package eventcatalog

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

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:"variant,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))
	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 event.OccasionKey == "" {
			event.OccasionKey = 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{}{}
	}
	return nil
}

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
}