package middleware

import (
	"fmt"
	"os"
	"strconv"
	"sync"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/redis/go-redis/v9"
	"go.uber.org/zap"

	apperrors "veza-backend-api/internal/errors"
	"veza-backend-api/internal/response"
)

// RedisRateLimiter is a Redis-backed rate limiter with the same interface as SimpleRateLimiter.
// Uses INCR + EXPIRE atomically via Lua script for counting.
type RedisRateLimiter struct {
	client *redis.Client
	limit  int
	window time.Duration
	mu     sync.Mutex
}

// NewRedisRateLimiter creates a new Redis-backed rate limiter.
// limit: maximum number of requests per window
// window: time window (e.g. 1*time.Minute for 100 req/min)
func NewRedisRateLimiter(client *redis.Client, limit int, window time.Duration) *RedisRateLimiter {
	return &RedisRateLimiter{
		client: client,
		limit:  limit,
		window: window,
	}
}

// Lua script for atomic INCR + EXPIRE. Returns {allowed, remaining}.
// - allowed: 1 if request allowed, 0 if rate limit exceeded
// - remaining: remaining requests in window
var redisRateLimitScript = `
	local key = KEYS[1]
	local limit = tonumber(ARGV[1])
	local window = tonumber(ARGV[2])
	
	local current = redis.call('GET', key)
	if current == false then
		redis.call('SET', key, 1, 'EX', window)
		return {1, limit - 1}
	end
	
	local count = tonumber(current)
	if count < limit then
		redis.call('INCR', key)
		return {1, limit - count - 1}
	else
		return {0, 0}
	end
`

// Middleware returns the Gin middleware for rate limiting.
// Same interface as SimpleRateLimiter.
func (rl *RedisRateLimiter) Middleware() gin.HandlerFunc {
	return func(c *gin.Context) {
		if isExcludedPath(c.Request.URL.Path) {
			c.Next()
			return
		}

		if os.Getenv("APP_ENV") == "production" {
			// Continue to rate limit
		} else if os.Getenv("DISABLE_RATE_LIMIT_FOR_TESTS") == "true" {
			c.Next()
			return
		}

		ip := c.ClientIP()
		key := fmt.Sprintf("ratelimit:%s", ip)

		rl.mu.Lock()
		limit := rl.limit
		window := rl.window
		rl.mu.Unlock()

		windowSec := int(window.Seconds())
		result, err := rl.client.Eval(
			c.Request.Context(),
			redisRateLimitScript,
			[]string{key},
			limit,
			windowSec,
		).Result()

		if err != nil {
			zap.L().Error("Redis rate limit check failed",
				zap.Error(err),
				zap.String("ip", ip),
				zap.String("key", key))
			resetTime := time.Now().Add(window).Unix()
			retryAfter := windowSec
			c.Header("X-RateLimit-Limit", strconv.Itoa(limit))
			c.Header("X-RateLimit-Remaining", "0")
			c.Header("X-RateLimit-Reset", strconv.FormatInt(resetTime, 10))
			c.Header("Retry-After", strconv.Itoa(retryAfter))
			appErr := apperrors.New(apperrors.ErrCodeRateLimitExceeded, "Rate limit exceeded. Please try again later.")
			appErr.Details = []apperrors.ErrorDetail{{Field: "rate_limit", Message: fmt.Sprintf("You have exceeded the rate limit of %d requests per %v", limit, window)}}
			appErr.Context = map[string]interface{}{"retry_after": retryAfter, "limit": limit, "remaining": 0, "reset": resetTime}
			response.RespondWithAppError(c, appErr)
			c.Abort()
			return
		}

		results := result.([]interface{})
		allowed := results[0].(int64) == 1
		remaining := int(results[1].(int64))

		now := time.Now()
		resetTime := now.Add(window).Unix()

		if !allowed {
			retryAfter := windowSec
			c.Header("X-RateLimit-Limit", strconv.Itoa(limit))
			c.Header("X-RateLimit-Remaining", "0")
			c.Header("X-RateLimit-Reset", strconv.FormatInt(resetTime, 10))
			c.Header("Retry-After", strconv.Itoa(retryAfter))
			appErr := apperrors.New(apperrors.ErrCodeRateLimitExceeded, "Rate limit exceeded. Please try again later.")
			appErr.Details = []apperrors.ErrorDetail{{Field: "rate_limit", Message: fmt.Sprintf("You have exceeded the rate limit of %d requests per %v", limit, window)}}
			appErr.Context = map[string]interface{}{"retry_after": retryAfter, "limit": limit, "remaining": 0, "reset": resetTime}
			response.RespondWithAppError(c, appErr)
			c.Abort()
			return
		}

		c.Header("X-RateLimit-Limit", strconv.Itoa(limit))
		c.Header("X-RateLimit-Remaining", strconv.Itoa(remaining))
		c.Header("X-RateLimit-Reset", strconv.FormatInt(resetTime, 10))

		c.Next()
	}
}

// UpdateLimits updates the rate limit configuration (hot reload without restart).
func (rl *RedisRateLimiter) UpdateLimits(limit int, window time.Duration) {
	rl.mu.Lock()
	defer rl.mu.Unlock()
	rl.limit = limit
	rl.window = window
}