package eventcatalog

import (
	"errors"
	"fmt"
	"regexp"
	"strings"
	"time"
)

var canonicalOccasionKeyPattern = regexp.MustCompile(`^[a-z][a-z0-9]*(?:-[a-z0-9]+)*$`)

var jalaliBreaks = [...]int{-61, 9, 38, 199, 426, 686, 756, 818, 1111, 1181, 1210, 1635, 2060, 2097, 2192, 2262, 2324, 2394, 2456, 3178}

type EventType string
type Tone string
type CommercialPosture string
type Recurrence string

const (
	TypePublicHoliday EventType = "PUBLIC_HOLIDAY"
	TypeReligious     EventType = "RELIGIOUS"
	TypeNational      EventType = "NATIONAL"
	TypeCultural      EventType = "CULTURAL"
	TypeCommercial    EventType = "COMMERCIAL"
	TypeSeasonal      EventType = "SEASONAL"
	TypeEducation     EventType = "EDUCATION"
	TypeEconomic      EventType = "ECONOMIC"
	TypeEmergency     EventType = "EMERGENCY_CLOSURE"

	ToneCelebratory Tone = "CELEBRATORY"
	ToneJoyful      Tone = "JOYFUL"
	ToneNeutral     Tone = "NEUTRAL"
	ToneSolemn      Tone = "SOLEMN"
	ToneMourning    Tone = "MOURNING"
	ToneMemorial    Tone = "MEMORIAL"

	PosturePromote     CommercialPosture = "PROMOTE"
	PostureCaution     CommercialPosture = "CAUTION"
	PostureNoPromotion CommercialPosture = "NO_PROMOTION"

	RecurrenceBlackFriday Recurrence = "BLACK_FRIDAY"
	RecurrenceCyberMonday Recurrence = "CYBER_MONDAY"
)

type Event struct {
	ID                 string            `json:"id"`
	OccasionKey        string            `json:"occasionKey,omitempty"`
	Variant            string            `json:"eventVariant,omitempty"`
	JalaliYear         int               `json:"jalaliYear,omitempty"`
	TitleFA            string            `json:"titleFa"`
	TitleEN            string            `json:"titleEn,omitempty"`
	Aliases            []string          `json:"aliases,omitempty"`
	Themes             []string          `json:"themes,omitempty"`
	CampaignTags       []string          `json:"campaignTags,omitempty"`
	StartDate          string            `json:"startDate"`
	EndDate            string            `json:"endDate"`
	Recurrence         Recurrence        `json:"recurrence,omitempty"`
	Type               EventType         `json:"eventType"`
	Tone               Tone              `json:"tone"`
	CommercialPosture  CommercialPosture `json:"commercialPosture"`
	OfficialHoliday    bool              `json:"officialHoliday"`
	SourceURI          string            `json:"sourceUri"`
	SourceVersion      string            `json:"sourceVersion"`
	SourceChecksum     string            `json:"sourceChecksum,omitempty"`
	InclusionRationale string            `json:"inclusionRationale"`
	GeographicScope    string            `json:"geographicScope"`
	MerchantCategories []string          `json:"merchantCategories,omitempty"`
	BehavioralChannels []string          `json:"behavioralChannels,omitempty"`
	LeadDays           int               `json:"leadDays"`
	LagDays            int               `json:"lagDays"`
	RelevanceBPS       int               `json:"relevanceBps"`
	ConfidenceBPS      int               `json:"confidenceBps"`
	ImportanceBPS      int               `json:"importanceBps,omitempty"`
}

func ResolveRecurrence(rule Recurrence, year int, location *time.Location) (time.Time, error) {
	if year < 1900 || year > 2200 {
		return time.Time{}, errors.New("event catalog: recurrence year out of range")
	}
	thanksgiving := nthWeekday(year, time.November, time.Thursday, 4, location)
	switch rule {
	case RecurrenceBlackFriday:
		return thanksgiving.AddDate(0, 0, 1), nil
	case RecurrenceCyberMonday:
		return thanksgiving.AddDate(0, 0, 4), nil
	default:
		return time.Time{}, fmt.Errorf("event catalog: unsupported recurrence %q", rule)
	}
}

