package model

import (
	"errors"
	"fmt"
	"net/http"
)

var (
	ErrNotFound     = errors.New("resource not found")
	ErrDuplicate    = errors.New("resource already exists")
	ErrUnauthorized = errors.New("unauthorized")
	ErrForbidden    = errors.New("forbidden")
)

// AppError is a service-layer error that carries an HTTP status, a user-safe
// message, and an optional internal cause for logging. Handlers unpack it
// transparently via api.RespondError.
type AppError struct {
	Status  int    // HTTP status code
	Message string // safe for API response
	Err     error  // internal cause (nil = user-caused, skip logging)
}

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

// NewInternalError creates a 500 AppError with a wrapped internal cause.
// msg describes the operation that failed; cause is the underlying error.
func NewInternalError(msg string, cause error) *AppError {
	return &AppError{
		Status:  http.StatusInternalServerError,
		Message: "internal server error",
		Err:     fmt.Errorf("%s: %w", msg, cause),
	}
}