// mail-router.ts: hand each email that arrives in ~/Maildir/new to its val.
// Mail to <val>@<vm>.exe.xyz (or <val>+anything@) goes to ~/vals/<val>, if
// its .env names a VAL_EMAIL file; run.ts runs it in a process of its own,
// with that val's .env. Handled mail moves to ~/Maildir/cur, mail whose
// handler failed to ~/Maildir/failed, mail for no val to cur (and the log).
const HOME = Deno.env.get("HOME")!;
const MAIL = `${HOME}/Maildir`;
const KIT = new URL(".", import.meta.url).pathname;
await Deno.mkdir(`${MAIL}/new`, { recursive: true });
await Deno.mkdir(`${MAIL}/cur`, { recursive: true });
await Deno.mkdir(`${MAIL}/failed`, { recursive: true });

async function deliver(name: string) {
  const path = `${MAIL}/new/${name}`;
  let head: string;
  try {
    head = (await Deno.readTextFile(path)).slice(0, 64 * 1024);
  } catch {
    return; // already moved
  }
  const to = head.match(/^Delivered-To:\s*(\S+)/im)?.[1] ?? "";
  if (!to && Date.now() - ((await Deno.stat(path)).mtime?.getTime() ?? 0) < 10_000) {
    setTimeout(drain, 2000); // still being written; look again shortly
    return;
  }
  const val = to.split("@")[0].split("+")[0].toLowerCase();
  let env = "";
  if (/^[a-z0-9_-]+$/.test(val)) {
    try {
      env = await Deno.readTextFile(`${HOME}/vals/${val}/.env`);
    } catch { /* no such val */ }
  }
  let dest = `${MAIL}/cur/${name}:2,S`;
  if (!/^VAL_EMAIL=/m.test(env)) {
    console.log(`${name}: no val takes mail for ${to}`);
  } else {
    const { code } = await new Deno.Command(Deno.execPath(), {
      args: ["run", "--allow-all", "--config=deno.json", "--env-file=.env", `${KIT}run.ts`, "email", path],
      cwd: `${HOME}/vals/${val}`,
    }).spawn().status;
    console.log(`${name}: ${to} -> ${val}: exit ${code}`);
    if (code !== 0) dest = `${MAIL}/failed/${name}`;
  }
  await Deno.rename(path, dest);
}

let running = false, again = false;
async function drain() {
  if (running) return void (again = true);
  running = true;
  do {
    again = false;
    for await (const e of Deno.readDir(`${MAIL}/new`)) if (e.isFile) await deliver(e.name);
  } while (again);
  running = false;
}
await drain();
for await (const _ of Deno.watchFs(`${MAIL}/new`)) drain();