// UI wiring for the smol mail client: identity setup, folders, reading,
// composing, fetching with verify-before-ack, and the §4/§7 trust surfaces.

import { hex, timingSafeEqual, unhex, utf8Bytes } from "./crypto.js";
import {
  DEFAULT_PORT, ID_LEN, MAX_CHAIN, TOKEN_LEN, SmolError, acceptMac, authenticate, b32decode,
  b32encode, buildFrontmatter, deleteOp, fetchOp, fingerprint, identitySeed, identityFromSeed,
  makeCert, messageId, newMaster, openSession, parseAddress, parseFrontmatter, registerOp,
  resolveOp, seal, sendOp, tokenFor, unseal, walkChain,
} from "./proto.js";
import * as store from "./store.js";
import { connectStream } from "./transport.js";
import { PRESET_SERVER } from "./config.js";

const $ = (id) => document.getElementById(id);

// Everything is built as nodes rather than markup, so no message content can
// ever reach innerHTML. Null children are dropped, which keeps conditional
// pieces inline at the call site.
function el(tag, props = {}, ...children) {
  const node = Object.assign(document.createElement(tag), props);
  node.append(...children.filter(child => child != null));
  return node;
}

// SVG lives in its own namespace, so el()'s createElement cannot build these;
// each is a reference into the sprite in index.html.
function icon(name) {
  const svg = document.createElementNS("http://www.w3.org/2000/svg", "svg");
  svg.setAttribute("class", "icon");
  svg.setAttribute("aria-hidden", "true");
  const use = document.createElementNS("http://www.w3.org/2000/svg", "use");
  use.setAttribute("href", `#i-${name}`);
  svg.append(use);
  return svg;
}

const placeholder = (text, warn = false) =>
  el("p", { className: warn ? "placeholder warn" : "placeholder", textContent: text });

// A native <dialog> shown with showModal() renders in the browser's top
// layer, above the rest of the page — a toast anchored to <body> sits
// visually behind an open dialog's backdrop no matter its z-index. Keeping
// the toast inside whichever dialog is open puts it in that same top-layer
// subtree, so a status raised while settings or compose is open (e.g. after
// "register") actually gets seen instead of landing, barely visible, behind it.
function reparentStatus() {
  const toast = $("status");
  const target = document.querySelector("dialog[open]") ?? document.body;
  if (toast.parentElement !== target) target.append(toast);
}
for (const dialog of document.querySelectorAll("dialog")) dialog.addEventListener("close", reparentStatus);

// The status line is a toast: click to dismiss, empty means hidden. Plain
// notices fade; warnings stay until dismissed, since those carry the §4/§8
// trust messages the user must actually read.
let toastTimer = null;
function status(text, warn = false) {
  reparentStatus();
  const toast = $("status");
  toast.textContent = text;
  toast.hidden = !text;
  toast.className = warn ? "toast warn" : "toast";
  clearTimeout(toastTimer);
  if (text && !warn) toastTimer = setTimeout(() => status(""), 6000);
}
$("status").onclick = () => status("");

const fmtTime = (seconds) =>
  new Date(seconds * 1000).toLocaleString(undefined, { dateStyle: "medium", timeStyle: "short" });

// Gmail-style row stamp: time for today, date within this year, full date older.
const fmtRowTime = (seconds) => {
  const date = new Date(seconds * 1000), today = new Date();
  if (date.toDateString() === today.toDateString())
    return date.toLocaleTimeString(undefined, { hour: "numeric", minute: "2-digit" });
  if (date.getFullYear() === today.getFullYear())
    return date.toLocaleDateString(undefined, { month: "short", day: "numeric" });
  return date.toLocaleDateString(undefined, { year: "numeric", month: "short", day: "numeric" });
};

// A copy button beats asking the user to select 64 hex characters by hand.
// Flashes its own label rather than a toast — settings' rows need feedback
// that doesn't float away from the row that caused it.
function copyButton(text, what) {
  return el("button", { type: "button", className: "copy", title: `copy the ${what}`, textContent: "copy",
    onclick: async (event) => {
      const button = event.currentTarget;
      const resting = button.textContent;
      try {
        await navigator.clipboard.writeText(text);
        button.textContent = "copied";
      } catch {
        button.textContent = "failed";
      }
      setTimeout(() => { button.textContent = resting; }, 1500);
    } });
}

// The stored account as an address object, default port included when custom.
function accountAddress() {
  const account = store.account();
  if (!account) return null;
  const suffix = account.port === DEFAULT_PORT ? "" : `:${account.port}`;
  return parseAddress(`${account.user}@${account.host}${suffix}`);
}

// --- appearance ----------------------------------------------------------------

// Three states, because "follow the system" is a real preference and not the
// absence of one. The CSS does the rest: color-scheme decides which half of
// every light-dark() token applies, so nothing here touches a colour.
const THEMES = [
  { value: null, icon: "auto", label: "theme: following the system" },
  { value: "light", icon: "sun", label: "theme: light" },
  { value: "dark", icon: "moon", label: "theme: dark" },
];

function applyTheme() {
  const mode = THEMES.find(t => t.value === store.theme()) ?? THEMES[0];
  if (mode.value) document.documentElement.dataset.theme = mode.value;
  else delete document.documentElement.dataset.theme;
  const button = $("theme");
  button.querySelector("use").setAttribute("href", `#i-${mode.icon}`);
  button.title = mode.label;
  button.setAttribute("aria-label", mode.label);
}

$("theme").onclick = () => {
  const current = THEMES.findIndex(t => t.value === store.theme());
  store.setTheme(THEMES[(current + 1) % THEMES.length].value);
  applyTheme();
  status(THEMES.find(t => t.value === store.theme()).label);
};

// --- connection --------------------------------------------------------------

// §4: registration and fetching demand a pinned key; sending to a recipient
// whose key we already hold tolerates an unpinned server.
async function connect(addr, { requirePin }) {
  const pinned = store.serverPin(addr.host);
  if (requirePin && !pinned)
    throw new SmolError(`no pinned key for ${addr.host}. Obtain it from the operator through a ` +
      `trusted channel, then pin it under settings → server.`);
  const timeoutMs = store.timeoutSeconds() * 1000;
  const stream = await connectStream(addr.host, addr.port, timeoutMs);
  const opened = await openSession(stream, addr.host, pinned, timeoutMs);
  if (!pinned)
    status(`${addr.host} is not pinned; its key is ${b32encode(opened.serverStatic)}.\n` +
      `Lookups from this session are UNVERIFIED.`, true);
  return opened;
}

// --- identity setup ------------------------------------------------------------

// Nothing in the top bar works before an identity exists, so it stays hidden
// rather than offering buttons that can only answer "no identity yet".
function showSetup() {
  $("setup").hidden = false;
  $("app").hidden = true;
  $("search").hidden = true;
  $("top-actions").hidden = true;
  $("account").textContent = "";
}

function showApp() {
  $("setup").hidden = true;
  $("app").hidden = false;
  $("search").hidden = false;
  $("top-actions").hidden = false;
  renderAccount();
  renderFolder();
}

