import { parseAtUri } from './at-uri.ts';
import { gunzipToString, listMarkdownFilesInDiff } from './patch.ts';
import type { PullRecord } from './types.ts';

export type FetchImpl = (input: string | URL, init?: RequestInit) => Promise<Response>;

export function latestPatchCid(pull: PullRecord): string | null {
  const rounds = pull.rounds ?? [];
  const latest = rounds[rounds.length - 1];
  return latest?.patchBlob?.ref?.$link ?? null;
}

/** Fetch and gunzip a patch blob from the author's PDS. Returns null on any failure. */
export async function fetchPatchText(
  pds: string,
  authorDid: string,
  patchCid: string,
  fetchImpl: FetchImpl = fetch,
): Promise<string | null> {
  const url = new URL('/xrpc/com.atproto.sync.getBlob', pds);
  url.searchParams.set('did', authorDid);
  url.searchParams.set('cid', patchCid);
  const res = await fetchImpl(url);
  if (!res.ok) return null;
  const bytes = new Uint8Array(await res.arrayBuffer());
  try {
    return await gunzipToString(bytes);
  } catch {
    return null;
  }
}

export interface PullPatchDeps {
  resolvePds: (did: string) => Promise<string>;
  fetchImpl?: FetchImpl;
}

/** Resolve the pull author's PDS, fetch the latest patch, and return the `.md` paths it touches. */
export async function pullMarkdownPaths(
  pullUri: string,
  pull: PullRecord,
  deps: PullPatchDeps,
): Promise<string[]> {
  const cid = latestPatchCid(pull);
  const parsed = parseAtUri(pullUri);
  if (!cid || !parsed) return [];
  let pds: string;
  try {
    pds = await deps.resolvePds(parsed.did);
  } catch {
    return [];
  }
  const text = await fetchPatchText(pds, parsed.did, cid, deps.fetchImpl);
  if (!text) return [];
  return listMarkdownFilesInDiff(text).map((entry) => entry.path);
}