import { treeDiff, type FileChange } from "./git/walk.ts";
import { diffLines } from "./git/diff.ts";
import { topbar } from "./historical.tsx";
import { href, type Site, type View } from "./route.ts";
import { identityDate, looksBinary, looksGenerated, plural, utf8 } from "./util.ts";

const highlightedLines = (path: string, source: string) =>
  import("./highlight.ts").then(module => module.highlightedLines(path, source));

export async function commitView(site: Site, view: View): Promise<Node[]> {
  const { repo } = site;
  const { oid } = view;
  await repo.prefetch([oid], { smart: "commit-diff" });
  const commit = await repo.commit(oid);
  const parentTree = commit.parents.length > 0
    ? (await repo.commit(commit.parents[0])).tree
    : null;
  const changes = await treeDiff(repo, parentTree, commit.tree);
  const blobs = changes.flatMap(change =>
    [change.oldOid, change.newOid].filter(oid => oid !== null)
  );
  await repo.prefetch(blobs, { depth: 0 });
  const files = await Promise.all(changes.map(change => fileSection(site, oid, change)));
  const adds = files.reduce((n, f) => n + f.adds, 0);
  const dels = files.reduce((n, f) => n + f.dels, 0);

  const [subject, ...rest] = commit.message.trimEnd().split("\n");
  const body = rest.join("\n").trim();

  const meta = (<table class="commit-meta" />) as HTMLTableElement;
  const row = (key: string, value: Node | string) =>
    meta.append(
      <tr>
        <th>{key}</th>
        <td _also={el => el.append(typeof value === "string" ? document.createTextNode(value) : value)} />
      </tr>,
    );
  row("author", `${commit.author.name} <${commit.author.email}>`);
  row("date", identityDate(commit.author));
  row("commit", <span class="sha">{oid}</span>);
  for (const parent of commit.parents) {
    row("parent", <a class="sha" href={`#commit/${parent}`}>{parent}</a>);
  }
  if (commit.changeId) row("change-id", <span class="cid">{commit.changeId}</span>);

  const browse = <a href={await href(site, { kind: "tree", oid, path: [] })}>browse files</a>;
  return [
    await topbar(site, view, [], [browse]),
    <h2 class="commit-subject">{subject}</h2>,
    ...(body ? [<pre class="commit-body">{body}</pre>] : []),
    meta,
    <p class="meta diffstat">
      <span class="add-count">+{String(adds)}</span>
      <span class="del-count">-{String(dels)}</span>
      <span>{plural(changes.length, "changed file")}</span>
    </p>,
    ...files.map(f => f.element),
  ];
}

interface FileSection {
  element: HTMLElement;
  adds: number;
  dels: number;
}

async function fileSection(site: Site, revision: string, change: FileChange): Promise<FileSection> {
  const { repo } = site;
  const generated = looksGenerated(change.path);
  const actions = (<span class="file-actions" />) as HTMLElement;
  if (change.status !== "modified") {
    actions.append(<span class={`status ${change.status}`}>{change.status}</span>);
  }
  if (change.newOid) {
    const view = await href(site, { kind: "blob", oid: revision, path: change.path.split("/") });
    actions.append(<a class="status" href={view}>view</a>);
  }
  if (generated) actions.append(<span class="generated-note">generated</span>);
  const header = (
    <summary>
      <span class="file-summary-content">
        <span class="path">{change.path}</span>
        {actions}
      </span>
    </summary>
  ) as HTMLElement;
  const section = (<details class="file-diff">{header}</details>) as HTMLDetailsElement;
  section.open = !generated;

  const [oldData, newData] = await Promise.all([
    change.oldOid ? repo.blob(change.oldOid) : Promise.resolve(new Uint8Array()),
    change.newOid ? repo.blob(change.newOid) : Promise.resolve(new Uint8Array()),
  ]);
  if (looksBinary(oldData) || looksBinary(newData)) {
    section.append(<p class="meta binary-note">binary file</p>);
    return { element: section, adds: 0, dels: 0 };
  }

  const oldText = utf8.decode(oldData);
  const newText = utf8.decode(newData);
  const hunks = diffLines(oldText, newText);
  const cells: Array<{ cell: HTMLTableCellElement; old: boolean; line: number }> = [];
  let adds = 0;
  let dels = 0;
  const table = (<table class="diff" />) as HTMLTableElement;
  for (const hunk of hunks) {
    table.append(
      <tr class="hunk">
        <td class="ln" />
        <td class="ln" />
        <td>{`@@ -${hunk.aStart},${hunk.aLines} +${hunk.bStart},${hunk.bLines} @@`}</td>
      </tr>,
    );
    let aLine = hunk.aStart;
    let bLine = hunk.bStart;
    for (const line of hunk.lines) {
      const kind = line.sign === "+" ? "add" : line.sign === "-" ? "del" : "ctx";
      const old = line.sign === "-";
      const sourceLine = (old ? aLine : bLine) - 1;
      if (line.sign === "+") adds++;
      if (line.sign === "-") dels++;
      const cell = (<td class="text">{line.text}</td>) as HTMLTableCellElement;
      cells.push({ cell, old, line: sourceLine });
      table.append(
        <tr class={kind}>
          <td class="ln">{line.sign === "+" ? "" : String(aLine++)}</td>
          <td class="ln">{line.sign === "-" ? "" : String(bLine++)}</td>
          {/* the +/- marker is CSS ::before so copied text stays clean */}
          {cell}
        </tr>,
      );
    }
  }
  actions.prepend(
    <span class="add-count">+{String(adds)}</span>,
    <span class="del-count">-{String(dels)}</span>,
  );
  section.append(table);
  void Promise.all([
    change.oldOid ? highlightedLines(change.path, oldText) : Promise.resolve(null),
    change.newOid ? highlightedLines(change.path, newText) : Promise.resolve(null),
  ]).then(([oldLines, newLines]) => {
    for (const target of cells) {
      const line = (target.old ? oldLines : newLines)?.[target.line];
      if (line) target.cell.replaceChildren(...line.map(node => node.cloneNode(true)));
    }
  }).catch(err => console.warn("arborium:", err));
  return { element: section, adds, dels };
}