import { readFileSync } from 'node:fs';

// Gitea exposes its event payload through the GitHub-compatible runner variables.
export function readCiContext() {
	const env = process.env;
	const eventName = env.GITHUB_EVENT_NAME;
	if (!['push', 'pull_request', 'workflow_dispatch'].includes(eventName)) {
		throw new Error('Only push, pull_request and workflow_dispatch events are supported.');
	}
	const event = JSON.parse(readFileSync(env.GITHUB_EVENT_PATH, 'utf8'));
	const commit = env.GITHUB_SHA;
	if (!/^[a-f0-9]{40}$/.test(commit ?? '')) throw new Error('A commit SHA is required.');
	const pullRequest = eventName === 'pull_request' ? event.pull_request : undefined;
	if (eventName === 'pull_request' && pullRequest?.head?.sha !== commit) {
		throw new Error('CI must validate the pull request head commit.');
	}
	const tag = env.GITHUB_REF?.startsWith('refs/tags/') ? env.GITHUB_REF.slice(10) : '';
	const branch = pullRequest
		? pullRequest.head.ref
		: env.GITHUB_REF?.startsWith('refs/heads/')
			? env.GITHUB_REF.slice(11)
			: '';
	if (!tag && !branch) throw new Error('A branch or tag ref is required.');
	const slug = branch
		.toLowerCase()
		.replace(/[^a-z0-9]/g, '-')
		.slice(0, 63)
		.replace(/^-+|-+$/g, '');
	const publish =
		eventName === 'push' ||
		(eventName === 'pull_request' &&
			Boolean(env.GITHUB_REPOSITORY) &&
			pullRequest.head.repo?.full_name === env.GITHUB_REPOSITORY);
	return { commit, tag, branch, slug, publish, pullRequest, before: event.before };
}