func ValidateEvents(events []Event) error {
	seen := make(map[string]struct{}, len(events))
	canonical := make(map[string]struct{}, len(events))
	canonicalYears := make(map[string]struct{}, len(events))
	for _, event := range events {
		if strings.TrimSpace(event.ID) == "" || strings.TrimSpace(event.TitleFA) == "" || strings.TrimSpace(event.SourceURI) == "" || strings.TrimSpace(event.SourceVersion) == "" || strings.TrimSpace(event.InclusionRationale) == "" || strings.TrimSpace(event.GeographicScope) == "" {
			return fmt.Errorf("event catalog: event %q is incomplete", event.ID)
		}
		if _, exists := seen[event.ID]; exists {
			return fmt.Errorf("event catalog: duplicate event %q", event.ID)
		}
		seen[event.ID] = struct{}{}
		if !canonicalOccasionKeyPattern.MatchString(event.OccasionKey) {
			return fmt.Errorf("event catalog: event %q has invalid canonical occasion key", event.ID)
		}
		if hasYearSegment(event.OccasionKey) {
			return fmt.Errorf("event catalog: event %q has year-specific occasion key", event.ID)
		}
		if event.Variant == "" {
			event.Variant = "PRIMARY"
		}
		if event.Variant != "PRIMARY" && event.Variant != "CAMPAIGN_WINDOW" && event.Variant != "OPERATIONAL_WINDOW" {
			return fmt.Errorf("event catalog: event %q has invalid variant", event.ID)
		}
		start, err := time.Parse(time.DateOnly, event.StartDate)
		if err != nil {
			return fmt.Errorf("event catalog: event %q start date: %w", event.ID, err)
		}
		end, err := time.Parse(time.DateOnly, event.EndDate)
		if err != nil || end.Before(start) {
			return fmt.Errorf("event catalog: event %q has invalid end date", event.ID)
		}
		if !validType(event.Type) || !validTone(event.Tone) || !validPosture(event.CommercialPosture) {
			return fmt.Errorf("event catalog: event %q has invalid classification", event.ID)
		}
		if (event.Tone == ToneMourning || event.Tone == ToneMemorial) && event.CommercialPosture == PosturePromote {
			return fmt.Errorf("event catalog: event %q cannot promote during mourning or memorial", event.ID)
		}
		if event.LeadDays < 0 || event.LagDays < 0 || event.RelevanceBPS < 0 || event.RelevanceBPS > 10_000 || event.ConfidenceBPS < 0 || event.ConfidenceBPS > 10_000 || event.ImportanceBPS < 0 || event.ImportanceBPS > 10_000 {
			return fmt.Errorf("event catalog: event %q has invalid impact metadata", event.ID)
		}
		if event.LeadDays > 90 || event.LagDays > 90 {
			return fmt.Errorf("event catalog: event %q lead or lag window exceeds 90 days", event.ID)
		}
		if event.Recurrence != "" {
			resolved, err := ResolveRecurrence(event.Recurrence, start.Year(), time.UTC)
			if err != nil {
				return fmt.Errorf("event catalog: event %q recurrence: %w", event.ID, err)
			}
			if !resolved.Equal(start) || !end.Equal(start) {
				return fmt.Errorf("event catalog: event %q does not match its resolved recurrence", event.ID)
			}
		}
		canonicalKey := strings.Join([]string{event.OccasionKey, event.Variant, event.StartDate, event.EndDate}, "\x00")
		if _, exists := canonical[canonicalKey]; exists {
			return fmt.Errorf("event catalog: duplicate canonical occurrence %q", event.ID)
		}
		canonical[canonicalKey] = struct{}{}
		if event.JalaliYear != 0 {
			canonicalYearKey := fmt.Sprintf("%s\x00%s\x00%d", event.OccasionKey, event.Variant, event.JalaliYear)
			if _, exists := canonicalYears[canonicalYearKey]; exists {
				return fmt.Errorf("event catalog: duplicate canonical occurrence in Jalali year %d for event %q", event.JalaliYear, event.ID)
			}
			canonicalYears[canonicalYearKey] = struct{}{}
		}
	}
	return nil
}

