        = lipgloss.NewStyle().Faint(true)
	focusedLabelStyle = lipgloss.NewStyle().Bold(true).Foreground(lipgloss.Color("62"))
	// Both boxes are pinned to the same width: a focused input renders one
	// extra cell for the cursor, which would otherwise shift the border as
	// the cursor moves between fields.
	boxStyle = lipgloss.NewStyle().Border(lipgloss.RoundedBorder()).
			BorderForeground(lipgloss.Color("240")).Padding(0, 1).Width(ruleInputWidth + 2)
	focusedBoxStyle = lipgloss.NewStyle().Border(lipgloss.RoundedBorder()).
			BorderForeground(lipgloss.Color("62")).Padding(0, 1).Width(ruleInputWidth + 2)
	// flatBoxStyle is the same field with its border dropped, for a form too
	// tall for the terminal. The padding puts the value in the same column the
	// border's own padding would, so the fields still line up beside a boxed one.
	flatBoxStyle    = lipgloss.NewStyle().PaddingLeft(2).Width(ruleInputWidth + 2)
	hintStyle       = lipgloss.NewStyle().Faint(true).PaddingLeft(2)
	matchCountStyle = lipgloss.NewStyle().Bold(true).PaddingLeft(2)
	ruleFormStyle   = lipgloss.NewStyle().Width(ruleFormWidth)

	// The report's time axis. The header is bold and indented like the table's
	// own header beside it, so the two panels read as one grid.
	periodHeaderStyle   = lipgloss.NewStyle().Bold(true).PaddingLeft(2).Width(periodListWidth)
	periodStyle         = lipgloss.NewStyle().Faint(true).Width(periodListWidth)
	periodSelectedStyle = lipgloss.NewStyle().Bold(true).Foreground(lipgloss.Color("62")).Width(periodListWidth)
)

// Run starts the interface.
func Run(root string, db *store.DB, accounts []*config.Account, engine *rules.Engine,
	links *transfers.Engine) error {

	m := New(root, db, accounts, engine, links)
	if err := m.reload(); err != nil {
		return err
	}
	_, err := tea.NewProgram(m, tea.WithAltScreen()).Run()
	return err
}

// New builds the root model.
func New(root string, db *store.DB, accounts []*config.Account, engine *rules.Engine,
	links *transfers.Engine) *Model {

	ti := textinput.New()
	ti.Prompt = ""
	ti.CharLimit = 64

	newInput := func(placeholder string) textinput.Model {
		in := textinput.New()
		in.Prompt = ""
		in.CharLimit = 80
		in.Width = ruleInputWidth
		in.Placeholder = placeholder
		return in
	}

	// Account slugs and tags are typed over and over, and a typo in either
	// silently produces a rule that catches nothing, so both fields complete
	// against what already exists.
	completing := func(in textinput.Model) textinput.Model {
		in.ShowSuggestions = true
		return in
	}

	sp := spinner.New()
	sp.Spinner = spinner.Dot
	sp.Style = lipgloss.NewStyle().Foreground(lipgloss.Color("62"))

	styles := table.DefaultStyles()
	styles.Header = styles.Header.Bold(true)
	styles.Selected = styles.Selected.Bold(true).Foreground(lipgloss.Color("15")).Background(lipgloss.Color("62"))

	newTable := func(cols []table.Column) table.Model {
		return table.New(table.WithColumns(cols), table.WithFocused(true),
			table.WithHeight(15), table.WithStyles(styles))
	}

	m := &Model{
		root:     root,
		db:       db,
		accounts: accounts,
		engine:   engine,
		links:    links,
		view:     viewAccounts,
		text:     ti,
		spinner:  sp,
		accountTable: newTable([]table.Column{
			{Title: "Account", Width: 20},
			{Title: "Balance", Width: 14},
			{Title: "Cur", Width: 4},
			{Title: "Txns", Width: 6},
		}),
		txnTable: newTable([]table.Column{
			{Title: "Date", Width: 10},
			{Title: "Account", Width: 12},
			{Title: "Amount", Width: 12},
			{Title: "Tag", Width: 14},
			{Title: "Description", Width: 40},
		}),
		ruleGlob:    newInput("*LIDL*"),
		ruleAccount: completing(newInput("blank = every account")),
		ruleTag:     completing(newInput("groceries")),
		ruleNote:    newInput("optional"),
		ruleTable: newTable([]table.Column{
			{Title: " ", Width: 1},
			{Title: "Untagged description", Width: 44},
			{Title: "N", Width: 4},
		}),
		ruleListTable: newTable([]table.Column{
			{Title: "#", Width: 3},
			{Title: " ", Width: 1},
			{Title: "Pattern", Width: 34},
			{Title: "Account", Width: 12},
			{Title: "Tag", Width: 14},
			{Title: "Txns", Width: 6},
			{Title: "Note", Width: 24},
		}),
		transferFrom:      completing(newInput("nlb")),
		transferFromDesc:  newInput("*TO REVOLUT*"),
		transferTo:        completing(newInput("revolut")),
		transferToDesc:    newInput("*FROM NLB*"),
		transferTolerance: newInput("0"),
		transferNote:      newInput("optional"),
		transferTable: newTable([]table.Column{
			{Title: " ", Width: 1},
			{Title: "Date", Width: 10},
			// Wide enough for both sides of an exchange, e.g. "500.00 → 977.90".
			{Title: "Amount", Width: 20},
			{Title: "Movement", Width: 22},
			{Title: "Description", Width: 30},
		}),
		transferListTable: newTable([]table.Column{
			{Title: "#", Width: 3},
			{Title: " ", Width: 1},
			{Title: "From", Width: 26},
			{Title: "To", Width: 26},
			{Title: "Pairs", Width: 6},
			{Title: "Unpaired", Width: 9},
			{Title: "Tol", Width: 6},
			{Title: "Note", Width: 20},
		}),
		reportTable: newTable(slices.Clone(reportColumns)),
	}
	// The default order needs its marker as much as a chosen one does.
	m.markSortedColumn()
	return m
}

// reportColumns are the report's headings before the sort marker is added.
// They live here rather than being written into the table once, because
// markSortedColumn rebuilds them every time the order changes.
var reportColumns = []table.Column{
	{Title: "Tag", Width: 20},
	{Title: "Cur", Width: 4},
	{Title: "Out", Width: 14},
	{Title: "In", Width: 14},
	{Title: "Net", Width: 14},
	{Title: "N", Width: 5},
}

// markSortedColumn moves the marker onto the heading the rows are ordered by,
// so the sort is visible where it is acting rather than only in the key list.
func (m *Model) markSortedColumn() {
	marker := " ▾"
	if m.reportOrder.Ascending() {
		marker = " ▴"
	}
	cols := slices.Clone(reportColumns)
	for i := range cols {
		if cols[i].Title == m.reportOrder.Column() {
			cols[i].Title += marker
			break
		}
	}
	m.reportTable.SetColumns(cols)
}

// setOrder cycles the report to the next arrangement of the same rows.
func (m *Model) setOrder(o report.Order) {
	m.reportOrder = o
	m.markSortedColumn()
	m.status = "sort: " + o.Label()
	m.reportTable.SetCursor(0)
	m.err = m.reloadReport()
}

// Init implements tea.Model.
func (m *Model) Init() tea.Cmd { return nil }

// reload refreshes whichever view is active from the index.
func (m *Model) reload() error {
	if err := m.reloadAccounts(); err != nil {
		return err
	}
	if err := m.reloadPeriods(); err != nil {
		return err
	}
	return m.reloadTxns()
}

// reloadPeriods rebuilds the report's time axis from the months the index now
// holds, staying on the window the user was looking at if it is still there.
// An import that reaches further back grows the axis, so it cannot simply be
// built once at startup; but it must not throw the user back to the default
// either, since the import they just ran is usually the reason they are looking.
func (m *Model) reloadPeriods() error {
	months, err := m.db.Months()
	if err != nil {
		return err
	}
	var was string
	if p, ok := m.currentPeriod(); ok {
		was = p.Label
	}
	m.indexEmpty = len(months) == 0
	m.reportPeriods = report.Periods(time.Now(), months)
	m.reportPeriod = report.DefaultIndex(m.reportPeriods)
	for i, p := range m.reportPeriods {
		if p.Label == was {
			m.reportPeriod = i
			break
		}
	}
	return nil
}

// currentPeriod is the window the report is on, if the axis has been built.
func (m *Model) currentPeriod() (report.Period, bool) {
	if m.reportPeriod < 0 || m.reportPeriod >= len(m.reportPeriods) {
		return report.Period{}, false
	}
	return m.reportPeriods[m.reportPeriod], true
}

