// Quick-unlock PIN for the password vault.
//
// The PIN is an alias for the master password, never a replacement: it
// encrypts the master password (PBKDF2-SHA256 -> AES-256-GCM), and the
// result is sealed again with Electron safeStorage (DPAPI on Windows,
// Keychain on macOS, libsecret on Linux), so a copied vault-pin.json is
// useless on another machine or OS account.
//
// The OS seal does not stop anything that runs as this OS user, nor a disk
// image plus the Windows password; for those a 6-digit PIN falls to an
// offline search in minutes. Where a TPM is available the PIN is therefore
// also the authorization value of a TPM key (lib/tpm-pin.cjs) whose secret is
// mixed into the AES key, and the chip's own lockout limits guesses to about
// 144 a day however the file was obtained. Without a TPM the PIN is
// software-only, and status().hardware says so.
//
// Nothing is stored without a real OS keystore: set() refuses, and an
// unsealed record from an older build is deleted. On Linux the basic_text
// backend (a constant key compiled into Chromium) counts as no keystore.
//
// Three wrong PINs in a row switch to "master password required". That flag
// lives in the same file, so restarting Theseus does not reset it; only a
// successful master-password unlock does. Anyone who can write the file can
// reset it, which is why the TPM lockout, not this counter, is the limit that
// matters against an attacker on the machine.
//
// File: { v: 1, sealed: true, data: <b64 safeStorage blob>, fails, requireMaster }
//   blob = { salt, iv, ct, iters, hw? } (all b64 except iters)
//   hw   = { kind: "tpm", key: <TPM key name>, wrapped: <b64> }

"use strict";

const fs = require("node:fs");
const crypto = require("node:crypto");
const tpmPin = require("./tpm-pin.cjs");

const MAX_FAILS = 3;
const ITERATIONS = 600_000;
const PIN_RE = /^\d{6}$/;

function createVaultPin({ file, safeStorage, tpm = tpmPin, log = () => {} }) {
  const sealAvailable = () => {
    try {
      if (!safeStorage || !safeStorage.isEncryptionAvailable()) return false;
      if (process.platform === "linux") {
        const backend = typeof safeStorage.getSelectedStorageBackend === "function" ? safeStorage.getSelectedStorageBackend() : "unknown";
        if (backend === "basic_text" || backend === "unknown") return false;
      }
      return true;
    } catch { return false; }
  };
  let tpmUnavailable = false;

  function read() {
    let rec;
    try { rec = JSON.parse(fs.readFileSync(file, "utf8")); } catch { return null; }
    if (rec && !rec.sealed) {
      // Written by a build that stored the blob in the clear when the OS
      // keystore was missing. Never use it; drop it.
      try { fs.unlinkSync(file); } catch {}
      return null;
    }
    return rec;
  }
  function write(rec) {
    const tmp = file + ".tmp";
    fs.writeFileSync(tmp, JSON.stringify(rec), { mode: 0o600 });
    fs.renameSync(tmp, file);
  }

  function blobOf(rec) {
    if (!rec) return null;
    if (!sealAvailable()) throw new Error("this PIN was sealed by the system keystore, which is not available now");
    return JSON.parse(safeStorage.decryptString(Buffer.from(rec.data, "base64")));
  }
  function blobOrNull(rec) { try { return blobOf(rec); } catch { return null; } }

  const keyFor = (pin, salt, iters) => new Promise((resolve, reject) =>
    crypto.pbkdf2(String(pin), salt, iters, 32, "sha256", (e, k) => (e ? reject(e) : resolve(k))));

  return {
    MAX_FAILS,

    status() {
      const rec = read();
      const b = rec ? blobOrNull(rec) : null;
      return {
        pinSet: !!rec,
        fails: rec ? rec.fails || 0 : 0,
        requireMaster: !!(rec && rec.requireMaster),
        sealed: !!(rec && rec.sealed),
        hardware: b ? (b.hw ? "tpm" : "none") : null,
        storable: sealAvailable(),
      };
    },

