package handlers

import (
	"crypto/rand"
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"fmt"
	"net/http"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/golang-jwt/jwt/v5"
	"golang.org/x/crypto/bcrypt"

	"git.gobha.me/xcaliber/chat-switchboard/config"
	"git.gobha.me/xcaliber/chat-switchboard/database"
)

const (
	accessTokenDuration  = 15 * time.Minute
	refreshTokenDuration = 7 * 24 * time.Hour
	bcryptCost           = 12
)

// Claims is the JWT access token payload.
type Claims struct {
	UserID string `json:"user_id"`
	Email  string `json:"email"`
	Role   string `json:"role"`
	jwt.RegisteredClaims
}

// ── Request / Response types ────────────────

type registerRequest struct {
	Username string `json:"username" binding:"required,min=3,max=50"`
	Email    string `json:"email"    binding:"required,email"`
	Password string `json:"password" binding:"required,min=8,max=128"`
}

type loginRequest struct {
	Login    string `json:"login"    binding:"required"` // email or username
	Password string `json:"password" binding:"required"`
}

type refreshRequest struct {
	RefreshToken string `json:"refresh_token" binding:"required"`
}

type authResponse struct {
	AccessToken  string `json:"access_token"`
	RefreshToken string `json:"refresh_token"`
	ExpiresIn    int    `json:"expires_in"` // seconds
	User         userResponse `json:"user"`
}

type userResponse struct {
	ID          string  `json:"id"`
	Username    string  `json:"username"`
	Email       string  `json:"email"`
	DisplayName *string `json:"display_name"`
	Role        string  `json:"role"`
}

// AuthHandler holds dependencies for auth endpoints.
type AuthHandler struct {
	cfg *config.Config
}

// NewAuthHandler creates a new auth handler.
func NewAuthHandler(cfg *config.Config) *AuthHandler {
	return &AuthHandler{cfg: cfg}
}

// ── Register ────────────────────────────────

func (h *AuthHandler) Register(c *gin.Context) {
	var req registerRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	req.Email = strings.ToLower(strings.TrimSpace(req.Email))
	req.Username = strings.TrimSpace(req.Username)

	// Check if this is the first user (will become admin)
	var userCount int
	_ = database.DB.QueryRow(`SELECT COUNT(*) FROM users`).Scan(&userCount)
	isFirstUser := userCount == 0

	// If not first user, check if registration is enabled
	if !isFirstUser {
		if !IsRegistrationEnabled() {
			c.JSON(http.StatusForbidden, gin.H{"error": "registration is disabled"})
			return
		}
	}

	// Hash password
	hash, err := bcrypt.GenerateFromPassword([]byte(req.Password), bcryptCost)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to hash password"})
		return
	}

	// First user gets admin role
	role := "user"
	if isFirstUser {
		role = "admin"
	}

	// Insert user
	var user userResponse
	err = database.DB.QueryRow(`
		INSERT INTO users (username, email, password_hash, role)
		VALUES ($1, $2, $3, $4)
		RETURNING id, username, email, display_name, role
	`, req.Username, req.Email, string(hash), role).Scan(
		&user.ID, &user.Username, &user.Email, &user.DisplayName, &user.Role,
	)
	if err != nil {
		if strings.Contains(err.Error(), "duplicate key") {
			field := "email"
			if strings.Contains(err.Error(), "username") {
				field = "username"
			}
			c.JSON(http.StatusConflict, gin.H{"error": fmt.Sprintf("%s already taken", field)})
			return
		}
		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to create user"})
		return
	}

	// Generate tokens
	resp, err := h.generateTokenPair(user)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to generate tokens"})
		return
	}

	c.JSON(http.StatusCreated, resp)
}

// IsRegistrationEnabled checks the global_settings table.
// Returns true if the table doesn't exist (pre-migration), DB is nil, or setting is enabled.
func IsRegistrationEnabled() bool {
	if database.DB == nil {
		return true
	}
	var enabled bool
	err := database.DB.QueryRow(`
		SELECT COALESCE((value->>'enabled')::boolean, true)
		FROM global_settings WHERE key = 'registration'
	`).Scan(&enabled)
	if err != nil {
		return true // Default to open if setting missing
	}
	return enabled
}

// ── Login ───────────────────────────────────

func (h *AuthHandler) Login(c *gin.Context) {
	var req loginRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	req.Login = strings.TrimSpace(req.Login)

	// Look up user by email or username
	var user userResponse
	var passwordHash string
	var isActive bool

	err := database.DB.QueryRow(`
		SELECT id, username, email, display_name, role, password_hash, is_active
		FROM users
		WHERE email = $1 OR username = $1
	`, req.Login).Scan(
		&user.ID, &user.Username, &user.Email, &user.DisplayName,
		&user.Role, &passwordHash, &isActive,
	)
	if err == sql.ErrNoRows {
		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid credentials"})
		return
	}
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "authentication failed"})
		return
	}

	if !isActive {
		c.JSON(http.StatusForbidden, gin.H{"error": "account disabled"})
		return
	}

