// Package config loads the two hand-edited files the tool reads: the
// data-root-wide rules.toml, and one account.toml per account folder.
package config

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"github.com/BurntSushi/toml"
)

const (
	// RulesFile is the rules file at the root of the data directory.
	RulesFile = "rules.toml"
	// AccountFile is the per-account config inside each account folder.
	AccountFile = "account.toml"
	// StateDir holds the rebuildable SQLite index.
	StateDir = ".money"
	// IndexFile is the SQLite index inside StateDir.
	IndexFile = "index.db"
)

// Rule is one entry in rules.toml. Rules are evaluated in file order and the
// first one whose Match (and optional Account) matches wins.
type Rule struct {
	Match    string `toml:"match"`
	Tag      string `toml:"tag"`
	Transfer bool   `toml:"transfer"`
	Account  string `toml:"account"` // optional: restrict to one account slug
	// Counterparty matches the other side's account number, which for
	// movements between the user's own accounts is often the only reliable
	// signal. Optional; when set, it must match as well as Match.
	Counterparty string `toml:"counterparty"`
	// Type matches the bank's own classification, e.g. Revolut's CARD_PAYMENT.
	// Optional; when set, it must match as well as Match.
	Type string `toml:"type"`
}

// Rules is the parsed rules.toml.
type Rules struct {
	Rule []Rule `toml:"rule"`
}

// LoadRules reads rules.toml from the data root. A missing file is not an
// error: it just means nothing is tagged automatically yet.
func LoadRules(root string) (*Rules, error) {
	path := filepath.Join(root, RulesFile)
	var r Rules
	if _, err := toml.DecodeFile(path, &r); err != nil {
		if os.IsNotExist(err) {
			return &r, nil
		}
		return nil, fmt.Errorf("%s: %w", path, err)
	}
	for i, rule := range r.Rule {
		if rule.Match == "" && rule.Counterparty == "" && rule.Type == "" {
			return nil, fmt.Errorf("%s: rule %d has no match, counterparty or type pattern", path, i+1)
		}
		if rule.Tag == "" && !rule.Transfer {
			return nil, fmt.Errorf("%s: rule %d (%q) sets neither tag nor transfer", path, i+1, rule.Match)
		}
	}
	return &r, nil
}

// Column locates one field in a CSV row.
type Column struct {
	Col       int    `toml:"col"`
	Layout    string `toml:"layout"`    // date only, Go reference layout
	Decimal   string `toml:"decimal"`   // amount only, default "."
	Thousands string `toml:"thousands"` // amount only, default ""
}

// CSVConfig describes how to read a delimited statement.
type CSVConfig struct {
	Delimiter   string  `toml:"delimiter"`
	SkipRows    int     `toml:"skip_rows"`
	Encoding    string  `toml:"encoding"` // "" or "utf-8"; other encodings unsupported for now
	Date        Column  `toml:"date"`
	Description Column  `toml:"description"`
	Amount      *Column `toml:"amount"` // single signed column...
	Debit       *Column `toml:"debit"`  // ...or a debit/credit pair
	Credit      *Column `toml:"credit"`
	// Invert flips the sign of the parsed amount, for statements that report
	// outflows as positive numbers.
	Invert bool `toml:"invert"`
}

// CmdConfig runs an external extractor (e.g. one of the existing Python
// scripts) and reads normalised CSV from its stdout.
type CmdConfig struct {
	// Argv is the command to run. The literal token "{{file}}" is replaced
	// with the absolute path of the statement being imported.
	Argv []string `toml:"argv"`
	// Layout is the date layout the script emits; defaults to 2006-01-02.
	Layout string `toml:"layout"`
	// SkipRows skips leading rows of the script's output (e.g. a header).
	SkipRows int `toml:"skip_rows"`
}

// Account is a parsed account.toml.
type Account struct {
	Slug        string // folder name, filled in by LoadAccounts
	Dir         string // absolute path to the account folder
	Name        string `toml:"name"`
	Currency    string `toml:"currency"`
	MinorDigits *int   `toml:"minor_digits"`
	Parser      string `toml:"parser"`
	// Include restricts which files in the folder are treated as statements.
	// Defaults to every regular file except account.toml and dotfiles.
	Include []string   `toml:"include"`
	CSV     *CSVConfig `toml:"csv"`
	Cmd     *CmdConfig `toml:"cmd"`
}

// Digits returns the configured minor-unit scale, defaulting to 2.
func (a *Account) Digits() int {
	if a.MinorDigits != nil {
		return *a.MinorDigits
	}
	return 2
}