// Generate-or-recover an identity, establish trust in a server, then bind a
// name to it — three concerns, three screens, no bleed-through between them.
const SETUP_SECTIONS = {
  intro: "setup-intro",
  "seed-shown": "setup-seed",
  "seed-restore": "setup-restore",
  "server-setup": "setup-server",
  "account-setup": "setup-account",
};

function showSetupStage(stage) {
  for (const [key, id] of Object.entries(SETUP_SECTIONS)) $(id).hidden = key !== stage;
  if (stage === "server-setup") renderServerScreen();
}

// Discards the identity screens 2 and 4 can still walk away from — nothing is
// bound to an account yet, so nothing is lost: the same seed typed again on
// screen 3 regenerates the identical identity.
function discardSetupIdentity() {
  store.discardIdentity();
  serverFetchedKey = null;
  $("server-host").value = "";
  showSetupStage("intro");
}

// A deployment that baked in a server key already knows its own host, so
// screen 4 starts from it rather than asking again.
function enterServerSetup() {
  if (!$("server-host").value && PRESET_SERVER) $("server-host").value = PRESET_SERVER.host;
  showSetupStage("server-setup");
}

$("create-identity").onclick = () => {
  const seed = newMaster();
  store.setIdentity(seed);
  $("setup-seed-value").textContent = hex(seed);
  showSetupStage("seed-shown");
};

$("show-restore").onclick = () => showSetupStage("seed-restore");

$("seed-saved").onclick = () => {
  store.setMasterSaved(true);
  enterServerSetup();
};
$("seed-back").onclick = () => discardSetupIdentity();

// A master secret in either of its two interchangeable encodings: 64 hex
// characters, or the base32 form used everywhere else a key is shown.
function parseSeedText(text) {
  text = text.trim();
  if (/^[0-9a-fA-F]{64}$/.test(text)) return unhex(text);
  try {
    const bytes = b32decode(text);
    if (bytes.length === 32) return bytes;
  } catch { /* fall through to the error below */ }
  throw new SmolError("not a valid secret — paste the 64 hex characters or the base32 form");
}

$("restore-form").onsubmit = (event) => {
  event.preventDefault();
  $("restore-error").textContent = "";
  let seed;
  try {
    seed = parseSeedText($("restore-master").value);
  } catch (err) {
    $("restore-error").textContent = err.message;
    return;
  }
  // §2: a master alone does not say which rotation index a server has bound;
  // account-setup's "existing address" mode discovers it once a server can be
  // asked. Either way the accepted-correspondent set is unknown, so it must
  // not overwrite the server's (syncOk: false).
  store.restoreMaster(seed, 0);
  enterServerSetup();
};

$("restore-back").onclick = () => {
  $("restore-master").value = "";
  $("restore-error").textContent = "";
  showSetupStage("intro");
};

// Holds a key fetched this screen visit but not yet pinned, tied to the host
// it came from — editing the host field makes renderServerScreen() stop
// showing it, since it only ever matches the host currently typed.
let serverFetchedKey = null;
// The host screen 4 ends on, carried into screen 5 to build the full address.
let setupHost = null;

function renderServerScreen() {
  const host = $("server-host").value.trim().toLowerCase();
  const pinned = host ? store.serverPin(host) : null;
  const fetched = host && serverFetchedKey?.host === host ? serverFetchedKey.key : null;
  const key = pinned ?? fetched;
  const area = $("server-key-area");
  area.hidden = !key;
  area.replaceChildren();
  if (key) {
    area.append(
      field("fingerprint", fingerprint(key)),
      field("key", b32encode(key)),
      el("p", { className: "hint", textContent: "If the server operator published a key or " +
        "fingerprint, make sure it matches before trusting it." }));
  }
  $("server-action").textContent = key ? "continue" : "fetch the server's key";
  $("server-error").textContent = "";
}

$("server-host").oninput = renderServerScreen;

function setServerBusy(busy) {
  for (const node of [$("server-host"), $("server-action"), $("server-back")]) node.disabled = busy;
}

$("server-form").onsubmit = async (event) => {
  event.preventDefault();
  $("server-error").textContent = "";
  let host;
  try {
    host = cleanHost($("server-host").value);
  } catch (err) {
    $("server-error").textContent = err.message;
    return;
  }
  const pinned = store.serverPin(host);
  const fetched = serverFetchedKey?.host === host ? serverFetchedKey.key : null;
  if (pinned || fetched) {
    if (!pinned) store.pinServer(host, fetched);
    serverFetchedKey = null;
    setupHost = host;
    showSetupStage("account-setup");
    return;
  }
  setServerBusy(true);
  try {
    // Bypassed connect(): its "UNVERIFIED" status toast is right everywhere
    // else a session proceeds unpinned, but here the whole point of the
    // fetch is that nothing is pinned yet — the toast would just sit over
    // the button that is about to pin it.
    const timeoutMs = store.timeoutSeconds() * 1000;
    const stream = await connectStream(host, DEFAULT_PORT, timeoutMs);
    const opened = await openSession(stream, host, null, timeoutMs);
    opened.session.stream.close();
    serverFetchedKey = { host, key: opened.serverStatic };
    renderServerScreen();
  } catch (err) {
    $("server-error").textContent = err.message;
  } finally {
    setServerBusy(false);
  }
};

$("server-back").onclick = () => discardSetupIdentity();

let accountMode = "new";

function setAccountMode(mode) {
  accountMode = mode;
  for (const button of document.querySelectorAll("#account-mode button"))
    button.classList.toggle("active", button.dataset.mode === mode);
  $("account-token-label").hidden = mode !== "new";
  $("account-action").textContent = mode === "new" ? "register" : "restore access";
  $("account-error").textContent = "";
}

for (const button of document.querySelectorAll("#account-mode button"))
  button.onclick = () => setAccountMode(button.dataset.mode);

function setAccountBusy(busy) {
  for (const node of [$("account-user"), $("account-token"), $("account-action"), $("account-back"),
      ...document.querySelectorAll("#account-mode button")])
    node.disabled = busy;
}

$("account-form").onsubmit = async (event) => {
  event.preventDefault();
  $("account-error").textContent = "";
  const me = store.identity();
  const button = $("account-action");
  const resting = button.textContent;
  let addr;
  try {
    addr = parseAddress(`${$("account-user").value.trim()}@${setupHost}`);
  } catch (err) {
    $("account-error").textContent = err.message;
    return;
  }
  setAccountBusy(true);
  button.textContent = accountMode === "new" ? "registering…" : "restoring…";
  try {
    if (accountMode === "new") {
      const opened = await connect(addr, { requirePin: true });
      try {
        await registerOp(opened.session, opened.serverStatic,
          { username: addr.user, identity: me, token: $("account-token").value.trim() });
      } finally {
        opened.session.stream.close();
      }
      store.setAccount(addr);
    } else {
      await recallAndDiscoverRotation(store.master(), addr.short);
    }
    showApp();
    status(`welcome, ${addr.short}`);
  } catch (err) {
    $("account-error").textContent = err.message;
  } finally {
    setAccountBusy(false);
    button.textContent = resting;
  }
};

$("account-back").onclick = () => showSetupStage("server-setup");

// --- header ---------------------------------------------------------------------

function renderAccount() {
  const me = store.identity();
  const account = store.account();
  $("account").textContent = me
    ? (account ? `${account.user}@${account.host}` : "not registered")
    : "";
  $("avatar").textContent = account ? account.user[0].toUpperCase() : "·";
}

