/**
 * Chronos-2 Zero-Shot Demo - Frontend
 * Real-time input -> debounce -> fetch forecast -> chart update
 * Tab: Forecast | Compare
 */

(function () {
  const API_BASE = '';

  const tsInput = document.getElementById('ts-input');
  const sampleSelect = document.getElementById('sample-select');
  const predStepsInput = document.getElementById('pred-steps');
  const forecastValue = document.getElementById('forecast-value');
  const forecastRange = document.getElementById('forecast-range');
  const loadingEl = document.getElementById('loading');
  const errorEl = document.getElementById('error');
  const downloadBtn = document.getElementById('download-csv');

  let chart = null;
  let lastResult = null;
  let debounceTimer = null;

  // ---------------------------------------------------------------------------
  // Tabs
  // ---------------------------------------------------------------------------
  function initTabs() {
    const tabBtns = document.querySelectorAll('.tab-btn');
    const tabContents = document.querySelectorAll('.tab-content');

    tabBtns.forEach((btn) => {
      btn.addEventListener('click', () => {
        const tabId = btn.getAttribute('data-tab');
        tabBtns.forEach((b) => b.classList.remove('active'));
        tabContents.forEach((c) => {
          c.classList.toggle('active', c.id === 'tab-' + tabId);
        });
        btn.classList.add('active');
      });
    });
  }
  initTabs();

  // ---------------------------------------------------------------------------
  // Parse
  // ---------------------------------------------------------------------------
  function parseValues(text) {
    if (!text || !text.trim()) return [];
    const parts = text.trim().split(/[\s,;\n]+/);
    const values = [];
    for (const p of parts) {
      const n = parseFloat(p);
      if (!isNaN(n)) values.push(n);
    }
    return values;
  }

  function debounce(fn, ms) {
    return function () {
      clearTimeout(debounceTimer);
      debounceTimer = setTimeout(fn, ms);
    };
  }

  async function fetchForecast(values, predictionLength) {
    const res = await fetch(`${API_BASE}/api/forecast`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ values, prediction_length: predictionLength }),
    });
    if (!res.ok) {
      const err = await res.json().catch(() => ({ detail: res.statusText }));
      const d = err.detail;
      const msg = Array.isArray(d)
        ? d.map((x) => x.msg || JSON.stringify(x)).join('; ')
        : typeof d === 'string'
          ? d
          : JSON.stringify(d || err);
      throw new Error(msg || `HTTP ${res.status}`);
    }
    return res.json();
  }

  function setLoading(loading) {
    loadingEl.style.display = loading ? 'block' : 'none';
    errorEl.style.display = 'none';
  }

  function setError(msg) {
    errorEl.textContent = msg;
    errorEl.style.display = msg ? 'block' : 'none';
    loadingEl.style.display = 'none';
  }

  function updateForecastDisplay(result) {
    downloadBtn.disabled = !result || !result.forecast.length;
    if (!result || !result.forecast.length) {
      forecastValue.textContent = '—';
      forecastRange.textContent = '';
      return;
    }
    const f = result.forecast[0];
    forecastValue.textContent = f.median.toFixed(2);
    forecastRange.textContent = ` (${f.low.toFixed(1)} ~ ${f.high.toFixed(1)})`;
    if (result.forecast.length > 1) {
      forecastRange.textContent += ` · ${result.forecast.length} steps`;
    }
  }

  function updateChart(historical, forecast) {
    const histLabels = (historical || []).map((_, i) => String(i));
    const histData = (historical || []).map((h) => h.value);
    const forecastLabels = (forecast || []).map((f) => String(f.index));
    const forecastMedians = (forecast || []).map((f) => f.median);

    const allLabels = histLabels.concat(forecastLabels);
    const histFull = histData.concat(forecastMedians.map(() => null));
    const fcastFull = histLabels.map(() => null).concat(forecastMedians);

    if (!chart) {
      chart = new Chart(document.getElementById('chart'), {
        type: 'line',
        data: {
          labels: allLabels,
          datasets: [
            {
              label: 'Historical',
              data: histFull,
              borderColor: 'rgb(59, 130, 246)',
              fill: false,
              tension: 0.2,
            },
            {
              label: 'Forecast (median)',
              data: fcastFull,
              borderColor: 'rgb(239, 68, 68)',
              borderDash: [5, 5],
              fill: false,
              tension: 0.2,
            },
          ],
        },
        options: {
          responsive: true,
          maintainAspectRatio: true,
          plugins: { legend: { position: 'top' } },
          scales: {
            x: { title: { display: true, text: 'Index' } },
            y: { title: { display: true, text: 'Value' } },
          },
        },
      });
    } else {
      chart.data.labels = allLabels;
      chart.data.datasets[0].data = histFull;
      chart.data.datasets[1].data = fcastFull;
      chart.update();
    }
  }

  async function triggerForecast() {
    const values = parseValues(tsInput.value);
    const predictionLength = Math.max(1, parseInt(predStepsInput.value, 10) || 1);

    if (values.length === 0) {
      lastResult = null;
      updateForecastDisplay(null);
      updateChart([], []);
      setError('');
      return;
    }

    setLoading(true);
    setError('');

    try {
      const result = await fetchForecast(values, predictionLength);
      lastResult = result;
      updateForecastDisplay(result);
      updateChart(result.historical, result.forecast);
    } catch (err) {
      setError(err.message || '예측 중 오류가 발생했습니다.');
      lastResult = null;
      updateForecastDisplay(null);
      updateChart(
        values.map((v, i) => ({ index: i, value: v })),
        []
      );
    } finally {
      setLoading(false);
    }
  }

  const debouncedForecast = debounce(triggerForecast, 500);

  async function loadSample(name) {
    try {
      const res = await fetch(`${API_BASE}/static/samples/${name}.json`);
      if (!res.ok) throw new Error('Sample not found');
      const data = await res.json();
      const values = data.values || data;
      tsInput.value = Array.isArray(values) ? values.join(', ') : String(values);
      debouncedForecast();
    } catch (err) {
      setError('샘플을 불러올 수 없습니다.');
    }
  }

  function downloadCsv() {
    if (!lastResult || !lastResult.forecast.length) return;
    const headers = ['index', 'median', 'low', 'high'];
    const rows = lastResult.forecast.map((f) => [f.index, f.median, f.low, f.high].join(','));
    const csv = [headers.join(','), ...rows].join('\n');
    const blob = new Blob([csv], { type: 'text/csv' });
    const a = document.createElement('a');
    a.href = URL.createObjectURL(blob);
    a.download = 'chronos2_forecast.csv';
    a.click();
    URL.revokeObjectURL(a.href);
  }

  tsInput.addEventListener('input', debouncedForecast);
  predStepsInput.addEventListener('change', debouncedForecast);

  sampleSelect.addEventListener('change', function () {
    const v = this.value;
    if (v) {
      loadSample(v);
      this.value = '';
    }
  });

  downloadBtn.addEventListener('click', downloadCsv);

  updateForecastDisplay(null);
  updateChart([], []);

  // 페이지 로드 시 GFK 샘플 데이터를 기본값으로 로드
  loadSample('gfk_sample');
})();