package router

import (
	"context"
	"errors"
	"log"
	"time"

	"github.com/kami/maven/internal/decision"
)

// Config — wires the cascade. Build via New; a zero-value Router is unusable.
type Config struct {
	// Grammars — stage-0 exact-match rules. DefaultGrammars(actMatcher) wires
	// the wake-word act fast path; the daemon may append more.
	Grammars []Grammar
	// Classifier — stage-1 nearest-centroid classifier. Must be seeded with
	// ~10 examples/intent at bootstrap (per spec) before free-form routing
	// is trustworthy; until then Route returns ErrNoIntents on free-form input.
	Classifier *Classifier
	// Extractor — stage-2 per-intent slot extraction. Any nil sub-parser just
	// leaves the corresponding Has* flag false for that intent.
	Extractor Extractor
	// Threshold — stage-3 confidence gate. Below ⇒ Clarify, don't guess. The
	// spec leaves this open (defines how often maven asks vs guesses on free-
	// form input; the whole reactive mvp feel rides on it). The daemon sets it.
	Threshold float64
	// LLM — optional agentic router. When set, Route consults it after stage-0
	// and before the classifier cascade, classifying the utterance via a
	// grammar-constrained call to the resident model (Qwen3-1.7B). On any
	// error/parse failure, falls through to the classifier (never fails the
	// turn on the model).
	LLM *LLMRouter
	// Heads — optional routing heads over the fine-tuned embedder copy. When
	// set, Route consults them after stage 0 and before the LLM router. They
	// decline below their own confidence threshold, so a low-confidence turn
	// reaches the model exactly as it does today. Nil is the shipped-before
	// behaviour and costs nothing.
	Heads *RouterHeads
}

// Router — the deterministic cascade. Route never guesses: stage 0 wins
// outright, stage 1 scores, stage 2 extracts, stage 3 gates. The SLM only
// phrases the reply — it never owns the route.
type Router struct {
	grammars   []Grammar
	classifier *Classifier
	extractor  Extractor
	threshold  float64
	llm        *LLMRouter
	heads      *RouterHeads
}

func New(cfg Config) *Router {
	return &Router{
		grammars:   cfg.Grammars,
		classifier: cfg.Classifier,
		extractor:  cfg.Extractor,
		threshold:  cfg.Threshold,
		llm:        cfg.LLM,
		heads:      cfg.Heads,
	}
}

// Route — the cascade: stage 0 (exact match) → 1 (classify) → 2 (extract) →
// 3 (confidence gate).
//
//	Stage 0 wins outright: returns at confidence 1.0, no classifier.
//	Otherwise the classifier scores every intent; the best wins; slots are
//	extracted for that intent. If the winning score < threshold the Decision
//	is flagged Clarify (the daemon asks rather than guesses — same shape as
//	since(key)==null → don't fire: a misrouted fact is a confident wrong write,
//	worse than a gap).
func (r *Router) Route(ctx context.Context, input NormalizedInput, now time.Time) (Decision, error) {
	utterance := input.Text

	// stage 0 — deterministic fast path. First match wins; grammars are ordered.
	fast, err := r.TryFastPath(ctx, input, now)
	if err != nil {
		return Decision{}, err
	}
	if fast.Matched {
		return fast.Decision, nil
	}