// --- folders and list ---------------------------------------------------------

let folder = "inbox";
let selectedId = null;
let query = "";
// Bumped per render, so a superseded pass stops appending rows mid-flight.
let renderToken = 0;
// Rows opened per turn: a cold folder yields between batches rather than
// blocking the tab for an X25519 and an Ed25519 verification per message.
const BATCH = 20;

for (const button of $("folders").querySelectorAll("button"))
  button.onclick = () => {
    folder = button.dataset.folder;
    for (const b of $("folders").querySelectorAll("button")) {
      const active = b === button;
      b.classList.toggle("active", active);
      if (active) b.setAttribute("aria-current", "true");
      else b.removeAttribute("aria-current");
    }
    selectedId = null;
    resetView();
    renderFolder();
  };

// The reader empties when a folder changes, so a stale message cannot linger
// under a different list.
function resetView() {
  $("app").classList.remove("reading");
  $("view").replaceChildren(placeholder(folder === "contacts"
    ? "contacts and their keys are listed alongside"
    : "select a message"));
}

// Counted from ids and read markers alone, independent of the visible folder —
// leaving the inbox used to blank the badge.
async function updateUnreadBadge() {
  $("count-inbox").textContent = (await store.unreadCount()) || "";
  $("count-requests").textContent = (await store.requestsUnreadCount()) || "";
}

async function renderFolder() {
  const list = $("list");
  updateUnreadBadge();
  // The toolbar carries the current folder's action, not a fixed one.
  const contacts = folder === "contacts";
  $("mail-tools").hidden = contacts;
  $("import-form").hidden = !contacts;
  // The filter never reaches past the open folder, so the field says which one.
  $("search").placeholder = `search ${folder}`;
  $("search").setAttribute("aria-label", `search ${folder}`);
  if (contacts) return renderContacts(list);
  const token = ++renderToken;
  const rows = await store.listMessages(folder);  // newest first
  if (token !== renderToken) return;
  list.replaceChildren();
  if (!rows.length) {
    list.append(placeholder(folder === "inbox" ? "no mail — fetch"
      : folder === "requests" ? "no unsolicited mail" : "nothing sent"));
    return void updateListStatus();
  }
  for (let offset = 0; offset < rows.length; offset += BATCH) {
    if (offset) await new Promise(resolve => setTimeout(resolve));
    if (token !== renderToken) return;
    list.append(...rows.slice(offset, offset + BATCH).map(messageRow));
    applyQuery();
  }
}

// A real button, so every row is reachable and openable from the keyboard.
function messageRow(row) {
  const opened = describe(row);
  // Both mail tiers have a read state; sent copies were never "unread".
  const inbound = folder === "inbox" || folder === "requests";
  const unread = inbound && !store.isRead(row.id);
  const item = el("button", {
    type: "button",
    className: `item${row.id === selectedId ? " selected" : ""}${unread ? " unread" : ""}`,
    onclick: () => openMessage(row.id),
  });
  if (row.id === selectedId) item.setAttribute("aria-current", "true");
  const who = el("div", { className: "who",
    textContent: folder === "sent" ? row.recipient : (opened.fromShort ?? "?") });
  if (inbound && !opened.error && !opened.knownSender)
    who.append(el("span", { className: "dot", title: "sender key not bound to an address" }));
  item.append(who,
    el("div", { className: "mid" },
      el("span", { className: "subject", textContent: opened.error
        ? `<unreadable: ${opened.error}>` : (opened.subject || "(no subject)") }),
      el("span", { className: "snippet", textContent: opened.error ? "" : ` — ${opened.snippet}` })),
    el("div", { className: "when",
      textContent: fmtRowTime(folder === "sent" ? row.sentAt : (opened.time ?? row.receivedAt)) }));
  // Sender or recipient, their key, the subject and the whole body — not the
  // snippet, and not the timestamp.
  item.dataset.search = (opened.error
    ? `${row.recipient ?? ""} ${opened.error}`
    : [row.recipient ?? "", opened.from, b32encode(opened.sender), opened.subject, opened.body].join(" ")
  ).toLowerCase();
  return item;
}

// Filters the current folder client-side; nothing leaves the page. Each row
// carries its own haystack, built from the fields worth matching rather than
// from whatever the row happens to render. Re-applied after every render, so a
// redraw cannot silently drop it.
function applyQuery() {
  for (const item of $("list").querySelectorAll(".item"))
    item.hidden = Boolean(query) && !(item.dataset.search ?? "").includes(query);
  updateListStatus();
}

// The toolbar's right side, which also makes a narrowed search visible.
function updateListStatus() {
  const items = [...$("list").querySelectorAll(".item")];
  const shown = items.filter(item => !item.hidden).length;
  $("list-status").textContent = !items.length ? ""
    : shown === items.length ? `${items.length} message${items.length === 1 ? "" : "s"}`
    : `${shown} of ${items.length}`;
}

$("search").oninput = () => {
  query = $("search").value.trim().toLowerCase();
  applyQuery();
};

// Opening an envelope costs an X25519 agreement and an Ed25519 verification, and
// an envelope's plaintext never changes — so the result is kept. Failures are
// cached too, so one bad message is not retried on every render.
const openedCache = new Map();

function openEnvelope(row) {
  let entry = openedCache.get(row.id);
  if (!entry) {
    try {
      const opened = unseal(store.identities(), row.envelope);
      const { fields, body } = parseFrontmatter(new TextDecoder().decode(opened.body));
      entry = { ...opened, fields, body,
        subject: fields.subject || "",
        snippet: body.replace(/\s+/g, " ").trim().slice(0, 140) };
    } catch (err) {
      entry = { error: err.message };
    }
    openedCache.set(row.id, entry);
  }
  return entry;
}

// What is known about a sender changes as the user binds addresses to keys, so
// this layer sits over the cached envelope and is recomputed per render — it is
// a map lookup, not crypto. The wire carries no sender name, so an unknown key
// can only be shown as its fingerprint until bound, which a signed Reply-To
// field lets the sender do in-band.
function describe(row) {
  const opened = openEnvelope(row);
  if (opened.error) return opened;
  const known = store.addressForKey(opened.sender);
  let replyAddress = null;
  if (opened.fields["reply-to"]) {
    try {
      const claimed = parseAddress(opened.fields["reply-to"]);
      // Only a full smol:// address whose key matches the signer counts;
      // anything else is ordinary text.
      if (claimed.identity && timingSafeEqual(claimed.identity, opened.sender))
        replyAddress = claimed;
    } catch { /* malformed claim: display, never bind */ }
  }
  return {
    ...opened,
    from: known ?? "unknown sender",
    // rows stay narrow: the full fingerprint belongs to the reader
    fromShort: known ?? `unknown · ${b32encode(opened.sender).slice(0, 4)}`,
    knownSender: Boolean(known),
    verifiedSender: Boolean(known && store.contact(known)?.verified),
    replyAddress,
  };
}

// A label/value row; `empty` marks a value that is guidance rather than data.
const field = (label, value, empty = false, extra = null) =>
  el("div", { className: "field" },
    el("span", { className: "field-label", textContent: label }),
    el("span", { className: empty ? "field-value empty" : "field-value", textContent: value }),
    extra);