// setPeriod moves the report along its axis, clamping at both ends: the axis
// runs from all time down to the oldest month, and wrapping round from one to
// the other would land somewhere nobody aimed for.
func (m *Model) setPeriod(i int) {
	if i < 0 || i >= len(m.reportPeriods) || i == m.reportPeriod {
		return
	}
	m.reportPeriod = i
	m.status = "period: " + m.reportPeriods[i].String()
	m.reportTable.SetCursor(0)
	m.err = m.reloadReport()
}

func (m *Model) reloadAccounts() error {
	accounts, err := m.db.Accounts()
	if err != nil {
		return err
	}
	rows := make([]table.Row, 0, len(accounts))
	for _, a := range accounts {
		bal, err := m.db.Balance(a.ID)
		if err != nil {
			return err
		}
		n, err := m.db.Count(a.ID)
		if err != nil {
			return err
		}
		rows = append(rows, table.Row{
			a.Name, model.FormatMinor(bal, a.MinorDigits), a.Currency, fmt.Sprintf("%d", n),
		})
	}
	m.accountTable.SetRows(rows)
	return nil
}

func (m *Model) reloadTxns() error {
	f := m.filter
	f.Untagged = m.onlyUntagged
	txns, err := m.db.Transactions(f)
	if err != nil {
		return err
	}
	m.txns = txns

	rows := make([]table.Row, 0, len(txns))
	for _, t := range txns {
		rows = append(rows, table.Row{
			t.Date, t.AccountSlug, t.FormatAmount(), t.DisplayTag(), t.Description,
		})
	}
	// Keep the cursor in range after the row count shrinks (e.g. a new rule
	// tagging the last untagged row while the untagged filter is on).
	cursor := m.txnTable.Cursor()
	m.txnTable.SetRows(rows)
	if cursor >= len(rows) {
		cursor = len(rows) - 1
	}
	if cursor < 0 {
		cursor = 0
	}
	m.txnTable.SetCursor(cursor)

	return m.reloadReport()
}

// The two rows the report grows below TOTAL. They are bracketed like
// report.Untagged and model.TransferTag because they are the same kind of
// thing: a label the tool supplies for something no rule named. Neither is a
// tag, and neither can be matched or completed against.
const (
	transfersRow = "(transfers)"
	feesRow      = "  ⤷ fees"
)

// reloadReport re-queries under the report's own time window.
//
// It cannot reuse the rows the transaction list is showing: the period narrows
// the report and only the report, so that opening on last month does not also
// hide the rest of the index from the list beside it. Everything else about the
// scope — the account, the search, the untagged toggle — is shared, so the two
// screens still answer for the same selection of transactions.
func (m *Model) reloadReport() error {
	f := m.filter
	f.Untagged = m.onlyUntagged
	if p, ok := m.currentPeriod(); ok {
		f.From, f.To = p.From, p.To
	}
	txns, err := m.db.Transactions(f)
	if err != nil {
		return err
	}

	rows := report.ByTag(txns, m.reportOrder)
	out := make([]table.Row, 0, len(rows)+2)
	for _, r := range rows {
		out = append(out, table.Row{
			r.Tag, r.Currency,
			model.FormatMinor(r.Out, r.Digits),
			model.FormatMinor(r.In, r.Digits),
			model.FormatMinor(r.Net(), r.Digits),
			fmt.Sprintf("%d", r.Count),
		})
	}
	for _, c := range report.Totals(rows) {
		out = append(out, table.Row{
			"TOTAL", c.Currency,
			model.FormatMinor(c.Out, c.Digits),
			model.FormatMinor(c.In, c.Digits),
			model.FormatMinor(c.Net(), c.Digits),
			"",
		})
	}
	// Below the total, what ByTag held out — otherwise the report quietly
	// disagrees with the account balances by the amount moved between accounts,
	// and by any fee a tolerant definition swallowed along with it.
	for _, x := range report.Excluded(txns) {
		out = append(out, table.Row{
			transfersRow, x.Currency,
			model.FormatMinor(x.Out, x.Digits),
			model.FormatMinor(x.In, x.Digits),
			model.FormatMinor(x.In-x.Out, x.Digits),
			fmt.Sprintf("%d", x.Legs),
		})
		if x.Fee != 0 {
			out = append(out, table.Row{
				feesRow, x.Currency,
				model.FormatMinor(x.Fee, x.Digits), "",
				model.FormatMinor(-x.Fee, x.Digits),
				fmt.Sprintf("%d", x.Pairs),
			})
		}
	}
	m.reportTable.SetRows(out)
	return nil
}

// ruleFormWidth is the width of the rule builder's left-hand form, and
// ruleInputWidth the editable area inside its boxes. The form must stay wider
// than a box plus its border, padding and the block cursor, or lipgloss wraps
// the border and the panel falls apart.
const (
	ruleInputWidth = 26
	ruleFormWidth  = ruleInputWidth + 12
)

// descGroup is one distinct description the builder previews against, and how
// often it occurs. Grouping matters: a statement holds the same payee dozens of
// times, and a rule is written against the description, not against individual
// rows.
type descGroup struct {
	Description string
	Accounts    map[string]bool
	Count       int
	// Claimed marks a description the rule being edited currently tags. Nothing
	// sets it for a new rule, where every candidate is untagged by definition.
	Claimed bool
}

// reloadPreviewGroups rebuilds the alphabetical list of descriptions the rule
// builder previews against: everything still waiting for a rule, plus — when a
// rule is being edited — what that rule already claims.
//
// The addition is what makes editing legible. Those rows are tagged, so none of
// them is in the untagged list, and the preview for a rule that works perfectly
// would otherwise be empty. They are also exactly what an edit is judged
// against: narrowing a glob is a decision about which of them to let go.
func (m *Model) reloadPreviewGroups() error {
	txns, err := m.db.Transactions(store.Filter{Untagged: true})
	if err != nil {
		return err
	}
	claimedFrom := len(txns) // everything appended below is claimed by the edited rule
	if m.ruleEditing {
		seen := make(map[int64]bool, len(txns))
		for _, t := range txns {
			seen[t.ID] = true
		}
		all, err := m.db.Transactions(store.Filter{})
		if err != nil {
			return err
		}
		for _, t := range all {
			// An index written before rules.toml last changed can hold a row
			// that is untagged on disk and claimed by the engine in memory;
			// counting it twice would overstate the group.
			if seen[t.ID] || m.engine.MatchIndex(t.AccountSlug, t) != m.ruleEditPos {
				continue
			}
			txns = append(txns, t)
		}
	}

	byDesc := map[string]*descGroup{}
	for i, t := range txns {
		key := model.NormalizeDescription(t.Description)
		g, ok := byDesc[key]
		if !ok {
			g = &descGroup{Description: t.Description, Accounts: map[string]bool{}}
			byDesc[key] = g
		}
		g.Accounts[t.AccountSlug] = true
		g.Count++
		g.Claimed = g.Claimed || i >= claimedFrom
	}

	m.previewGroups = make([]descGroup, 0, len(byDesc))
	for _, g := range byDesc {
		m.previewGroups = append(m.previewGroups, *g)
	}
	m.sortPreviewGroups()
	return nil
}

// sortPreviewGroups puts the preview in the order the user last chose, marks
// the column it is sorted by, and re-renders it.
func (m *Model) sortPreviewGroups() {
	sort.Slice(m.previewGroups, func(i, j int) bool {
		a, b := m.previewGroups[i], m.previewGroups[j]
		// Count first when asked, but ties still fall back to the alphabetical
		// order rather than to map order, or the list would reshuffle under the
		// cursor every time it is rebuilt.
		if m.previewSort == sortByCount && a.Count != b.Count {
			return a.Count > b.Count
		}
		x, y := model.NormalizeDescription(a.Description), model.NormalizeDescription(b.Description)
		if x != y {
			return x < y
		}
		return a.Description < b.Description
	})

	// Each column says what is in it. The description changes with the mode —
	// an edit's rows are on screen precisely because they are *not* waiting for
	// a rule — and the ↓ names the column the order is read from, since two
	// sorts of one list are otherwise told apart only by squinting at it.
	cols := m.ruleTable.Columns()
	cols[1].Title = "Untagged description"
	if m.ruleEditing {
		cols[1].Title = "Description"
	}
	cols[2].Title = "N"
	if m.previewSort == sortByCount {
		cols[2].Title += " ↓"
	} else {
		cols[1].Title += " ↓"
	}
	m.ruleTable.SetColumns(cols)

	m.refreshRulePreview()
}

// refreshRulePreview re-filters the preview against whatever is typed right
// now. It runs on every keystroke, so the glob is checked against descriptions
// only, never against the database.
//
// Once a glob is typed the list is exactly what the rule would claim: the
// non-matching rows go, rather than staying on as unmarked context. With the
// glob still empty there is nothing to filter by, so the list is everything
// still waiting for a rule — which is the other question this screen answers.
// Either way the count beside the form is measured against everything in view,
// so a glob that has narrowed the list to three of forty still says so.
//
// A description the rule being edited currently tags is the one exception to
// the rows going: losing one is the thing worth seeing before saving, so it
// stays on screen marked “−” instead of vanishing silently with the rest.
func (m *Model) refreshRulePreview() {
	var (
		pattern = strings.TrimSpace(m.ruleGlob.Value())
		account = strings.TrimSpace(m.ruleAccount.Value())
		rows    = make([]table.Row, 0, len(m.previewGroups))
	)
	m.ruleMatches, m.ruleCandidates, m.ruleDropped = 0, 0, 0

	for _, g := range m.previewGroups {
		// An account filter narrows the preview the same way the saved rule
		// will narrow its matching.
		inAccount := account == "" || g.Accounts[account]
		if inAccount {
			m.ruleCandidates++
		}
		matched := inAccount &&
			(pattern == "" || glob.Match(pattern, model.NormalizeDescription(g.Description)))

		marker := " "
		switch {
		case matched && pattern != "":
			marker = "▸"
			m.ruleMatches++
		case matched:
			// No glob yet, so the row is context rather than an answer.
		case g.Claimed:
			marker = "−"
			m.ruleDropped++
		default:
			continue
		}
		rows = append(rows, table.Row{marker, g.Description, fmt.Sprintf("%d", g.Count)})
	}

	cursor := m.ruleTable.Cursor()
	m.ruleTable.SetRows(rows)
	if cursor >= len(rows) {
		cursor = len(rows) - 1
	}
	if cursor < 0 {
		cursor = 0
	}
	m.ruleTable.SetCursor(cursor)
}

