package pattern

import (
	"fmt"
	"math"
	"strings"
)

// ProposedRoutine is a detected recurring pattern that the system wants to
// suggest as a reminder. Returned by Detect when intervals are stable.
type ProposedRoutine struct {
	Action       string
	Object       string
	IntervalDays float64 // mean interval in days (float for sub-day precision)
	N            int     // number of events used
}

// MaxIntervalRatio is the maximum ratio between the longest and shortest
// interval for a pattern to be considered stable. ±50% variance allowed.
const MaxIntervalRatio = 1.5

// MinEvents is the minimum number of events needed to detect a pattern.
// With N events there are N-1 intervals, so 4 events means 3 intervals.
//
// This used to be 3 (two intervals), which is not a pattern — it is a
// coincidence with a mean. Two gaps of similar length happen constantly:
// water the plants on a Sunday, again the next Sunday, once more the Sunday
// after, and a detector with a ±50% band calls that a weekly routine. The
// cost of being wrong is asymmetric now that the digestion tick scans all of
// history on its own schedule and can announce what it finds: a false
// positive is something the owner has to read and dismiss, and a dismissal
// is permanent, so one bad guess burns that action+object pair forever.
// Three intervals is the cheapest bar that makes a run distinguishable from
// a repeat. False negatives cost one more observation and nothing else.
const MinEvents = 4

// Detect checks whether a sequence of events for the same action+object
// forms a stable recurring pattern. Returns a ProposedRoutine when:
//   - At least MinEvents events exist (≥2 intervals)
//   - The ratio longest/shortest interval ≤ MaxIntervalRatio
//
// Returns nil when there aren't enough events or the intervals are too
// irregular — false negatives are harmless. The only dangerous mistake
// is a false positive, and this detector makes none: the confirmation
// gate (voice park or web page) catches any we do produce.
func Detect(events []Event) (*ProposedRoutine, error) {
	if len(events) < MinEvents {
		return nil, nil // not enough data
	}

	nIntervals := len(events) - 1
	intervals := make([]float64, nIntervals)

	var sum float64
	var min float64 = math.MaxFloat64
	var max float64

	for i := 0; i < nIntervals; i++ {
		diff := events[i+1].Ts.Sub(events[i].Ts)
		days := diff.Hours() / 24.0
		if days <= 0 {
			// Two events at the same timestamp — can't compute a meaningful
			// interval. Skip this candidate silently.
			return nil, nil
		}
		intervals[i] = days
		sum += days
		if days < min {
			min = days
		}
		if days > max {
			max = days
		}
	}

	// Stability check: the most extreme intervals shouldn't differ by
	// more than MaxIntervalRatio. A ratio of 1.5 means a 7-day pattern
	// can have intervals between ~5.6 and ~8.4 days.
	if min > 0 && max/min > MaxIntervalRatio {
		return nil, nil // too irregular
	}

	mean := sum / float64(nIntervals)

	return &ProposedRoutine{
		Action:       events[0].Action,
		Object:       events[0].Object,
		IntervalDays: math.Round(mean*10) / 10, // round to 1 decimal
		N:            len(events),
	}, nil
}

// PhraseRoutine generates a human-readable suggestion string for a
// detected routine. Returns a Russian phrase like
// "ты заправляешь поилку раз в 7 дней — напоминать?"
func PhraseRoutine(p *ProposedRoutine) string {
	actionWord := p.Action
	objectWord := p.Object

	days := int(math.Round(p.IntervalDays))
	// Russian grammatical gender/hardcoded — matches maven's existing persona.
	var intervalPhrase string
	switch {
	case days < 1:
		intervalPhrase = "каждый день"
	case days == 1:
		intervalPhrase = "каждый день"
	case days < 7:
		intervalPhrase = fmt.Sprintf("раз в %d дня", days)
		if days%10 == 1 && days%100 != 11 {
			intervalPhrase = fmt.Sprintf("раз в %d день", days)
		}
	case days == 7:
		intervalPhrase = "раз в неделю"
	case days%7 == 0:
		intervalPhrase = fmt.Sprintf("раз в %d недели", days/7)
		if (days/7)%10 == 1 && (days/7)%100 != 11 {
			intervalPhrase = fmt.Sprintf("раз в %d неделю", days/7)
		}
	case days < 30:
		intervalPhrase = fmt.Sprintf("раз в %d дней", days)
	default:
		intervalPhrase = fmt.Sprintf("каждые %d дней", days)
	}

	objectDisplay := strings.ReplaceAll(objectWord, "_", " ")
	return fmt.Sprintf("ты %s %s %s — напоминать?", actionVerb(actionWord), objectDisplay, intervalPhrase)
}

// actionVerb returns a conjugated Russian verb form for "you do" (ты-form).
func actionVerb(action string) string {
	switch action {
	case "refill":
		return "заправляешь"
	case "feed":
		return "кормишь"
	case "change":
		return "меняешь"
	case "clean":
		return "чистишь"
	case "take":
		return "принимаешь"
	case "walk":
		return "выгуливаешь"
	case "water":
		return "поливаешь"
	default:
		return action + " (делаешь)"
	}
}