package bot

import (
	"fmt"
	"log/slog"
	"strings"
	"time"

	"worktimeBot/internal/db"
)

// XP earned per second of work.
const xpPerSecond int64 = 1

// xpForLevel returns the total XP required to reach level n.
// Quadratic curve: totalXP(n) = n * (n + 1) * xpCurveMultiplier
// Level 1 = 100 XP, Level 10 = 5500 XP, Level 50 = 127500 XP
func xpForLevel(n int) int64 {
	return int64(n) * int64(n+1) * xpCurveMultiplier
}

// levelForXP returns the level for a given total XP amount.
func levelForXP(xp int64) int {
	l := 1
	for xpForLevel(l) <= xp {
		l++
	}
	return l - 1
}

// xpForWorkSeconds calculates XP earned for a given amount of work.
// Base: 1 XP per second.
func xpForWorkSeconds(sec int64) int64 {
	return sec / xpPerSecond
}

// streakBonus returns bonus XP for maintaining a streak.
// +xpCurveMultiplier XP per day of current streak, capped at streakBonusCap.
func streakBonus(streak int) int64 {
	b := int64(streak) * xpCurveMultiplier
	if b > streakBonusCap {
		b = streakBonusCap
	}
	return b
}

// computeAndAwardXP calculates XP for a work session and updates the DB.
// Returns the new total XP and whether the user leveled up.
func (h *Handler) computeAndAwardXP(userID int64, workSeconds int64, streak int, date string) (newXP int64, leveledUp bool, newLevel int, err error) {
	stats, err := h.DB.GetOrCreateRPGStats(userID)
	if err != nil {
		return 0, false, 0, err
	}

	baseXP := xpForWorkSeconds(workSeconds)
	bonus := streakBonus(streak)
	totalXP := baseXP + bonus

	if totalXP < 0 {
		totalXP = 0
	}

	stats.XP += totalXP
	newLevel = levelForXP(stats.XP)
	leveledUp = newLevel > stats.Level
	stats.Level = newLevel
	stats.TotalWorkSeconds += workSeconds

	if err := h.DB.UpdateRPGStats(stats); err != nil {
		return 0, false, 0, err
	}

	if err := h.DB.UpsertDailyXP(userID, date, totalXP, workSeconds); err != nil {
		slog.Warn("failed to upsert daily xp", "user_id", userID, "error", err)
	}

	return stats.XP, leveledUp, newLevel, nil
}

// updateStreak advances or resets the user's streak based on today's activity.
// Returns the updated streak count.
func (h *Handler) updateStreak(userID int64, date string, hasWorkToday bool) (int, error) {
	stats, err := h.DB.GetOrCreateRPGStats(userID)
	if err != nil {
		return 0, err
	}

	if !hasWorkToday {
		stats.CurrentStreak = 0
		if err := h.DB.UpdateRPGStats(stats); err != nil {
			return 0, err
		}
		return 0, nil
	}

	// Parse yesterday to check continuity
	t, err := time.Parse(DateLayout, date)
	if err != nil {
		return 0, err
	}
	yesterday := t.AddDate(0, 0, -1).Format(DateLayout)

	prevEvents, err := h.DB.EventsForDayByDate(userID, yesterday)
	hadWorkYesterday := err == nil && len(prevEvents) > 0

	if hadWorkYesterday {
		stats.CurrentStreak++
	} else {
		stats.CurrentStreak = 1
	}

	if stats.CurrentStreak > stats.LongestStreak {
		stats.LongestStreak = stats.CurrentStreak
	}

	if err := h.DB.UpdateRPGStats(stats); err != nil {
		return 0, err
	}

	return stats.CurrentStreak, nil
}

// checkAchievements evaluates and unlocks any newly earned achievements.
func (h *Handler) checkAchievements(userID int64, stats *db.RPGStats, workSeconds int64, date string, isWeekend bool) []string {
	unlocker := newAchievementUnlocker(h, userID)
	h.checkEarlyAchievements(unlocker, workSeconds)
	h.checkEventTimeAchievements(unlocker, userID, date)
	h.checkStreakAchievements(unlocker, stats)
	h.checkHourAchievements(unlocker, stats)
	h.checkSessionAchievements(unlocker, workSeconds, isWeekend)
	h.checkLevelAchievements(unlocker, stats)
	return unlocker.unlocked
}

type achievementUnlocker struct {
	h        *Handler
	userID   int64
	unlocked []string
}

func newAchievementUnlocker(h *Handler, userID int64) *achievementUnlocker {
	return &achievementUnlocker{h: h, userID: userID}
}

func (u *achievementUnlocker) unlock(code string) {
	a, err := u.h.DB.GetAchievementByCode(code)
	if err != nil {
		return
	}
	ok, err := u.h.DB.UnlockAchievement(u.userID, a.ID)
	if err != nil {
		slog.Error("unlock achievement", "code", code, "error", err)
		return
	}
	if ok {
		u.unlocked = append(u.unlocked, a.Name)
	}
}

func (h *Handler) checkEarlyAchievements(u *achievementUnlocker, workSeconds int64) {
	has, _ := h.DB.HasAchievement(u.userID, "first_clockin")
	if !has && workSeconds > 0 {
		u.unlock("first_clockin")
	}
}