// saveRule writes the composed rule to rules.toml — appending it, or rewriting
// the rule being edited in place — then reloads the engine and retags, so the
// effect is visible immediately.
func (m *Model) saveRule() error {
	r := config.Rule{
		Match:   strings.TrimSpace(m.ruleGlob.Value()),
		Account: strings.TrimSpace(m.ruleAccount.Value()),
		Tag:     strings.TrimSpace(m.ruleTag.Value()),
		Note:    strings.TrimSpace(m.ruleNote.Value()),
	}
	if m.ruleEditing {
		// The form has no type field, so an edit carries the rule's type
		// through untouched rather than quietly dropping a pattern it never
		// showed the user. It is also why a type rule can have no glob at all.
		r.Type = m.ruleEditOrig.Type
	}
	if r.Match == "" && r.Type == "" {
		return fmt.Errorf("enter a glob first, e.g. *LIDL*")
	}
	if r.Tag == "" {
		return fmt.Errorf("enter a tag to apply")
	}
	if r.Account != "" && !m.knownAccount(r.Account) {
		return fmt.Errorf("no account called %q; leave it blank to apply to every account", r.Account)
	}

	if m.ruleEditing {
		if err := config.ReplaceRule(m.root, m.ruleEditPos, r); err != nil {
			return err
		}
	} else if err := config.AppendRule(m.root, r); err != nil {
		return err
	}
	if err := m.reloadConfig(); err != nil {
		return fmt.Errorf("rule saved, but re-reading rules.toml failed: %w", err)
	}

	n, err := m.engine.Retag(m.db)
	if err != nil {
		return err
	}

	if m.ruleEditing {
		m.status = fmt.Sprintf("rule %d is now %s → %s, %d transactions retagged",
			m.ruleEditPos+1, rulePattern(r), r.Tag, n)
		// The account came from the rule rather than from the user, so it goes
		// with the rest; an appended rule keeps it, since the next one written
		// is usually for the same account.
		m.ruleEditing = false
		m.ruleEditOrig = config.Rule{}
		m.ruleAccount.SetValue("")
	} else {
		m.status = fmt.Sprintf("saved rule %s → %s, %d transactions retagged", r.Match, r.Tag, n)
	}
	m.ruleGlob.SetValue("")
	m.ruleTag.SetValue("")
	m.ruleNote.SetValue("")
	m.setRuleFocus(0)
	if err := m.reloadSuggestions(); err != nil {
		return err
	}
	return m.reload()
}

// reloadConfig re-reads rules.toml and rebuilds both engines from it, rather
// than patching the in-memory ones, so what runs is exactly what is now on
// disk. Both are rebuilt together because both come out of the same file.
func (m *Model) reloadConfig() error {
	loaded, err := config.LoadRules(m.root)
	if err != nil {
		return err
	}
	m.engine = rules.New(loaded)
	m.links = transfers.New(loaded)
	return nil
}

func (m *Model) knownAccount(slug string) bool {
	return slices.Contains(m.accountSlugs(), slug)
}

// accountSlugs lists every account slug worth completing: those configured on
// disk, plus those the index already holds so accounts still resolve when the
// caller passed no config (as the tests do).
func (m *Model) accountSlugs() []string {
	configured := make([]string, 0, len(m.accounts))
	for _, a := range m.accounts {
		configured = append(configured, a.Slug)
	}
	var imported []string
	if accounts, err := m.db.Accounts(); err == nil {
		for _, a := range accounts {
			imported = append(imported, a.Slug)
		}
	}
	return sortedSet(configured, imported)
}

// knownTags lists the tags in use in the index plus those only named by a rule.
// A rule that has not caught anything yet is exactly where a tag lives before
// it appears on a transaction, and those are the ones most likely to be
// mistyped into a second, near-identical tag.
func (m *Model) knownTags() ([]string, error) {
	tagged, err := m.db.Tags()
	if err != nil {
		return nil, err
	}
	rs := m.engine.Rules()
	fromRules := make([]string, 0, len(rs))
	for _, r := range rs {
		fromRules = append(fromRules, r.Tag)
	}
	return sortedSet(tagged, fromRules), nil
}

// sortedSet merges the groups into one sorted list with blanks and duplicates
// removed. Completion cycles in this order, so it has to be stable.
func sortedSet(groups ...[]string) []string {
	seen := map[string]bool{}
	var out []string
	for _, g := range groups {
		for _, v := range g {
			if v == "" || seen[v] {
				continue
			}
			seen[v] = true
			out = append(out, v)
		}
	}
	sort.Strings(out)
	return out
}

// reloadSuggestions refreshes what the account and tag fields complete against.
// It runs whenever the builder is opened and after every save, since saving a
// rule can introduce a tag that did not exist a moment ago.
func (m *Model) reloadSuggestions() error {
	m.ruleAccount.SetSuggestions(m.accountSlugs())
	tags, err := m.knownTags()
	if err != nil {
		return err
	}
	m.ruleTag.SetSuggestions(tags)
	return nil
}

// pendingCompletion returns the suggestion an input is currently offering, or
// "" when there is nothing left to accept. Matching is case-insensitive, so a
// suggestion differing only in case is not worth rewriting what was typed.
func pendingCompletion(in *textinput.Model) string {
	s := in.CurrentSuggestion()
	if s == "" || strings.EqualFold(s, in.Value()) {
		return ""
	}
	return s
}

// acceptCompletion takes the offered completion into the field, reporting
// whether there was one. The suggestion list is re-set afterwards because
// SetValue does not re-match it, which would otherwise leave ctrl+n cycling
// through candidates that no longer share the new prefix.
func acceptCompletion(in *textinput.Model) bool {
	s := pendingCompletion(in)
	if s == "" {
		return false
	}
	in.SetValue(s)
	in.CursorEnd()
	in.SetSuggestions(in.AvailableSuggestions())
	return true
}

// reloadRuleList counts, for every rule, how many transactions it actually
// claims. A rule can match nothing because no description fits it, or because
// a more specific rule already took everything it would have caught; both show
// up here as a zero. The rows stay in file order — that is the number the user
// can find in rules.toml, and precedence is not read off it any more.
func (m *Model) reloadRuleList() error {
	txns, err := m.db.Transactions(store.Filter{})
	if err != nil {
		return err
	}
	rs := m.engine.Rules()
	m.ruleUsage = m.engine.Usage(txns)

	rows := make([]table.Row, 0, len(rs))
	for i, r := range rs {
		marker := " "
		if m.ruleUsage[i] == 0 {
			marker = "✗"
		}
		account := r.Account
		if account == "" {
			account = "(all)"
		}
		rows = append(rows, table.Row{
			fmt.Sprintf("%d", i+1), marker, rulePattern(r), account, r.Tag,
			fmt.Sprintf("%d", m.ruleUsage[i]), r.Note,
		})
	}

	cursor := m.ruleListTable.Cursor()
	m.ruleListTable.SetRows(rows)
	if cursor >= len(rows) {
		cursor = len(rows) - 1
	}
	if cursor < 0 {
		cursor = 0
	}
	m.ruleListTable.SetCursor(cursor)
	return nil
}

// rulePattern renders whichever patterns a rule sets, labelled so a type rule
// is not mistaken for a description one.
func rulePattern(r config.Rule) string {
	var parts []string
	if r.Match != "" {
		parts = append(parts, r.Match)
	}
	if r.Type != "" {
		parts = append(parts, "type:"+r.Type)
	}
	return strings.Join(parts, " + ")
}

// unusedRules lists the positions of every rule claiming no transactions.
func (m *Model) unusedRules() []int {
	var out []int
	for i, n := range m.ruleUsage {
		if n == 0 {
			out = append(out, i)
		}
	}
	return out
}

// deleteRules removes rules from rules.toml, then reloads and retags so the
// counts on screen reflect the new file.
func (m *Model) deleteRules(positions []int) error {
	n, err := config.DeleteRules(m.root, positions)
	if err != nil {
		return err
	}
	if err := m.reloadConfig(); err != nil {
		return fmt.Errorf("rules deleted, but re-reading rules.toml failed: %w", err)
	}

	retagged, err := m.engine.Retag(m.db)
	if err != nil {
		return err
	}
	m.status = fmt.Sprintf("deleted %d rule(s), %d transactions retagged", n, retagged)

	if err := m.reload(); err != nil {
		return err
	}
	return m.reloadRuleList()
}

// openRuleList switches to the rule list, remembering where to return to.
func (m *Model) openRuleList() {
	if m.view != viewRuleList && m.view != viewRules {
		m.ruleListReturn = m.view
	}
	m.showRuleList()
}

// showRuleList switches to the rule list without recording where esc goes.
// Coming back from the builder must not record it as the way out, or esc from
// the list would bounce back into the form the user just left.
func (m *Model) showRuleList() {
	m.view = viewRuleList
	m.confirm = confirmNone
	if err := m.reloadRuleList(); err != nil {
		m.err = err
	}
}

