package auth

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"

	"github.com/golang-jwt/jwt/v5"
)

var (
	ErrInvalidToken = errors.New("invalid or expired token")
	ErrNoToken      = errors.New("no authorization token")
)

// Claims for our JWT (minimal, matching original style).
type Claims struct {
	UserID int      `json:"user_id"`
	Email  string   `json:"email"`
	Name   string   `json:"name"`
	Roles  []string `json:"roles"`
	jwt.RegisteredClaims
}

// Context key for user info.
type contextKey string

const UserContextKey contextKey = "user"

// JWTManager handles signing and validation.
type JWTManager struct {
	secret []byte
}

// NewJWTManager creates a manager. In real use, load secret from secure store or env (never commit real secret).
// For demo we accept a secret; in production rotate and use env/JWT_SECRET or db meta.
func NewJWTManager(secret string) *JWTManager {
	if secret == "" {
		secret = "dev-only-insecure-secret-change-in-prod"
	}
	return &JWTManager{secret: []byte(secret)}
}

// GenerateToken creates a JWT for the given user (1 hour expiry like typical).
func (m *JWTManager) GenerateToken(userID int, email, name string, roles []string) (string, error) {
	now := time.Now()
	if roles == nil {
		roles = []string{}
	}
	claims := Claims{
		UserID: userID,
		Email:  email,
		Name:   name,
		Roles:  roles,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(now.Add(1 * time.Hour)),
			IssuedAt:  jwt.NewNumericDate(now),
			NotBefore: jwt.NewNumericDate(now),
			Issuer:    "helix-proxy",
		},
	}
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString(m.secret)
}

// ValidateToken parses and validates the token, returns claims.
func (m *JWTManager) ValidateToken(tokenStr string) (*Claims, error) {
	token, err := jwt.ParseWithClaims(tokenStr, &Claims{}, func(t *jwt.Token) (interface{}, error) {
		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("unexpected signing method: %v", t.Header["alg"])
		}
		return m.secret, nil
	})
	if err != nil {
		return nil, ErrInvalidToken
	}
	if claims, ok := token.Claims.(*Claims); ok && token.Valid {
		return claims, nil
	}
	return nil, ErrInvalidToken
}

// Middleware returns a chi/http middleware that validates Bearer token and injects user into context.
// Skips if no token (for public endpoints like /login we handle separately).
// On failure returns 401.
func (m *JWTManager) Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		authHeader := r.Header.Get("Authorization")
		if authHeader == "" {
			// No token: let handler decide (some endpoints public)
			next.ServeHTTP(w, r)
			return
		}

		parts := strings.SplitN(authHeader, " ", 2)
		if len(parts) != 2 || !strings.EqualFold(parts[0], "Bearer") {
			http.Error(w, "invalid authorization header", http.StatusUnauthorized)
			return
		}

		claims, err := m.ValidateToken(parts[1])
		if err != nil {
			http.Error(w, "invalid token", http.StatusUnauthorized)
			return
		}

		// Inject into context
		ctx := context.WithValue(r.Context(), UserContextKey, claims)
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

// GetUserFromContext extracts claims if present (for handlers that require auth).
func GetUserFromContext(ctx context.Context) (*Claims, bool) {
	claims, ok := ctx.Value(UserContextKey).(*Claims)
	return claims, ok
}

// RequireAuth is a simple helper that can be used inside handlers for protected routes
// (alternative to middleware if you want per-route).
func RequireAuth(w http.ResponseWriter, r *http.Request) (*Claims, bool) {
	claims, ok := GetUserFromContext(r.Context())
	if !ok {
		http.Error(w, "authentication required", http.StatusUnauthorized)
		return nil, false
	}
	return claims, true
}