var  Q = require("q");
var _ = require("lodash");
var url = require("url");
var tmp = require("tmp");
var path = require("path");
var crc = require("crc");
var exec = Q.denodeify(require("child_process").exec);

var fs = require("./fs");

var GIT_PREFIX = "git+";
var GIT_TMP = null;


// Check if an url is a git dependency url
function checkGitUrl(giturl) {
	return (giturl.indexOf(GIT_PREFIX) === 0);
}

// Validates a SHA in hexadecimal
function validateSha(str) {
    return (/[0-9a-f]{40}/).test(str);
}

// Parse and extract infos
function parseGitUrl(giturl) {
	if (!checkGitUrl(giturl)) return null;
	giturl = giturl.slice(GIT_PREFIX.length);

	var parts = url.parse(giturl);

	var ref = parts.hash;

	// Extract file inside the repo (after the .git)
	var fileParts = parts.pathname.split(".git");
	var filepath = fileParts.length > 1? fileParts.slice(1).join(".git") : "";
	if (filepath[0] == "/") filepath = filepath.slice(1);

	// Rebuild
	parts.pathname = _.first(fileParts)+".git";
	var githost = url.format(parts);

	return {
		host: githost,
		ref: ref,
		filepath: filepath
	};
}

// Clone a git repo from a specific ref
function cloneGitRepo(host, ref) {
	var isBranch = false;

	ref = ref || "master";
	if (!validateSha(ref)) isBranch = true;

	return Q()

	// Create temporary folder to store git repos
	.then(function() {
		if (GIT_TMP) return;
		return fs.tmp.dir()
			.then(function(_tmp) {
				GIT_TMP = _tmp;
			});
	})

	// Return or clone the git repo
	.then(function() {
		// Unique ID for repo/ref combinaison
		var repoId = crc.crc32(host+"#"+ref).toString(16);

		// Absolute path to the folder
		var repoPath = path.resolve(GIT_TMP, repoId);

		return fs.exists(repoPath)
			.then(function(doExists) {
				if (doExists) return;

				// Clone repo
				return exec("git clone "+host+" "+repoPath)
				.then(function() {
					return exec("git checkout "+ref, { cwd: repoPath });
				})
			})
			.thenResolve(repoPath);
	});
}


// Get file from a git repo
function resolveFileFromGit(giturl) {
	if (_.isString(giturl)) giturl = parseGitUrl(giturl);
	if (!giturl) return Q(null);

	// Clone or get from cache
	return cloneGitRepo(giturl.host, giturl.ref)
	.then(function(repo) {

		// Resolve relative path
		return path.resolve(repo, giturl.filepath);
	});
};


module.exports = {
	checkUrl: checkGitUrl,
	parseUrl: parseGitUrl,
	resolveFile: resolveFileFromGit
};