import { createHash } from "node:crypto";

// Tangled exposes the PR source branch, but no documented PR number environment variable.
export function previewName(branch: string): string {
	if (!branch || branch === "main") {
		throw new Error("A preview needs a non-main source branch.");
	}

	const slug =
		branch
			.toLowerCase()
			.replaceAll(/[^a-z0-9]+/g, "-")
			.slice(0, 24)
			.replace(/-+$/, "") || "branch";

	const hash = createHash("sha256").update(branch).digest("hex").slice(0, 12);

	return `pr-${slug}-${hash}`;
}