// LoadAccounts finds every account folder under root. A folder is an account
// if it contains an account.toml.
func LoadAccounts(root string) ([]*Account, error) {
	entries, err := os.ReadDir(root)
	if err != nil {
		return nil, fmt.Errorf("read data root %s: %w", root, err)
	}
	var accounts []*Account
	for _, e := range entries {
		if !e.IsDir() || strings.HasPrefix(e.Name(), ".") {
			continue
		}
		dir := filepath.Join(root, e.Name())
		cfgPath := filepath.Join(dir, AccountFile)
		if _, err := os.Stat(cfgPath); err != nil {
			continue // not an account folder
		}
		a, err := loadAccount(dir, e.Name(), cfgPath)
		if err != nil {
			return nil, err
		}
		accounts = append(accounts, a)
	}
	sort.Slice(accounts, func(i, j int) bool { return accounts[i].Slug < accounts[j].Slug })
	return accounts, nil
}

func loadAccount(dir, slug, cfgPath string) (*Account, error) {
	var a Account
	if _, err := toml.DecodeFile(cfgPath, &a); err != nil {
		return nil, fmt.Errorf("%s: %w", cfgPath, err)
	}
	a.Slug = slug
	a.Dir = dir
	if a.Name == "" {
		a.Name = slug
	}
	if a.Currency == "" {
		return nil, fmt.Errorf("%s: currency is required", cfgPath)
	}
	if a.Parser == "" {
		return nil, fmt.Errorf("%s: parser is required", cfgPath)
	}
	if a.Digits() < 0 || a.Digits() > 8 {
		return nil, fmt.Errorf("%s: minor_digits must be between 0 and 8", cfgPath)
	}
	return &a, nil
}

// IndexPath returns the location of the SQLite index for a data root.
func IndexPath(root string) string {
	return filepath.Join(root, StateDir, IndexFile)
}

// UserConfig is the small file in the user's config directory that says where
// the data root lives, so the tool can be run from anywhere without flags.
type UserConfig struct {
	Root string `toml:"root"`
}

// UserConfigPath returns the config file location, following the XDG base
// directory spec: $XDG_CONFIG_HOME/money/config.toml, falling back to
// ~/.config/money/config.toml.
func UserConfigPath() (string, error) {
	if dir := os.Getenv("XDG_CONFIG_HOME"); dir != "" {
		return filepath.Join(dir, "money", "config.toml"), nil
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("cannot locate the home directory: %w", err)
	}
	return filepath.Join(home, ".config", "money", "config.toml"), nil
}

// LoadUserConfig reads the config file. A missing file is not an error: it
// just means nothing overrides the default data root.
func LoadUserConfig() (*UserConfig, string, error) {
	path, err := UserConfigPath()
	if err != nil {
		return &UserConfig{}, "", err
	}
	var c UserConfig
	if _, err := toml.DecodeFile(path, &c); err != nil {
		if os.IsNotExist(err) {
			return &UserConfig{}, path, nil
		}
		return nil, path, fmt.Errorf("%s: %w", path, err)
	}
	return &c, path, nil
}

// RootSource records where a resolved data root came from, so the tool can
// explain itself when the path is not what the user expected.
type RootSource string

// The ways a data root can be chosen, in order of precedence.
const (
	RootFromFlag    RootSource = "--root flag"
	RootFromEnv     RootSource = "MONEY_ROOT"
	RootFromConfig  RootSource = "config file"
	RootFromDefault RootSource = "default"
)

// ResolveRoot decides which data root to use. An explicit flag wins, then
// $MONEY_ROOT, then the config file, then ~/money.
func ResolveRoot(flagRoot string) (root string, source RootSource, err error) {
	switch {
	case flagRoot != "":
		root, source = flagRoot, RootFromFlag
	default:
		if env := os.Getenv("MONEY_ROOT"); env != "" {
			root, source = env, RootFromEnv
		} else {
			c, _, err := LoadUserConfig()
			if err != nil {
				return "", "", err
			}
			if c.Root != "" {
				root, source = c.Root, RootFromConfig
			} else {
				home, err := os.UserHomeDir()
				if err != nil {
					return "", "", fmt.Errorf("cannot locate the home directory: %w", err)
				}
				root, source = filepath.Join(home, "money"), RootFromDefault
			}
		}
	}

	if root, err = expandHome(root); err != nil {
		return "", "", err
	}
	if root, err = filepath.Abs(root); err != nil {
		return "", "", err
	}
	return root, source, nil
}

// expandHome resolves a leading ~, which a hand-written config file is likely
// to contain and which the shell does not expand for us.
func expandHome(path string) (string, error) {
	if path != "~" && !strings.HasPrefix(path, "~/") {
		return path, nil
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("cannot expand %q: %w", path, err)
	}
	return filepath.Join(home, strings.TrimPrefix(strings.TrimPrefix(path, "~"), "/")), nil
}