// --- reading ------------------------------------------------------------------

async function openMessage(id) {
  const row = await store.getMessage(folder, id);
  if (!row) return;
  selectedId = id;
  store.markRead(id);
  renderFolder();
  const opened = describe(row);
  const view = $("view");
  // Under the narrow breakpoint the reader covers the list, so it needs a way back.
  $("app").classList.add("reading");
  const back = el("button", { type: "button", className: "back",
    onclick: () => { $("app").classList.remove("reading"); } }, icon("back"), "messages");
  if (opened.error) return void view.replaceChildren(back, placeholder(opened.error, true));

  // "accept" and "in-reply-to" are protocol machinery (§5.5, §5.8), not content.
  const fields = Object.entries(opened.fields).filter(([k]) => k !== "subject" && k !== "accept");
  const actions = el("div", { className: "actions" });
  view.replaceChildren(...[
    back,
    el("h2", { textContent: opened.subject || "(no subject)" }),
    el("div", { className: "meta", textContent: folder === "sent"
      ? `to: ${row.recipient}\nid: ${row.id}\nsent: ${fmtTime(row.sentAt)}`
      : `from: ${opened.from}\nid: ${row.id}\ndate: ${fmtTime(opened.time)}` }),
    trustRow(opened),
    fields.length ? el("div", { className: "fields",
      textContent: fields.map(([k, v]) => `${k}: ${v}`).join("\n") }) : null,
    el("pre", { textContent: opened.body }),
    actions,
  ].filter(node => node != null));

  // Deleting removes the local copy, and the server's too if "leave mail on
  // server" left one there to remove (settings; SPEC.md §10).
  actions.append(el("button", { type: "button", onclick: async () => {
    try {
      await deleteMessage(folder, row);
      status("message deleted");
      selectedId = null;
      resetView();
      renderFolder();
    } catch (err) {
      status(err.message, true);  // the local copy is kept if a needed server delete failed
    }
  } }, "delete"));

  if (folder !== "inbox" && folder !== "requests") return;

  if (folder === "requests" && opened.knownSender) {
    const known = store.addressForKey(opened.sender);
    if (!store.accepted(known)?.active) {
      actions.before(placeholder(
        `unsolicited mail from ${known}, not yet accepted into your main tier`));
      actions.append(el("button", { type: "button", onclick: () => acceptContact(known) },
        "accept — future mail lands in your main tier"));
    }
  }

  if (opened.knownSender) {
    actions.append(el("button", { type: "button", onclick: () => startReply(row) },
      icon("reply"), "reply"));
  } else if (opened.replyAddress) {
    // The sender signed their own smol:// address into the payload, so binding
    // it is one click. A pinned conflicting key is refused (§8).
    actions.before(placeholder(
      `this message carries the sender's signed address: ${opened.replyAddress.short}`));
    actions.append(el("button", { type: "button", textContent: "save sender & reply", onclick: () => {
      try {
        bindReplyAddress(opened.replyAddress, opened.sender);
        status(`${opened.replyAddress.short} saved for this sender (verified key)`);
        renderFolder();
        openMessage(row.id);
        startReply(row);
      } catch (err) {
        status(err.message, true);
      }
    } }));
  } else {
    // The wire gives only a signed key; a reply needs the sender's address,
    // which the user supplies once and we bind to that exact key.
    const input = el("input", { placeholder: "alice@example.org or smol://…", spellcheck: false });
    const submit = el("button", { textContent: "name sender & reply" });
    const form = el("form", { className: "name-sender" }, input, submit);
    form.onsubmit = async (event) => {
      event.preventDefault();
      submit.disabled = true;
      try {
        await nameSender(input.value, opened.sender);
        openMessage(row.id);  // the sender is named now; the reply button appears
        startReply(row);
      } catch (err) {
        status(err.message, true);
      } finally {
        submit.disabled = false;
      }
    };
    actions.before(placeholder("The wire carries no sender name, only this signed key. " +
      "To reply, give the sender's address — it is checked against this key:"));
    actions.append(form);
  }
}

// Deletes a message locally, and from the server too if it might still be
// sitting there (only possible when "leave mail on server" was on when it was
// fetched — SPEC.md §10). Sent copies are local-only; there is nothing
// server-side to remove for them (§5.6). Throws, leaving the local copy in
// place, if a needed server-side delete fails — otherwise a message could
// look gone locally while silently persisting on the server.
async function deleteMessage(folder, row) {
  if (folder !== "sent" && row.keptOnServer) {
    const me = store.identity();
    const addr = accountAddress();
    if (!me || !addr) throw new SmolError("not registered; cannot reach the server to delete this message");
    const opened = await connect(addr, { requirePin: true });
    try {
      await authenticate(opened.session, opened.handshakeHash, addr.user, me);
      await deleteOp(opened.session, [unhex(row.id)]);
    } finally {
      opened.session.stream.close();
    }
  }
  await store.removeMessage(folder, row.id);
}

// §4/§8: a signature always verifies here, because unseal() throws otherwise.
// What can be weak is the binding between that key and an address, so that is
// what the chip reports.
function trustRow(opened) {
  if (folder === "sent")
    return el("div", { className: "trust" },
      el("span", { className: "badge", textContent: "your own sealed copy" }));
  const chip = opened.verifiedSender ? ["badge ok", "verified sender key"]
    : opened.knownSender ? ["badge", "key pinned on first use"]
    : ["badge alert", "key bound to no address"];
  return el("div", { className: "trust" },
    el("span", { className: chip[0], textContent: chip[1] }),
    el("div", { className: "keyblock" },
      el("div", { textContent: fingerprint(opened.sender) }),
      el("div", { className: "full", textContent: b32encode(opened.sender) })));
}

const replySubject = (subject) =>
  !subject ? "" : subject.startsWith("Re:") ? subject : `Re: ${subject}`;

// One path for all three ways a reply can start, so the Re: rule lives once.
function startReply(row) {
  const opened = describe(row);
  openCompose({
    to: store.addressForKey(opened.sender) ?? "",
    subject: replySubject(opened.subject),
    replyTo: row.id,
  });
}

// Bind a user-supplied address to the key that signed a message. A smol://
// address carries its own key (verified); a short address is resolved and the
// result kept on first use. Anything that binds a different key is refused.
async function nameSender(text, senderKey) {
  const addr = parseAddress(text.trim());
  let key = addr.identity, verified = true;
  if (!key) {
    const opened = await connect(addr, { requirePin: false });
    try {
      ({ identity: key } = await resolveOp(opened.session, addr.user));
    } finally {
      opened.session.stream.close();
    }
    verified = false;  // trust on first use, as with any RESOLVE
  }
  if (!timingSafeEqual(key, senderKey))
    throw new SmolError("that address carries a different key than this message's sender");
  store.saveContact(addr.short, senderKey, verified);
  status(`${addr.short} saved for this sender${verified ? " (verified key)" : ""}`);
  renderFolder();
}

