// Package apperr defines AppError, the single error type returned by every
// service/repo function. Handlers translate AppError into HTTP responses.
package apperr

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

type AppError struct {
	Code       int    // HTTP status to return
	Message    string // user-facing message (safe to expose)
	Field      string // optional: which field caused the error
	RetryAfter int    // seconds, for 429
	Err        error  // original error for logging (never exposed)
}

func (e *AppError) Error() string {
	if e.Err != nil {
		return fmt.Sprintf("%s: %v", e.Message, e.Err)
	}
	return e.Message
}

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

// As reports whether err is or wraps an *AppError.
func As(err error) (*AppError, bool) {
	var ae *AppError
	if errors.As(err, &ae) {
		return ae, true
	}
	return nil, false
}

// ---------------------------------------------------------------------------
// Constructors
// ---------------------------------------------------------------------------

func BadRequest(msg, field string, err error) *AppError {
	return &AppError{Code: http.StatusBadRequest, Message: msg, Field: field, Err: err}
}

func Unauthorized(msg string) *AppError {
	return &AppError{Code: http.StatusUnauthorized, Message: msg}
}

func Forbidden(msg string) *AppError {
	return &AppError{Code: http.StatusForbidden, Message: msg}
}

func NotFound(msg string) *AppError {
	return &AppError{Code: http.StatusNotFound, Message: msg}
}

func Conflict(msg string, err error) *AppError {
	return &AppError{Code: http.StatusConflict, Message: msg, Err: err}
}

func PayloadTooLarge(msg string) *AppError {
	return &AppError{Code: http.StatusRequestEntityTooLarge, Message: msg}
}

func UnprocessableEntity(msg string) *AppError {
	return &AppError{Code: http.StatusUnprocessableEntity, Message: msg}
}

func TooManyRequests(retryAfterSeconds int) *AppError {
	return &AppError{
		Code:       http.StatusTooManyRequests,
		Message:    "rate limit exceeded",
		RetryAfter: retryAfterSeconds,
	}
}

func Internal(err error) *AppError {
	return &AppError{Code: http.StatusInternalServerError, Message: "internal server error", Err: err}
}