	// stage 0b — routing heads (when wired). A softmax over the label set, so
	// it cannot name an intent or a destination that does not exist, and its
	// max is a real confidence. It runs before the model because it is three
	// orders of magnitude faster and scores better on both halves of the route.
	//
	// It declines below its threshold rather than clarifying. A declined turn
	// carries on to the model and then the classifier, which is what a box with
	// no weights file does on every turn.
	if r.heads != nil {
		res, ok, err := r.heads.Route(ctx, utterance)
		switch {
		case err != nil:
			log.Printf("router: heads fell through to the rest of the cascade: %v", err)
			decision.Note(ctx, decision.Claim{
				Stage: decision.StageRoute, Claimant: claimantHeads,
				Outcome: decision.Declined, Reason: "error: " + err.Error(),
			})
		case !ok:
			decision.Note(ctx, decision.Scored(decision.StageRoute, claimantHeads,
				string(res.Intent), res.Confidence, decision.Declined,
				"below the heads confidence threshold"))
		default:
			d := Decision{
				Utterance:  utterance,
				Stage:      2,
				Intent:     res.Intent,
				Confidence: res.Confidence,
				Source:     res.Source,
				Clarify:    res.Clarify,
				Producer:   RouteProducerHeads,
			}
			r.fillSlots(ctx, &d, now)
			applyCapabilityToSlots(&d, SelectCapability(d, r.extractor.Acts))
			// The clarify head relearned the English assumption that one word
			// cannot be a sentence. Russian verbs carry subject and tense, and a
			// deterministic fact parser which also found a key gives both halves
			// of a complete write. That structural evidence outranks this one
			// learned veto; question-shaped turns remain untouched.
			clarifyOverruled := d.Clarify && completeParsedSingleVerbFact(d)
			if clarifyOverruled {
				d.Clarify = false
			}
			decision.Note(ctx, decision.Claim{
				Stage: decision.StageRoute, Claimant: claimantLLM,
				Outcome: decision.NeverAsked, Reason: "the routing heads answered",
			})
			decision.Note(ctx, decision.Claim{
				Stage: decision.StageRoute, Claimant: claimantClassifier,
				Outcome: decision.NeverAsked, Reason: "the routing heads answered",
			})
			outcome, reason := decision.Won, ""
			if d.Clarify {
				outcome, reason = decision.Thinned, "the clarify head says there is too little here to act on"
			} else if clarifyOverruled {
				reason = "a parsed single-token Russian verb is a complete fact"
			}
			decision.Note(ctx, decision.Scored(decision.StageRoute, claimantHeads,
				string(d.Intent), d.Confidence, outcome, reason))
			return d, nil
		}
	} else {
		decision.Note(ctx, decision.Claim{
			Stage: decision.StageRoute, Claimant: claimantHeads,
			Outcome: decision.NeverAsked, Reason: "no routing heads are wired",
		})
	}

	// stage 1a — LLM router (when wired). It reasons over the utterance instead
	// of nearest-centroid guessing. On any error/parse-fail, fall through to the
	// classifier cascade (never fail the turn on the model).
	if r.llm != nil {
		if d, ok, err := r.llm.Route(ctx, utterance, now); err == nil && ok {
			d.Utterance = utterance
			d.Producer = RouteProducerLLM
			r.fillSlots(ctx, &d, now)
			// Capability selection: after fillSlots populates Text, SelectCapability
			// tries the LLM-cleaned text against the allowlist when the raw
			// utterance did not match. This replaces the former LLM text backfill
			// that was embedded in fillSlots. Must run before gateLLMDecision so
			// the gate sees the correct resolution state for acts.
			sel := SelectCapability(d, r.extractor.Acts)
			applyCapabilityToSlots(&d, sel)
			before := d.Confidence
			r.gateLLMDecision(&d)
			// The classifier is the floor and it never ran, which is the whole
			// reason a wrong LLM route reads as unexplainable (V-564).
			decision.Note(ctx, decision.Claim{
				Stage: decision.StageRoute, Claimant: claimantClassifier,
				Outcome: decision.NeverAsked, Reason: "the LLM router answered",
			})
			outcome, reason := decision.Won, ""
			if d.Confidence < before {
				outcome, reason = decision.Thinned, thinReason(&d)
			}
			decision.Note(ctx, decision.Scored(decision.StageRoute, claimantLLM,
				string(d.Intent), d.Confidence, outcome, reason))
			return d, nil
		} else if err != nil {
			log.Printf("router: llm route fell back to classifier: %v", err)
			decision.Note(ctx, decision.Claim{
				Stage: decision.StageRoute, Claimant: claimantLLM,
				Outcome: decision.Declined, Reason: "error: " + err.Error(),
			})
		} else {
			decision.Note(ctx, decision.Claim{
				Stage: decision.StageRoute, Claimant: claimantLLM,
				Outcome: decision.Declined, Reason: "no parsable route in the reply",
			})
		}
	} else {
		decision.Note(ctx, decision.Claim{
			Stage: decision.StageRoute, Claimant: claimantLLM,
			Outcome: decision.NeverAsked, Reason: "no LLM router is wired",
		})
	}