// A signed Reply-To is the sender's own claim, verified the moment unseal()
// verified the message's signature — no further trust step to gate behind a
// click. Never overwrites an address already pinned to a different key (§8:
// a key change without a rotation chain needs out-of-band confirmation). No
// UI side effects: callers (the reader's button, fetch's auto-bind) decide
// how to report the result and whether many need batching into one summary.
function bindReplyAddress(addr, senderKey) {
  const existing = store.contact(addr.short);
  if (existing && !timingSafeEqual(existing.key, senderKey))
    throw new SmolError(`${addr.short} is already known with a different key — ` +
      `verify out of band before replying`);
  store.saveContact(addr.short, senderKey, true);
}

// --- compose and send -----------------------------------------------------------

const compose = $("compose");

function openCompose({ to = "", subject = "", body = "", replyTo = null } = {}) {
  const form = compose.querySelector("form");
  form.to.value = to;
  form.subject.value = subject;
  form.body.value = body;
  form.dataset.replyTo = replyTo ?? "";
  $("compose-error").textContent = "";
  compose.showModal();
}

$("write").onclick = () => openCompose();

$("compose-cancel").onclick = () => compose.close();

// Every submission is a send: cancel is a plain button, and Enter in a field
// submits with no submitter — which the old check read as cancel, discarding
// the draft.
compose.querySelector("form").onsubmit = async (event) => {
  event.preventDefault();
  const form = event.target;
  const send = $("send");
  $("compose-error").textContent = "";
  send.disabled = true;  // one click, one envelope: a second seals a second message
  try {
    await sendMail(form.to.value, form.subject.value, form.body.value, form.dataset.replyTo,
      form.elements.anonymous.checked);
    compose.close();
  } catch (err) {
    $("compose-error").textContent = err.message;
  } finally {
    send.disabled = false;
  }
};

async function sendMail(toText, subject, body, replyTo, anonymous) {
  const me = store.identity();
  const master = store.master();
  if (!me || !master) throw new SmolError("no identity yet");
  const addr = parseAddress(toText);
  const recipient = await resolveRecipient(addr);
  const account = accountAddress();
  const fields = [["Subject", subject], ["In-Reply-To", replyTo]];
  // A signed Reply-To lets a first-time recipient name and answer us (§5.5
  // allows unknown keys); "anonymous" omits it.
  if (account && !anonymous) fields.push(["Reply-To", account.uri(me.publicKey)]);
  // §5.8: hand an accepted correspondent the token for our own mailbox, so a
  // first reply from them reaches our main tier.
  const accepted = store.accepted(addr.short);
  if (accepted?.active) fields.push(["Accept", b32encode(tokenFor(master, accepted.identity))]);
  const bodyBytes = utf8Bytes(buildFrontmatter(fields.filter(([, v]) => v),
    body.replace(/\s+$/, "") + "\n"));
  const envelope = seal(me, recipient, bodyBytes);
  // §5.8: our token for their mailbox, if they have given us one.
  const held = store.tokenFrom(addr.short);
  const mac = held ? acceptMac(held, messageId(envelope)) : null;
  const opened = await connect(addr, { requirePin: false });
  try {
    await sendOp(opened.session, envelope, mac);
  } finally {
    opened.session.stream.close();
  }
  // §5.6: the ephemeral is gone, so keep a copy sealed to ourselves.
  await store.storeMessage("sent", {
    id: hex(messageId(envelope)),
    recipient: addr.short,
    envelope: seal(me, me.publicKey, bodyBytes),
    sentAt: Math.floor(Date.now() / 1000),
  });
  status(`sent to ${addr.short}${mac ? " (accepted)" : ""}`);
  if (folder === "sent") renderFolder();
}

// Prefer a key we already trust; fall back to RESOLVE with trust on first use.
async function resolveRecipient(addr) {
  if (addr.identity) {
    store.saveContact(addr.short, addr.identity, true);
    return addr.identity;
  }
  const known = store.contact(addr.short);
  if (known) return known.key;
  const opened = await connect(addr, { requirePin: false });
  let current;
  try {
    ({ identity: current } = await resolveOp(opened.session, addr.user));
  } finally {
    opened.session.stream.close();
  }
  store.saveContact(addr.short, current, false);
  status(`${addr.short} pinned (trust on first use${opened.pinned ? "" : ", UNVERIFIED server"})`);
  return current;
}

// --- fetch ----------------------------------------------------------------------

// The address we know a signer by: a contact, or the Reply-To it signed for
// itself. Naming a mailbox is not trusting a key, so nothing is pinned here
// (§5.7, §8).
function addressOfSigner(sender, replyToField) {
  const known = store.addressForKey(sender);
  if (known) return known;
  if (!replyToField) return null;
  try {
    const parsed = parseAddress(replyToField);
    if (parsed.identity && timingSafeEqual(parsed.identity, sender)) return parsed.short;
  } catch { /* malformed claim: no address to learn a token under */ }
  return null;
}

// §5.8: an Accept field is bound to the signer of the message that carried
// it, which unseal() has already verified.
function learnTokenFrom(unsealed, opened) {
  const raw = opened.fields["accept"];
  if (!raw) return;
  let token;
  try {
    token = b32decode(raw);
  } catch {
    return;
  }
  if (token.length !== TOKEN_LEN) return;
  const address = addressOfSigner(unsealed.sender, opened.fields["reply-to"]);
  if (address) store.learnToken(address, token);
}

$("fetch").onclick = async () => {
  const me = store.identity();
  const master = store.master();
  const addr = accountAddress();
  if (!me || !master) return status("no identity yet", true);
  if (!addr) return status("not registered yet — claim an address in settings", true);
  const button = $("fetch"), label = button.querySelector(".label");
  const resting = label.textContent;
  button.disabled = true;  // one session at a time; the icon spins while it is
  label.textContent = "fetching…";
  status("fetching…");
  let stored = 0, verified = 0;
  const rejected = [];
  // §10: acknowledging (deleting) is the default; "leave mail on server" pages
  // forward by cursor instead, so already-fetched mail is never re-downloaded
  // even though it isn't deleted (storeIfNew also dedupes, as a second line
  // of defense).
  const leaveOnServer = store.leaveOnServer();
  let [afterTime, afterId] = store.cursor();
  try {
    const opened = await connect(addr, { requirePin: true });
    try {
      const { sync, tokens } = store.tokenSet(master);
      await authenticate(opened.session, opened.handshakeHash, addr.user, me, { sync, tokens });
      for (;;) {
        const records = await fetchOp(opened.session, afterTime, afterId);
        if (!records.length) break;
        const acked = [];
        for (const record of records) {
          afterTime = record.receivedAt;
          afterId = record.id;
          let unsealed;
          try {
            if (!timingSafeEqual(messageId(record.envelope), record.id))
              throw new SmolError("id does not match the envelope");
            unsealed = unseal(store.identities(), record.envelope);
          } catch (err) {
            // Left on the server rather than destroyed, so a client-side bug
            // cannot lose mail. Collected rather than announced, because the
            // closing summary would overwrite each one in turn.
            rejected.push(`${hex(record.id)}: ${err.message}`);
            continue;
          }
          const row = { id: hex(record.id), envelope: record.envelope, receivedAt: record.receivedAt,
            tier: record.isRequest ? store.TIER_REQUESTS : store.TIER_MAIN, keptOnServer: leaveOnServer };
          if (await store.storeIfNew("inbox", row)) {
            stored++;
            // A signed Reply-To is exactly as verified as the signature
            // unseal() just checked — see bindReplyAddress(). describe()
            // both parses the same claim the reader would show and warms its
            // cache, so opening the message right after costs nothing extra.
            const described = describe(row);
            if (described.replyAddress) {
              try {
                bindReplyAddress(described.replyAddress, unsealed.sender);
                verified++;
              } catch { /* already known under a different key: leave it be */ }
            }
            learnTokenFrom(unsealed, described);
          }
          acked.push(record.id);
        }
        if (leaveOnServer) {
          // Persisted per batch, so an interrupted fetch resumes here rather
          // than re-paging from the start next time.
          store.setCursor(afterTime, afterId);
        } else if (acked.length) {
          await deleteOp(opened.session, acked);
        }
      }
    } finally {
      opened.session.stream.close();
    }
    // Everything acknowledged is deleted, so the next fetch starts fresh; a
    // record left on the server (rejected above) simply resurfaces then.
    if (!leaveOnServer) store.setCursor(0, new Uint8Array(ID_LEN));
    status([`${stored} new, ${rejected.length} rejected`,
      verified ? `${verified} sender${verified === 1 ? "" : "s"} verified from a signed Reply-To` : null,
      ...rejected.map(line => `  ${line}`),
      rejected.length ? "left on the server" : null].filter(Boolean).join("\n"),
      rejected.length > 0);
  } catch (err) {
    status(err.message, true);
  } finally {
    button.disabled = false;
    label.textContent = resting;
  }
  renderFolder();
};

