/* Brain of Reese — chat shell.
 *
 * Renders suggestions, shows KB health, and runs chat turns against
 * POST /api/chat (SSE, PLAN §4): deltas render live into the Brain bubble,
 * the done event appends source chips (and "Maybe try" chips when the
 * turn was deflected — honesty gate, phase 04), errors surface as a red
 * banner. The full feedback state machine lands with the loading-feedback
 * story; this keeps the "never stale" contract: the button is busy for the
 * whole turn and is always re-enabled at the end.
 * 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`;
}

/* ---------- chat turn (SSE streaming, PLAN §4) ---------- */

/* Parse an SSE response body into JSON events. */
async function readSSE(response, onEvent) {
  const reader = response.body.getReader();
  const decoder = new TextDecoder();
  let buf = "";
  for (;;) {
    const { done, value } = await reader.read();
    if (done) break;
    buf += decoder.decode(value, { stream: true });
    let sep;
    while ((sep = buf.indexOf("\n\n")) !== -1) {
      const frame = buf.slice(0, sep).trim();
      buf = buf.slice(sep + 2);
      if (!frame.startsWith("data:")) continue;
      const payload = frame.slice(5).trim();
      if (!payload || payload === "[DONE]") continue;
      onEvent(JSON.parse(payload));
    }
  }
}

/* Source chips (mono, source/path) under a Brain bubble. */
function appendSources(wrap, sources) {
  if (!sources || !sources.length) return;
  const body = wrap.querySelector(".msg-body");
  const meta = document.createElement("div");
  meta.className = "msg-meta";
  meta.setAttribute("role", "list");
  meta.setAttribute("aria-label", "Sources");
  for (const s of sources) {
    const label = `${s.source}/${s.path}`;
    const chip = document.createElement("a");
    chip.className = "source-chip";
    chip.setAttribute("role", "listitem");
    chip.href = "/sources.html";
    chip.textContent = label;
    chip.title = label;
    meta.appendChild(chip);
  }
  body.appendChild(meta);
  // Accessible full path whenever the pill visually truncates.
  for (const chip of meta.children) {
    if (chip.scrollWidth > chip.clientWidth) chip.setAttribute("aria-label", chip.title);
  }
}

/* "Maybe try:" chips under a deflected bubble (honesty gate, phase 04).
   Same .suggestion-chip component as onboarding; clicking wires what
   exists today — fill the input + focus. One-tap submit lands with the
   phase 05 chip component. The group is accessible (role=list +
   aria-label) and wraps cleanly at every width. */
function appendMaybeTry(wrap, suggestions) {
  if (!suggestions || !suggestions.length) return;
  const body = wrap.querySelector(".msg-body");
  const group = document.createElement("div");
  group.className = "maybe-try";
  group.setAttribute("role", "list");
  group.setAttribute("aria-label", "Maybe try");
  const label = document.createElement("span");
  label.className = "visually-hidden";
  label.textContent = "Maybe try:";
  group.appendChild(label);
  for (const s of suggestions) {
    const btn = document.createElement("button");
    btn.type = "button";
    btn.className = "suggestion-chip";
    btn.setAttribute("role", "listitem");
    btn.textContent = s;
    btn.addEventListener("click", () => {
      input.value = s;
      autoGrow();
      input.focus();
    });
    group.appendChild(btn);
  }
  body.appendChild(group);
}

function showErrorBanner(detail) {
  banner.hidden = false;
  banner.classList.add("is-error");
  banner.setAttribute("role", "alert");
  bannerText.textContent = `${detail} Try your question again — I'm ready.`;
}

function clearErrorBanner() {
  if (banner.classList.contains("is-error")) {
    banner.classList.remove("is-error");
    banner.setAttribute("role", "status");
    bannerText.textContent = "";
    banner.hidden = true;
  }
}

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

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

  let wrap = null;
  let acc = "";
  let res = null;
  try {
    res = await fetch("/api/chat", {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({ message: text }),
    });
    if (!res.ok || !res.body) {
      let detail = `Brain's API answered with HTTP ${res.status}.`;
      try {
        const body = await res.json();
        if (body.detail) detail = body.detail;
      } catch { /* non-JSON error body */ }
      throw new Error(detail);
    }
    await readSSE(res, (ev) => {
      if (ev.type === "delta") {
        acc += ev.text || "";
        if (!wrap) {
          removeTyping();
          wrap = addMessage("brain", "");
        }
        wrap.querySelector(".bubble").innerHTML = renderMarkdown(acc);
        wrap.scrollIntoView({ behavior: "smooth", block: "end" });
      } else if (ev.type === "done") {
        if (!wrap) {
          removeTyping();
          wrap = addMessage("brain", "…");
        }
        if (ev.deflected) {
          wrap.classList.add("is-deflected");
          appendMaybeTry(wrap, ev.suggestions);
        }
        appendSources(wrap, ev.sources);
      } else if (ev.type === "error") {
        throw new Error(ev.detail || "Something went wrong on my side.");
      }
    });
    if (!wrap) {
      removeTyping();
      addMessage("brain", "Hmm — that came back empty. Ask me again?");
    }
  } catch (err) {
    removeTyping();
    showErrorBanner(err.message || "Something went wrong on my side.");
  } finally {
    try { res?.body?.cancel(); } catch { /* stream already closed */ }
    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();