package middleware

import (
	"context"
	"fmt"
	"net/http"
	"os"
	"strconv"
	"sync"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/redis/go-redis/v9"
)

// EndpointLimiterConfig configuration pour les limites par endpoint
type EndpointLimiterConfig struct {
	RedisClient *redis.Client
	KeyPrefix   string
}

// EndpointLimits définit les limites pour chaque endpoint
type EndpointLimits struct {
	// Login: 5 tentatives/15min par IP
	LoginAttempts int
	LoginWindow   time.Duration

	// Register: 3 comptes/heure par IP
	RegisterAttempts int
	RegisterWindow   time.Duration

	// Password reset: 3 tentatives/heure
	PasswordResetAttempts int
	PasswordResetWindow   time.Duration

	// Upload: 10 fichiers/heure par user
	UploadAttempts int
	UploadWindow   time.Duration
}

// DefaultEndpointLimits retourne les limites par défaut
func DefaultEndpointLimits() *EndpointLimits {
	return &EndpointLimits{
		LoginAttempts:         5,
		LoginWindow:           15 * time.Minute,
		RegisterAttempts:      3,
		RegisterWindow:        time.Hour,
		PasswordResetAttempts: 3,
		PasswordResetWindow:   time.Hour,
		UploadAttempts:        10,
		UploadWindow:          time.Hour,
	}
}

// endpointInMemoryEntry holds in-memory rate limit state for fallback
type endpointInMemoryEntry struct {
	count       int
	windowStart time.Time
}

// EndpointLimiter gère les limites par endpoint
type EndpointLimiter struct {
	config        *EndpointLimiterConfig
	limits        *EndpointLimits
	inMemoryStore map[string]*endpointInMemoryEntry
	inMemoryMu    sync.RWMutex
}

// NewEndpointLimiter crée un nouveau endpoint limiter
func NewEndpointLimiter(config *EndpointLimiterConfig, limits *EndpointLimits) *EndpointLimiter {
	return &EndpointLimiter{
		config:        config,
		limits:        limits,
		inMemoryStore: make(map[string]*endpointInMemoryEntry),
	}
}

// LoginRateLimit middleware pour limiter les tentatives de login
func (el *EndpointLimiter) LoginRateLimit() gin.HandlerFunc {
	return el.createEndpointLimit(
		"login",
		el.limits.LoginAttempts,
		el.limits.LoginWindow,
		"Too many login attempts",
	)
}

// RegisterRateLimit middleware pour limiter les inscriptions
func (el *EndpointLimiter) RegisterRateLimit() gin.HandlerFunc {
	return el.createEndpointLimit(
		"register",
		el.limits.RegisterAttempts,
		el.limits.RegisterWindow,
		"Too many registration attempts",
	)
}

// PasswordResetRateLimit middleware pour limiter les reset de mot de passe
func (el *EndpointLimiter) PasswordResetRateLimit() gin.HandlerFunc {
	return el.createEndpointLimit(
		"password_reset",
		el.limits.PasswordResetAttempts,
		el.limits.PasswordResetWindow,
		"Too many password reset attempts",
	)
}

// VerifyEmailRateLimit middleware pour limiter les tentatives de vérification d'email
// BE-SEC-005: Implement rate limiting for authentication endpoints
func (el *EndpointLimiter) VerifyEmailRateLimit() gin.HandlerFunc {
	return el.createEndpointLimit(
		"verify_email",
		5,         // 5 tentatives par heure
		time.Hour, // Fenêtre de 1 heure
		"Too many email verification attempts",
	)
}

// ResendVerificationRateLimit middleware pour limiter les renvois de vérification
// BE-SEC-005: Implement rate limiting for authentication endpoints
func (el *EndpointLimiter) ResendVerificationRateLimit() gin.HandlerFunc {
	return el.createEndpointLimit(
		"resend_verification",
		3,         // 3 tentatives par heure
		time.Hour, // Fenêtre de 1 heure
		"Too many verification resend attempts",
	)
}

// CheckUsernameRateLimit middleware pour limiter l'énumération de noms d'utilisateur (SEC-009)
func (el *EndpointLimiter) CheckUsernameRateLimit() gin.HandlerFunc {
	return el.createEndpointLimit(
		"check_username",
		30,          // 30 requêtes par minute
		time.Minute, // Fenêtre de 1 minute
		"Too many username check attempts",
	)
}

// RefreshRateLimit middleware pour limiter le token grinding sur /auth/refresh (SEC-010)
func (el *EndpointLimiter) RefreshRateLimit() gin.HandlerFunc {
	return el.createEndpointLimit(
		"refresh",
		10,          // 10 requêtes par minute
		time.Minute, // Fenêtre de 1 minute
		"Too many token refresh attempts",
	)
}

// ValidateRateLimit middleware pour limiter les appels à POST /validate (A01)
func (el *EndpointLimiter) ValidateRateLimit() gin.HandlerFunc {
	return el.createEndpointLimit(
		"validate",
		10,          // 10 requêtes par minute par IP
		time.Minute, // Fenêtre de 1 minute
		"Too many validation requests",
	)
}