// --- contacts -------------------------------------------------------------------

function renderContacts(list) {
  const contacts = store.allContacts();
  list.replaceChildren(...contacts.map(({ address, key, verified, history }) => {
    const accepted = store.accepted(address);
    const item = el("button", {
      type: "button",
      className: `item contact${address === selectedId ? " selected" : ""}`,
      onclick: () => openContact(address),
    });
    if (address === selectedId) item.setAttribute("aria-current", "true");
    item.append(
      el("div", { className: "who", textContent: address }),
      el("div", { className: "mid" },
        el("div", { textContent: fingerprint(b32decode(key)) }),
        el("span", { className: verified ? "badge ok" : "badge",
          textContent: verified ? "verified key" : "tofu" }),
        accepted?.active ? el("span", { className: "badge ok", textContent: "accepted" }) : null,
        history.length ? el("span", { className: "badge",
          textContent: `${history.length} previous` }) : null));
    item.dataset.search =
      `${address} ${key} ${fingerprint(b32decode(key))} ${history.map(h => h.key).join(" ")}`.toLowerCase();
    return item;
  }));
  if (!contacts.length)
    list.append(placeholder("no contacts yet — import a smol:// address above, or write to someone"));
}

// The full key, the address to hand out, and any key this one replaced — the
// row can only afford a fingerprint, and §8 turns on the user being able to
// inspect exactly what changed.
function openContact(address) {
  const known = store.contact(address);
  if (!known) return;
  selectedId = address;
  renderFolder();
  const addr = parseAddress(address);
  const view = $("view");
  $("app").classList.add("reading");

  const refresh = el("button", { type: "button", onclick: async (event) => {
    event.target.disabled = true;
    try {
      await refreshContact(address);
    } finally {
      event.target.disabled = false;
    }
  } }, icon("refresh"), "re-resolve");

  const isAccepted = Boolean(store.accepted(address)?.active);
  const tokenButton = el("button", { type: "button",
    textContent: isAccepted ? "block" : "accept",
    onclick: async (event) => {
      event.target.disabled = true;
      try {
        if (isAccepted) await blockContact(address); else await acceptContact(address);
      } finally {
        event.target.disabled = false;
      }
    } });

  view.replaceChildren(...[
    el("button", { type: "button", className: "back",
      onclick: () => { $("app").classList.remove("reading"); } }, icon("back"), "contacts"),
    el("h2", { textContent: address }),
    el("div", { className: "trust" },
      el("span", { className: known.verified ? "badge ok" : "badge",
        textContent: known.verified ? "verified key" : "key pinned on first use" })),
    field("fingerprint", fingerprint(known.key)),
    field("public key", b32encode(known.key)),
    field("address", addr.uri(known.key), false, copyButton(addr.uri(known.key), "address")),
    el("div", { className: "seed-card" },
      el("h4", { textContent: "accept token" }),
      el("p", { className: "hint", textContent: isAccepted
        ? "This contact's mail lands in your main tier."
        : "This contact's mail lands in requests until accepted." }),
      el("div", { className: "actions" }, tokenButton)),
    known.history.length ? el("section", { className: "history" },
      el("h3", { textContent: `previous keys (${known.history.length})` }),
      el("p", { className: "hint", textContent:
        "Replaced by a signed rotation chain. Mail signed with these was sent " +
        "before the change; rotation is not revocation, so a stolen key can still rotate onward." }),
      ...known.history.map(({ key, until }) => el("div", { className: "keyblock" },
        el("div", { textContent: fingerprint(b32decode(key)) }),
        el("div", { className: "full", textContent: key }),
        el("div", { className: "replaced", textContent: `replaced ${fmtTime(Math.floor(until / 1000))}` }))))
      : null,
    el("div", { className: "actions" }, refresh),
  ].filter(node => node != null));
}

// Re-resolve a contact and apply §8: a valid rotation chain is accepted and
// surfaced; anything else requires out-of-band verification.
async function refreshContact(address) {
  try {
    const addr = parseAddress(address);
    if (addr.identity) throw new SmolError("that address already carries a key; use import instead");
    const known = store.contact(addr.short);
    const opened = await connect(addr, { requirePin: false });
    let current, chain;
    try {
      ({ identity: current, chain } = await resolveOp(opened.session, addr.user));
    } finally {
      opened.session.stream.close();
    }
    if (!known) {
      store.saveContact(addr.short, current, false);
      status(`${addr.short} pinned (trust on first use${opened.pinned ? "" : ", UNVERIFIED server"})`);
    } else if (timingSafeEqual(known.key, current)) {
      status(`${addr.short}: key unchanged`);
    } else if (walkChain(addr.user, known.key, current, chain)) {
      store.saveContact(addr.short, current, known.verified);
      status(`${addr.short} rotated its key; a signed chain confirms it.\nnow ${b32encode(current)}`, true);
    } else {
      status(`${addr.short} presents a different key with no valid rotation chain.\n` +
        `Verify out of band, then import the new smol:// address.`, true);
    }
  } catch (err) {
    status(err.message, true);
  }
  if (folder === "contacts" && selectedId === address) openContact(address);
  else renderFolder();
}

// --- accept tokens (§5.8) --------------------------------------------------------

// An accept or a block only takes effect once the server holds the changed
// set, so it is pushed right away rather than at the next fetch.
async function pushTokens() {
  const me = store.identity();
  const master = store.master();
  const addr = accountAddress();
  if (!me || !master) throw new SmolError("no identity yet");
  if (!addr) {
    status("not registered; the set will be pushed with your first fetch", true);
    return 0;
  }
  const opened = await connect(addr, { requirePin: true });
  try {
    const { sync, tokens } = store.tokenSet(master);
    return await authenticate(opened.session, opened.handshakeHash, addr.user, me, { sync, tokens });
  } finally {
    opened.session.stream.close();
  }
}

