import { exec as execCb } from 'node:child_process';
import * as fs from 'node:fs/promises';
import * as path from 'node:path';
import { env } from 'node:process';
import { promisify } from 'node:util';

const __debug = env.NODE_ENV === 'debug';

const exec = promisify(execCb);

/**
 * @param {string} repoPath
 * @returns {string?}
 */
async function getRemoteBranchName(repoPath) {
	let branchName;
	try {
		branchName = (await exec('git symbolic-ref --short HEAD', { cwd: repoPath })).stdout.trim();
		if (!branchName) throw 'Empty local branch name';
	} catch (error) {
		if (__debug) {
			console.warn(`Failed to read git local branch name`);
			console.error(error);
		}
		return null;
	}

	let remoteBranchName;
	try {
		remoteBranchName = (
			await exec(`git for-each-ref --format="%(upstream:short)" refs/heads/${branchName}`, {
				cwd: repoPath
			})
		).stdout.trim();
		const [remote, branch] = remoteBranchName.split('/');
		if (!branch) throw 'Empty remote branch name';
		remoteBranchName = branch;
	} catch (error) {
		if (__debug) {
			console.warn(`Failed to read git remote branch name`);
			console.error(error);
		}
		return null;
	}

	return remoteBranchName;
}

// https://stackoverflow.com/q/3651860#answer-67151923
const REF_REGEX = /ref:\s+refs\/heads\/(?<branch>[^\s\x00-\x1F\:\?\[\\\^\~]+)/;
const GITHUB_REF_REGEX = /^refs\/heads\//;

/**
 * @param {string} repoPath
 * @returns {Promise<string[]>}
 */
export async function getGitBranches(repoPath) {
	const branches = ['main', 'master'];

	if (env.GITHUB_HEAD_REF) {
		branches.unshift(env.GITHUB_HEAD_REF);
	} else if (env.GITHUB_REF) {
		branches.unshift(env.GITHUB_REF.replace(GITHUB_REF_REGEX, ''));
	}

	const remoteBranchName = await getRemoteBranchName(repoPath);
	if (remoteBranchName) {
		branches.unshift(remoteBranchName);
	} else {
		let head;
		try {
			head = await fs.readFile(path.join(repoPath, '.git', 'HEAD'), { encoding: 'utf8' });
		} catch (error) {
			if (__debug) {
				console.warn(`Failed to read git HEAD file`);
				console.error(error);
			}
			return branches;
		}

		const match = REF_REGEX.exec(head);
		if (match?.groups?.branch) branches.unshift(match.groups.branch);
	}

	return branches;
}