package middleware

import (
	"sync"
	"time"

	"github.com/gofiber/fiber/v2"
)

type TierConfig struct {
	Max    int
	Window time.Duration
}

type TieredRateLimitConfig struct {
	Tiers       map[string]TierConfig
	DefaultTier string
	KeyFunc     func(*fiber.Ctx) string
	GetTierFunc func(*fiber.Ctx) string
}

type tieredRateLimiter struct {
	requests map[string][]time.Time
	mu       sync.RWMutex
	tiers    map[string]TierConfig
}

func newTieredRateLimiter(tiers map[string]TierConfig) *tieredRateLimiter {
	rl := &tieredRateLimiter{
		requests: make(map[string][]time.Time),
		tiers:    tiers,
	}
	go rl.cleanup()
	return rl
}

func (rl *tieredRateLimiter) cleanup() {
	ticker := time.NewTicker(time.Minute)
	for range ticker.C {
		rl.mu.Lock()
		now := time.Now()
		for key, times := range rl.requests {
			var valid []time.Time
			for _, t := range times {
				if now.Sub(t) < 5*time.Minute {
					valid = append(valid, t)
				}
			}
			if len(valid) == 0 {
				delete(rl.requests, key)
			} else {
				rl.requests[key] = valid
			}
		}
		rl.mu.Unlock()
	}
}

func (rl *tieredRateLimiter) allow(key string, tier string) (bool, int, int) {
	rl.mu.Lock()
	defer rl.mu.Unlock()

	cfg, ok := rl.tiers[tier]
	if !ok {
		cfg = rl.tiers["free"]
	}

	now := time.Now()
	windowStart := now.Add(-cfg.Window)

	times := rl.requests[key]
	var valid []time.Time
	for _, t := range times {
		if t.After(windowStart) {
			valid = append(valid, t)
		}
	}

	remaining := cfg.Max - len(valid)
	if remaining <= 0 {
		rl.requests[key] = valid
		return false, 0, cfg.Max
	}

	rl.requests[key] = append(valid, now)
	return true, remaining - 1, cfg.Max
}

func TieredRateLimit(config TieredRateLimitConfig) fiber.Handler {
	if config.Tiers == nil {
		config.Tiers = map[string]TierConfig{
			"free":     {Max: 60, Window: time.Minute},
			"pro":      {Max: 300, Window: time.Minute},
			"business": {Max: 1000, Window: time.Minute},
		}
	}
	if config.DefaultTier == "" {
		config.DefaultTier = "free"
	}
	if config.KeyFunc == nil {
		config.KeyFunc = func(c *fiber.Ctx) string {
			userID := GetUserID(c)
			if userID != "" {
				return "user:" + userID
			}
			return "ip:" + c.IP()
		}
	}
	if config.GetTierFunc == nil {
		config.GetTierFunc = func(c *fiber.Ctx) string {
			tier := GetUserTier(c)
			if tier == "" {
				return config.DefaultTier
			}
			return tier
		}
	}

	limiter := newTieredRateLimiter(config.Tiers)

	return func(c *fiber.Ctx) error {
		key := config.KeyFunc(c)
		tier := config.GetTierFunc(c)

		allowed, remaining, limit := limiter.allow(key, tier)

		c.Set("X-RateLimit-Limit", formatInt(limit))
		c.Set("X-RateLimit-Remaining", formatInt(remaining))
		c.Set("X-RateLimit-Tier", tier)

		if !allowed {
			c.Set("Retry-After", "60")
			return c.Status(429).JSON(fiber.Map{
				"error":     "Rate limit exceeded",
				"tier":      tier,
				"limit":     limit,
				"retryAfter": 60,
			})
		}

		return c.Next()
	}
}

func formatInt(n int) string {
	if n < 0 {
		n = 0
	}
	s := ""
	if n == 0 {
		return "0"
	}
	for n > 0 {
		s = string(rune('0'+n%10)) + s
		n /= 10
	}
	return s
}