// Admit a contact to the main tier; their token travels in our next message
// to them.
async function acceptContact(address) {
  try {
    const key = store.contact(address)?.key;
    if (!key) throw new SmolError(`no key for ${address} yet`);
    store.accept(address, key);
    store.setSyncOk(true);
    const held = await pushTokens();
    status(`${address} accepted; server now holds ${held} accept token(s)`);
    renderFolder();
    if (folder === "contacts" && selectedId === address) openContact(address);
  } catch (err) {
    status(err.message, true);
  }
}

// Withdraw a contact's accept token; their mail lands in requests from their
// next message on.
async function blockContact(address) {
  try {
    store.block(address);
    const held = await pushTokens();
    status(`${address} blocked; server now holds ${held} accept token(s)`);
    renderFolder();
    if (folder === "contacts" && selectedId === address) openContact(address);
  } catch (err) {
    status(err.message, true);
  }
}

// --- settings ---------------------------------------------------------------------

const settings = $("settings");
const settingsTabs = [...$("settings-tabs").querySelectorAll("button")];
const settingsPanels = [...$("settings-panels").querySelectorAll(".panel")];

function showTab(name) {
  for (const button of settingsTabs) {
    const active = button.dataset.tab === name;
    button.classList.toggle("active", active);
    if (active) button.setAttribute("aria-current", "true");
    else button.removeAttribute("aria-current");
  }
  for (const panel of settingsPanels) panel.hidden = panel.dataset.panel !== name;
  $("settings-panels").scrollTop = 0;
}

for (const button of settingsTabs) button.onclick = () => showTab(button.dataset.tab);

function openSettings() {
  renderSettings();
  showTab("identity");
  if (!settings.open) settings.showModal();
  // showModal() focuses the first focusable node, which is the close button;
  // the current tab says where you are instead.
  $("settings-tabs").querySelector("button.active").focus();
}

$("settings-open").onclick = () => openSettings();
$("settings-close").onclick = () => settings.close();

$("leave-on-server").onchange = (event) => store.setLeaveOnServer(event.target.checked);

// --- settings panels --------------------------------------------------------------

// One renderer per panel, all of them cheap, so every mutation below can just
// call this rather than reason about which panel it touched.
function renderSettings() {
  $("leave-on-server").checked = store.leaveOnServer();
  $("backup-error").textContent = "";
  renderIdentityPanel();
  renderServerPanel();
  renderAdvancedPanel();
}

// A reusable Cancel/confirm modal for the advanced panel's two irreversible
// actions. <dialog>'s own cancel path (Escape, backdrop click) counts as
// Cancel, same as clicking the button.
function confirmDialog({ title, body, confirmLabel, danger = false }) {
  return new Promise((resolve) => {
    $("confirm-title").textContent = title;
    $("confirm-text").textContent = body;
    const ok = $("confirm-ok");
    ok.textContent = confirmLabel;
    ok.className = danger ? "danger" : "filled";
    const dialog = $("confirm");
    let decided = false;
    const finish = (result) => { decided = true; resolve(result); dialog.close(); };
    $("confirm-cancel").onclick = () => finish(false);
    ok.onclick = () => finish(true);
    dialog.addEventListener("close", () => { if (!decided) resolve(false); }, { once: true });
    dialog.showModal();
  });
}

function renderServerPanel() {
  const account = store.account();
  const host = account?.host ?? null;
  const key = host ? store.serverPin(host) : null;
  $("server-connection").replaceChildren(
    field("Host", host ?? "not registered yet", !host, host ? copyButton(host, "host") : null),
    field("Public Key", key ? b32encode(key) : "not pinned yet", !key,
      key ? copyButton(b32encode(key), "public key") : null),
    el("div", { className: "spin-row" },
      el("div", { className: "spin-text" },
        el("span", { className: "check-title", textContent: "Timeout" }),
        el("span", { className: "hint", textContent: "Seconds before a network call gives up" })),
      el("input", { type: "number", min: 1, max: 600, step: 1, value: store.timeoutSeconds(),
        onchange: (event) => {
          store.setTimeoutSeconds(event.target.value);
          event.target.value = store.timeoutSeconds();  // reflects clamping or an ignored non-numeric edit
        } })));
}

function renderIdentityPanel() {
  const me = store.identity();
  const account = store.account();
  const fields = $("identity-fields");
  fields.replaceChildren();
  const secret = $("identity-secret");
  secret.replaceChildren();
  if (!me) return;

  const address = account ? `${account.user}@${account.host}` : "not registered yet";
  const key = b32encode(me.publicKey);
  const uri = account ? accountAddress().uri(me.publicKey) : "claim an address to get one";
  fields.append(
    field("Address", address, !account, account ? copyButton(address, "address") : null),
    field("Key", key, false, copyButton(key, "key")),
    field("Fingerprint", fingerprint(me.publicKey), false, copyButton(fingerprint(me.publicKey), "fingerprint")),
    field("URI", uri, !account, account ? copyButton(uri, "uri") : null));

  const masterBytes = store.master();
  if (!masterBytes) return;
  // Revealed on request rather than on open: the panel a new user is sent to
  // first is a poor place to paint the only secret there is across the screen.
  const masked = "\u2022".repeat(64);
  const seedText = hex(masterBytes);
  const seed = el("div", { className: "seed", textContent: masked });
  const reveal = el("button", { type: "button", textContent: "reveal", title: "reveal the recovery secret",
    onclick: (event) => {
      const showing = seed.textContent !== masked;
      seed.textContent = showing ? masked : seedText;
      event.currentTarget.textContent = showing ? "reveal" : "hide";
      event.currentTarget.title = showing ? "reveal the recovery secret" : "hide the recovery secret";
    } });

  secret.append(el("div", { className: "seed-card" },
    el("div", { className: "row" }, seed, reveal, copyButton(seedText, "recovery secret")),
    el("p", { textContent: "Anyone who holds this can read your mail and write as you, and losing " +
      "it loses the address with it — there is no reset. Keep it in a password manager." })));
}

function renderAdvancedPanel() {
  $("rotations-count").replaceChildren(field("Completed", String(store.rotations())));
  $("rotate-error").textContent = "";
  $("logout-error").textContent = "";
}

// A pin is keyed by bare host — connect() strips the port before looking one
// up (parseAddress splits user@host:port into three), so "user@host" or
// "host:port" here would silently pin a string nothing ever looks up again,
// exactly the mistake that produced "pinned <address>" followed by a
// confusing "no pinned key" from recall right after. Shared by the settings
// pin form and the onboarding server screen.
function cleanHost(hostText) {
  const host = hostText.trim().toLowerCase();
  if (host.includes("@"))
    throw new SmolError(`"${host}" looks like an address, not a server — the part after the @ goes here`);
  if (host.includes(":"))
    throw new SmolError(`"${host}": a pin is by host only, no port — just the part before the colon`);
  return host;
}

