// Generates CHANGELOG.md from frontend/src/content/release-notes/en.json — the same entries the app
// shows under Release Notes, so a self-hoster deciding whether to upgrade reads the same text an
// in-app user does, without having to install the app first (DX-14).
//
// Why derive rather than hand-write: two lists of "what changed in 0.80.0" WILL drift, and the
// in-app one is the one that gets written during a release. This makes the file a build product of it.
//
//   node scripts/gen-changelog.mjs           # write CHANGELOG.md
//   node scripts/gen-changelog.mjs --check   # exit 1 if CHANGELOG.md is stale (used by `siftlode release`)

import { readFile, writeFile } from "node:fs/promises";
import { fileURLToPath } from "node:url";
import path from "node:path";

const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
const SOURCE = path.join(root, "frontend", "src", "content", "release-notes", "en.json");
const TARGET = path.join(root, "CHANGELOG.md");

async function loadEntries() {
  const entries = JSON.parse(await readFile(SOURCE, "utf8"));
  if (!Array.isArray(entries) || entries.length === 0) {
    throw new Error(`${SOURCE} is not a non-empty array of release notes.`);
  }
  return entries;
}

function section(title, items) {
  if (!items || items.length === 0) return "";
  return `### ${title}\n\n${items.map((line) => `- ${line}`).join("\n")}\n\n`;
}

function render(entries) {
  const head = [
    "# Changelog",
    "",
    "Every released version of Siftlode, newest first.",
    "",
    "**Generated from `frontend/src/content/release-notes/en.json` by `scripts/gen-changelog.mjs` — do not edit by hand;**",
    "edit the release notes and re-run the generator.",
    "",
    "Upgrading, pinning a version and rolling back: [docs/self-hosting.md](docs/self-hosting.md#upgrading).",
    "",
    "",
  ].join("\n");

  const body = entries
    .map((e) => {
      const sha = e.sha ? ` (\`${e.sha}\`)` : "";
      let out = `## ${e.version} — ${e.date}${sha}\n\n`;
      out += section("New", e.new);
      out += section("Fixed", e.fixed);
      // A release that carried only internal work (none has since the owner's E28 rule).
      if (e.new.length === 0 && e.fixed.length === 0) out += "Internal changes only.\n\n";
      return out;
    })
    .join("");

  return `${head}${body}`.replace(/\n{3,}$/, "\n");
}

const entries = await loadEntries();
const rendered = render(entries);

if (process.argv.includes("--check")) {
  const current = await readFile(TARGET, "utf8").catch(() => null);
  if (current !== rendered) {
    console.error(
      `CHANGELOG.md is out of date with the release notes (newest entry: ${entries[0].version}).\n` +
        "Run: node scripts/gen-changelog.mjs   — then commit the result.",
    );
    process.exit(1);
  }
  console.log(
    `CHANGELOG.md is current (${entries.length} releases, newest ${entries[0].version}).`,
  );
} else {
  await writeFile(TARGET, rendered, "utf8");
  console.log(`Wrote CHANGELOG.md — ${entries.length} releases, newest ${entries[0].version}.`);
}