import type { Database } from "bun:sqlite";
import { type Bucket, BucketWriteError, KEPR_PREFIX } from "../bucket/reader.ts";
import { filesAt, objectBytes, tarballGeneration } from "../mirror/queries.ts";
import { knownSave } from "../mirror/store.ts";
import { buildTarball } from "./tar.ts";

const tarballsOf = (repo: string) => `${KEPR_PREFIX}tarballs/${repo}/`;

/**
 * A save's tarball, kept in the bucket under Kepr's own folder (June, 2026-09-30) as
 * `.kepr/tarballs/<repo>/<generation>/<id>.tar.gz` once first requested (`tarballGeneration`).
 * If the bucket refuses the write nothing is kept, and each request builds it again. Null when the
 * save is gone from the mirror, as it is for a moment while a rebuild runs.
 */
export async function cachedTarball(
	bucket: Bucket,
	db: Database,
	repo: string,
	saveId: string,
): Promise<Uint8Array | null> {
	for (;;) {
		const generation = tarballGeneration(db);
		const key = `${tarballsOf(repo)}${generation}/${saveId}.tar.gz`;
		const stored = await bucket.get(key);
		// A strip, a hidden-path change or a rebuild may land during any await, and the sync's thread
		// can land one between any two statements: the generation and the files are read in one
		// snapshot, so what is built matches the key it files under, and bytes are served only for
		// the generation still current.
		const read = db.transaction(() => {
			if (tarballGeneration(db) !== generation) return "moved";
			if (stored) return "stored";
			if (!knownSave(db, saveId)) return "unknown";
			return filesAt(db, saveId).map((file) => {
				const bytes = objectBytes(db, file.hash);
				if (!bytes) throw new Error(`${repo}: object ${file.hash} is missing from the mirror`);
				return { path: file.path, bytes, executable: file.executable };
			});
		})();
		if (read === "moved") continue;
		if (read === "stored") return stored;
		if (read === "unknown") return null;
		const tarball = buildTarball(`${repo}-${saveId.slice(0, 8)}`, read);
		try {
			await bucket.put(key, tarball, "application/gzip");
		} catch (error) {
			if (!(error instanceof BucketWriteError)) throw error;
		}
		if (tarballGeneration(db) === generation) return tarball;
	}
}

/** Deletes a repo's kept tarballs to free space; stale ones are never looked up anyway. */
export async function dropTarballs(bucket: Bucket, repo: string): Promise<void> {
	for (const key of await bucket.list(tarballsOf(repo))) await bucket.remove(key);
}