const path = require('path');
const fs = require('fs');

exports.getGitVersion = function(repo) {
	var git = path.join(repo, '.git');
	var headPath = path.join(git, 'HEAD');
	var head;

	try {
		head = fs.readFileSync(headPath, 'utf8').trim();
	} catch (e) {
		return void 0;
	}

	if (/^[0-9a-f]{40}$/i.test(head)) {
		return head;
	}

	var refMatch = /^ref: (.*)$/.exec(head);

	if (!refMatch) {
		return void 0;
	}

	var ref = refMatch[1];
	var refPath = path.join(git, ref);

	try {
		return fs.readFileSync(refPath, 'utf8').trim();
	} catch (e) {
		// noop
	}

	var packedRefsPath = path.join(git, 'packed-refs');
	var refsRaw;

	try {
		refsRaw = fs.readFileSync(packedRefsPath, 'utf8').trim();
	} catch (e) {
		return void 0;
	}

	var refsRegex = /^([0-9a-f]{40})\s+(.+)$/gm;
	var refsMatch;
	var refs = {};

	while (refsMatch = refsRegex.exec(refsRaw)) {
		refs[refsMatch[2]] = refsMatch[1];
	}

	return refs[ref];
};