// Package urlutil provides helper function to check if a given build-context
// location should be considered a URL or a remote Git repository.
//
// This package is specifically written for use with docker build contexts, and
// should not be used as a general-purpose utility.
package urlutil // import "github.com/docker/docker/builder/remotecontext/urlutil"

import (
	"regexp"
	"strings"
)

// urlPathWithFragmentSuffix matches fragments to use as Git reference and build
// context from the Git repository. See IsGitURL for details.
var urlPathWithFragmentSuffix = regexp.MustCompile(`\.git(?:#.+)?$`)

// IsURL returns true if the provided str is an HTTP(S) URL by checking if it
// has a http:// or https:// scheme. No validation is performed to verify if the
// URL is well-formed.
func IsURL(str string) bool {
	return strings.HasPrefix(str, "https://") || strings.HasPrefix(str, "http://")
}

// IsGitURL returns true if the provided str is a remote git repository "URL".
//
// This function only performs a rudimentary check (no validation is performed
// to ensure the URL is well-formed), and is written specifically for use with
// docker build, with some logic for backward compatibility with older versions
// of docker: do not use this function as a general-purpose utility.
//
// The following patterns are considered to be a Git URL:
//
//   - https://(.*).git(?:#.+)?$  git repository URL with optional fragment, as known to be used by GitHub and GitLab.
//   - http://(.*).git(?:#.+)?$   same, but non-TLS
//   - git://(.*)                 URLs using git:// scheme
//   - git@(.*)
//   - github.com/                see description below
//
// The github.com/ prefix is a special case used to treat context-paths
// starting with "github.com/" as a git URL if the given path does not
// exist locally. The "github.com/" prefix is kept for backward compatibility,
// and is a legacy feature.
//
// Going forward, no additional prefixes should be added, and users should
// be encouraged to use explicit URLs (https://github.com/user/repo.git) instead.
//
// Note that IsGitURL does not check if "github.com/" prefixes exist as a local
// path. Code using this function should check if the path exists locally before
// using it as a URL.
//
// # Fragments
//
// Git URLs accept context configuration in their fragment section, separated by
// a colon (`:`). The first part represents the reference to check out, and can
// be either a branch, a tag, or a remote reference. The second part represents
// a subdirectory inside the repository to use as the build context.
//
// For example,the following URL uses a directory named "docker" in the branch
// "container" in the https://github.com/myorg/my-repo.git repository:
//
// https://github.com/myorg/my-repo.git#container:docker
//
// The following table represents all the valid suffixes with their build
// contexts:
//
// | Build Syntax Suffix            | Git reference used   | Build Context Used |
// |--------------------------------|----------------------|--------------------|
// | my-repo.git                    | refs/heads/master    | /                  |
// | my-repo.git#mytag              | refs/tags/my-tag     | /                  |
// | my-repo.git#mybranch           | refs/heads/my-branch | /                  |
// | my-repo.git#pull/42/head       | refs/pull/42/head    | /                  |
// | my-repo.git#:directory         | refs/heads/master    | /directory         |
// | my-repo.git#master:directory   | refs/heads/master    | /directory         |
// | my-repo.git#mytag:directory    | refs/tags/my-tag     | /directory         |
// | my-repo.git#mybranch:directory | refs/heads/my-branch | /directory         |
func IsGitURL(str string) bool {
	if IsURL(str) && urlPathWithFragmentSuffix.MatchString(str) {
		return true
	}
	for _, prefix := range []string{"git://", "github.com/", "git@"} {
		if strings.HasPrefix(str, prefix) {
			return true
		}
	}
	return false
}
