package api

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"log"
	"net/http"
	"strings"
	"sync"
	"time"

	"github.com/mish/dealspace/lib"
)

type contextKey string

const (
	ctxUserID contextKey = "user_id"
)

// UserIDFromContext extracts the authenticated user ID from the request context.
func UserIDFromContext(ctx context.Context) string {
	v, _ := ctx.Value(ctxUserID).(string)
	return v
}

// AuthMiddleware validates JWT tokens and sets user context.
func AuthMiddleware(db *lib.DB, jwtSecret []byte) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			auth := r.Header.Get("Authorization")
			if !strings.HasPrefix(auth, "Bearer ") {
				ErrorResponse(w, http.StatusUnauthorized, "missing_token", "Authorization header required")
				return
			}
			token := strings.TrimPrefix(auth, "Bearer ")

			claims, err := validateJWT(token, jwtSecret)
			if err != nil {
				ErrorResponse(w, http.StatusUnauthorized, "invalid_token", "Invalid or expired token")
				return
			}

			session, err := lib.SessionByID(db, claims.SessionID)
			if err != nil || session == nil || session.Revoked {
				ErrorResponse(w, http.StatusUnauthorized, "session_revoked", "Session has been revoked")
				return
			}
			if session.ExpiresAt < time.Now().UnixMilli() {
				ErrorResponse(w, http.StatusUnauthorized, "session_expired", "Session has expired")
				return
			}

			ctx := context.WithValue(r.Context(), ctxUserID, claims.UserID)
			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

// OAuthBearerAuth validates OAuth 2.0 bearer tokens for MCP endpoints.
func OAuthBearerAuth(db *lib.DB) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			auth := r.Header.Get("Authorization")
			if !strings.HasPrefix(auth, "Bearer ") {
				w.Header().Set("WWW-Authenticate", "Bearer")
				ErrorResponse(w, http.StatusUnauthorized, "missing_token", "Bearer token required")
				return
			}
			tokenStr := strings.TrimPrefix(auth, "Bearer ")

			token, err := lib.OAuthTokenValidate(db, tokenStr)
			if err != nil || token == nil {
				w.Header().Set("WWW-Authenticate", "Bearer error=\"invalid_token\"")
				ErrorResponse(w, http.StatusUnauthorized, "invalid_token", "Invalid or expired token")
				return
			}

			ctx := context.WithValue(r.Context(), ctxUserID, token.UserID)
			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

// LoggingMiddleware logs HTTP requests.
func LoggingMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		wrapped := &statusWriter{ResponseWriter: w, status: 200}
		next.ServeHTTP(wrapped, r)
		log.Printf("%s %s %d %s", r.Method, r.URL.Path, wrapped.status, time.Since(start))
	})
}

type statusWriter struct {
	http.ResponseWriter
	status int
}

func (w *statusWriter) WriteHeader(code int) {
	w.status = code
	w.ResponseWriter.WriteHeader(code)
}

// RateLimitMiddleware implements per-IP rate limiting.
func RateLimitMiddleware(requestsPerMinute int) func(http.Handler) http.Handler {
	var mu sync.Mutex
	clients := make(map[string]*rateLimitEntry)

	go func() {
		for {
			time.Sleep(time.Minute)
			mu.Lock()
			now := time.Now()
			for ip, entry := range clients {
				if now.Sub(entry.windowStart) > time.Minute {
					delete(clients, ip)
				}
			}
			mu.Unlock()
		}
	}()

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			ip := realIP(r)

			mu.Lock()
			entry, exists := clients[ip]
			now := time.Now()
			if !exists || now.Sub(entry.windowStart) > time.Minute {
				entry = &rateLimitEntry{windowStart: now, count: 0}
				clients[ip] = entry
			}
			entry.count++
			count := entry.count
			mu.Unlock()

			if count > requestsPerMinute {
				ErrorResponse(w, http.StatusTooManyRequests, "rate_limited", "Too many requests")
				return
			}

			next.ServeHTTP(w, r)
		})
	}
}

type rateLimitEntry struct {
	windowStart time.Time
	count       int
}


// allowedOrigins is the list of origins allowed for CORS.
var allowedOrigins = map[string]bool{
	"https://muskepo.com":       true,
	"https://www.muskepo.com":   true,
	"https://app.muskepo.com":   true,
	"https://dealspace.io":      true,
	"https://app.dealspace.io":  true,
	"http://localhost:8080":     true,
	"http://localhost:3000":     true,
}

// CORSMiddleware handles CORS headers with origin allowlist.
func CORSMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		origin := r.Header.Get("Origin")
		
		// Check if origin is allowed
		if allowedOrigins[origin] {
			w.Header().Set("Access-Control-Allow-Origin", origin)
			w.Header().Set("Vary", "Origin")
		}
		