// updateRuleList drives the rule list, including the delete confirmations.
func (m *Model) updateRuleList(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
	if m.confirm != confirmNone {
		pending := m.confirm
		m.confirm = confirmNone
		if msg.String() != "y" {
			m.status = "cancelled"
			return m, nil
		}
		m.err = nil
		switch pending {
		case confirmDeleteRule:
			if i := m.ruleListTable.Cursor(); i >= 0 && i < len(m.ruleUsage) {
				if err := m.deleteRules([]int{i}); err != nil {
					m.err = err
				}
			}
		case confirmPruneRules:
			if err := m.deleteRules(m.unusedRules()); err != nil {
				m.err = err
			}
		}
		return m, nil
	}

	switch msg.String() {
	case "q", "ctrl+c":
		return m, tea.Quit
	case "esc":
		m.view = m.ruleListReturn
		return m, nil
	case "1":
		m.view = viewAccounts
		return m, nil
	case "2":
		m.view = viewTxns
		return m, nil
	case "3":
		m.view = viewReport
		return m, nil
	case "4":
		return m, m.openRuleBuilder()
	case "6":
		return m, m.openTransferBuilder()
	case "7":
		m.openTransferList()
		return m, nil

	case "e":
		return m, m.openRuleEditor(m.ruleListTable.Cursor())

	case "d":
		i := m.ruleListTable.Cursor()
		rs := m.engine.Rules()
		if i < 0 || i >= len(rs) {
			return m, nil
		}
		m.confirm = confirmDeleteRule
		m.status = fmt.Sprintf("delete rule %d (%s → %s), used by %d transactions? y/n",
			i+1, rulePattern(rs[i]), rs[i].Tag, m.ruleUsage[i])
		return m, nil

	case "p":
		unused := m.unusedRules()
		if len(unused) == 0 {
			m.status = "no unused rules to prune"
			return m, nil
		}
		m.confirm = confirmPruneRules
		m.status = fmt.Sprintf("delete all %d rules that match nothing? y/n", len(unused))
		return m, nil

	case "r":
		m.err = m.reloadRuleList()
		m.status = "counts refreshed"
		return m, nil
	}

	var cmd tea.Cmd
	m.ruleListTable, cmd = m.ruleListTable.Update(msg)
	return m, cmd
}

// openRuleBuilder switches to the rule builder on a new rule, seeding the
// account field from whatever account is being browsed.
func (m *Model) openRuleBuilder() tea.Cmd {
	// Leaving an edit, the fields still hold that rule. A new rule starting out
	// as a copy of the one just edited would be saved as a second, almost
	// identical rule, so the form is emptied on the way out of edit mode.
	if m.ruleEditing {
		m.ruleEditing = false
		m.ruleEditOrig = config.Rule{}
		for _, in := range m.ruleInputs() {
			in.SetValue("")
		}
	}
	if m.ruleAccount.Value() == "" && m.filter.AccountSlug != "" {
		m.ruleAccount.SetValue(m.filter.AccountSlug)
	}
	return m.showRuleBuilder()
}

// openRuleEditor switches to the rule builder on the rule at a file position:
// the fields start filled in from it, and saving rewrites it where it sits
// rather than appending a near-duplicate.
func (m *Model) openRuleEditor(pos int) tea.Cmd {
	rs := m.engine.Rules()
	if pos < 0 || pos >= len(rs) {
		return nil
	}
	r := rs[pos]
	m.ruleEditing, m.ruleEditPos, m.ruleEditOrig = true, pos, r
	m.ruleGlob.SetValue(r.Match)
	m.ruleAccount.SetValue(r.Account)
	m.ruleTag.SetValue(r.Tag)
	m.ruleNote.SetValue(r.Note)
	return m.showRuleBuilder()
}

// showRuleBuilder switches to the builder and loads what the preview needs,
// remembering where to return to on esc.
func (m *Model) showRuleBuilder() tea.Cmd {
	if m.view != viewRules {
		m.ruleReturn = m.view
	}
	m.view = viewRules
	m.setRuleFocus(0)
	if err := m.reloadSuggestions(); err != nil {
		m.err = err
	}
	// Last: what the preview lists depends on whether a rule is being edited.
	if err := m.reloadPreviewGroups(); err != nil {
		m.err = err
	}
	return textinput.Blink
}

// ruleInputs lists the form fields in tab order.
func (m *Model) ruleInputs() []*textinput.Model {
	return []*textinput.Model{&m.ruleGlob, &m.ruleAccount, &m.ruleTag, &m.ruleNote}
}

// setRuleFocus moves the cursor between the form fields, wrapping around.
func (m *Model) setRuleFocus(i int) { m.ruleFocus = focusField(m.ruleInputs(), i) }

// focusField gives the cursor to one field of a form and takes it from the
// rest, wrapping the index so tabbing past either end comes back round.
func focusField(inputs []*textinput.Model, i int) int {
	n := len(inputs)
	focus := ((i % n) + n) % n
	for j, in := range inputs {
		if j == focus {
			in.Focus()
			in.CursorEnd()
			continue
		}
		in.Blur()
	}
	return focus
}

// openTransferBuilder switches to the transfer builder, remembering where to
// return to and loading the transactions the preview pairs against.
func (m *Model) openTransferBuilder() tea.Cmd {
	if m.view != viewTransfers {
		m.transferReturn = m.view
	}
	m.view = viewTransfers
	m.setTransferFocus(0)

	slugs := m.accountSlugs()
	m.transferFrom.SetSuggestions(slugs)
	m.transferTo.SetSuggestions(slugs)

	// The preview pairs across accounts, so it needs everything, not the
	// filtered view the transaction list is showing.
	txns, err := m.db.Transactions(store.Filter{})
	if err != nil {
		m.err = err
	}
	m.allTxns = txns
	m.refreshTransferPreview()
	return textinput.Blink
}

// transferInputs lists the form fields in tab order: the two sides in the
// order the money travels, then the tolerance and the note.
func (m *Model) transferInputs() []*textinput.Model {
	return []*textinput.Model{
		&m.transferFrom, &m.transferFromDesc,
		&m.transferTo, &m.transferToDesc,
		&m.transferTolerance, &m.transferNote,
	}
}

// setTransferFocus moves the cursor between the form fields, wrapping around.
func (m *Model) setTransferFocus(i int) {
	m.transferFocus = focusField(m.transferInputs(), i)
}

// draftTransfer is the definition the form currently describes. A tolerance
// that does not parse yet previews as none at all — the field is retyped a
// character at a time, and "1." must not stop the preview from updating.
// saveTransfer is where a bad value is refused.
func (m *Model) draftTransfer() config.Transfer {
	pct, _ := m.draftTolerance()
	return config.Transfer{
		FromAccount:  strings.TrimSpace(m.transferFrom.Value()),
		FromDesc:     strings.TrimSpace(m.transferFromDesc.Value()),
		ToAccount:    strings.TrimSpace(m.transferTo.Value()),
		ToDesc:       strings.TrimSpace(m.transferToDesc.Value()),
		TolerancePct: pct,
		Note:         strings.TrimSpace(m.transferNote.Value()),
	}
}

// draftTolerance reads the tolerance field. Empty means none, which is what a
// definition without the key means too.
func (m *Model) draftTolerance() (float64, error) {
	s := strings.TrimSpace(strings.TrimSuffix(strings.TrimSpace(m.transferTolerance.Value()), "%"))
	if s == "" {
		return 0, nil
	}
	pct, err := strconv.ParseFloat(s, 64)
	if err != nil {
		return 0, fmt.Errorf("tolerance %q is not a number", s)
	}
	return pct, nil
}

// refreshTransferPreview re-pairs against whatever is typed right now.
//
// The draft is analysed *after* the definitions already on disk, exactly where
// saving would put it, so the preview cannot promise pairs that an existing
// definition would claim first. A half-written definition still previews: the
// side that is filled in shows its legs as unpaired, which is the fastest way
// to see that a glob is wrong.
func (m *Model) refreshTransferPreview() {
	draft := m.draftTransfer()
	defs := append(append([]config.Transfer(nil), m.links.Transfers()...), draft)
	res := transfers.New(&config.Rules{Transfer: defs}).Analyze(m.allTxns)
	mine := len(defs) - 1

	type entry struct {
		date string
		row  table.Row
	}
	var entries []entry
	m.previewFees, m.previewFeeDigits = 0, 0
	for _, p := range res.Pairs {
		if p.Def != mine {
			continue
		}
		m.previewFees += p.Fee()
		m.previewFeeDigits = p.Out.MinorDigits
		// Whenever the two legs disagree, both numbers are worth seeing: across
		// currencies they are the only place the rate the bank used shows up,
		// and within one they are the fee a tolerance let through, which is
		// exactly the thing to eyeball before saving the definition.
		amount := model.FormatMinor(-p.Out.AmountMinor, p.Out.MinorDigits)
		if p.In.Currency != p.Out.Currency || p.Fee() != 0 {
			amount += " → " + model.FormatMinor(p.In.AmountMinor, p.In.MinorDigits)
		}
		entries = append(entries, entry{p.Out.Date, table.Row{
			"▸", p.Out.Date, amount,
			p.Out.AccountSlug + " → " + p.In.AccountSlug, p.Out.Description,
		}})
	}
	for _, l := range res.Unmatched {
		if l.Def != mine {
			continue
		}
		amount, movement := l.Txn.AmountMinor, "? → "+l.Txn.AccountSlug
		if l.Out {
			amount, movement = -amount, l.Txn.AccountSlug+" → ?"
		}
		entries = append(entries, entry{l.Txn.Date, table.Row{
			"⚠", l.Txn.Date, model.FormatMinor(amount, l.Txn.MinorDigits),
			movement, l.Txn.Description,
		}})
	}
	// Newest first, like the transaction list: the movement worth checking is
	// usually the one that just came in.
	sort.SliceStable(entries, func(i, j int) bool { return entries[i].date > entries[j].date })

	rows := make([]table.Row, 0, len(entries))
	for _, e := range entries {
		rows = append(rows, e.row)
	}
	m.previewPairs = res.Paired[mine]
	m.previewUnmatched = res.Orphaned[mine]

	cursor := m.transferTable.Cursor()
	m.transferTable.SetRows(rows)
	if cursor >= len(rows) {
		cursor = len(rows) - 1
	}
	if cursor < 0 {
		cursor = 0
	}
	m.transferTable.SetCursor(cursor)
}