func (h *Handler) checkEventTimeAchievements(u *achievementUnlocker, userID int64, date string) {
	t, _ := time.Parse(DateLayout, date)
	dayStart := t.Unix()
	dayEnd := t.Add(24 * time.Hour).Unix()

	events, err := h.DB.EventsForDayByDate(userID, date)
	if err != nil {
		return
	}
	for _, e := range events {
		if e.OccurredAt < dayStart || e.OccurredAt > dayEnd {
			continue
		}
		et := time.Unix(e.OccurredAt, 0)
		hh, mm, _ := et.Clock()
		minutes := hh*60 + mm
		if e.EventType == "in" && minutes < 7*60 {
			u.unlock("early_bird")
		}
		if e.EventType == "out" && minutes >= 22*60 {
			u.unlock("night_owl")
		}
	}
}

func (h *Handler) checkStreakAchievements(u *achievementUnlocker, stats *db.RPGStats) {
	if stats.CurrentStreak >= 5 {
		u.unlock("iron_streak_5")
	}
	if stats.CurrentStreak >= 10 {
		u.unlock("iron_streak_10")
	}
	if stats.CurrentStreak >= 30 {
		u.unlock("iron_streak_30")
	}
}

func (h *Handler) checkHourAchievements(u *achievementUnlocker, stats *db.RPGStats) {
	hoursWorked := float64(stats.TotalWorkSeconds) / secondsPerHour
	if hoursWorked >= 100.0 {
		u.unlock("hundred_hours")
	}
	if hoursWorked >= 500.0 {
		u.unlock("five_hundred_hours")
	}
}

func (h *Handler) checkSessionAchievements(u *achievementUnlocker, workSeconds int64, isWeekend bool) {
	if workSeconds > 10*secondsPerHour {
		u.unlock("overtime_hero")
	}
	if isWeekend && workSeconds > 0 {
		u.unlock("weekend_warrior")
	}
}

func (h *Handler) checkLevelAchievements(u *achievementUnlocker, stats *db.RPGStats) {
	if stats.Level >= 5 {
		u.unlock("level_5")
	}
	if stats.Level >= 10 {
		u.unlock("level_10")
	}
	if stats.Level >= 25 {
		u.unlock("level_25")
	}
	if stats.Level >= 50 {
		u.unlock("level_50")
	}
}

// buildRPGStatus returns a formatted string showing the user's RPG stats.
func (h *Handler) buildRPGStatus(userID int64) string {
	stats, err := h.DB.GetOrCreateRPGStats(userID)
	if err != nil {
		return "RPG stats unavailable"
	}

	nextLevelXP := xpForLevel(stats.Level + 1)
	currentLevelXP := xpForLevel(stats.Level)
	xpIntoLevel := stats.XP - currentLevelXP
	xpNeeded := nextLevelXP - currentLevelXP

	var b strings.Builder
	b.WriteString(fmt.Sprintf("Level: %d\n", stats.Level))
	b.WriteString(fmt.Sprintf("XP: %d / %d (%d%%)\n", stats.XP, nextLevelXP, xpIntoLevel*100/xpNeeded))
	b.WriteString(fmt.Sprintf("Streak: %d days (best: %d)\n", stats.CurrentStreak, stats.LongestStreak))

	hoursTotal := float64(stats.TotalWorkSeconds) / secondsPerHour
	b.WriteString(fmt.Sprintf("Total work: %.1f hours\n", hoursTotal))

	// Show achievements count
	achs, _ := h.DB.GetUserAchievements(userID)
	if len(achs) > 0 {
		b.WriteString(fmt.Sprintf("Achievements: %d unlocked\n", len(achs)))
	}

	return b.String()
}

// buildAchievementsList returns the user's unlocked achievements.
func (h *Handler) buildAchievementsList(userID int64) string {
	achs, err := h.DB.GetUserAchievements(userID)
	if err != nil {
		return "Achievements unavailable"
	}
	if len(achs) == 0 {
		return "No achievements unlocked yet.\nWork consistently to earn them!"
	}

	var b strings.Builder
	b.WriteString(fmt.Sprintf("Achievements (%d):\n\n", len(achs)))
	for _, a := range achs {
		t := time.Unix(a.UnlockedAt, 0)
		b.WriteString(fmt.Sprintf("  %s\n    %s - %s\n", a.Name, a.Description, t.Format(DateLayout)))
	}
	return b.String()
}

// rpgStatus returns the user's RPG stats.
func (h *Handler) rpgStatus(chatID int64) (string, error) {
	user, err := h.getOrCreateUser(chatID)
	if err != nil {
		return "", err
	}
	st, err := h.DB.GetOrCreateSettings(user.ID)
	if err != nil {
		return "", err
	}
	if !st.RPGEnabled {
		return "RPG system is disabled. Enable it in Settings or use /rpgtoggle.", nil
	}
	return h.buildRPGStatus(user.ID), nil
}

// achievementsList returns the user's unlocked achievements.
func (h *Handler) achievementsList(chatID int64) (string, error) {
	user, err := h.getOrCreateUser(chatID)
	if err != nil {
		return "", err
	}
	st, err := h.DB.GetOrCreateSettings(user.ID)
	if err != nil {
		return "", err
	}
	if !st.RPGEnabled {
		return "RPG system is disabled. Enable it in Settings or use /rpgtoggle.", nil
	}
	return h.buildAchievementsList(user.ID), nil
}