		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
		w.Header().Set("Access-Control-Allow-Headers", "Authorization, Content-Type")
		w.Header().Set("Access-Control-Max-Age", "86400")

		if r.Method == "OPTIONS" {
			w.WriteHeader(http.StatusNoContent)
			return
		}

		next.ServeHTTP(w, r)
	})
}

// SecurityHeadersMiddleware adds security headers to all responses.
func SecurityHeadersMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Prevent clickjacking
		w.Header().Set("X-Frame-Options", "DENY")
		// Prevent MIME type sniffing
		w.Header().Set("X-Content-Type-Options", "nosniff")
		// XSS protection (legacy but still useful)
		w.Header().Set("X-XSS-Protection", "1; mode=block")
		// Referrer policy
		w.Header().Set("Referrer-Policy", "strict-origin-when-cross-origin")
		// Content Security Policy - restrictive default
		w.Header().Set("Content-Security-Policy", "default-src 'self'; script-src 'self' 'unsafe-inline' https://cdn.tailwindcss.com; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' data: https://fonts.gstatic.com; img-src 'self' data: https:; connect-src 'self' https://api.fireworks.ai https://fonts.googleapis.com")
		
		next.ServeHTTP(w, r)
	})
}

// blockedExtensions lists file extensions that must NEVER be served or accepted,
// regardless of authentication level, role, or any other condition.
// This is a hard platform rule: raw database files are never accessible via the portal.
var blockedExtensions = []string{".db", ".sqlite", ".sqlite3", ".sql", ".mdb", ".accdb"}

// isBlockedExtension returns true if the filename ends with a blocked extension.
func isBlockedExtension(filename string) bool {
	lower := strings.ToLower(strings.TrimSpace(filename))
	for _, ext := range blockedExtensions {
		if strings.HasSuffix(lower, ext) {
			return true
		}
	}
	return false
}

// BlockDatabaseMiddleware is a hard stop on any request that attempts to serve or
// accept a raw database file. This rule cannot be overridden by role, auth level,
// or any user action — it is enforced at the transport layer before handlers run.
func BlockDatabaseMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Check the URL path itself
		if isBlockedExtension(r.URL.Path) {
			http.Error(w, "Forbidden", http.StatusForbidden)
			return
		}
		// Check common query params used for file serving
		for _, param := range []string{"filename", "name", "file", "path"} {
			if isBlockedExtension(r.URL.Query().Get(param)) {
				http.Error(w, "Forbidden", http.StatusForbidden)
				return
			}
		}
		next.ServeHTTP(w, r)
	})
}

// ErrorResponse sends a standard JSON error response.
func ErrorResponse(w http.ResponseWriter, status int, code, message string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(map[string]string{
		"error": message,
		"code":  code,
	})
}

// JSONResponse sends a standard JSON success response.
func JSONResponse(w http.ResponseWriter, status int, data any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(data)
}

func realIP(r *http.Request) string {
	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
		parts := strings.SplitN(xff, ",", 2)
		return strings.TrimSpace(parts[0])
	}
	if xri := r.Header.Get("X-Real-IP"); xri != "" {
		return xri
	}
	addr := r.RemoteAddr
	if idx := strings.LastIndex(addr, ":"); idx != -1 {
		return addr[:idx]
	}
	return addr
}

// JWT

type jwtClaims struct {
	UserID    string `json:"sub"`
	SessionID string `json:"sid"`
	ExpiresAt int64  `json:"exp"`
	IssuedAt  int64  `json:"iat"`
}

// createJWT creates a signed JWT with the given claims.
func createJWT(userID, sessionID string, secret []byte, duration int64) (string, error) {
	now := time.Now().Unix()
	claims := jwtClaims{
		UserID:    userID,
		SessionID: sessionID,
		ExpiresAt: now + duration,
		IssuedAt:  now,
	}

	header := base64.RawURLEncoding.EncodeToString([]byte(`{"alg":"HS256","typ":"JWT"}`))
	payloadJSON, err := json.Marshal(claims)
	if err != nil {
		return "", err
	}
	payload := base64.RawURLEncoding.EncodeToString(payloadJSON)

	signingInput := header + "." + payload
	mac := hmac.New(sha256.New, secret)
	mac.Write([]byte(signingInput))
	sig := base64.RawURLEncoding.EncodeToString(mac.Sum(nil))

	return signingInput + "." + sig, nil
}

func validateJWT(token string, secret []byte) (*jwtClaims, error) {
	parts := strings.Split(token, ".")
	if len(parts) != 3 {
		return nil, lib.ErrAccessDenied
	}

	// Verify HMAC-SHA256 signature
	signingInput := parts[0] + "." + parts[1]
	mac := hmac.New(sha256.New, secret)
	mac.Write([]byte(signingInput))
	expectedSig := mac.Sum(nil)

	sig, err := base64.RawURLEncoding.DecodeString(parts[2])
	if err != nil {
		return nil, lib.ErrAccessDenied
	}
	if !hmac.Equal(sig, expectedSig) {
		return nil, lib.ErrAccessDenied
	}

	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return nil, lib.ErrAccessDenied
	}

	var claims jwtClaims
	if err := json.Unmarshal(payload, &claims); err != nil {
		return nil, lib.ErrAccessDenied
	}

	if claims.ExpiresAt < time.Now().Unix() {
		return nil, lib.ErrAccessDenied
	}

	return &claims, nil
}