// saveTransfer appends the composed definition to rules.toml, re-pairs, and
// leaves the two account fields filled in, since the next transfer written is
// usually the same route in the other direction.
func (m *Model) saveTransfer() error {
	t := m.draftTransfer()
	switch {
	case t.FromAccount == "":
		return fmt.Errorf("name the account the money leaves")
	case t.FromDesc == "":
		return fmt.Errorf("enter a glob for the leaving leg, e.g. *TO REVOLUT*")
	case t.ToAccount == "":
		return fmt.Errorf("name the account the money arrives in")
	case t.ToDesc == "":
		return fmt.Errorf("enter a glob for the arriving leg, e.g. *FROM NLB*")
	}
	for _, slug := range []string{t.FromAccount, t.ToAccount} {
		if !m.knownAccount(slug) {
			return fmt.Errorf("no account called %q", slug)
		}
	}
	// draftTransfer swallowed this so the preview could keep up with typing;
	// saving is where a value that never became a number has to be refused,
	// rather than written out as a silent 0.
	if _, err := m.draftTolerance(); err != nil {
		return err
	}

	if err := config.AppendTransfer(m.root, t); err != nil {
		return err
	}
	if err := m.reloadConfig(); err != nil {
		return fmt.Errorf("transfer saved, but re-reading rules.toml failed: %w", err)
	}

	paired, unpaired, err := m.links.Link(m.db)
	if err != nil {
		return err
	}
	m.status = fmt.Sprintf("saved transfer %s → %s, %d matched, %d leg(s) unpaired",
		t.FromAccount, t.ToAccount, paired, unpaired)

	m.transferFromDesc.SetValue("")
	m.transferToDesc.SetValue("")
	// Cleared with the globs rather than kept with the accounts: a tolerance
	// carried silently into the next definition would loosen a route that never
	// asked for one, and the reverse direction rarely charges the same fee.
	m.transferTolerance.SetValue("")
	m.transferNote.SetValue("")
	// The accounts are kept, so land on the first field that was cleared.
	m.setTransferFocus(1)

	if err := m.reload(); err != nil {
		return err
	}
	txns, err := m.db.Transactions(store.Filter{})
	if err != nil {
		return err
	}
	m.allTxns = txns
	m.refreshTransferPreview()
	return nil
}

// openTransferList switches to the transfer list, remembering where to return.
// As on the rule list, the builder is not somewhere to return to: it is reached
// from here, and esc would bounce between the two.
func (m *Model) openTransferList() {
	if m.view != viewTransferList && m.view != viewTransfers {
		m.transferListReturn = m.view
	}
	m.view = viewTransferList
	m.confirm = confirmNone
	if err := m.reloadTransferList(); err != nil {
		m.err = err
	}
}

// reloadTransferList recomputes what every definition currently pairs.
//
// Two counts are shown because they mean different things: a definition with
// no pairs and no legs matches nothing at all and can go, while one with
// unpaired legs is catching money leaving that never arrives — a wrong glob on
// the other side, a statement not imported yet, or a movement that genuinely
// went missing.
func (m *Model) reloadTransferList() error {
	txns, err := m.db.Transactions(store.Filter{})
	if err != nil {
		return err
	}
	defs := m.links.Transfers()
	m.transferResult = m.links.Analyze(txns)

	rows := make([]table.Row, 0, len(defs))
	for i, t := range defs {
		marker := " "
		switch {
		case m.transferResult.Orphaned[i] > 0:
			marker = "⚠"
		case m.transferResult.Paired[i] == 0:
			marker = "✗"
		}
		rows = append(rows, table.Row{
			fmt.Sprintf("%d", i+1), marker,
			t.FromAccount + " " + t.FromDesc,
			t.ToAccount + " " + t.ToDesc,
			fmt.Sprintf("%d", m.transferResult.Paired[i]),
			fmt.Sprintf("%d", m.transferResult.Orphaned[i]),
			formatTolerance(t.TolerancePct),
			t.Note,
		})
	}

	cursor := m.transferListTable.Cursor()
	m.transferListTable.SetRows(rows)
	if cursor >= len(rows) {
		cursor = len(rows) - 1
	}
	if cursor < 0 {
		cursor = 0
	}
	m.transferListTable.SetCursor(cursor)
	return nil
}

// formatTolerance renders a definition's tolerance for the list. The default
// is blank rather than "0%": every definition has it, so printing it down the
// whole column would bury the one or two rows where the amounts are actually
// allowed to disagree.
func formatTolerance(pct float64) string {
	if pct == 0 {
		return ""
	}
	return strconv.FormatFloat(pct, 'f', -1, 64) + "%"
}

// unusedTransfers lists the positions of every definition that catches nothing
// at all. A definition with unpaired legs is deliberately not in here: it is
// doing something, just not completing it, and deleting it would hide the
// problem instead of fixing it.
func (m *Model) unusedTransfers() []int {
	var out []int
	for i, n := range m.transferResult.Paired {
		if n == 0 && m.transferResult.Orphaned[i] == 0 {
			out = append(out, i)
		}
	}
	return out
}

// unpairedLegs counts the legs no definition could complete.
func (m *Model) unpairedLegs() int { return len(m.transferResult.Unmatched) }

// deleteTransfers removes definitions from rules.toml, then re-pairs so the
// counts on screen reflect the new file.
func (m *Model) deleteTransfers(positions []int) error {
	n, err := config.DeleteTransfers(m.root, positions)
	if err != nil {
		return err
	}
	if err := m.reloadConfig(); err != nil {
		return fmt.Errorf("transfers deleted, but re-reading rules.toml failed: %w", err)
	}

	paired, unpaired, err := m.links.Link(m.db)
	if err != nil {
		return err
	}
	m.status = fmt.Sprintf("deleted %d transfer(s), %d matched, %d leg(s) unpaired",
		n, paired, unpaired)

	if err := m.reload(); err != nil {
		return err
	}
	return m.reloadTransferList()
}

// updateTransferList drives the transfer list, including the confirmations.
func (m *Model) updateTransferList(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
	if m.confirm != confirmNone {
		pending := m.confirm
		m.confirm = confirmNone
		if msg.String() != "y" {
			m.status = "cancelled"
			return m, nil
		}
		m.err = nil
		switch pending {
		case confirmDeleteTransfer:
			if i := m.transferListTable.Cursor(); i >= 0 && i < len(m.links.Transfers()) {
				if err := m.deleteTransfers([]int{i}); err != nil {
					m.err = err
				}
			}
		case confirmPruneTransfers:
			if err := m.deleteTransfers(m.unusedTransfers()); err != nil {
				m.err = err
			}
		}
		return m, nil
	}

	switch msg.String() {
	case "q", "ctrl+c":
		return m, tea.Quit
	case "esc":
		m.view = m.transferListReturn
		return m, nil
	case "1":
		m.view = viewAccounts
		return m, nil
	case "2":
		m.view = viewTxns
		return m, nil
	case "3":
		m.view = viewReport
		return m, nil
	case "4":
		return m, m.openRuleBuilder()
	case "5":
		m.openRuleList()
		return m, nil
	case "6":
		return m, m.openTransferBuilder()

	case "d":
		i := m.transferListTable.Cursor()
		defs := m.links.Transfers()
		if i < 0 || i >= len(defs) {
			return m, nil
		}
		m.confirm = confirmDeleteTransfer
		m.status = fmt.Sprintf("delete transfer %d (%s → %s), %d matched? y/n",
			i+1, defs[i].FromAccount, defs[i].ToAccount, m.transferResult.Paired[i])
		return m, nil

	case "p":
		unused := m.unusedTransfers()
		if len(unused) == 0 {
			m.status = "no transfers to prune; only ones matching nothing at all are pruned"
			return m, nil
		}
		m.confirm = confirmPruneTransfers
		m.status = fmt.Sprintf("delete all %d transfers that match nothing? y/n", len(unused))
		return m, nil

	case "r":
		m.err = m.reloadTransferList()
		m.status = "pairing refreshed"
		return m, nil
	}

	var cmd tea.Cmd
	m.transferListTable, cmd = m.transferListTable.Update(msg)
	return m, cmd
}

// updateTransfers drives the transfer builder form. Like the rule builder it
// owns every printable key, so the global keymap must not reach it.
func (m *Model) updateTransfers(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
	switch msg.String() {
	case "ctrl+c":
		return m, tea.Quit
	case "esc":
		m.view = m.transferReturn
		return m, nil
	case "tab":
		if acceptCompletion(m.transferInputs()[m.transferFocus]) {
			m.refreshTransferPreview()
			return m, nil
		}
		m.setTransferFocus(m.transferFocus + 1)
		return m, nil
	case "down":
		m.setTransferFocus(m.transferFocus + 1)
		return m, nil
	case "shift+tab", "up":
		m.setTransferFocus(m.transferFocus - 1)
		return m, nil
	case "right":
		in := m.transferInputs()[m.transferFocus]
		if in.Position() == len([]rune(in.Value())) && acceptCompletion(in) {
			m.refreshTransferPreview()
			return m, nil
		}
	case "pgdown":
		m.transferTable.MoveDown(10)
		return m, nil
	case "pgup":
		m.transferTable.MoveUp(10)
		return m, nil
	case "enter":
		m.err = nil
		if err := m.saveTransfer(); err != nil {
			m.err = err
		}
		return m, nil
	}

	var cmd tea.Cmd
	inputs := m.transferInputs()
	*inputs[m.transferFocus], cmd = inputs[m.transferFocus].Update(msg)
	m.refreshTransferPreview()
	return m, cmd
}

