package api

import (
	"context"
	"net/http"
	"sort"
	"strconv"
	"time"

	"pargar/backend/internal/service"
)

type lbEntry struct {
	UserID        int64   `json:"userId"`
	Name          string  `json:"name"`
	Email         string  `json:"email"`
	XP            float64 `json:"xp"`
	Rank          int     `json:"rank"`
	Tier          string  `json:"tier"`
	AvatarVariant string  `json:"avatarVariant"`
	AvatarPalette string  `json:"avatarPalette"`
	AvatarPhoto   string  `json:"avatarPhoto,omitempty"`
}

// tierFromRank assigns a league tier based on rank relative to total participants.
// Thresholds: rank 1 = champion, top 10% = gold, top 30% = silver, rest = bronze.
func tierFromRank(rank, total int) string {
	if rank <= 0 || total <= 0 {
		return "bronze"
	}
	if rank == 1 {
		return "champion"
	}
	if rank*10 <= total {
		return "gold"
	}
	if rank*10 <= total*3 {
		return "silver"
	}
	return "bronze"
}

func (s *Server) handleWeeklyLeaderboard(w http.ResponseWriter, r *http.Request) {
	u := currentUser(r)
	key := "lb:" + service.ISOWeek(time.Now())

	type scored struct {
		userID int64
		xp     float64
	}
	var scoredList []scored
	var totalParticipants int64

	if s.redis != nil {
		z, err := s.redis.ZRevRangeWithScores(context.Background(), key, 0, 19).Result()
		if err == nil {
			for _, member := range z {
				id, _ := strconv.ParseInt(member.Member.(string), 10, 64)
				scoredList = append(scoredList, scored{userID: id, xp: member.Score})
			}
		}
		if count, err := s.redis.ZCard(context.Background(), key).Result(); err == nil {
			totalParticipants = count
		}
	}

	// Fallback to DB if Redis is empty (e.g. dev bootstrap).
	if len(scoredList) == 0 {
		rows, err := s.store.Pool().Query(context.Background(),
			`SELECT user_id, xp FROM weekly_leaderboard WHERE week=$1
			 ORDER BY xp DESC, user_id ASC LIMIT 20`,
			service.ISOWeek(time.Now()))
		if err == nil {
			for rows.Next() {
				var id int64
				var xp int
				if rows.Scan(&id, &xp) == nil {
					scoredList = append(scoredList, scored{userID: id, xp: float64(xp)})
				}
			}
			rows.Close()
		}
		if err := s.store.Pool().QueryRow(context.Background(),
			`SELECT COUNT(*) FROM weekly_leaderboard WHERE week=$1`,
			service.ISOWeek(time.Now())).Scan(&totalParticipants); err != nil {
			totalParticipants = int64(len(scoredList))
		}
	}

	// Deterministic tie-breaking: XP descending, then user_id ascending.
	sort.SliceStable(scoredList, func(i, j int) bool {
		if scoredList[i].xp != scoredList[j].xp {
			return scoredList[i].xp > scoredList[j].xp
		}
		return scoredList[i].userID < scoredList[j].userID
	})

	ids := make([]int64, len(scoredList))
	for i, sc := range scoredList {
		ids[i] = sc.userID
	}
	usersMap, _ := s.store.GetUsersByIDs(context.Background(), ids)

	entries := make([]lbEntry, 0, len(scoredList))
	for i, sc := range scoredList {
		usr, ok := usersMap[sc.userID]
		if !ok {
			continue
		}
		s.signUserMedia(usr)
		rank := i + 1
		entries = append(entries, lbEntry{
			UserID:        sc.userID,
			Name:          usr.Name,
			Email:         usr.Email,
			XP:            sc.xp,
			Rank:          rank,
			Tier:          tierFromRank(rank, int(totalParticipants)),
			AvatarVariant: usr.AvatarVariant,
			AvatarPalette: usr.AvatarPalette,
			AvatarPhoto:   usr.AvatarPhoto,
		})
	}

	// Current user's position (may be outside top 20).
	myRank := -1
	var myXP float64
	if s.redis != nil {
		if rank, err := s.redis.ZRevRank(context.Background(), key, strconv.FormatInt(u.ID, 10)).Result(); err == nil {
			myRank = int(rank) + 1
		}
		if score, err := s.redis.ZScore(context.Background(), key, strconv.FormatInt(u.ID, 10)).Result(); err == nil {
			myXP = score
		}
	}

	if entries == nil {
		entries = []lbEntry{}
	}
	writeJSON(w, http.StatusOK, map[string]any{
		"week":              service.ISOWeek(time.Now()),
		"entries":           entries,
		"totalParticipants": totalParticipants,
		"me": map[string]any{
			"rank":   myRank,
			"xp":     myXP,
			"streak": u.StreakCurrent,
			"tier":   tierFromRank(myRank, int(totalParticipants)),
		},
	})
}