// UploadRateLimit middleware pour limiter les uploads par utilisateur
func (el *EndpointLimiter) UploadRateLimit() gin.HandlerFunc {
	return func(c *gin.Context) {
		// Récupérer l'ID utilisateur depuis le contexte
		userID, exists := c.Get("user_id")
		if !exists {
			c.JSON(http.StatusUnauthorized, gin.H{"error": "Authentication required"})
			c.Abort()
			return
		}

		key := fmt.Sprintf("%s:upload:user:%v", el.config.KeyPrefix, userID)
		allowed, remaining, err := el.checkLimit(c.Request.Context(), key, el.limits.UploadAttempts, el.limits.UploadWindow)

		if err != nil {
			// Fallback in-memory when Redis fails (fail-secure)
			allowed, remaining = el.checkLimitInMemory(key, el.limits.UploadAttempts, el.limits.UploadWindow)
		}

		c.Header("X-UploadLimit-Limit", strconv.Itoa(el.limits.UploadAttempts))
		c.Header("X-UploadLimit-Remaining", strconv.Itoa(remaining))
		c.Header("X-UploadLimit-Reset", strconv.FormatInt(time.Now().Add(el.limits.UploadWindow).Unix(), 10))

		if !allowed {
			c.JSON(http.StatusTooManyRequests, gin.H{
				"error":       "Upload limit exceeded",
				"retry_after": int(el.limits.UploadWindow.Seconds()),
			})
			c.Abort()
			return
		}

		c.Next()
	}
}

// createEndpointLimit crée un middleware de limitation pour un endpoint
func (el *EndpointLimiter) createEndpointLimit(
	endpoint string,
	attempts int,
	window time.Duration,
	errorMessage string,
) gin.HandlerFunc {
	return func(c *gin.Context) {
		// SEC-011: Never bypass rate limiting in production.
		// E2E: Completely disable in test environment (APP_ENV=test) to prevent flaky tests.
		if os.Getenv("APP_ENV") == "production" {
			// Continue to rate limit — NEVER bypass in production
		} else if os.Getenv("APP_ENV") == "test" || os.Getenv("DISABLE_RATE_LIMIT_FOR_TESTS") == "true" {
			c.Next()
			return
		}

		key := fmt.Sprintf("%s:%s:ip:%s", el.config.KeyPrefix, endpoint, c.ClientIP())
		allowed, remaining, err := el.checkLimit(c.Request.Context(), key, attempts, window)

		if err != nil {
			// Fallback in-memory when Redis fails (fail-secure)
			allowed, remaining = el.checkLimitInMemory(key, attempts, window)
		}

		headerPrefix := fmt.Sprintf("X-%sLimit", capitalize(endpoint))
		c.Header(headerPrefix+"-Limit", strconv.Itoa(attempts))
		c.Header(headerPrefix+"-Remaining", strconv.Itoa(remaining))
		c.Header(headerPrefix+"-Reset", strconv.FormatInt(time.Now().Add(window).Unix(), 10))

		if !allowed {
			c.JSON(http.StatusTooManyRequests, gin.H{
				"error":       errorMessage,
				"retry_after": int(window.Seconds()),
			})
			c.Abort()
			return
		}

		c.Next()
	}
}

// checkLimit vérifie si une limite est respectée
func (el *EndpointLimiter) checkLimit(ctx context.Context, key string, attempts int, window time.Duration) (bool, int, error) {
	// Use in-memory fallback when Redis is not configured (e.g. integration tests)
	if el.config == nil || el.config.RedisClient == nil {
		allowed, remaining := el.checkLimitInMemory(key, attempts, window)
		return allowed, remaining, nil
	}

	// Script Lua pour l'atomicité
	script := `
		local key = KEYS[1]
		local attempts = 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, attempts - 1}
		end
		
		local count = tonumber(current)
		if count < attempts then
			redis.call('INCR', key)
			return {1, attempts - count - 1}
		else
			return {0, 0}
		end
	`

	result, err := el.config.RedisClient.Eval(
		ctx,
		script,
		[]string{key},
		attempts,
		int(window.Seconds()),
	).Result()

	if err != nil {
		return false, 0, err
	}

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

	return allowed, remaining, nil
}

// checkLimitInMemory implements rate limiting in-memory when Redis fails (fail-secure)
func (el *EndpointLimiter) checkLimitInMemory(key string, attempts int, window time.Duration) (bool, int) {
	el.inMemoryMu.Lock()
	defer el.inMemoryMu.Unlock()

	now := time.Now()
	entry := el.inMemoryStore[key]
	if entry == nil {
		entry = &endpointInMemoryEntry{count: 0, windowStart: now}
		el.inMemoryStore[key] = entry
	}

	if now.Sub(entry.windowStart) >= window {
		entry.count = 0
		entry.windowStart = now
	}

	entry.count++
	remaining := attempts - entry.count
	if remaining < 0 {
		remaining = 0
	}
	return entry.count <= attempts, remaining
}

// capitalize met en majuscule la première lettre
func capitalize(s string) string {
	if len(s) == 0 {
		return s
	}
	return string(s[0]-32) + s[1:]
}

// RateLimitByUser middleware pour limiter par utilisateur (pour endpoints génériques)
func (el *EndpointLimiter) RateLimitByUser(attempts int, window time.Duration, errorMessage string) gin.HandlerFunc {
	return func(c *gin.Context) {
		userID, exists := c.Get("user_id")
		if !exists {
			c.JSON(http.StatusUnauthorized, gin.H{"error": "Authentication required"})
			c.Abort()
			return
		}

		key := fmt.Sprintf("%s:user:%v", el.config.KeyPrefix, userID)
		allowed, remaining, err := el.checkLimit(c.Request.Context(), key, attempts, window)

		if err != nil {
			// Fallback in-memory when Redis fails (fail-secure)
			allowed, remaining = el.checkLimitInMemory(key, attempts, window)
		}

		c.Header("X-UserLimit-Limit", strconv.Itoa(attempts))
		c.Header("X-UserLimit-Remaining", strconv.Itoa(remaining))
		c.Header("X-UserLimit-Reset", strconv.FormatInt(time.Now().Add(window).Unix(), 10))

		if !allowed {
			c.JSON(http.StatusTooManyRequests, gin.H{
				"error":       errorMessage,
				"retry_after": int(window.Seconds()),
			})
			c.Abort()
			return
		}

		c.Next()
	}
}