// transfersView puts the form on the left and the live pairing on the right.
func (m *Model) transfersView() string {
	return lipgloss.JoinHorizontal(lipgloss.Top, m.transferFormView(), m.transferTable.View())
}

func (m *Model) transferFormView() string {
	// Six fields need more room than the rule builder's four, so the form gives
	// ground in three stages: the blank lines first, then the hints on unfocused
	// fields, then their borders. Labels and values never go — six anonymous
	// boxes would be worse than a form that scrolls.
	room := m.height - 6
	spaced := m.height <= 0 || room >= 37
	hints := m.height <= 0 || room >= 31
	boxed := m.height <= 0 || room >= 25

	inputs := m.transferInputs()
	field := func(i int, label, help string) string {
		name := labelStyle.Render("  " + label)
		box := flatBoxStyle.Render(inputs[i].View())
		if boxed {
			box = boxStyle.Render(inputs[i].View())
		}
		if i == m.transferFocus {
			name = focusedLabelStyle.Render("▸ " + label)
			box = focusedBoxStyle.Render(inputs[i].View())
		}
		out := name + "\n" + box + "\n"
		if hints || i == m.transferFocus {
			out += hintStyle.Render(help) + "\n"
		}
		if spaced {
			out += "\n"
		}
		return out
	}

	var b strings.Builder
	b.WriteString(field(0, "from account", completionHint(inputs[0], m.transferFocus == 0, "money leaves here")))
	b.WriteString(field(1, "from desc", "glob vs. the leaving leg"))
	b.WriteString(field(2, "to account", completionHint(inputs[2], m.transferFocus == 2, "money arrives here")))
	b.WriteString(field(3, "to desc", "glob vs. the arriving leg"))
	b.WriteString(field(4, "tolerance %", "0 = amounts must match exactly"))
	b.WriteString(field(5, "note", "why this transfer exists"))

	summary := fmt.Sprintf("%d pairs · %d unpaired", m.previewPairs, m.previewUnmatched)
	if m.previewPairs == 0 && m.previewUnmatched == 0 {
		summary = "nothing matches yet"
	}
	// Fees are the reason the tolerance field exists, so the preview says what
	// it is admitting rather than only how many pairs it bought.
	if fee := m.previewFees; fee != 0 {
		summary += fmt.Sprintf(" · %s in fees", model.FormatMinor(fee, m.previewFeeDigits))
	}
	b.WriteString(matchCountStyle.Render(summary))

	return ruleFormStyle.Render(b.String())
}

// selected returns the transaction under the cursor, if any.
func (m *Model) selected() (model.Transaction, bool) {
	i := m.txnTable.Cursor()
	if i < 0 || i >= len(m.txns) {
		return model.Transaction{}, false
	}
	return m.txns[i], true
}

// importDoneMsg carries the outcome of a background import back to the model.
type importDoneMsg struct {
	res importer.Result
	err error
}

// importCmd runs the import off the event loop. Only values are captured, and
// the model is left untouched until the result comes back as a message.
func (m *Model) importCmd() tea.Cmd {
	root, db, accounts, engine, links := m.root, m.db, m.accounts, m.engine, m.links
	return func() tea.Msg {
		res, err := importer.Run(root, db, accounts, engine, links, importer.Options{})
		return importDoneMsg{res: res, err: err}
	}
}

// Update implements tea.Model.
func (m *Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.WindowSizeMsg:
		m.width, m.height = msg.Width, msg.Height
		m.resize()
		return m, nil

	case spinner.TickMsg:
		if !m.importing {
			return m, nil // a stale tick from a finished import
		}
		var cmd tea.Cmd
		m.spinner, cmd = m.spinner.Update(msg)
		return m, cmd

	case importDoneMsg:
		return m.finishImport(msg)

	case tea.KeyMsg:
		if m.input != inputNone {
			return m.updateInput(msg)
		}
		// The builders are forms: every printable key belongs to the focused
		// input, so the global single-letter keymap cannot apply.
		switch m.view {
		case viewRules:
			return m.updateRules(msg)
		case viewTransfers:
			return m.updateTransfers(msg)
		case viewRuleList:
			return m.updateRuleList(msg)
		case viewTransferList:
			return m.updateTransferList(msg)
		}
		return m.updateNormal(msg)
	}
	return m, nil
}

// updateRules drives the rule builder form.
func (m *Model) updateRules(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
	switch msg.String() {
	case "ctrl+c":
		return m, tea.Quit
	case "esc":
		m.view = m.ruleReturn
		return m, nil
	case "tab":
		// Tab is overloaded on purpose: with a completion on offer it takes
		// it, and moving on is then one more tab. Without one it does what it
		// always did and moves to the next field.
		if acceptCompletion(m.ruleInputs()[m.ruleFocus]) {
			m.refreshRulePreview()
			return m, nil
		}
		m.setRuleFocus(m.ruleFocus + 1)
		return m, nil
	case "down":
		m.setRuleFocus(m.ruleFocus + 1)
		return m, nil
	case "shift+tab", "up":
		m.setRuleFocus(m.ruleFocus - 1)
		return m, nil
	case "right":
		// At the end of the line → has nothing else to do, so it accepts the
		// completion the way a shell does. Anywhere else it falls through and
		// moves the cursor.
		in := m.ruleInputs()[m.ruleFocus]
		if in.Position() == len([]rune(in.Value())) && acceptCompletion(in) {
			m.refreshRulePreview()
			return m, nil
		}
	case "pgdown":
		m.ruleTable.MoveDown(10)
		return m, nil
	case "pgup":
		m.ruleTable.MoveUp(10)
		return m, nil
	case "ctrl+s":
		// A form owns every printable key, so re-sorting has to be a chord:
		// "s" belongs to whichever glob is being typed.
		if m.previewSort == sortByName {
			m.previewSort = sortByCount
		} else {
			m.previewSort = sortByName
		}
		m.sortPreviewGroups()
		// The rows under the cursor are not the rows that were there a moment
		// ago, so start from the top rather than somewhere arbitrary.
		m.ruleTable.SetCursor(0)
		return m, nil
	case "enter":
		m.err = nil
		editing := m.ruleEditing // saveRule clears it on the way through
		if err := m.saveRule(); err != nil {
			m.err = err
			return m, nil
		}
		if editing {
			// An edit is a round trip from the rules screen, so it ends there
			// with the new counts rather than in an empty form.
			m.showRuleList()
			return m, nil
		}
		if err := m.reloadPreviewGroups(); err != nil {
			m.err = err
		}
		return m, nil
	}

	var cmd tea.Cmd
	inputs := m.ruleInputs()
	*inputs[m.ruleFocus], cmd = inputs[m.ruleFocus].Update(msg)
	m.refreshRulePreview()
	return m, cmd
}

func (m *Model) finishImport(msg importDoneMsg) (tea.Model, tea.Cmd) {
	m.importing = false
	if msg.err != nil {
		m.err = msg.err
		m.status = "import failed"
		return m, nil
	}

	_, added, skipped := msg.res.Total()
	m.status = fmt.Sprintf("imported: %d new, %d duplicate", added, skipped)
	if msg.res.Unpaired > 0 {
		m.status += fmt.Sprintf(" · %d transfer leg(s) unpaired", msg.res.Unpaired)
	}

	// A failed file and a warning are both worth surfacing, but the status
	// line only has room for the first thing that went wrong.
	if failures := msg.res.Errs(); len(failures) > 0 {
		m.err = fmt.Errorf("%s: %w", failures[0].Path, failures[0].Err)
	} else if warnings := firstWarning(msg.res); warnings != "" {
		m.status += " · " + warnings
	}

	if err := m.reload(); err != nil {
		m.err = err
	}
	return m, nil
}

func firstWarning(res importer.Result) string {
	total := 0
	first := ""
	for _, f := range res.Files {
		for _, w := range f.Warnings {
			if first == "" {
				first = fmt.Sprintf("%s: %s", f.Path, w)
			}
			total++
		}
	}
	if total > 1 {
		return fmt.Sprintf("%s (+%d more warnings)", first, total-1)
	}
	return first
}

func (m *Model) resize() {
	h := m.height - 6 // title, status, help, padding
	if h < 3 {
		h = 3
	}
	m.accountTable.SetHeight(h)
	m.txnTable.SetHeight(h)
	m.reportTable.SetHeight(h)
	m.ruleTable.SetHeight(h)
	m.ruleListTable.SetHeight(h)
	m.transferTable.SetHeight(h)
	m.transferListTable.SetHeight(h)

	// The preview list gets whatever the form does not use.
	if m.width > 0 {
		cols := m.ruleTable.Columns()
		desc := m.width - ruleFormWidth - cols[0].Width - cols[2].Width - 10
		if desc < 20 {
			desc = 20
		}
		cols[1].Width = desc
		m.ruleTable.SetColumns(cols)

		cols = m.transferTable.Columns()
		fixed := 0
		for _, c := range cols[:len(cols)-1] {
			fixed += c.Width + 2
		}
		desc = m.width - ruleFormWidth - fixed - 6
		if desc < 16 {
			desc = 16
		}
		cols[len(cols)-1].Width = desc
		m.transferTable.SetColumns(cols)
	}

