package router

import (
	"context"
	"time"
)

// FastPathResult is the outcome of the stage-0 deterministic fast path.
// Matched is true when a grammar accepted the input. Decision carries the
// full routing result for a match. When Matched is false the caller falls
// through to the general cascade (heads → LLM → classifier → extraction → gate).
type FastPathResult struct {
	Matched  bool
	Decision Decision
}

// TryFastPath runs the stage-0 exact-match grammars. It owns the ordered
// grammar list, first-match-wins semantics, wake-token alternate handling,
// slot filling, capability selection, and per-grammar trace recording.
//
// When no grammar matches, Matched is false and the caller falls through
// to the general cascade.
//
// TryFastPath receives NormalizedInput so later recognizers can opt into
// MatchText, but no existing grammar switches in this slice — they all
// receive input.Text (the raw utterance) exactly as they do today.
func (r *Router) TryFastPath(
	ctx context.Context,
	input NormalizedInput,
	now time.Time,
) (FastPathResult, error) {
	// stage 0 — exact match / grammar. First match wins; grammars are ordered.
	// Grammars like time/date/reminder don't expect a wake-word prefix, but
	// the STT often includes one (transcribed phonetically, any script) — try
	// the wake-stripped utterance too so those grammars still fire.
	stripped, hadWake := StripWakeToken(input.Text)
	// declinedBuild — the grammars that matched the shape and refused the
	// content, kept for the decision record (V-564) so a reader can tell that
	// rule from one whose pattern never fired.
	var declinedBuild map[int]bool
	for i, g := range r.grammars {
		d, matched, ok := g.Evaluate(input.Text)
		if !matched && hadWake {
			d, matched, ok = g.Evaluate(stripped)
		}
		if !matched {
			continue
		}
		if !ok {
			if declinedBuild == nil {
				declinedBuild = map[int]bool{}
			}
			declinedBuild[i] = true
			continue // grammar matched shape but not content → fall through
		}
		d.Utterance = input.Text
		d.Producer = RouteProducerGrammar
		// A literal pattern named that destination, which is the one provenance
		// allowed to take the personal boundary off a turn (V-666). Set here and
		// nowhere else, so no other arm of the cascade can claim it.
		d.SourceAnchored = d.Source != SourceUnknown
		// The grammar decided the intent; the extractor fills the slots it did
		// not match (V-572). See fillMatchedSlots for why every grammar gets it.
		r.fillMatchedSlots(ctx, &d, now)
		// Capability selection: deterministic grammars that already resolved Fn
		// (wakeword-act, praxis, task-status) bypass the general selector.
		// SelectCapability records the existing result with
		// InputKind=SelectionDeterministic.
		applyCapabilityToSlots(&d, SelectCapability(d, r.extractor.Acts))
		r.noteGrammarOutcomes(ctx, i+1, declinedBuild, g.Name, d.Intent)
		return FastPathResult{Matched: true, Decision: d}, nil
	}
	r.noteGrammarOutcomes(ctx, len(r.grammars), declinedBuild, "", "")
	return FastPathResult{}, nil
}