package apperror

import (
	"errors"
	"fmt"
	"strings"

	"github.com/go-sql-driver/mysql"
)

// AppError is a structured application error with an HTTP status code.
// JSON response format: {"error": "<code>", "message": "<human-readable message>"}
type AppError struct {
	Code    string `json:"error"`
	Message string `json:"message"`
	Status  int    `json:"-"`
}

func (e *AppError) Error() string { return e.Message }

// New creates a new AppError.
func New(code string, message string, status int) *AppError {
	return &AppError{Code: code, Message: message, Status: status}
}

// Wrap creates a new AppError that wraps a cause error.
func Wrap(code string, message string, status int, cause error) *AppError {
	return &AppError{Code: code, Message: fmt.Sprintf("%s: %v", message, cause), Status: status}
}

// Common errors
var (
	ErrBadRequest   = &AppError{Code: "bad_request", Message: "잘못된 요청입니다", Status: 400}
	ErrUnauthorized = &AppError{Code: "unauthorized", Message: "인증이 필요합니다", Status: 401}
	ErrForbidden    = &AppError{Code: "forbidden", Message: "권한이 없습니다", Status: 403}
	ErrNotFound     = &AppError{Code: "not_found", Message: "리소스를 찾을 수 없습니다", Status: 404}
	ErrConflict     = &AppError{Code: "conflict", Message: "이미 존재합니다", Status: 409}
	ErrRateLimited  = &AppError{Code: "rate_limited", Message: "요청이 너무 많습니다", Status: 429}
	ErrInternal     = &AppError{Code: "internal_error", Message: "서버 오류가 발생했습니다", Status: 500}
)

// BadRequest creates a 400 error with a custom message.
func BadRequest(message string) *AppError {
	return &AppError{Code: "bad_request", Message: message, Status: 400}
}

// Unauthorized creates a 401 error with a custom message.
func Unauthorized(message string) *AppError {
	return &AppError{Code: "unauthorized", Message: message, Status: 401}
}

// NotFound creates a 404 error with a custom message.
func NotFound(message string) *AppError {
	return &AppError{Code: "not_found", Message: message, Status: 404}
}

// Conflict creates a 409 error with a custom message.
func Conflict(message string) *AppError {
	return &AppError{Code: "conflict", Message: message, Status: 409}
}

// Internal creates a 500 error with a custom message.
func Internal(message string) *AppError {
	return &AppError{Code: "internal_error", Message: message, Status: 500}
}

// ErrDuplicateUsername is returned when a username already exists.
var ErrDuplicateUsername = fmt.Errorf("이미 사용 중인 아이디입니다")

// IsDuplicateEntry checks if a GORM error is a MySQL duplicate key violation (error 1062).
func IsDuplicateEntry(err error) bool {
	var mysqlErr *mysql.MySQLError
	if errors.As(err, &mysqlErr) {
		return mysqlErr.Number == 1062
	}
	return strings.Contains(err.Error(), "Duplicate entry") || strings.Contains(err.Error(), "UNIQUE constraint")
}