const state = {
  session: null,
  selectedQuestion: null,
  lastAnswer: null,
  progress: null,
};

const els = {
  sessionForm: document.querySelector("#session-form"),
  answerForm: document.querySelector("#answer-form"),
  answerText: document.querySelector("#answer-text"),
  answerButton: document.querySelector("#answer-button"),
  questions: document.querySelector("#questions"),
  feedback: document.querySelector("#feedback"),
  progress: document.querySelector("#progress"),
  refreshProgress: document.querySelector("#refresh-progress"),
  status: document.querySelector("#status-line"),
  error: document.querySelector("#error-line"),
  title: document.querySelector("#session-title"),
};

els.sessionForm.addEventListener("submit", async (event) => {
  event.preventDefault();
  clearError();
  setStatus("Creating diagnostic session...");

  const payload = {
    user_id: value("#user-id"),
    target_role: value("#target-role"),
    stack: value("#stack").split(",").map((item) => item.trim()).filter(Boolean),
    interview_timeline: value("#timeline"),
  };

  try {
    const session = await request("/api/v1/diagnostic-sessions", {
      method: "POST",
      body: JSON.stringify(payload),
    });
    state.session = session;
    state.selectedQuestion = session.questions[0] || null;
    state.lastAnswer = null;
    renderSession();
    renderFeedback();
    setStatus(`Session ${session.id} ready`);
  } catch (error) {
    showError(error.message);
    setStatus("Ready");
  }
});

els.refreshProgress.addEventListener("click", async () => {
  clearError();
  await refreshProgress();
});

els.answerForm.addEventListener("submit", async (event) => {
  event.preventDefault();
  clearError();
  if (!state.session || !state.selectedQuestion) return;

  setStatus("Submitting answer...");
  els.answerButton.disabled = true;

  try {
    const answer = await request(`/api/v1/diagnostic-sessions/${state.session.id}/answers`, {
      method: "POST",
      body: JSON.stringify({
        question_id: state.selectedQuestion.id,
        answer_text: els.answerText.value,
      }),
    });
    state.lastAnswer = answer;
    renderFeedback();
    await refreshProgress();
    setStatus(`Answer graded as ${answer.grade.overall}`);
  } catch (error) {
    showError(error.message);
    setStatus("Session ready");
  } finally {
    els.answerButton.disabled = !state.selectedQuestion;
  }
});

function renderSession() {
  if (!state.session) return;
  els.title.textContent = `${state.session.target_role} · ${state.session.questions.length} questions`;
  els.questions.className = "question-list";
  els.questions.innerHTML = "";

  state.session.questions.forEach((question) => {
    const button = document.createElement("button");
    button.type = "button";
    button.className = "question-button";
    button.setAttribute("aria-pressed", String(state.selectedQuestion?.id === question.id));
    button.innerHTML = `<span class="question-id">${question.id}</span>${escapeHTML(question.prompt)}`;
    button.addEventListener("click", () => {
      state.selectedQuestion = question;
      els.answerText.value = "";
      renderSession();
      setStatus(`Selected ${question.id}`);
    });
    els.questions.append(button);
  });

  els.answerButton.disabled = !state.selectedQuestion;
}

async function refreshProgress() {
  if (!state.session) return;
  setStatus("Refreshing learning progress...");

  try {
    const userID = encodeURIComponent(state.session.user_id);
    const [memory, readiness, challenge] = await Promise.all([
      request(`/api/v1/learners/${userID}/memory`),
      request(`/api/v1/learners/${userID}/readiness-map`),
      request(`/api/v1/learners/${userID}/next-challenge`),
    ]);
    state.progress = { memory, readiness, challenge };
    renderProgress();
    setStatus("Learning progress updated");
  } catch (error) {
    showError(error.message);
    renderProgress();
  }
}

function renderProgress() {
  els.refreshProgress.disabled = !state.session;
  if (!state.progress) {
    els.progress.className = "feedback empty-state";
    els.progress.textContent = "Answer once to update learner memory and readiness.";
    return;
  }

  const { memory, readiness, challenge } = state.progress;
  const mastery = memory.mastery || [];
  els.progress.className = "feedback";
  els.progress.innerHTML = `
    <section>
      <div class="readiness-value">${readiness.readiness_percentage}%</div>
      <p class="status-line">${escapeHTML(memory.profile.target_role)} readiness</p>
    </section>
    <section>
      <h2>Concept memory</h2>
      <div>${mastery.map((item) => `<span class="concept-pill">${escapeHTML(item.concept.label)} · ${escapeHTML(item.state)}</span>`).join("")}</div>
    </section>
    <section>
      <h2>Next challenge</h2>
      <p class="status-line">${escapeHTML(challenge.concept.label)} · ${escapeHTML(challenge.ladder_level)}</p>
      <p>${escapeHTML(challenge.question)}</p>
    </section>
  `;
}

function renderFeedback() {
  if (!state.lastAnswer) {
    els.feedback.className = "feedback empty-state";
    els.feedback.textContent = "Submit an answer to see grade, evidence, and follow-up.";
    return;
  }

  const grade = state.lastAnswer.grade;
  els.feedback.className = "feedback";
  els.feedback.innerHTML = `
    <div>
      <div class="grade">${escapeHTML(grade.overall)}</div>
      <p class="status-line">${escapeHTML(grade.strengths?.[0] || "Answer was graded.")}</p>
    </div>
    ${scoreRows(grade.scores)}
    ${listBlock("Gaps", grade.gaps)}
    ${followUpBlock(grade.follow_up)}
    ${evidenceBlock(grade.evidence)}
  `;
}

function scoreRows(scores) {
  return Object.entries(scores || {})
    .map(([label, score]) => `
      <div class="metric-row">
        <span>${escapeHTML(label.replaceAll("_", " "))}</span>
        <strong>${score}/4</strong>
      </div>
    `)
    .join("");
}

function listBlock(title, items = []) {
  if (!items.length) return "";
  return `<section><h2>${title}</h2><ul class="small-list">${items.map((item) => `<li>${escapeHTML(item)}</li>`).join("")}</ul></section>`;
}

function followUpBlock(followUp) {
  if (!followUp?.needed) return "";
  return `<section><h2>Follow-up</h2><p class="status-line">${escapeHTML(followUp.question)}</p></section>`;
}

function evidenceBlock(evidence = []) {
  if (!evidence.length) return "";
  return `<section><h2>Evidence</h2><ul class="small-list">${evidence.map((item) => `<li>${escapeHTML(item.quote || item.id)}</li>`).join("")}</ul></section>`;
}

async function request(url, options = {}) {
  const response = await fetch(url, {
    headers: { "Content-Type": "application/json" },
    ...options,
  });
  const body = await response.json();
  if (!response.ok) {
    throw new Error(body.error || `Request failed: ${response.status}`);
  }
  return body;
}

function value(selector) {
  return document.querySelector(selector).value.trim();
}

function setStatus(message) {
  els.status.textContent = message;
}

function showError(message) {
  els.error.textContent = message;
}

function clearError() {
  els.error.textContent = "";
}

function escapeHTML(value) {
  return String(value)
    .replaceAll("&", "&amp;")
    .replaceAll("<", "&lt;")
    .replaceAll(">", "&gt;")
    .replaceAll('"', "&quot;")
    .replaceAll("'", "&#039;");
}