	// The free-text columns come last and get whatever is left over.
	m.stretchLastColumn(&m.txnTable, 20)
	m.stretchLastColumn(&m.ruleListTable, 12)
	m.stretchLastColumn(&m.transferListTable, 12)
}

// stretchLastColumn widens a table's final column to fill the window, down to
// a floor below which truncation is worse than letting the row overflow.
func (m *Model) stretchLastColumn(t *table.Model, min int) {
	if m.width <= 0 {
		return
	}
	cols := t.Columns()
	fixed := 0
	for _, c := range cols[:len(cols)-1] {
		fixed += c.Width + 2
	}
	last := m.width - fixed - 4
	if last < min {
		last = min
	}
	cols[len(cols)-1].Width = last
	t.SetColumns(cols)
}

// updateInput handles typing into the tag or search prompt.
func (m *Model) updateInput(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
	switch msg.Type {
	case tea.KeyEsc:
		m.input = inputNone
		m.text.Blur()
		m.text.SetValue("")
		return m, nil
	case tea.KeyEnter:
		value := strings.TrimSpace(m.text.Value())
		mode := m.input
		m.input = inputNone
		m.text.Blur()
		m.text.SetValue("")

		switch mode {
		case inputSearch:
			m.filter.Search = value
			m.status = "search: " + value
			if value == "" {
				m.status = "search cleared"
			}
		}
		m.err = m.reloadTxns()
		return m, nil
	}

	var cmd tea.Cmd
	m.text, cmd = m.text.Update(msg)
	return m, cmd
}

// updateNormal handles the main keymap.
func (m *Model) updateNormal(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
	switch msg.String() {
	case "q", "ctrl+c":
		return m, tea.Quit

	case "1":
		m.view = viewAccounts
		return m, nil
	case "2":
		m.view = viewTxns
		return m, nil
	case "3":
		m.view = viewReport
		return m, nil
	case "4":
		return m, m.openRuleBuilder()
	case "5":
		m.openRuleList()
		return m, nil
	case "6":
		return m, m.openTransferBuilder()
	case "7":
		m.openTransferList()
		return m, nil
	case "s":
		// Re-sorting only means anything where there is a breakdown to sort.
		if m.view != viewReport {
			break
		}
		m.setOrder(m.reportOrder.Next())
		return m, nil

	case "left", "right":
		// The report's time axis. Every other view leaves these to its table,
		// which is what breaking out of the switch here does.
		if m.view != viewReport {
			break
		}
		step := 1
		if msg.String() == "left" {
			step = -1
		}
		m.setPeriod(m.reportPeriod + step)
		return m, nil

	case "tab":
		m.view = (m.view + 1) % viewCount
		switch m.view {
		case viewRules:
			return m, m.openRuleBuilder()
		case viewRuleList:
			m.openRuleList()
		case viewTransfers:
			return m, m.openTransferBuilder()
		case viewTransferList:
			m.openTransferList()
		}
		return m, nil

	case "enter":
		// From the account list, drill into that account's transactions.
		if m.view == viewAccounts {
			accounts, err := m.db.Accounts()
			if err != nil {
				m.err = err
				return m, nil
			}
			i := m.accountTable.Cursor()
			if i >= 0 && i < len(accounts) {
				m.filter.AccountSlug = accounts[i].Slug
				m.status = "account: " + accounts[i].Slug
				m.view = viewTxns
				m.err = m.reloadTxns()
			}
		}
		return m, nil

	case "a":
		m.filter.AccountSlug = ""
		m.status = "all accounts"
		m.err = m.reloadTxns()
		return m, nil

	case "u":
		m.onlyUntagged = !m.onlyUntagged
		if m.onlyUntagged {
			m.status = "showing untagged only"
			m.view = viewTxns
		} else {
			m.status = "showing all transactions"
		}
		m.err = m.reloadTxns()
		return m, nil

	case "/":
		m.view = viewTxns
		m.input = inputSearch
		m.text.SetValue(m.filter.Search)
		m.text.CursorEnd()
		m.text.Focus()
		return m, nil

	case "r":
		if m.importing {
			m.status = "import in progress…"
			return m, nil
		}
		n, err := m.engine.Retag(m.db)
		if err != nil {
			m.err = err
			return m, nil
		}
		// Tags and transfers are both derived from rules.toml, so one key
		// re-derives both; leaving the pairing stale would quietly change what
		// the report holds out.
		paired, unpaired, err := m.links.Link(m.db)
		if err != nil {
			m.err = err
			return m, nil
		}
		m.status = fmt.Sprintf("rules re-applied, %d rows changed, %d transfers matched", n, paired)
		if unpaired > 0 {
			m.status += fmt.Sprintf(", %d leg(s) unpaired", unpaired)
		}
		m.err = m.reload()
		return m, nil

	case "i":
		if m.importing {
			return m, nil // already running; ignore the repeat press
		}
		m.importing = true
		m.err = nil
		m.status = ""
		return m, tea.Batch(m.spinner.Tick, m.importCmd())
	}

	var cmd tea.Cmd
	switch m.view {
	case viewAccounts:
		m.accountTable, cmd = m.accountTable.Update(msg)
	case viewTxns:
		m.txnTable, cmd = m.txnTable.Update(msg)
	case viewReport:
		m.reportTable, cmd = m.reportTable.Update(msg)
	}
	return m, cmd
}

// View implements tea.Model.
func (m *Model) View() string {
	var b strings.Builder

	b.WriteString(titleStyle.Render(m.title()))
	b.WriteString("\n")

	// An empty table is just a bare header, which says nothing about why it is
	// empty or what to do next.
	if empty := m.emptyMessage(); empty != "" {
		b.WriteString(emptyStyle.Render(empty))
	} else {
		switch m.view {
		case viewAccounts:
			b.WriteString(m.accountTable.View())
		case viewTxns:
			b.WriteString(m.txnTable.View())
		case viewReport:
			b.WriteString(m.reportView())
		case viewRules:
			b.WriteString(m.rulesView())
		case viewRuleList:
			b.WriteString(m.ruleListTable.View())
		case viewTransfers:
			b.WriteString(m.transfersView())
		case viewTransferList:
			b.WriteString(m.transferListTable.View())
		}
	}
	b.WriteString("\n")

	switch {
	case m.importing:
		b.WriteString(statusStyle.Render(m.spinner.View() + m.importingLabel()))
	case m.input == inputSearch:
		b.WriteString(statusStyle.Render("search: ") + m.text.View())
	case m.err != nil:
		b.WriteString(errStyle.Render("error: " + m.err.Error()))
	default:
		b.WriteString(statusStyle.Render(m.status))
	}
	b.WriteString("\n")
	// Wrap the key list rather than letting the terminal cut it off: the keys
	// at the end are as important as the ones at the start, and "q quit" was
	// the first casualty on a narrow window.
	help := helpStyle
	if m.width > 0 {
		help = help.Width(m.width)
	}
	b.WriteString(help.Render(m.help()))
	return b.String()
}

// periodListWidth is the width of the report's time axis, wide enough for the
// longest window name plus its cursor.
const periodListWidth = 18

// reportView puts the time axis to the left of the totals, so the window the
// numbers are for is visible without reading the title and ←/→ has something to
// point at. On a window too narrow for both, the totals win and the axis is
// dropped: the title still names the period, and truncated money columns would
// be worse than a hidden list of periods.
func (m *Model) reportView() string {
	axis := m.periodList()
	if axis == "" {
		return m.reportTable.View()
	}
	return lipgloss.JoinHorizontal(lipgloss.Top, axis, m.reportTable.View())
}

// periodList renders the axis, scrolled to keep the selected window on screen.
// Its header stands in for the table's own, which is a single unruled line, so
// the two panels line up row for row without a separator of their own.
func (m *Model) periodList() string {
	if len(m.reportPeriods) == 0 {
		return ""
	}
	if m.width > 0 && m.width < tableWidth(m.reportTable)+periodListWidth {
		return ""
	}

	h := m.reportTable.Height()
	if h <= 0 || h > len(m.reportPeriods) {
		h = len(m.reportPeriods)
	}
	// Centre the cursor where there is room, so the windows either side of the
	// one being read are visible and stepping has somewhere obvious to go.
	start := m.reportPeriod - h/2
	if start > len(m.reportPeriods)-h {
		start = len(m.reportPeriods) - h
	}
	if start < 0 {
		start = 0
	}

	var b strings.Builder
	b.WriteString(periodHeaderStyle.Render("Period"))
	for i := start; i < start+h; i++ {
		line := "  " + m.reportPeriods[i].Label
		style := periodStyle
		if i == m.reportPeriod {
			line = "▸ " + m.reportPeriods[i].Label
			style = periodSelectedStyle
		}
		b.WriteString("\n" + style.Render(line))
	}
	return b.String()
}

// tableWidth is how many cells a table renders across, the cell style's padding
// on either side of every column included.
func tableWidth(t table.Model) int {
	w := 0
	for _, c := range t.Columns() {
		w += c.Width + 2
	}
	return w
}

