// Generates CHANGELOG.md from frontend/src/lib/releaseNotes.ts — 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. RELEASE_NOTES is a plain data literal by design, so it is imported by stripping the single TS
// type annotation off the declaration — no transpiler, no dependency.
//
//   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", "lib", "releaseNotes.ts");
const TARGET = path.join(root, "CHANGELOG.md");

async function loadEntries() {
  const src = await readFile(SOURCE, "utf8");
  const decl = "export const RELEASE_NOTES";
  const at = src.indexOf(decl);
  if (at === -1) {
    throw new Error(`${SOURCE} no longer declares ${decl} — the generator's assumption broke, fix it rather than hand-writing the changelog.`);
  }
  const body = src.slice(at).replace(/^export const RELEASE_NOTES\s*:[^=]*=/, "export const RELEASE_NOTES =");
  const mod = await import(`data:text/javascript,${encodeURIComponent(body)}`);
  if (!Array.isArray(mod.RELEASE_NOTES) || mod.RELEASE_NOTES.length === 0) {
    throw new Error("RELEASE_NOTES imported as something other than a non-empty array.");
  }
  return mod.RELEASE_NOTES;
}

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/lib/releaseNotes.ts` 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`;
      if (e.summary) out += `${e.summary}\n\n`;
      out += section("Features", e.features);
      out += section("Fixes", e.fixes);
      out += section("Internal", e.chores);
      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 releaseNotes.ts (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}.`);
}