package handlers

import (
	"errors"
	"regexp"
	"strconv"
)

const (
	// appNameMinLength is the minimum allowed length for an app name.
	appNameMinLength = 2
	// appNameMaxLength is the maximum allowed length for an app name.
	appNameMaxLength = 63
)

// validAppNameRe matches runs of lowercase letters and digits joined by
// single dots or by hyphens, such as "my-app" or "sneak.berlin". Docker
// accepts every name it allows as the app's image name, upaas-<name>; a
// dot needs a letter or digit on both sides because Docker requires it.
// It also keeps the name from being "." or ".." or starting or ending
// with a dot, so it is safe as a directory and file name. The pattern
// attribute of the name field on the new and edit app forms is the same.
var validAppNameRe = regexp.MustCompile(`^[a-z0-9]+((\.|-+)[a-z0-9]+)*$`)

var (
	errAppNameLength = errors.New(
		"app name must be between " +
			strconv.Itoa(appNameMinLength) + " and " +
			strconv.Itoa(appNameMaxLength) + " characters",
	)
	errAppNamePattern = errors.New(
		"app name must contain only lowercase letters, numbers, hyphens, " +
			"and dots, must start and end with a letter or number, " +
			"and must have a letter or number on both sides of each dot",
	)
)

// validateAppName checks that the given app name is safe for use in Docker
// container names, image tags, and file system paths.
func validateAppName(name string) error {
	if len(name) < appNameMinLength || len(name) > appNameMaxLength {
		return errAppNameLength
	}

	if !validAppNameRe.MatchString(name) {
		return errAppNamePattern
	}

	return nil
}