    // Caller must have verified masterPassword against the vault first.
    async set(pin, masterPassword) {
      if (!PIN_RE.test(String(pin || ""))) throw new Error("the PIN must be 6 digits");
      if (!masterPassword) throw new Error("master password required");
      if (!sealAvailable()) throw new Error("this system has no protected keystore, so a PIN cannot be stored safely");
      const old = blobOrNull(read());
      let hw = null;
      if (tpm.supported() && !tpmUnavailable) {
        try { hw = await tpm.create(pin, "Theseus-PIN"); }
        catch (e) { tpmUnavailable = true; log("vault PIN: no TPM key:", e?.message || e); }
      }
      const salt = crypto.randomBytes(16);
      const iv = crypto.randomBytes(12);
      let key = await keyFor(pin, salt, ITERATIONS);
      if (hw) key = tpm.mixKey(hw.secret, key);
      const cipher = crypto.createCipheriv("aes-256-gcm", key, iv);
      const ct = Buffer.concat([cipher.update(String(masterPassword), "utf8"), cipher.final(), cipher.getAuthTag()]);
      const blob = { salt: salt.toString("base64"), iv: iv.toString("base64"), ct: ct.toString("base64"), iters: ITERATIONS };
      if (hw) blob.hw = { kind: "tpm", key: hw.keyName, wrapped: hw.wrapped };
      write({
        v: 1,
        sealed: true,
        data: safeStorage.encryptString(JSON.stringify(blob)).toString("base64"),
        fails: 0,
        requireMaster: false,
      });
      if (old?.hw?.key && old.hw.key !== hw?.keyName) tpm.remove(old.hw.key).catch(() => {});
      return { hardware: hw ? "tpm" : "none" };
    },

    clear() {
      const old = blobOrNull(read());
      if (old?.hw?.key) tpm.remove(old.hw.key).catch(() => {});
      try { fs.unlinkSync(file); } catch {}
    },

    // Returns the master password, or throws:
    //   { code: "no-pin" | "master-required" | "wrong-pin" | "tpm-locked", remaining }
    async open(pin) {
      const rec = read();
      if (!rec) throw Object.assign(new Error("no PIN is set"), { code: "no-pin" });
      if (rec.requireMaster) throw Object.assign(new Error("enter the master password"), { code: "master-required", remaining: 0 });
      // Count the guess before trying it, so a crash mid-check still costs one.
      const before = rec.fails || 0;
      rec.fails = before + 1;
      write(rec);
      let masterPassword = null;
      if (PIN_RE.test(String(pin || ""))) {
        try {
          const b = blobOf(rec);
          let secret = null;
          if (b.hw) {
            const r = await tpm.open(b.hw.key, b.hw.wrapped, pin);
            if (r.ok) secret = r.secret;
            else if (r.code === "locked" || r.code === "error") {
              rec.fails = before; write(rec);   // not a verdict on the PIN
              throw Object.assign(new Error(r.code === "locked"
                ? "The security chip is refusing PINs for a few minutes after too many wrong ones. Enter the master password, or wait."
                : "The security chip did not answer. Enter the master password."), { code: "tpm-locked", remaining: MAX_FAILS - before });
            } else if (r.code === "missing") {
              this.clear();
              throw Object.assign(new Error("This PIN was tied to a security chip that no longer has its key. Enter the master password, then set the PIN again."), { code: "master-required", remaining: 0 });
            }
          }
          if (!b.hw || secret) {
            const ct = Buffer.from(b.ct, "base64");
            let key = await keyFor(pin, Buffer.from(b.salt, "base64"), b.iters);
            if (b.hw) key = tpm.mixKey(secret, key);
            const decipher = crypto.createDecipheriv("aes-256-gcm", key, Buffer.from(b.iv, "base64"));
            decipher.setAuthTag(ct.subarray(ct.length - 16));
            masterPassword = Buffer.concat([decipher.update(ct.subarray(0, ct.length - 16)), decipher.final()]).toString("utf8");
          }
        } catch (e) {
          if (e && (e.code === "tpm-locked" || e.code === "master-required")) throw e;
          masterPassword = null;
        }
      }
      if (masterPassword == null) {
        if (rec.fails >= MAX_FAILS) rec.requireMaster = true;
        write(rec);
        const remaining = Math.max(0, MAX_FAILS - rec.fails);
        throw Object.assign(new Error(remaining ? "wrong PIN" : "too many wrong PINs, enter the master password"),
          { code: remaining ? "wrong-pin" : "master-required", remaining });
      }
      rec.fails = 0; write(rec);
      return masterPassword;
    },

    // A successful master-password unlock clears the strikes.
    resetFails() {
      const rec = read();
      if (rec && (rec.fails || rec.requireMaster)) { rec.fails = 0; rec.requireMaster = false; write(rec); }
    },
  };
}

module.exports = { createVaultPin, MAX_FAILS };