/**
 * Client-side BCH wallet UI.
 *
 * Uses @bitauth/libauth ESM build from a CDN. Wallets are generated with
 * BIP-39 (12 words) → BIP-32 (m/44'/145'/0'/0/0) → secp256k1 keypair.
 * Signatures follow "Bitcoin Signed Message" format so any BCH tool can verify.
 *
 * Storage: encrypted mnemonic in localStorage under 'hephaestus.wallet.v1'.
 * Encryption: AES-GCM with PBKDF2(SHA-256, 200k) from a user passphrase.
 * Passphrase never leaves the browser.
 */

import {
  deriveHdPath,
  deriveHdPrivateNodeFromSeed,
  deriveSeedFromBip39Mnemonic,
  encodeCashAddress,
  generateBip39Mnemonic,
  hash160,
  hash256,
  secp256k1,
  utf8ToBin,
  binToBase64,
  binToHex,
  CashAddressType,
} from "https://esm.sh/@bitauth/libauth@3.1.0-next.4";

const app = document.getElementById("app");
const state = app.dataset.state ?? "";
const redirectUri = app.dataset.redirectUri;

const STORAGE_KEY = "hephaestus.wallet.v1";

/* ---------- BCH wallet primitives ---------- */

const DERIVATION_PATH = "m/44'/145'/0'/0/0";

function encodeVarInt(n) {
  if (n < 0xfd) return new Uint8Array([n]);
  if (n <= 0xffff) return new Uint8Array([0xfd, n & 0xff, (n >> 8) & 0xff]);
  return new Uint8Array([
    0xfe, n & 0xff, (n >> 8) & 0xff, (n >> 16) & 0xff, (n >>> 24) & 0xff,
  ]);
}

function magicHash(message) {
  const magic = utf8ToBin("Bitcoin Signed Message:\n");
  const msg = utf8ToBin(message);
  const parts = [encodeVarInt(magic.length), magic, encodeVarInt(msg.length), msg];
  const total = parts.reduce((n, p) => n + p.length, 0);
  const buf = new Uint8Array(total);
  let off = 0;
  for (const p of parts) { buf.set(p, off); off += p.length; }
  return hash256(buf);
}

async function keypairFromMnemonic(mnemonic) {
  const seed = deriveSeedFromBip39Mnemonic(mnemonic);
  if (typeof seed === "string") throw new Error(seed);
  const root = deriveHdPrivateNodeFromSeed(seed);
  const child = deriveHdPath(root, DERIVATION_PATH);
  if (typeof child === "string") throw new Error(child);
  const privateKey = child.privateKey;
  const publicKey = secp256k1.derivePublicKeyCompressed(privateKey);
  if (typeof publicKey === "string") throw new Error(publicKey);
  const pkh = hash160(publicKey);
  const enc = encodeCashAddress({
    prefix: "bitcoincash",
    type: CashAddressType.p2pkh,
    payload: pkh,
  });
  const cashaddr = typeof enc === "string" ? enc : enc.address;
  return { privateKey, publicKey, cashaddr };
}

function signMessage(privateKey, message) {
  const digest = magicHash(message);
  const compact = secp256k1.signMessageHashRecoverableCompact(privateKey, digest);
  if (typeof compact === "string") throw new Error(compact);
  // Header byte: 27 + recid + 4 (compressed pubkey flag). libauth returns
  // {signature, recoveryId}; adapt to expected shape.
  const recid = compact.recoveryId;
  const sig65 = new Uint8Array(65);
  sig65[0] = 27 + recid + 4;
  sig65.set(compact.signature, 1);
  return binToBase64(sig65);
}

/* ---------- Encrypted storage ---------- */

async function deriveKey(passphrase, salt) {
  const enc = new TextEncoder();
  const material = await crypto.subtle.importKey(
    "raw", enc.encode(passphrase), "PBKDF2", false, ["deriveKey"],
  );
  return crypto.subtle.deriveKey(
    { name: "PBKDF2", salt, iterations: 200_000, hash: "SHA-256" },
    material,
    { name: "AES-GCM", length: 256 },
    false, ["encrypt", "decrypt"],
  );
}

async function encryptMnemonic(mnemonic, passphrase) {
  const salt = crypto.getRandomValues(new Uint8Array(16));
  const iv = crypto.getRandomValues(new Uint8Array(12));
  const key = await deriveKey(passphrase, salt);
  const ct = new Uint8Array(await crypto.subtle.encrypt(
    { name: "AES-GCM", iv }, key, new TextEncoder().encode(mnemonic),
  ));
  return {
    v: 1,
    salt: binToHex(salt),
    iv: binToHex(iv),
    ct: binToHex(ct),
  };
}

async function decryptMnemonic(blob, passphrase) {
  const salt = hexToBin(blob.salt);
  const iv = hexToBin(blob.iv);
  const ct = hexToBin(blob.ct);
  const key = await deriveKey(passphrase, salt);
  const pt = new Uint8Array(await crypto.subtle.decrypt(
    { name: "AES-GCM", iv }, key, ct,
  ));
  return new TextDecoder().decode(pt);
}

function hexToBin(h) {
  const out = new Uint8Array(h.length / 2);
  for (let i = 0; i < out.length; i++) out[i] = parseInt(h.substr(i * 2, 2), 16);
  return out;
}

function hasStoredWallet() { return !!localStorage.getItem(STORAGE_KEY); }
function loadStoredWallet() { return JSON.parse(localStorage.getItem(STORAGE_KEY)); }
function saveStoredWallet(blob) {
  localStorage.setItem(STORAGE_KEY, JSON.stringify(blob));
}

