package service

import (
	"errors"
	"math"
	"sort"
	"time"

	"gorm.io/gorm"

	"dating-app/internal/dto"
	"dating-app/internal/models"
	"dating-app/internal/repository"
	"dating-app/internal/utils"
)

const (
	DefaultMinAge      = 18
	DefaultMaxAge      = 60
	DiscoverBatchSize  = 60
	DiscoverResultSize = 20
)

var (
	ErrGenderNotSet    = errors.New("برای دیدن پیشنهادها اول باید جنسیتت مشخص شده باشه")
	ErrCannotSwipeSelf = errors.New("نمی‌تونی روی خودت سواپ بزنی")
	ErrAlreadySwiped   = errors.New("قبلاً روی این پروفایل تصمیم گرفتی")
)

// جنسیت مخالف کاربر رو برمی‌گردونه. این ساده‌ترین فرض ممکنه (هترو دیفالت)؛
// سیستم فعلاً فیلد جداگانه‌ای برای «ترجیح جنسیتی/گرایش» نداره.
func oppositeGender(g models.Gender) models.Gender {
	if g == models.GenderFemale {
		return models.GenderMale
	}
	return models.GenderFemale
}

type DiscoveryService struct {
	userRepo     *repository.UserRepository
	photoRepo    *repository.PhotoRepository
	swipeRepo    *repository.SwipeRepository
	matchRepo    *repository.MatchRepository
	optionRepo   *repository.OptionRepository
	questionRepo *repository.QuestionRepository
}

func NewDiscoveryService(
	userRepo *repository.UserRepository,
	photoRepo *repository.PhotoRepository,
	swipeRepo *repository.SwipeRepository,
	matchRepo *repository.MatchRepository,
	optionRepo *repository.OptionRepository,
	questionRepo *repository.QuestionRepository,
) *DiscoveryService {
	return &DiscoveryService{
		userRepo:     userRepo,
		photoRepo:    photoRepo,
		swipeRepo:    swipeRepo,
		matchRepo:    matchRepo,
		optionRepo:   optionRepo,
		questionRepo: questionRepo,
	}
}

type candidateWithDistance struct {
	user     models.User
	distance *float64
}

// GetFeed لیست پیشنهادهای صفحه‌ی دوستیابی رو برمی‌گردونه؛ نزدیک‌ترین‌ها اول.
func (s *DiscoveryService) GetFeed(user *models.User, maxDistanceKM *float64, minAge, maxAge int) ([]dto.DiscoverCandidate, error) {
	if user.Gender == nil {
		return nil, ErrGenderNotSet
	}
	if minAge <= 0 {
		minAge = DefaultMinAge
	}
	if maxAge <= 0 || maxAge < minAge {
		maxAge = DefaultMaxAge
	}

	candidates, err := s.userRepo.ListDiscoverable(user.ID, oppositeGender(*user.Gender), minAge, maxAge, DiscoverBatchSize)
	if err != nil {
		return nil, err
	}
	if len(candidates) == 0 {
		return []dto.DiscoverCandidate{}, nil
	}

	ids := make([]uint, len(candidates))
	for i, c := range candidates {
		ids[i] = c.ID
	}

	photos, err := s.photoRepo.ListByUserIDs(ids)
	if err != nil {
		return nil, err
	}
	photosByUser := map[uint][]string{}
	for _, p := range photos {
		photosByUser[p.UserID] = append(photosByUser[p.UserID], p.URL)
	}

	interestsByUser := s.batchInterests(ids)

	withDist := make([]candidateWithDistance, 0, len(candidates))
	for _, cand := range candidates {
		var dist *float64
		if user.Latitude != nil && user.Longitude != nil && cand.Latitude != nil && cand.Longitude != nil {
			km := math.Round(utils.HaversineKM(*user.Latitude, *user.Longitude, *cand.Latitude, *cand.Longitude))
			dist = &km
		}
		if maxDistanceKM != nil && dist != nil && *dist > *maxDistanceKM {
			continue
		}
		withDist = append(withDist, candidateWithDistance{user: cand, distance: dist})
	}

	sort.SliceStable(withDist, func(i, j int) bool {
		if withDist[i].distance == nil {
			return false
		}
		if withDist[j].distance == nil {
			return true
		}
		return *withDist[i].distance < *withDist[j].distance
	})

	if len(withDist) > DiscoverResultSize {
		withDist = withDist[:DiscoverResultSize]
	}

	result := make([]dto.DiscoverCandidate, 0, len(withDist))
	for _, wd := range withDist {
		result = append(result, dto.DiscoverCandidate{
			ID:         wd.user.ID,
			FirstName:  wd.user.FirstName,
			Age:        utils.CalcAge(wd.user.BirthDate),
			Photos:     photosByUser[wd.user.ID],
			DistanceKM: wd.distance,
			Interests:  interestsByUser[wd.user.ID],
		})
	}
	return result, nil
}

func (s *DiscoveryService) batchInterests(userIDs []uint) map[uint][]string {
	result := map[uint][]string{}
	cat, err := s.optionRepo.GetCategoryByKey(models.CategoryInterest)
	if err != nil {
		return result
	}
	for _, id := range userIDs {
		sels, err := s.optionRepo.GetUserSelections(id, cat.ID)
		if err != nil {
			continue
		}
		for _, sel := range sels {
			if sel.Option != nil {
				result[id] = append(result[id], sel.Option.Title)
			}
		}
	}
	return result
}

