// New enforces a timeout for each incoming request. If the timeout expires or
// any of the specified errors occur, fiber.ErrRequestTimeout is returned.
func New(h fiber.Handler, timeout time.Duration, tErrs ...error) fiber.Handler {
	return func(ctx fiber.Ctx) error {
		// If timeout <= 0, skip context.WithTimeout and run the handler as-is.
		if timeout <= 0 {
			return runHandler(ctx, h, tErrs)
		}

		// Create a context with the specified timeout; any operation exceeding
		// this deadline will be canceled automatically.
		timeoutContext, cancel := context.WithTimeout(ctx, timeout)
		defer cancel()

		// Run the handler and check for relevant errors.
		err := runHandler(ctx, h, tErrs)

		// If the context actually timed out, return a timeout error.
		if errors.Is(timeoutContext.Err(), context.DeadlineExceeded) {
			return fiber.ErrRequestTimeout
		}
		return err
	}
}

// runHandler executes the handler and returns fiber.ErrRequestTimeout if it
// sees a deadline exceeded error or one of the custom "timeout-like" errors.
func runHandler(c fiber.Ctx, h fiber.Handler, tErrs []error) error {
	// Execute the wrapped handler synchronously.
	err := h(c)
	// If the context has timed out, return a request timeout error.
	if err != nil && (errors.Is(err, context.DeadlineExceeded) || isCustomError(err, tErrs)) {
		return fiber.ErrRequestTimeout
	}
	return err
}

// isCustomError checks whether err matches any error in errList using errors.Is.
func isCustomError(err error, errList []error) bool {
	for _, e := range errList {
		if errors.Is(err, e) {
			return true
		}
	}
	return false
}