package router

import (
	"regexp"
	"strings"
)

// Grammar — one stage-0 exact-match pattern. Wake-word + known command grammar
// hits the allowlist directly, skips the classifier (lowest latency — the vosk
// command path). Boring high-frequency acts for free.
//
// A Grammar returns a fully-formed Decision (intent + slots) at confidence 1.0
// when its pattern matches AND its Build returns ok=true; the router stops the
// cascade. Grammar rules are code, not config — same boundary as rules-as-code
// in the loop. The tool registry populates the verb set at daemon wiring time.
type Grammar struct {
	Name    string
	Pattern *regexp.Regexp // matched against the raw utterance
	Build   func(match []string) (Decision, bool)
}

// wakeWordAct — "maven, restart nginx" / "maven restart nginx" → the remainder
// is matched against the act allowlist. A non-match returns ok=false so the
// cascade falls through to the classifier (a wakeword prefix alone doesn't
// guarantee a known command — "maven, i'm tired" is a fact, not an act).
var wakeWordAct = regexp.MustCompile(`(?i)^\s*(?:maven|мэйвен|мейвен|майвен|мавена?|мэвен)[,:.!\s]+(.+)$`)

// wakeToken matches a leading wake-word token in any script the STT commonly
// produces for "Maven" — Latin "maven" or a Cyrillic phonetic rendering. The
// STT is a Russian model, so it transcribes the spoken wake word phonetically
// almost every time; matching only the Latin spelling meant stage-0 grammars
// (time/date/reminder) silently missed nearly every wake-worded utterance and
// fell through to the classifier, which misroutes time queries into the
// reminder intent (dense time-vocab centroid, see SystemTimeDateGrammars).
var wakeToken = regexp.MustCompile(`(?i)^\s*(?:maven|мэйвен|мейвен|майвен|мавена?|мэвен)[,:.!\s]*`)

// StripWakeToken removes a leading wake-word token (any script/spelling seen
// in wakeToken) and reports whether one was found.
func StripWakeToken(u string) (string, bool) {
	loc := wakeToken.FindStringIndex(u)
	if loc == nil {
		return u, false
	}
	rest := strings.TrimSpace(u[loc[1]:])
	if rest == "" {
		return u, false
	}
	return rest, true
}

// DefaultGrammars — the wake-word act fast path. The ActMatcher is the same
// allowlist stage-2 act extraction uses (single source of truth for the fn
// list). Returns nil grammars if no matcher is wired (the daemon always wires
// one — the guard is for tests that only exercise the classifier).
func DefaultGrammars(actMatcher ActMatcher) []Grammar {
	if actMatcher == nil {
		return nil
	}
	return []Grammar{
		{
			Name:    "wakeword-act",
			Pattern: wakeWordAct,
			Build: func(m []string) (Decision, bool) {
				rest := strings.TrimSpace(m[1])
				fn, args, ok := actMatcher.Match(rest)
				if !ok {
					return Decision{}, false // fall through to classifier
				}
				return Decision{
					Stage:      0,
					Intent:     IntentAct,
					Confidence: 1.0,
					Slots:      Slots{Fn: fn, Args: args, HasFn: true, Text: rest},
				}, true
			},
		},
	}
}

// --- напомни / remind me stage-0 grammar ---
//
// "напомни через час выпить воды" / "remind me in 30 minutes to water plants"
// routes directly to IntentReminder, bypassing the classifier entirely.
// Without this grammar the reminder centroid (dense with time-lexicon) pulls
// non-reminder time queries toward it, and the verb+action overlap pushes
// actual reminders toward fact — a double contamination. Stage 0 fixes both.
//
// The grammar captures the part after "напомни"/"remind me" into Slots.Text
// so the daemon's time parser can extract the fire time from it. The grammar
// itself does NOT parse time — that's the extractor's job (stage 2), but
// stage 0 skips the extractor. The daemon's applyAction fallback calls the
// time parser for stage-0 reminders that arrive without HasTime.
func ReminderGrammar() Grammar {
	return Grammar{
		Name:    "reminder-wakeword",
		Pattern: regexp.MustCompile(`(?i)^\s*(?:напомни|remind me)[\s,:]+(.+)$`),
		Build: func(m []string) (Decision, bool) {
			rest := strings.TrimSpace(m[1])
			if rest == "" {
				return Decision{}, false
			}
			return Decision{
				Stage:      0,
				Intent:     IntentReminder,
				Confidence: 1.0,
				Slots:      Slots{Text: rest},
			}, true
		},
	}
}

// SystemTimeDateGrammars — stage-0 grammars for high-frequency system queries
// that replySystem handles deterministically (time, date, day-of-week).
// "сколько времени" is seeded in BOTH system.txt and query.txt (a centroid
// collision), and the reminder centroid contaminates any utterance with time
// vocabulary. These grammars route directly to IntentSystem, skipping the
// classifier entirely — the answer is always deterministic.
//
// The time-query grammar uses a broad pattern (prefix match) with a Build
// filter: utterances containing "прошло"/"осталось" or starting with "до"
// after the time expression are elapsed/duration queries that belong to the
// classifier, not to replySystem's "what time is it" handler.
func SystemTimeDateGrammars() []Grammar {
	return []Grammar{
		{
			Name:    "time-query",
			Pattern: regexp.MustCompile(`(?i)^\s*сколько\s+(сейчас\s+)?времени(.*)$`),
			Build:   timeQueryBuild,
		},
		{
			Name:    "clock-query",
			Pattern: regexp.MustCompile(`(?i)^\s*который\s+(сейчас\s+)?час(\s+у\s+нас|\s+в\s+\w+)?\s*[?!.]?\s*$`),
			Build:   timeDateBuild,
		},
		{
			Name:    "date-query",
			Pattern: regexp.MustCompile(`(?i)^\s*(?:какой\s+сегодня\s+(?:день|день\s+недели|число)|какое\s+сегодня\s+число)\s*[?!.]?\s*$`),
			Build:   timeDateBuild,
		},
	}
}

// timeQueryBuild — Build for the time-query grammar. Returns ok=false for
// elapsed/duration queries ("сколько времени прошло", "сколько времени
// осталось", "сколько времени до") so they fall through to the classifier.
// The classifier handles them as query intent (notes RAG), not system.
func timeQueryBuild(m []string) (Decision, bool) {
	suffix := strings.TrimSpace(m[2])
	if suffix != "" && !strings.HasPrefix(suffix, "?") {
		lower := strings.ToLower(suffix)
		// If the first word after "времени" is a duration marker, this is an
		// elapsed-time query, not a "what time is it" query.
		firstWord := strings.Fields(lower)
		if len(firstWord) > 0 {
			switch firstWord[0] {
			case "прошло", "осталось", "до", "пройдет", "минуло", "проходит":
				return Decision{}, false
			}
		}
	}
	return Decision{
		Stage:      0,
		Intent:     IntentSystem,
		Confidence: 1.0,
	}, true
}

// timeDateBuild — shared Build for clock-query and date-query grammars. Returns a
// Decision routed to IntentSystem with the original utterance intact, so the
// daemon's replySystem handler can keyword-match and answer it.
func timeDateBuild(m []string) (Decision, bool) {
	return Decision{
		Stage:      0,
		Intent:     IntentSystem,
		Confidence: 1.0,
	}, true
}