// Package importer walks the data root, extracts transactions from every
// statement file, and inserts the ones not already in the index.
package importer

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"git.petrovv.com/nikola/money/internal/config"
	"git.petrovv.com/nikola/money/internal/glob"
	"git.petrovv.com/nikola/money/internal/model"
	"git.petrovv.com/nikola/money/internal/parser"
	"git.petrovv.com/nikola/money/internal/rules"
	"git.petrovv.com/nikola/money/internal/store"
)

// FileResult is what happened to one statement file.
type FileResult struct {
	Account string
	Path    string // relative to the data root
	Parsed  int
	New     int
	Skipped int // already present, i.e. deduplicated
	Err     error
	// Warnings are non-fatal notes: rows the parser deliberately dropped, and
	// breaks in the statement's balance chain.
	Warnings []string
}

// Result summarises a whole import run.
type Result struct {
	Files    []FileResult
	Retagged int
}

// Total counts new rows across every file.
func (r Result) Total() (parsed, added, skipped int) {
	for _, f := range r.Files {
		parsed += f.Parsed
		added += f.New
		skipped += f.Skipped
	}
	return
}

// Errs collects per-file failures. One unreadable statement must not abort the
// whole run, so errors are reported rather than returned.
func (r Result) Errs() []FileResult {
	var out []FileResult
	for _, f := range r.Files {
		if f.Err != nil {
			out = append(out, f)
		}
	}
	return out
}

// Options tunes an import run.
type Options struct {
	// Force reimports statement files whose contents are unchanged. Without
	// it, files with a matching checksum are skipped entirely.
	Force bool
}

// Run imports every account under root into db and then applies the rules.
func Run(root string, db *store.DB, accounts []*config.Account, engine *rules.Engine, opts Options) (Result, error) {
	var res Result
	for _, acc := range accounts {
		accountID, err := db.UpsertAccount(model.Account{
			Slug:        acc.Slug,
			Name:        acc.Name,
			Currency:    acc.Currency,
			MinorDigits: acc.Digits(),
		})
		if err != nil {
			return res, err
		}

		p, err := parser.For(acc)
		if err != nil {
			// A misconfigured account is worth reporting, but the other
			// accounts should still import.
			res.Files = append(res.Files, FileResult{Account: acc.Slug, Path: acc.Slug, Err: err})
			continue
		}

		files, err := statementFiles(acc)
		if err != nil {
			return res, err
		}
		for _, path := range files {
			fr := importFile(root, db, acc, accountID, p, engine, path, opts)
			res.Files = append(res.Files, fr)
		}
	}

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

func importFile(root string, db *store.DB, acc *config.Account, accountID int64,
	p parser.Parser, engine *rules.Engine, path string, opts Options) FileResult {

	rel, err := filepath.Rel(root, path)
	if err != nil {
		rel = path
	}
	fr := FileResult{Account: acc.Slug, Path: rel}

	sum, err := checksum(path)
	if err != nil {
		fr.Err = err
		return fr
	}
	if !opts.Force {
		prev, seen, err := db.SourceFileSHA(accountID, rel)
		if err != nil {
			fr.Err = err
			return fr
		}
		if seen && prev == sum {
			return fr // unchanged since last import; nothing to do
		}
	}

	txns, err := p.Parse(path, acc)
	if err != nil {
		fr.Err = err
		return fr
	}
	fr.Parsed = len(txns)

	if w, ok := p.(parser.Warner); ok {
		fr.Warnings = append(fr.Warnings, w.Warnings()...)
	}
	fr.Warnings = append(fr.Warnings, checkBalances(txns, acc.Digits())...)

	sourceID, err := db.SourceFile(accountID, rel, sum, time.Now().UTC().Format(time.RFC3339))
	if err != nil {
		fr.Err = err
		return fr
	}

	// Identical lines within one statement (two coffees on the same day) are
	// distinguished by their ordinal, so both survive; the same line seen
	// again in an overlapping statement gets the same fingerprint and is
	// deduplicated.
	seen := map[string]int{}
	for _, t := range txns {
		key := fingerprintKey(t)
		ordinal := seen[key]
		seen[key]++

		txn := model.Transaction{
			AccountID:    accountID,
			SourceFileID: sourceID,
			Fingerprint:  fingerprint(key, ordinal),
			Date:         t.Date,
			Description:  t.Description,
			AmountMinor:  t.AmountMinor,
			Type:         t.Type,
			BalanceMinor: t.BalanceMinor,
		}
		txn.RuleTag = engine.ApplyTxn(acc.Slug, txn)
		added, err := db.InsertTransaction(txn)
		if err != nil {
			fr.Err = err
			return fr
		}
		if added {
			fr.New++
		} else {
			fr.Skipped++
		}
	}
	return fr
}

// checkBalances verifies that each reported balance is the previous one plus
// the transaction amount, which is what the original extraction scripts did.
// A break means a row was missed or misparsed, so it is worth saying out loud
// even though the import still proceeds.
func checkBalances(txns []parser.RawTxn, digits int) []string {
	var warnings []string
	var prev *parser.RawTxn

	for i := range txns {
		t := &txns[i]
		if t.BalanceMinor == nil {
			continue // this statement does not report running balances
		}
		if prev != nil {
			expected := *prev.BalanceMinor + t.AmountMinor
			if expected != *t.BalanceMinor {
				warnings = append(warnings, fmt.Sprintf(
					"balance chain breaks at %s %q: statement says %s, previous balance plus amount is %s",
					t.Date, truncate(t.Description, 40),
					model.FormatMinor(*t.BalanceMinor, digits),
					model.FormatMinor(expected, digits)))
			}
		}
		prev = t
	}
	return warnings
}

func truncate(s string, n int) string {
	r := []rune(s)
	if len(r) <= n {
		return s
	}
	return string(r[:n]) + "…"
}

func fingerprintKey(t parser.RawTxn) string {
	return strings.Join([]string{
		t.Date,
		fmt.Sprintf("%d", t.AmountMinor),
		model.NormalizeDescription(t.Description),
	}, "\x00")
}

func fingerprint(key string, ordinal int) string {
	sum := sha256.Sum256([]byte(fmt.Sprintf("%s\x00%d", key, ordinal)))
	return hex.EncodeToString(sum[:])
}

// statementFiles lists the files in an account folder that should be parsed:
// every regular file except account.toml and dotfiles, narrowed by the
// account's optional include globs.
func statementFiles(acc *config.Account) ([]string, error) {
	entries, err := os.ReadDir(acc.Dir)
	if err != nil {
		return nil, fmt.Errorf("read account dir %s: %w", acc.Dir, err)
	}
	var out []string
	for _, e := range entries {
		name := e.Name()
		if e.IsDir() || strings.HasPrefix(name, ".") || name == config.AccountFile {
			continue
		}
		if len(acc.Include) > 0 && !matchAny(acc.Include, name) {
			continue
		}
		out = append(out, filepath.Join(acc.Dir, name))
	}
	sort.Strings(out)
	return out, nil
}

func matchAny(patterns []string, name string) bool {
	for _, p := range patterns {
		if glob.Match(p, name) {
			return true
		}
	}
	return false
}

func checksum(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()
	h := sha256.New()
	if _, err := io.Copy(h, f); err != nil {
		return "", err
	}
	return hex.EncodeToString(h.Sum(nil)), nil
}