	// stage 1 — intent classifier.
	results, err := r.classifier.Classify(ctx, utterance)
	if err != nil {
		return Decision{}, err
	}
	best := results[0]
	// The runners-up are the interesting part: two intents a hundredth apart is
	// a different defect from one that won outright (V-564). Two are enough to
	// see that, and the rest of a seven-intent scoreboard is noise on the page.
	if rec := decision.From(ctx); rec != nil {
		for _, res := range results[1:min(len(results), 3)] {
			rec.Note(decision.Scored(decision.StageRoute, claimantClassifier,
				string(res.Intent), res.Score, decision.LostOnScore,
				"lower similarity than "+string(best.Intent)))
		}
	}

	// stage 2 — slot extraction for the winning intent.
	d := Decision{
		Utterance:  utterance,
		Stage:      2,
		Intent:     best.Intent,
		Confidence: best.Score,
		Slots:      r.extractor.Extract(ctx, best.Intent, utterance, now),
		Producer:   RouteProducerClassifier,
	}
	// Capability selection: for the classifier path, the raw extractor
	// already filled Slots.Fn/Args via Extract(IntentAct). SelectCapability
	// records this as a deterministic bypass. If the raw match missed,
	// there is no LLM text to fall back to (Text == Utterance), so the
	// selection remains unresolved.
	applyCapabilityToSlots(&d, SelectCapability(d, r.extractor.Acts))

	// stage 3 — confidence gate. Below threshold ⇒ clarify, don't guess.
	if d.Confidence < r.threshold {
		d.Stage = 3
		d.Clarify = true
	}
	outcome, reason := decision.Won, ""
	if d.Clarify {
		outcome, reason = decision.Thinned, "below the clarify threshold, so she asks instead"
	}
	decision.Note(ctx, decision.Scored(decision.StageRoute, claimantClassifier,
		string(d.Intent), d.Confidence, outcome, reason))
	return d, nil
}

func completeParsedSingleVerbFact(decision Decision) bool {
	return decision.Intent == IntentFact && decision.Slots.HasKey &&
		completeSingleVerb(decision.Utterance) && !IsQuestionShaped(decision.Utterance)
}

// fillMatchedSlots — run stage-2 extraction over a decision some earlier
// claimant produced, and fill only the slots that claimant left empty. A
// matched value always wins: the claimant read the sentence, the extractor
// guesses from keyword tables.
//
// Shared by the stage-0 grammars and the LLM router, which had the same hole
// for the same reason. A grammar asserts an intent at confidence 1.0 and says
// nothing about the slots, so "напомни в 11:00 позвонить маме" arrived with
// HasTime false however plainly the hour was spoken, and the daemon read the
// silence as absence and asked "Когда?" (V-572). The alternative was ten
// grammars each re-implementing extraction.
//
// It is applied to every stage-0 decision rather than to a chosen few, because
// for every intent but reminder it is inert: Extract fills Time for a reminder,
// Fn for an act and Key for a fact, and nothing at all for query, system, note
// or chat, which is what the query, clock, agenda, feed, list, task and
// narrative rules emit. The act rules — wakeword-act and the Praxis ones —
// already carry an Fn or they do not match, so there is nothing left for the
// matcher to fill. The reminder rule is the one that gains, and its time parse
// is a cost the daemon was already paying one layer down in actionReminder.
//
// Slots.Text is deliberately NOT filled here. Extract sets it to the raw
// utterance, and a grammar that left it empty meant it: agendaQueryBuild hands
// the query chain the utterance itself, and narrativeQueryBuild's Text is the
// topic, not the sentence.
//
// If a reminder still has no time, leave it missing. The daemon then says it
// could not read the time; inventing one would set a wrong alarm.
// Returns what the extractor read, so a caller that wants more of it does not
// pay for a second extraction — the reminder parser is the expensive one.
func (r *Router) fillMatchedSlots(ctx context.Context, d *Decision, now time.Time) Slots {
	ex := r.extractor.Extract(ctx, d.Intent, d.Utterance, now)
	if !d.Slots.HasTime && ex.HasTime {
		d.Slots.Time, d.Slots.HasTime = ex.Time, ex.HasTime
	}
	if !d.Slots.HasKey && ex.HasKey {
		d.Slots.Key, d.Slots.Value, d.Slots.HasKey = ex.Key, ex.Value, ex.HasKey
	}
	// Capability selection (Fn/Args/HasFn) is now handled by
	// SelectCapability, not here. The extractor still fills them via
	// Extract(IntentAct), but the authoritative record lives in
	// Decision.CapabilitySelection. See capability.go.
	if !d.Slots.HasFn && ex.HasFn {
		d.Slots.Fn, d.Slots.Args, d.Slots.HasFn, d.Slots.ResolvedBy = ex.Fn, ex.Args, ex.HasFn, ex.ResolvedBy
	}
	return ex
}