	// Verify password
	if err := bcrypt.CompareHashAndPassword([]byte(passwordHash), []byte(req.Password)); err != nil {
		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid credentials"})
		return
	}

	// Update last_login_at
	_, _ = database.DB.Exec(`UPDATE users SET last_login_at = NOW() WHERE id = $1`, user.ID)

	// Generate tokens
	resp, err := h.generateTokenPair(user)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to generate tokens"})
		return
	}

	c.JSON(http.StatusOK, resp)
}

// ── Refresh ─────────────────────────────────

func (h *AuthHandler) Refresh(c *gin.Context) {
	var req refreshRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	tokenHash := hashToken(req.RefreshToken)

	// Find and validate the refresh token
	var tokenID, userID string
	var expiresAt time.Time

	err := database.DB.QueryRow(`
		SELECT rt.id, rt.user_id, rt.expires_at
		FROM refresh_tokens rt
		WHERE rt.token_hash = $1 AND rt.revoked_at IS NULL
	`, tokenHash).Scan(&tokenID, &userID, &expiresAt)

	if err == sql.ErrNoRows {
		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid refresh token"})
		return
	}
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "token validation failed"})
		return
	}

	if time.Now().After(expiresAt) {
		// Revoke expired token
		_, _ = database.DB.Exec(`UPDATE refresh_tokens SET revoked_at = NOW() WHERE id = $1`, tokenID)
		c.JSON(http.StatusUnauthorized, gin.H{"error": "refresh token expired"})
		return
	}

	// Revoke the old token (rotation)
	_, _ = database.DB.Exec(`UPDATE refresh_tokens SET revoked_at = NOW() WHERE id = $1`, tokenID)

	// Look up user
	var user userResponse
	var isActive bool
	err = database.DB.QueryRow(`
		SELECT id, username, email, display_name, role, is_active
		FROM users WHERE id = $1
	`, userID).Scan(
		&user.ID, &user.Username, &user.Email, &user.DisplayName, &user.Role, &isActive,
	)
	if err != nil || !isActive {
		c.JSON(http.StatusUnauthorized, gin.H{"error": "account unavailable"})
		return
	}

	// Issue new pair
	resp, err := h.generateTokenPair(user)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to generate tokens"})
		return
	}

	c.JSON(http.StatusOK, resp)
}

// ── Logout ──────────────────────────────────

func (h *AuthHandler) Logout(c *gin.Context) {
	var req refreshRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		// No refresh token provided — just acknowledge
		c.JSON(http.StatusOK, gin.H{"message": "logged out"})
		return
	}

	tokenHash := hashToken(req.RefreshToken)

	// Revoke the refresh token
	_, _ = database.DB.Exec(`
		UPDATE refresh_tokens SET revoked_at = NOW()
		WHERE token_hash = $1 AND revoked_at IS NULL
	`, tokenHash)

	c.JSON(http.StatusOK, gin.H{"message": "logged out"})
}

// ── Token Generation ────────────────────────

func (h *AuthHandler) generateTokenPair(user userResponse) (*authResponse, error) {
	now := time.Now()

	// Access token (JWT)
	claims := Claims{
		UserID: user.ID,
		Email:  user.Email,
		Role:   user.Role,
		RegisteredClaims: jwt.RegisteredClaims{
			IssuedAt:  jwt.NewNumericDate(now),
			ExpiresAt: jwt.NewNumericDate(now.Add(accessTokenDuration)),
			Issuer:    "chat-switchboard",
		},
	}
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	accessToken, err := token.SignedString([]byte(h.cfg.JWTSecret))
	if err != nil {
		return nil, fmt.Errorf("sign access token: %w", err)
	}

	// Refresh token (opaque random string, stored hashed)
	refreshBytes := make([]byte, 32)
	if _, err := rand.Read(refreshBytes); err != nil {
		return nil, fmt.Errorf("generate refresh token: %w", err)
	}
	refreshToken := hex.EncodeToString(refreshBytes)
	refreshHash := hashToken(refreshToken)

	// Store refresh token
	_, err = database.DB.Exec(`
		INSERT INTO refresh_tokens (user_id, token_hash, expires_at)
		VALUES ($1, $2, $3)
	`, user.ID, refreshHash, now.Add(refreshTokenDuration))
	if err != nil {
		return nil, fmt.Errorf("store refresh token: %w", err)
	}

	return &authResponse{
		AccessToken:  accessToken,
		RefreshToken: refreshToken,
		ExpiresIn:    int(accessTokenDuration.Seconds()),
		User:         user,
	}, nil
}

// hashToken returns a SHA-256 hex digest of a token string.
// Refresh tokens are stored hashed so a DB leak doesn't
// compromise active sessions.
func hashToken(token string) string {
	h := sha256.Sum256([]byte(token))
	return hex.EncodeToString(h[:])
}