// Package rules applies the ordered glob rules from rules.toml to
// transactions, deciding their automatic tag.
//
// Only rule_tag is ever written. A tag set by hand in the TUI lives in its own
// column and survives any number of re-runs.
package rules

import (
	"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/store"
)

// Engine evaluates rules in file order; the first match wins.
type Engine struct {
	rules []config.Rule
}

// New builds an engine from the parsed rules file.
func New(r *config.Rules) *Engine {
	return &Engine{rules: r.Rule}
}

// Rules returns the ordered rules, as loaded from rules.toml.
func (e *Engine) Rules() []config.Rule { return e.rules }

// Match returns the first rule matching a transaction on the given account, or
// nil if none does.
func (e *Engine) Match(accountSlug string, t model.Transaction) *config.Rule {
	if i := e.MatchIndex(accountSlug, t); i >= 0 {
		return &e.rules[i]
	}
	return nil
}

// MatchIndex returns the position of the first rule matching a transaction, or
// -1 if none does. Every pattern a rule sets must match: a rule with both
// match and type is an "and", not an "or".
//
// The position matters as well as the rule: because the first match wins, a
// rule that is fully shadowed by an earlier one never applies to anything, and
// only the index reveals that.
func (e *Engine) MatchIndex(accountSlug string, t model.Transaction) int {
	var (
		description = model.NormalizeDescription(t.Description)
		kind        = model.NormalizeDescription(t.Type)
	)
	for i := range e.rules {
		r := &e.rules[i]
		if r.Account != "" && r.Account != accountSlug {
			continue
		}
		if r.Match != "" && !glob.Match(r.Match, description) {
			continue
		}
		if r.Type != "" && !glob.Match(r.Type, kind) {
			continue
		}
		return i
	}
	return -1
}

// Usage counts how many transactions each rule actually claims. A rule with a
// count of zero is dead: either nothing matches it, or an earlier rule takes
// everything it would have caught.
func (e *Engine) Usage(txns []model.Transaction) []int {
	counts := make([]int, len(e.rules))
	for _, t := range txns {
		if i := e.MatchIndex(t.AccountSlug, t); i >= 0 {
			counts[i]++
		}
	}
	return counts
}

// ApplyTxn returns the tag for a transaction, empty if no rule matches.
func (e *Engine) ApplyTxn(accountSlug string, t model.Transaction) string {
	if r := e.Match(accountSlug, t); r != nil {
		return r.Tag
	}
	return ""
}

// Apply is the description-only shorthand, for callers that have nothing else.
func (e *Engine) Apply(accountSlug, description string) string {
	return e.ApplyTxn(accountSlug, model.Transaction{Description: description})
}

// Retag recomputes rule verdicts for every transaction in the index and
// writes them back. It returns how many rows changed.
func (e *Engine) Retag(db *store.DB) (int, error) {
	txns, err := db.Transactions(store.Filter{})
	if err != nil {
		return 0, err
	}
	var changed []store.RuleAssignment
	for _, t := range txns {
		tag := e.ApplyTxn(t.AccountSlug, t)
		if tag == t.RuleTag {
			continue
		}
		changed = append(changed, store.RuleAssignment{ID: t.ID, Tag: tag})
	}
	if len(changed) == 0 {
		return 0, nil
	}
	if err := db.ApplyRuleResults(changed); err != nil {
		return 0, err
	}
	return len(changed), nil
}