// rulesView puts the form on the left and the live preview on the right.
func (m *Model) rulesView() string {
	return lipgloss.JoinHorizontal(lipgloss.Top, m.ruleFormView(), m.ruleTable.View())
}

func (m *Model) ruleFormView() string {
	// Spaced out, the four fields come to 25 lines, which is more than a short
	// window has left once the same allowance the tables get is taken off.
	// Give up the blank lines between fields first (21 lines) and the hints on
	// unfocused fields second (18), rather than letting the last field run off
	// the bottom. Below that the box borders are the floor.
	// An edit carrying a type pattern renders one line more, and two once the
	// fields are spaced out, so it asks for that much more room before either.
	typed := 0
	if m.ruleEditing && m.ruleEditOrig.Type != "" {
		typed = 1
	}
	room := m.height - 6
	spaced := m.height <= 0 || room >= 25+2*typed
	hints := m.height <= 0 || room >= 21+typed

	field := func(i int, label, help string) string {
		name := labelStyle.Render("  " + label)
		box := boxStyle.Render(m.ruleInputs()[i].View())
		if i == m.ruleFocus {
			name = focusedLabelStyle.Render("▸ " + label)
			box = focusedBoxStyle.Render(m.ruleInputs()[i].View())
		}
		out := name + "\n" + box + "\n"
		if hints || i == m.ruleFocus {
			out += hintStyle.Render(help) + "\n"
		}
		if spaced {
			out += "\n"
		}
		return out
	}

	var b strings.Builder
	inputs := m.ruleInputs()
	b.WriteString(field(0, "glob", "vs. the description"))
	// A type pattern has no field of its own, so an edit carrying one says so
	// rather than leaving the rule looking broader than it is.
	if m.ruleEditing && m.ruleEditOrig.Type != "" {
		b.WriteString(hintStyle.Render("+ type:"+m.ruleEditOrig.Type+" · kept") + "\n")
		if spaced {
			b.WriteString("\n")
		}
	}
	b.WriteString(field(1, "account", completionHint(inputs[1], m.ruleFocus == 1, "blank = all accounts")))
	b.WriteString(field(2, "tag", completionHint(inputs[2], m.ruleFocus == 2, "applied to matches")))
	b.WriteString(field(3, "note", "why this rule exists"))

	// The count is the whole point of the preview: it says what the rule will
	// do before it is written to disk.
	summary := fmt.Sprintf("%d of %d descriptions match", m.ruleMatches, m.ruleCandidates)
	if strings.TrimSpace(m.ruleGlob.Value()) == "" && !m.ruleEditing {
		summary = fmt.Sprintf("%d untagged descriptions", m.ruleCandidates)
	}
	// What an edit gives up is not visible in a count of what it keeps. It goes
	// on its own line because the two together overflow the form's width, and
	// lipgloss would wrap it mid-phrase.
	if m.ruleDropped > 0 {
		summary += fmt.Sprintf("\n%d no longer claimed", m.ruleDropped)
	}
	b.WriteString(matchCountStyle.Render(summary))

	return ruleFormStyle.Render(b.String())
}

// completionHint names the key that accepts the ghosted completion, replacing
// the field's usual hint while one is on offer. The hint sits directly under
// the box the ghost text appears in, which is where the question is asked.
func completionHint(in *textinput.Model, focused bool, fallback string) string {
	if !focused {
		return fallback
	}
	if pendingCompletion(in) == "" {
		return fallback
	}
	if n := len(in.MatchedSuggestions()); n > 1 {
		return fmt.Sprintf("tab completes · ctrl+n: %d more", n-1)
	}
	return "tab completes"
}

// emptyMessage explains an empty view and names the key that fixes it, or
// returns "" when there is something to show.
func (m *Model) emptyMessage() string {
	switch m.view {
	case viewAccounts:
		if len(m.accountTable.Rows()) > 0 {
			return ""
		}
		// An account.toml on disk is not enough: folders are only registered
		// in the index by an import, so say that rather than showing nothing.
		if n := len(m.accounts); n > 0 {
			return fmt.Sprintf(
				"No accounts imported yet.\n\n"+
					"%d account folder(s) configured in %s.\n"+
					"Press i to import their statements (same as running `money import`).",
				n, m.root)
		}
		return fmt.Sprintf(
			"No account folders found in %s.\n\n"+
				"An account is a folder containing an account.toml.\n"+
				"Create one, drop statements in, then press i to import.",
			m.root)

	case viewTxns:
		if len(m.txns) > 0 {
			return ""
		}
		switch {
		case m.filter.Search != "":
			return fmt.Sprintf("No transactions match /%s.\n\nPress / to change the search.", m.filter.Search)
		case m.onlyUntagged:
			return "Nothing untagged.\n\n" +
				"Every transaction here has a tag or belongs to a transfer.\n" +
				"Press u to see them all."
		case m.filter.AccountSlug != "":
			return fmt.Sprintf(
				"No transactions in %s.\n\nPress i to import, or a to see every account.",
				m.filter.AccountSlug)
		}
		return "No transactions yet.\n\nPress i to import (same as running `money import`)."

	case viewReport:
		if len(m.reportTable.Rows()) > 0 {
			return ""
		}
		// A period with nothing in it is not the same as an empty index, and
		// saying so matters most in the default window: statements for the month
		// that has just ended often have not been downloaded yet.
		if p, ok := m.currentPeriod(); ok && p.From != "" && !m.indexEmpty {
			return fmt.Sprintf("Nothing in %s.\n\nPress ←/→ for another period, or i to import.", p.String())
		}
		return "Nothing to report yet.\n\nPress i to import some statements first."

	case viewRuleList:
		if len(m.ruleListTable.Rows()) > 0 {
			return ""
		}
		return "No rules yet.\n\nPress 4 to build one, or write rules.toml by hand."

	case viewTransferList:
		if len(m.transferListTable.Rows()) > 0 {
			return ""
		}
		return "No transfers yet.\n\n" +
			"A transfer names both legs of money moved between your own accounts,\n" +
			"so the report can leave the pair out instead of counting it as spending.\n" +
			"Press 6 to build one, or write rules.toml by hand."
	}
	return ""
}

func (m *Model) title() string {
	scope := "all accounts"
	if m.filter.AccountSlug != "" {
		scope = m.filter.AccountSlug
	}
	if m.onlyUntagged {
		scope += " · untagged"
	}
	if m.filter.Search != "" {
		scope += " · /" + m.filter.Search
	}

	switch m.view {
	case viewAccounts:
		return "money · accounts"
	case viewRules:
		if m.ruleEditing {
			return fmt.Sprintf("money · editing rule %d · rewrites it in rules.toml", m.ruleEditPos+1)
		}
		return "money · rule builder · writes to rules.toml"
	case viewRuleList:
		unused := len(m.unusedRules())
		if unused == 0 {
			return fmt.Sprintf("money · rules · %d rules, all in use", len(m.engine.Rules()))
		}
		return fmt.Sprintf("money · rules · %d rules · %d match nothing", len(m.engine.Rules()), unused)
	case viewTransfers:
		return "money · transfer builder · writes to rules.toml"
	case viewTransferList:
		n := len(m.links.Transfers())
		if legs := m.unpairedLegs(); legs > 0 {
			return fmt.Sprintf("money · transfers · %d definitions · %d leg(s) unpaired", n, legs)
		}
		return fmt.Sprintf("money · transfers · %d definitions · every leg paired", n)
	case viewReport:
		if p, ok := m.currentPeriod(); ok {
			return "money · report · " + p.String() + " · " + scope
		}
		return "money · report · " + scope
	default:
		return fmt.Sprintf("money · transactions · %s · %d rows", scope, len(m.txns))
	}
}

// importingLabel names what the import is working through, since extracting
// text from PDFs is where the wait actually comes from.
func (m *Model) importingLabel() string {
	if n := len(m.accounts); n > 0 {
		return fmt.Sprintf("importing %d account(s)… parsing statements can take a while for PDFs", n)
	}
	return "importing…"
}

func (m *Model) help() string {
	if m.importing {
		return "importing… · q quit"
	}
	if m.input != inputNone {
		return "enter confirm · esc cancel"
	}
	switch m.view {
	case viewAccounts:
		return "enter open · 2 transactions · 3 report · 4 new rule · 5 rules · 6 new transfer · 7 transfers · i import · r retag · q quit"
	case viewRules:
		save := "enter save rule"
		if m.ruleEditing {
			save = "enter save changes"
		}
		// The key is named by what pressing it does now, not by the order the
		// list is already in.
		order := "ctrl+s sort by count"
		if m.previewSort == sortByCount {
			order = "ctrl+s sort by name"
		}
		return "tab complete/next field · ↑↓ field · ctrl+n/p other completions · pgup/pgdn scroll list · " +
			order + " · " + save + " · esc back · ctrl+c quit"
	case viewRuleList:
		if m.confirm != confirmNone {
			return "y confirm · any other key cancels"
		}
		return "e edit rule · d delete rule · p prune all unused · r refresh counts · 4 new rule · 7 transfers · 1 accounts · esc back · q quit"
	case viewTransfers:
		return "tab complete/next field · ↑↓ field · pgup/pgdn scroll pairs · enter save transfer · esc back · ctrl+c quit"
	case viewTransferList:
		if m.confirm != confirmNone {
			return "y confirm · any other key cancels"
		}
		return "d delete transfer · p prune all unmatched · r refresh pairing · 6 new transfer · 5 rules · 1 accounts · esc back · q quit"
	case viewReport:
		// The key is named by what pressing it does now, not by the order the
		// rows are already in.
		return "←/→ period · s sort by " + m.reportOrder.Next().String() +
			" · 1 accounts · 2 transactions · 4 new rule · 5 rules · 7 transfers · u untagged · a all accounts · q quit"
	default:
		return "4 new rule · / search · u untagged · a all · i import · r retag · 5 rules · 7 transfers · q quit"
	}
}