package auth

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"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
}

const jwtSecretFilename = ".jwt_secret"

// LoadOrCreateSecret returns JWT_SECRET from the environment if set, otherwise
// a per-install secret persisted at dir/.jwt_secret (created on first run).
func LoadOrCreateSecret(dir string) (string, error) {
	if s := strings.TrimSpace(os.Getenv("JWT_SECRET")); s != "" {
		return s, nil
	}
	if strings.TrimSpace(dir) == "" {
		return "", fmt.Errorf("jwt secret directory is required when JWT_SECRET is unset")
	}
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return "", fmt.Errorf("create jwt secret dir: %w", err)
	}
	path := filepath.Join(dir, jwtSecretFilename)
	if b, err := os.ReadFile(path); err == nil {
		s := strings.TrimSpace(string(b))
		if s != "" {
			return s, nil
		}
	} else if !errors.Is(err, os.ErrNotExist) {
		return "", fmt.Errorf("read jwt secret: %w", err)
	}
	s, err := randomSecret()
	if err != nil {
		return "", err
	}
	if err := os.WriteFile(path, []byte(s+"\n"), 0o600); err != nil {
		return "", fmt.Errorf("write jwt secret: %w", err)
	}
	return s, nil
}

func randomSecret() (string, error) {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		return "", fmt.Errorf("generate jwt secret: %w", err)
	}
	return hex.EncodeToString(b), nil
}

// NewJWTManager creates a manager. Pass a secret from LoadOrCreateSecret or JWT_SECRET.
// An empty secret is replaced with a random in-memory value (tokens will not survive restart).
func NewJWTManager(secret string) *JWTManager {
	if secret == "" {
		s, err := randomSecret()
		if err != nil {
			panic(err)
		}
		secret = s
	}
	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
}