// Swipe یک تصمیم (لایک/ردّ/سوپرلایک) ثبت می‌کنه و در صورت لایک متقابل، مچ می‌سازه.
func (s *DiscoveryService) Swipe(user *models.User, targetID uint, action models.SwipeAction) (*dto.SwipeResponse, error) {
	if targetID == user.ID {
		return nil, ErrCannotSwipeSelf
	}
	target, err := s.userRepo.FindByID(targetID)
	if err != nil {
		return nil, err
	}

	alreadySwiped, err := s.swipeRepo.Exists(user.ID, targetID)
	if err != nil {
		return nil, err
	}
	if alreadySwiped {
		return nil, ErrAlreadySwiped
	}

	if err := s.swipeRepo.Create(&models.Swipe{SwiperID: user.ID, SwipedID: targetID, Action: action}); err != nil {
		return nil, err
	}

	if action == models.SwipePass {
		return &dto.SwipeResponse{Matched: false}, nil
	}

	theyLikedMe, err := s.swipeRepo.HasLiked(targetID, user.ID)
	if err != nil {
		return nil, err
	}
	if !theyLikedMe {
		return &dto.SwipeResponse{Matched: false}, nil
	}

	match, _, err := s.matchRepo.FindOrCreate(user.ID, targetID)
	if err != nil {
		return nil, err
	}

	photos, _ := s.photoRepo.ListByUser(target.ID)
	urls := make([]string, len(photos))
	for i, p := range photos {
		urls[i] = p.URL
	}

	return &dto.SwipeResponse{
		Matched: true,
		Match: &dto.MatchView{
			ID:        match.ID,
			UserID:    target.ID,
			FirstName: target.FirstName,
			Photos:    urls,
			CreatedAt: match.CreatedAt.Format(time.RFC3339),
		},
	}, nil
}

// GetCandidateDetail پروفایل کامل یک کاربر دیگه رو برای نمایش صفحه‌ی جزئیات برمی‌گردونه
func (s *DiscoveryService) GetCandidateDetail(viewer *models.User, targetID uint) (*dto.CandidateDetail, error) {
	target, err := s.userRepo.FindByID(targetID)
	if err != nil {
		return nil, err
	}
	if !target.IsOnboarded || target.ApprovalStatus != models.ApprovalApproved || !target.IsActive {
		return nil, gorm.ErrRecordNotFound
	}

	photos, _ := s.photoRepo.ListByUser(target.ID)
	urls := make([]string, len(photos))
	for i, p := range photos {
		urls[i] = p.URL
	}

	var distance *float64
	if viewer.Latitude != nil && viewer.Longitude != nil && target.Latitude != nil && target.Longitude != nil {
		km := math.Round(utils.HaversineKM(*viewer.Latitude, *viewer.Longitude, *target.Latitude, *target.Longitude))
		distance = &km
	}

	detail := &dto.CandidateDetail{
		ID:         target.ID,
		FirstName:  target.FirstName,
		Age:        utils.CalcAge(target.BirthDate),
		Photos:     urls,
		DistanceKM: distance,
		HeightCM:   target.HeightCM,
		WeightKG:   target.WeightKG,
	}

	detail.Education = s.firstSelectionTitle(target.ID, models.CategoryEducationLevel)
	detail.FieldOfStudy = s.firstSelectionTitle(target.ID, models.CategoryFieldOfStudy)
	detail.LookingFor = s.firstSelectionTitle(target.ID, models.CategoryLookingFor)
	detail.Occupations = s.allSelectionTitles(target.ID, models.CategoryOccupation)
	detail.Interests = s.allSelectionTitles(target.ID, models.CategoryInterest)
	detail.ImportantInRelationship = s.allSelectionTitles(target.ID, models.CategoryImportantInRelationship)

	if answers, err := s.questionRepo.GetUserAnswers(target.ID); err == nil {
		for _, a := range answers {
			if a.Question == nil {
				continue
			}
			detail.Answers = append(detail.Answers, dto.CandidateAnswer{
				Question: a.Question.Text,
				Answer:   a.Answer,
			})
		}
	}

	return detail, nil
}

func (s *DiscoveryService) allSelectionTitles(userID uint, key models.CategoryKey) []string {
	cat, err := s.optionRepo.GetCategoryByKey(key)
	if err != nil {
		return nil
	}
	sels, err := s.optionRepo.GetUserSelections(userID, cat.ID)
	if err != nil {
		return nil
	}
	titles := make([]string, 0, len(sels))
	for _, sel := range sels {
		if sel.Option != nil {
			titles = append(titles, sel.Option.Title)
		}
	}
	return titles
}

func (s *DiscoveryService) firstSelectionTitle(userID uint, key models.CategoryKey) string {
	titles := s.allSelectionTitles(userID, key)
	if len(titles) == 0 {
		return ""
	}
	return titles[0]
}