// ValidateDeclaredCoverage verifies that each year advertised by an import has
// at least one dated event. JalaliYear is explicit review metadata: it avoids
// guessing calendar boundaries from Gregorian dates during catalog approval.
func ValidateDeclaredCoverage(events []Event, startJalaliYear, endJalaliYear int) error {
	if startJalaliYear <= 0 || endJalaliYear < startJalaliYear {
		return errors.New("event catalog: invalid declared Jalali coverage")
	}
	covered := make(map[int]struct{}, endJalaliYear-startJalaliYear+1)
	for _, event := range events {
		if event.JalaliYear < startJalaliYear || event.JalaliYear > endJalaliYear {
			return fmt.Errorf("event catalog: event %q lacks valid Jalali year within declared coverage", event.ID)
		}
		start, err := time.Parse(time.DateOnly, event.StartDate)
		if err != nil {
			return fmt.Errorf("event catalog: event %q start date: %w", event.ID, err)
		}
		end, err := time.Parse(time.DateOnly, event.EndDate)
		if err != nil {
			return fmt.Errorf("event catalog: event %q end date: %w", event.ID, err)
		}
		startJalaliYear := gregorianToJalaliYear(start)
		endJalaliYear := gregorianToJalaliYear(end)
		belongsToOccurrenceYear := startJalaliYear == event.JalaliYear || endJalaliYear == event.JalaliYear
		preparesImmediateNextYear := event.Variant == "CAMPAIGN_WINDOW" && endJalaliYear+1 == event.JalaliYear && gregorianToJalaliYear(end.AddDate(0, 0, 1)) == event.JalaliYear
		if !belongsToOccurrenceYear && !preparesImmediateNextYear {
			return fmt.Errorf("event catalog: event %q Jalali year is inconsistent with its Gregorian date", event.ID)
		}
		covered[event.JalaliYear] = struct{}{}
	}
	for year := startJalaliYear; year <= endJalaliYear; year++ {
		if _, exists := covered[year]; !exists {
			return fmt.Errorf("event catalog: declared coverage has no event in Jalali year %d", year)
		}
	}
	return nil
}

func hasYearSegment(value string) bool {
	digits := 0
	for _, character := range value {
		if character >= '0' && character <= '9' {
			digits++
			if digits >= 4 {
				return true
			}
		} else {
			digits = 0
		}
	}
	return false
}

func gregorianToJalaliYear(date time.Time) int {
	jy := date.Year() - 621
	firstFarvardin := gregorianDayNumber(date.Year(), 3, jalaliMarchDay(jy))
	if gregorianDayNumber(date.Year(), int(date.Month()), date.Day()) < firstFarvardin {
		jy--
	}
	return jy
}

func jalaliMarchDay(jy int) int {
	gy := jy + 621
	leapJ := -14
	previousBreak := jalaliBreaks[0]
	jump := 0
	for index := 1; index < len(jalaliBreaks); index++ {
		currentBreak := jalaliBreaks[index]
		jump = currentBreak - previousBreak
		if jy < currentBreak {
			break
		}
		leapJ += jump/33*8 + (jump%33)/4
		previousBreak = currentBreak
	}
	n := jy - previousBreak
	leapJ += n/33*8 + (n%33+3)/4
	if jump%33 == 4 && jump-n == 4 {
		leapJ++
	}
	leapG := gy/4 - ((gy/100+1)*3)/4 - 150
	return 20 + leapJ - leapG
}

func gregorianDayNumber(gy, gm, gd int) int {
	dayNumber := ((gy+(gm-8)/6+100100)*1461)/4 + (153*((gm+9)%12)+2)/5 + gd - 34840408
	return dayNumber - (((gy+100100+(gm-8)/6)/100)*3)/4 + 752
}

func nthWeekday(year int, month time.Month, weekday time.Weekday, occurrence int, location *time.Location) time.Time {
	first := time.Date(year, month, 1, 0, 0, 0, 0, location)
	offset := (int(weekday) - int(first.Weekday()) + 7) % 7
	return first.AddDate(0, 0, offset+7*(occurrence-1))
}

func validType(value EventType) bool {
	switch value {
	case TypePublicHoliday, TypeReligious, TypeNational, TypeCultural, TypeCommercial, TypeSeasonal, TypeEducation, TypeEconomic, TypeEmergency:
		return true
	default:
		return false
	}
}

func validTone(value Tone) bool {
	switch value {
	case ToneCelebratory, ToneJoyful, ToneNeutral, ToneSolemn, ToneMourning, ToneMemorial:
		return true
	default:
		return false
	}
}

func validPosture(value CommercialPosture) bool {
	return value == PosturePromote || value == PostureCaution || value == PostureNoPromotion
}