import type { Commit, LocatedObject } from "./git/types.ts";
import { log, type PathChange, pathHistory } from "./git/walk.ts";
import { paginate } from "./pagination.tsx";
import { canonical, type Site, type View } from "./route.ts";
import { kindAtTip, topbar } from "./tree.tsx";
import { commitTime, plural } from "./util.ts";

const TREE = 0o040000;
const HISTORY_PREFETCH = 25;

async function* commitHistory(
  site: Site,
  start: string,
  scanned: (count: number) => void,
): AsyncGenerator<PathChange> {
  for await (const commit of log(site.repo, [start], HISTORY_PREFETCH)) {
    scanned(1);
    yield { commit, object: { oid: commit.tree, mode: TREE } };
  }
}

const snapshotKind = (object: LocatedObject): "tree" | "blob" =>
  (object.mode & 0o170000) === TREE ? "tree" : "blob";

export async function historyView(site: Site, view: View): Promise<Node[]> {
  const { oid, path } = view;
  const commitList = path.length === 0;
  const atTip = await kindAtTip(site, path);
  const list = (<ol class="log history-log" />) as HTMLOListElement;
  const status = (<p class="meta history-status" />) as HTMLElement;
  const control = (<p class="meta log-pagination" />) as HTMLElement;
  let scanned = 0;
  const scannedCommits = (count: number) => {
    scanned += count;
    status.textContent = `scanned ${plural(scanned, "commit")}`;
  };
  paginate<PathChange>({
    list,
    control,
    open: () => {
      scanned = 0;
      return commitList
        ? commitHistory(site, oid, scannedCommits)
        : pathHistory(site.repo, [oid], path, scannedCommits);
    },
    key: change => change.commit.oid,
    render: change => {
      // rows of a file's history link to the file at that commit, not the commit's diff
      const target = !commitList && change.object
        ? canonical(site.page, { kind: snapshotKind(change.object), oid: change.commit.oid, path }, atTip)
        : `#commit/${change.commit.oid}`;
      const who = (
        <span class="who">
          <span>{change.commit.author.name}</span>
          {commitTime(change.commit.author)}
        </span>
      ) as HTMLElement;
      if (!change.object) who.append(<span class="deleted">deleted</span>);
      const item = (<li />) as HTMLLIElement;
      if (change.commit.changeId) {
        item.append(<a class="cid" href={target}>{change.commit.changeId.slice(0, 8)}</a>, " ");
      }
      item.append(
        <a class="sha" href={target}>{change.commit.oid.slice(0, 7)}</a>,
        who,
        <span class="msg">{change.commit.message.split("\n")[0]}</span>,
      );
      return item;
    },
    onShow: count => {
      status.replaceChildren(<span>{plural(count, commitList ? "commit" : "change")}</span>);
    },
    onError: err => {
      status.textContent = `history failed: ${String(err)}`;
    },
  });

  return [
    await topbar(site, view, [commitList ? "commit history" : "change history"]),
    status,
    list,
    control,
  ];
}