package listing

import (
	"context"
	"errors"
	"time"

	"hfb_jysh/backend/internal/model"

	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

const (
	// CollectionKindHistory 浏览记录；CollectionKindFavorite 收藏。
	CollectionKindHistory  = "history"
	CollectionKindFavorite = "favorite"

	maxCollectionItems = 100
)

var ErrCollectionKindInvalid = errors.New("invalid collection kind")

type collectionEntry struct {
	ListingID  uint64
	OccurredAt time.Time
}

// CollectionItem 返回给前端的足迹项：商品快照 + 发生时间。
type CollectionItem struct {
	Listing    ListingDTO `json:"listing"`
	OccurredAt time.Time  `json:"occurred_at"`
}

type CollectionCounts struct {
	History  int64 `json:"history"`
	Favorite int64 `json:"favorite"`
}

type CollectionList struct {
	Items  []CollectionItem `json:"items"`
	Counts CollectionCounts `json:"counts"`
}

func validCollectionKind(kind string) bool {
	return kind == CollectionKindHistory || kind == CollectionKindFavorite
}

// UpsertCollection 写入浏览或收藏记录；同一用户+商品+类型只更新时间。
func (r *Repository) UpsertCollection(ctx context.Context, userID, listingID uint64, kind string) error {
	now := time.Now()
	entry := model.ListingCollection{
		UserID:     userID,
		ListingID:  listingID,
		Kind:       kind,
		OccurredAt: now,
	}
	return r.db.WithContext(ctx).Clauses(clause.OnConflict{
		Columns: []clause.Column{{Name: "user_id"}, {Name: "listing_id"}, {Name: "kind"}},
		DoUpdates: clause.Assignments(map[string]any{
			"occurred_at": now,
			"updated_at":  now,
		}),
	}).Create(&entry).Error
}

func (r *Repository) DeleteCollection(ctx context.Context, userID, listingID uint64, kind string) error {
	return r.db.WithContext(ctx).
		Where("user_id = ? AND listing_id = ? AND kind = ?", userID, listingID, kind).
		Delete(&model.ListingCollection{}).Error
}

func (r *Repository) ClearCollection(ctx context.Context, userID uint64, kind string) error {
	return r.db.WithContext(ctx).
		Where("user_id = ? AND kind = ?", userID, kind).
		Delete(&model.ListingCollection{}).Error
}

func (r *Repository) ListCollectionEntries(ctx context.Context, userID uint64, kind string, limit int) ([]collectionEntry, error) {
	if limit <= 0 || limit > maxCollectionItems {
		limit = maxCollectionItems
	}
	var rows []model.ListingCollection
	if err := r.db.WithContext(ctx).
		Select("listing_id, occurred_at").
		Where("user_id = ? AND kind = ?", userID, kind).
		Order("occurred_at DESC, id DESC").
		Limit(limit).
		Find(&rows).Error; err != nil {
		return nil, err
	}
	entries := make([]collectionEntry, 0, len(rows))
	for _, row := range rows {
		entries = append(entries, collectionEntry{ListingID: row.ListingID, OccurredAt: row.OccurredAt})
	}
	return entries, nil
}

func (r *Repository) CountCollections(ctx context.Context, userID uint64) (CollectionCounts, error) {
	var rows []struct {
		Kind  string
		Total int64
	}
	if err := r.db.WithContext(ctx).
		Model(&model.ListingCollection{}).
		Select("kind, COUNT(*) AS total").
		Where("user_id = ?", userID).
		Group("kind").
		Scan(&rows).Error; err != nil {
		return CollectionCounts{}, err
	}
	counts := CollectionCounts{}
	for _, row := range rows {
		switch row.Kind {
		case CollectionKindHistory:
			counts.History = row.Total
		case CollectionKindFavorite:
			counts.Favorite = row.Total
		}
	}
	return counts, nil
}

func (r *Repository) ListingExists(ctx context.Context, listingID uint64) (bool, error) {
	var count int64
	if err := r.db.WithContext(ctx).
		Model(&model.RentalListing{}).
		Where("id = ?", listingID).
		Count(&count).Error; err != nil {
		return false, err
	}
	return count > 0, nil
}

// listingsByIDs 复用公开列表的联表与出图逻辑，保证足迹页展示与详情页一致。
func (r *Repository) listingsByIDs(ctx context.Context, ids []uint64) (map[uint64]ListingDTO, error) {
	result := make(map[uint64]ListingDTO, len(ids))
	if len(ids) == 0 {
		return result, nil
	}
	var rows []listingRow
	if err := r.baseQuery(ctx).Where("l.id IN ?", ids).Scan(&rows).Error; err != nil {
		return nil, err
	}
	for _, item := range publicListings(rowsToDTO(rows)) {
		result[item.ID] = item
	}
	return result, nil
}

func (s *Service) RecordCollectionView(ctx context.Context, userID, listingID uint64) error {
	if s.repo == nil {
		return ErrDependencyUnavailable
	}
	exists, err := s.repo.ListingExists(ctx, listingID)
	if err != nil {
		return err
	}
	if !exists {
		return gorm.ErrRecordNotFound
	}
	return s.repo.UpsertCollection(ctx, userID, listingID, CollectionKindHistory)
}

func (s *Service) AddCollectionFavorite(ctx context.Context, userID, listingID uint64) error {
	if s.repo == nil {
		return ErrDependencyUnavailable
	}
	exists, err := s.repo.ListingExists(ctx, listingID)
	if err != nil {
		return err
	}
	if !exists {
		return gorm.ErrRecordNotFound
	}
	return s.repo.UpsertCollection(ctx, userID, listingID, CollectionKindFavorite)
}

func (s *Service) RemoveCollectionFavorite(ctx context.Context, userID, listingID uint64) error {
	if s.repo == nil {
		return ErrDependencyUnavailable
	}
	return s.repo.DeleteCollection(ctx, userID, listingID, CollectionKindFavorite)
}

func (s *Service) RemoveCollectionHistory(ctx context.Context, userID, listingID uint64) error {
	if s.repo == nil {
		return ErrDependencyUnavailable
	}
	return s.repo.DeleteCollection(ctx, userID, listingID, CollectionKindHistory)
}

func (s *Service) ClearCollectionHistory(ctx context.Context, userID uint64) error {
	if s.repo == nil {
		return ErrDependencyUnavailable
	}
	return s.repo.ClearCollection(ctx, userID, CollectionKindHistory)
}

func (s *Service) ListCollections(ctx context.Context, userID uint64, kind string) (*CollectionList, error) {
	if s.repo == nil {
		return nil, ErrDependencyUnavailable
	}
	if !validCollectionKind(kind) {
		return nil, ErrCollectionKindInvalid
	}
	entries, err := s.repo.ListCollectionEntries(ctx, userID, kind, maxCollectionItems)
	if err != nil {
		return nil, err
	}
	ids := make([]uint64, 0, len(entries))
	for _, entry := range entries {
		ids = append(ids, entry.ListingID)
	}
	listings, err := s.repo.listingsByIDs(ctx, ids)
	if err != nil {
		return nil, err
	}
	items := make([]CollectionItem, 0, len(entries))
	for _, entry := range entries {
		listing, ok := listings[entry.ListingID]
		if !ok {
			// 商品被物理删除时跳过，避免整页 500。
			continue
		}
		items = append(items, CollectionItem{Listing: listing, OccurredAt: entry.OccurredAt})
	}
	counts, err := s.repo.CountCollections(ctx, userID)
	if err != nil {
		return nil, err
	}
	return &CollectionList{Items: items, Counts: counts}, nil
}