// fillSlots — fillMatchedSlots for an LLM decision, plus the text backfill.
// Capability selection (Fn/Args) is now handled by SelectCapability, called
// after fillSlots in the routing pipeline. This function fills only time, key,
// and text slots.
func (r *Router) fillSlots(ctx context.Context, d *Decision, now time.Time) {
	ex := r.fillMatchedSlots(ctx, d, now)
	// The extractor's Text is the raw utterance, which is the payload for a
	// note, a query or a chat turn but not for a reminder — there Text is the
	// subject, what she says at the hour. Backfilling it made Text impossible
	// to be empty, so StillMissing never reported SlotText and "О чём
	// напомнить?" was unaskable; the answer to a question she did manage to
	// ask then overwrote the whole request instead of filling one gap
	// (Vikunja #383). A reminder with no subject stays empty and is gated
	// below into a question.
	if d.Slots.Text == "" && d.Intent != IntentReminder {
		d.Slots.Text = ex.Text
	}
	// Stage stays 1: it says who decided the route, and that was the LLM.
}

// gateLLMDecision — stage 3 for the LLM path (Vikunja #359). This used to be
// the classifier's job alone (see the threshold check at the bottom of
// Route): the LLM branch returned straight from fillSlots and never touched
// r.threshold at all, so a hardcoded Confidence: 1.0 in llmrouter.go could
// never gate. Two more structural holes are checked here, after fillSlots
// has had a chance to fill them from the deterministic parsers — checking
// before fillSlots would flag e.g. every keyless fact the fact parser goes
// on to resolve (TestLLMFactGetsKeyFromParser):
//   - a fact with no key even after the parser tried — nothing to write, or
//     worse, a confident write under the wrong key;
//   - an act that never resolved to an allowlisted fn — a confident guess
//     here means either silently doing nothing or, if the daemon is lax,
//     running something never on the allowlist. Don't guess; ask.
//
// Anything below threshold gets the exact same Clarify=true treatment the
// classifier path already produces — same field, same daemon-side consumer
// (cmd/mavend/clarify.go), nothing new to wire.
//
// The act check now reads CapabilitySelection.Resolved (set by
// SelectCapability before this function runs) rather than Slots.HasFn.
func (r *Router) gateLLMDecision(d *Decision) {
	if d.Intent == IntentFact && !d.Slots.HasKey && d.Confidence > llmThinConfidence {
		d.Confidence = llmThinConfidence
	}
	if d.Intent == IntentAct && !d.CapabilitySelection.Resolved && d.Confidence > llmThinConfidence {
		d.Confidence = llmThinConfidence
	}
	// A reminder with no subject: she knows when but not what to say then.
	// Setting it anyway fires an empty reminder at the hour, which reads as a
	// bug to him and cannot be repaired after the fact. Ask (Vikunja #383).
	//
	// The test is what the text slot CONTAINS, not whether it is set. It was the
	// latter until 05-08-2026, and the slot is never empty: fillSlots hands it
	// the utterance, so "напомни" arrived here with Text:напомни and the gate
	// never fired (V-457). See remindersubject.go.
	if d.Intent == IntentReminder && !reminderHasSubject(d.Slots.Text) && d.Confidence > llmThinConfidence {
		d.Confidence = llmThinConfidence
	}
	if d.Confidence < r.threshold {
		d.Clarify = true
	}
}

// CorrectMisroute — the user corrected a bad classification. Appends a new
// example for the corrected intent (append-only — grows the classifier, no
// retrain). Same shape as nudges.outcome tuning cooldowns: more reliable over
// time, introspectable, no model surgery.
func (r *Router) CorrectMisroute(ctx context.Context, utterance string, corrected Intent) error {
	if r == nil || r.classifier == nil {
		// The LLM router can run with no classifier wired. The correction has
		// nowhere to land then, and the caller redoes the request anyway.
		return errors.New("router: no classifier to correct")
	}
	return r.classifier.AddExample(ctx, corrected, utterance)
}