/* ---------- UI ---------- */

function render() {
  if (hasStoredWallet()) return renderUnlock();
  return renderTabs();
}

function el(html) {
  const t = document.createElement("template");
  t.innerHTML = html.trim();
  return t.content.firstElementChild;
}

function renderTabs() {
  app.innerHTML = "";
  app.appendChild(el(`
    <div>
      <h1>Sign in to Hephaestus</h1>
      <p class="lede">No email. No password reset. Your wallet is your identity.</p>
      <div class="tab-row" role="tablist">
        <button class="tab" aria-selected="true"  data-tab="generate">Generate new</button>
        <button class="tab" aria-selected="false" data-tab="import">Import existing</button>
      </div>
      <div id="panel"></div>
    </div>
  `));
  app.querySelectorAll(".tab").forEach((b) => {
    b.addEventListener("click", () => {
      app.querySelectorAll(".tab").forEach((x) =>
        x.setAttribute("aria-selected", x === b ? "true" : "false"));
      renderPanel(b.dataset.tab);
    });
  });
  renderPanel("generate");
}

function renderPanel(kind) {
  const panel = document.getElementById("panel");
  panel.innerHTML = "";
  if (kind === "generate") {
    const mnemonic = generateBip39Mnemonic();
    panel.appendChild(el(`
      <div>
        <label>Your new recovery phrase (write it down — this is the only way to recover your account)</label>
        <div class="mnemonic-box">${mnemonic}</div>
        <label>Set a passphrase to encrypt this wallet in your browser</label>
        <input type="password" id="pw" autocomplete="new-password" placeholder="min 8 chars">
        <p class="small">The passphrase never leaves your device. If you lose both the phrase and the passphrase your account is gone — we cannot help.</p>
        <button class="primary" id="go">Create wallet & sign in</button>
        <p class="warn hidden" id="err"></p>
      </div>
    `));
    panel.querySelector("#go").addEventListener("click", async () => {
      const pw = panel.querySelector("#pw").value;
      if (pw.length < 8) return showErr(panel, "passphrase must be at least 8 chars");
      await onboardAndLogin(mnemonic, pw, panel);
    });
  } else {
    panel.appendChild(el(`
      <div>
        <label>Paste your BIP-39 recovery phrase (12 or 24 words)</label>
        <textarea id="mn" spellcheck="false" autocomplete="off"></textarea>
        <label>Set a passphrase to encrypt this wallet in your browser</label>
        <input type="password" id="pw" autocomplete="new-password" placeholder="min 8 chars">
        <button class="primary" id="go">Import & sign in</button>
        <p class="warn hidden" id="err"></p>
      </div>
    `));
    panel.querySelector("#go").addEventListener("click", async () => {
      const mn = panel.querySelector("#mn").value.trim().replace(/\s+/g, " ");
      const pw = panel.querySelector("#pw").value;
      if (pw.length < 8) return showErr(panel, "passphrase must be at least 8 chars");
      try { await keypairFromMnemonic(mn); }
      catch { return showErr(panel, "invalid recovery phrase"); }
      await onboardAndLogin(mn, pw, panel);
    });
  }
}

function renderUnlock() {
  app.innerHTML = "";
  app.appendChild(el(`
    <div>
      <h1>Unlock your wallet</h1>
      <p class="lede">Enter the passphrase you set when you created this wallet in this browser.</p>
      <label>Passphrase</label>
      <input type="password" id="pw" autocomplete="current-password">
      <button class="primary" id="go">Unlock & sign in</button>
      <p class="warn hidden" id="err"></p>
      <p class="small" style="margin-top:16px">
        Wrong browser? <a href="#" id="reset">Forget this wallet and start over</a>.
      </p>
    </div>
  `));
  app.querySelector("#reset").addEventListener("click", (e) => {
    e.preventDefault();
    localStorage.removeItem(STORAGE_KEY);
    renderTabs();
  });
  app.querySelector("#go").addEventListener("click", async () => {
    const pw = app.querySelector("#pw").value;
    const blob = loadStoredWallet();
    let mnemonic;
    try { mnemonic = await decryptMnemonic(blob, pw); }
    catch { return showErr(app, "wrong passphrase"); }
    await signInWithMnemonic(mnemonic, app);
  });
}

async function onboardAndLogin(mnemonic, passphrase, root) {
  const btn = root.querySelector("button.primary");
  btn.disabled = true;
  try {
    const blob = await encryptMnemonic(mnemonic, passphrase);
    saveStoredWallet(blob);
    await signInWithMnemonic(mnemonic, root);
  } catch (e) {
    btn.disabled = false;
    showErr(root, e.message ?? String(e));
  }
}

async function signInWithMnemonic(mnemonic, root) {
  const btn = root.querySelector("button.primary");
  if (btn) btn.disabled = true;
  try {
    const { privateKey, cashaddr } = await keypairFromMnemonic(mnemonic);
    const chalRes = await fetch("challenge", {
      method: "POST",
      headers: { "content-type": "application/json" },
      body: JSON.stringify({ cashaddr, state, redirect_uri: redirectUri }),
    });
    if (!chalRes.ok) throw new Error("challenge request failed");
    const { nonce, message } = await chalRes.json();
    const signature = signMessage(privateKey, message);
    const verRes = await fetch("verify", {
      method: "POST",
      headers: { "content-type": "application/json" },
      body: JSON.stringify({ nonce, signature }),
    });
    if (!verRes.ok) throw new Error("signature rejected");
    const { redirect } = await verRes.json();
    window.location.href = redirect;
  } catch (e) {
    if (btn) btn.disabled = false;
    showErr(root, e.message ?? String(e));
  }
}

function showErr(root, msg) {
  const box = root.querySelector("#err");
  if (!box) return;
  box.textContent = msg;
  box.classList.remove("hidden");
}

render();