/* Brain of Reese — chat shell.
 *
 * Scaffolding-stage behavior: renders suggestions, shows KB health, and
 * echoes a friendly placeholder answer. The real RAG streaming chat is
 * implemented in the chat-rag phase (see .agent/user_stories/).
 * All DOM ids match frontend/index.html.
 */

const messagesEl = document.querySelector("#messages");
const emptyState = document.querySelector("#empty-state");
const suggestionsEl = document.querySelector("#suggestions");
const composer = document.querySelector("#composer");
const input = document.querySelector("#message-input");
const sendBtn = document.querySelector("#send-btn");
const sendLabel = document.querySelector("#send-label");
const sendStatus = document.querySelector("#send-status");
const banner = document.querySelector("#kb-banner");
const bannerText = document.querySelector("#kb-banner-text");
const versionEl = document.querySelector("#app-version");

/* ---------- tiny, safe markdown renderer (no external libs, no CDN) ---------- */
export function escapeHtml(s) {
  return s.replace(/[&<>"']/g, (c) => ({
    "&": "&amp;", "<": "&lt;", ">": "&gt;", '"': "&quot;", "'": "&#39;",
  }[c]));
}

export function renderMarkdown(md) {
  // 1. Protect fenced code blocks.
  const codeBlocks = [];
  let text = md.replace(/```(\w*)\n([\s\S]*?)```/g, (_m, _lang, code) => {
    codeBlocks.push(`<pre><code>${escapeHtml(code.replace(/\n$/, ""))}</code></pre>`);
    return `\u0000CODE${codeBlocks.length - 1}\u0000`;
  });

  // 2. Escape everything else, then apply inline + block transforms.
  text = escapeHtml(text)
    .replace(/`([^`\n]+)`/g, "<code>$1</code>")
    .replace(/\*\*([^*]+)\*\*/g, "<strong>$1</strong>")
    .replace(/(^|[\s(])\*([^*\n]+)\*/g, "$1<em>$2</em>")
    .replace(/^### (.*)$/gm, "<h4>$1</h4>")
    .replace(/^## (.*)$/gm, "<h3>$1</h3>")
    .replace(/^# (.*)$/gm, "<h3>$1</h3>")
    .replace(/^\s*[-*] (.*)$/gm, "<li>$1</li>")
    .replace(/(<li>[\s\S]*?<\/li>)(?!\s*<li>)/g, "<ul>$1</ul>")
    .replace(/^\d+\. (.*)$/gm, "<li>$1</li>");

  // 3. Paragraphs (double newline separated).
  text = text
    .split(/\n{2,}/)
    .map((block) => {
      const b = block.trim();
      if (!b) return "";
      if (/^<(h\d|ul|ol|pre|li)/.test(b)) return b;
      return `<p>${b.replace(/\n/g, "<br>")}</p>`;
    })
    .join("");

  // 4. Restore code blocks.
  return text.replace(/\u0000CODE(\d+)\u0000/g, (_m, i) => codeBlocks[Number(i)]);
}

/* ---------- messages ---------- */
function addMessage(who, html) {
  if (emptyState) emptyState.hidden = true;
  const wrap = document.createElement("div");
  wrap.className = `msg ${who}`;
  wrap.innerHTML = `
    <span class="avatar" aria-hidden="true">${who === "brain" ? "🧠" : "🧑"}</span>
    <div class="msg-body">
      <div class="bubble">${html}</div>
    </div>`;
  messagesEl.appendChild(wrap);
  wrap.scrollIntoView({ behavior: "smooth", block: "end" });
  return wrap;
}

function addTyping() {
  if (emptyState) emptyState.hidden = true;
  const wrap = document.createElement("div");
  wrap.className = "msg brain";
  wrap.id = "typing-indicator";
  wrap.innerHTML = `
    <span class="avatar" aria-hidden="true">🧠</span>
    <div class="msg-body">
      <div class="bubble typing" role="status" aria-label="Brain of Reese is thinking">
        <span></span><span></span><span></span>
      </div>
    </div>`;
  messagesEl.appendChild(wrap);
  wrap.scrollIntoView({ behavior: "smooth", block: "end" });
}

function removeTyping() {
  document.querySelector("#typing-indicator")?.remove();
}

/* ---------- suggestions ---------- */
async function loadSuggestions() {
  try {
    const r = await fetch("/api/suggestions");
    if (!r.ok) return;
    const { suggestions } = await r.json();
    suggestionsEl.innerHTML = "";
    for (const s of suggestions) {
      const btn = document.createElement("button");
      btn.type = "button";
      btn.className = "suggestion-chip";
      btn.textContent = s;
      btn.setAttribute("role", "listitem");
      btn.addEventListener("click", () => {
        input.value = s;
        input.focus();
      });
      suggestionsEl.appendChild(btn);
    }
  } catch {
    /* suggestions are progressive enhancement */
  }
}

/* ---------- health / version ---------- */
async function loadHealth() {
  try {
    const r = await fetch("/api/health");
    const body = await r.json();
    versionEl.textContent = `v${body.version}`;
    if (body.db === "down") {
      bannerText.textContent =
        "Knowledge base is offline — start Postgres with `podman compose up -d db`.";
      banner.hidden = false;
    }
  } catch {
    /* API unreachable: page still renders, composer will explain on send */
  }
}

/* ---------- composer ---------- */
function setBusy(busy) {
  sendBtn.disabled = busy;
  sendBtn.querySelector(".spinner").hidden = !busy;
  sendLabel.textContent = busy ? "Thinking…" : "Send";
  sendStatus.textContent = busy ? "Brain of Reese is working" : "";
}

function autoGrow() {
  input.style.height = "auto";
  input.style.height = `${Math.min(input.scrollHeight, 192)}px`;
}

async function handleSend(e) {
  e.preventDefault();
  const text = input.value.trim();
  if (!text || sendBtn.disabled) return;

  addMessage("user", renderMarkdown(text));
  input.value = "";
  autoGrow();
  setBusy(true);
  addTyping();

  try {
    // TODO(chat-rag phase): replace with POST /api/chat (SSE streaming).
    await new Promise((res) => setTimeout(res, 500));
    const reply =
      "I'm still getting my neurons wired up — the real me ships in the " +
      "next phase! Keep the questions coming, you're on a roll. 🚀";
    removeTyping();
    addMessage("brain", renderMarkdown(reply));
  } catch {
    removeTyping();
    addMessage("brain", "Something went wrong on my side — please try again in a moment.");
  } finally {
    setBusy(false);
    input.focus();
  }
}

input.addEventListener("input", autoGrow);
input.addEventListener("keydown", (e) => {
  if (e.key === "Enter" && !e.shiftKey) {
    e.preventDefault();
    composer.requestSubmit();
  }
});
composer.addEventListener("submit", handleSend);

loadSuggestions();
loadHealth();