$("import-form").onsubmit = (event) => {
  event.preventDefault();
  const form = event.target;
  try {
    const addr = parseAddress(form.uri.value.trim());
    if (!addr.identity) throw new SmolError("import needs a smol:// address carrying a key");
    store.saveContact(addr.short, addr.identity, true);
    status(`imported ${addr.short}  ${b32encode(addr.identity)}  (verified)\n` +
      `fingerprint: ${fingerprint(addr.identity)}`);
    renderFolder();
    form.reset();
  } catch (err) {
    status(err.message, true);
  }
};

// §2: a master alone does not say which rotation index a server has bound,
// so restoring resolves the address and walks indices 0..MAX_CHAIN until one
// derives the key RESOLVE returned, correcting restore-identity's default
// guess of index 0. Also binds "account" — onboarding's only path to it now.
async function recallAndDiscoverRotation(masterBytes, text) {
  const addr = parseAddress(text.trim());
  const opened = await connect(addr, { requirePin: true });
  let current;
  try {
    ({ identity: current } = await resolveOp(opened.session, addr.user));
  } finally {
    opened.session.stream.close();
  }
  let found = null;
  for (let n = 0; n <= MAX_CHAIN; n++) {
    if (timingSafeEqual(identityFromSeed(identitySeed(masterBytes, n)).publicKey, current)) {
      found = n;
      break;
    }
  }
  if (found === null)
    throw new SmolError(`the key bound to ${addr.short} is not derived from this master ` +
      `within ${MAX_CHAIN} rotations`);
  store.setRotationIndex(found);
  store.setAccount(addr);
  return addr;
}

// The File System Access API gives a real save dialog with a suggested name;
// where it is unavailable (Firefox, Safari), a plain download is the
// equivalent a browser can offer. Either way nothing is shown on success —
// the file landing where the user put it is the confirmation.
$("export-data").onclick = async () => {
  $("backup-error").textContent = "";
  try {
    const data = await store.exportData();
    const stamp = new Date(data.exportedAt).toISOString().slice(0, 10);
    const filename = `gsmol-export-${stamp}.json`;
    const text = JSON.stringify(data);
    if (window.showSaveFilePicker) {
      const handle = await window.showSaveFilePicker({ suggestedName: filename,
        types: [{ description: "gsmol backup", accept: { "application/json": [".json"] } }] });
      const writable = await handle.createWritable();
      await writable.write(text);
      await writable.close();
    } else {
      const blob = new Blob([text], { type: "application/json" });
      const url = URL.createObjectURL(blob);
      Object.assign(document.createElement("a"), { href: url, download: filename }).click();
      URL.revokeObjectURL(url);
    }
  } catch (err) {
    if (err.name !== "AbortError") $("backup-error").textContent = err.message;  // AbortError: picker cancelled
  }
};

// Shared by both the File System Access path and the <input type=file>
// fallback it reduces to where that API is unavailable.
async function importBackupText(text) {
  if (!text.trim()) return;  // empty or whitespace-only content does nothing
  await store.importData(JSON.parse(text));
  renderSettings();
  renderFolder();
}

$("import-data-trigger").onclick = async () => {
  $("backup-error").textContent = "";
  if (!window.showOpenFilePicker) return $("import-data").click();
  try {
    const [handle] = await window.showOpenFilePicker({
      types: [{ description: "gsmol backup", accept: { "application/json": [".json"] } }] });
    await importBackupText(await (await handle.getFile()).text());
  } catch (err) {
    if (err.name !== "AbortError") $("backup-error").textContent = err.message;
  }
};

$("import-data").onchange = async (event) => {
  const file = event.target.files[0];
  event.target.value = "";  // same file re-selected twice must still fire change
  if (!file) return;
  try {
    await importBackupText(await file.text());
  } catch (err) {
    $("backup-error").textContent = err.message;
  }
};

// A confirm dialog's body repeats its group's description verbatim, read
// straight from the panel rather than duplicated here so the two can never
// drift apart. textContent carries the HTML source's line-wrap whitespace,
// which this collapses back to plain prose.
const panelText = (id) => $(id).textContent.replace(/\s+/g, " ").trim();

// §7: rotate to the next index's derived key and rebind the account with a
// signed certificate. The superseded key stays derivable from the master,
// since mail sealed to it stays readable with nothing else.
async function rotateIdentity() {
  const me = store.identity();
  const master = store.master();
  const addr = accountAddress();
  $("rotate-error").textContent = "";
  if (!me || !master || !addr) {
    $("rotate-error").textContent = "rotate needs a registered account";
    return;
  }
  const confirmed = await confirmDialog({
    title: "Rotate the identity?", body: panelText("rotations-description"), confirmLabel: "Rotate" });
  if (!confirmed) return;
  const button = $("rotate-identity");
  const resting = button.textContent;
  button.disabled = true;  // a round trip to the server takes a moment; say so rather than sit inert
  button.textContent = "rotating…";
  try {
    const freshSeed = identitySeed(master, store.rotations() + 1);
    const fresh = identityFromSeed(freshSeed);
    const cert = makeCert(addr.user, me, freshSeed);
    const opened = await connect(addr, { requirePin: true });
    try {
      await registerOp(opened.session, opened.serverStatic, { username: addr.user, identity: fresh, cert });
    } finally {
      opened.session.stream.close();
    }
    store.advanceRotation();
    // The key set grew, so a cached "not one of our keys" failure may be stale.
    openedCache.clear();
    renderAccount();
    renderSettings();
    renderFolder();
  } catch (err) {
    $("rotate-error").textContent = err.message;
  } finally {
    button.disabled = false;
    button.textContent = resting;
  }
}
$("rotate-identity").onclick = rotateIdentity;

// Unlike rotate, nothing is kept: this is the master's only local copy, gone.
async function logout() {
  $("logout-error").textContent = "";
  const confirmed = await confirmDialog({ title: "Log out and delete all data?",
    body: panelText("logout-description"), confirmLabel: "Log Out", danger: true });
  if (!confirmed) return;
  try {
    await store.clearAll();
    location.reload();
  } catch (err) {
    $("logout-error").textContent = err.message;
  }
}
$("logout").onclick = logout;

// --- boot --------------------------------------------------------------------------

// A deployment MAY bake in a server key (the NixOS module's `presetServer`),
// which only makes sense when whoever serves this page and whoever runs that
// smolmaild are the same trusted party: the value arrives over this
// deployment's own TLS, which is the trusted channel SPEC.md §4 asks a pin to
// come from. This only seeds the first run — once written it is an ordinary
// pin, editable and removable in settings like any other, and never
// overwrites a host the user (or a previous boot) already pinned.
function applyPresetServer() {
  if (!PRESET_SERVER || store.serverPin(PRESET_SERVER.host)) return;
  try {
    store.pinServer(PRESET_SERVER.host, b32decode(PRESET_SERVER.publicKey));
  } catch { /* malformed preset: leave unpinned rather than block boot */ }
}

applyPresetServer();
applyTheme();

// An identity not yet bound to an account always resumes at the server
// screen, however it was reached — there is nothing a banner needs to remind
// the user of afterward, since showApp() is unreachable until both are done.
if (!store.identity()) {
  showSetupStage("intro");
  showSetup();
} else if (!store.account()) {
  enterServerSetup();
  showSetup();
} else {
  showApp();
}