// 座標を滑らかにする Chaikin アルゴリズム
  function smoothLineCoordinates(coords, iterations = 3) {
    if (coords.length <= 2) return coords;
    let current = coords;
    for (let it = 0; it < iterations; it++) {
      const smoothed = [current[0]];
      for (let i = 0; i < current.length - 1; i++) {
        const p0 = current[i];
        const p1 = current[i + 1];
        const q = [0.75 * p0[0] + 0.25 * p1[0], 0.75 * p0[1] + 0.25 * p1[1]];
        const r = [0.25 * p0[0] + 0.75 * p1[0], 0.25 * p0[1] + 0.75 * p1[1]];
        smoothed.push(q, r);
      }
      smoothed.push(current[current.length - 1]);
      current = smoothed;
    }
    return current;
  }

  // 2. 外部 JSON の読み込み & MapLibre へのレイヤー登録
  map.on('load', async () => {
    try {
      const response = await fetch('rail_data.json');
      if (!response.ok) throw new Error(`HTTP error! status: ${response.status}`);
      geojsonData = await response.json();

      // 読み込み直後に全線区の座標を平滑化
      geojsonData.features.forEach(f => {
        f.geometry.coordinates = smoothLineCoordinates(f.geometry.coordinates, 3);
      });

      injectCurrentYearDensity();

      map.addSource('railways', {
        type: 'geojson',
        data: geojsonData
      });

      // 路線レイヤー（外枠・ハイライト用）
      map.addLayer({
        id: 'rail-lines-case',
        type: 'line',
        source: 'railways',
        layout: {
          'line-join': 'round',
          'line-cap': 'round'
        },
        paint: {
          'line-color': '#ffffff',
          'line-width': ['interpolate', ['linear'], ['get', 'current_density'],
            0, 4,
            1000, 5,
            4000, 6,
            20000, 8,
            100000, 10
          ],
          'line-opacity': 0.8
        }
      });

      // 路線レイヤー（本体色）
      map.addLayer({
        id: 'rail-lines',
        type: 'line',
        source: 'railways',
        layout: {
          'line-join': 'round',
          'line-cap': 'round'
        },
        paint: {
          'line-color': [
            'step', ['get', 'current_density'],
            '#991b1b', // < 1,000
            1000, '#dc2626', // 1,000 - 2,000
            2000, '#ea580c', // 2,000 - 4,000
            4000, '#ca8a04', // 4,000 - 20,000
            20000, '#16a34a', // 20,000 - 100,000
            100000, '#0284c7'  // >= 100,000
          ],
          'line-width': [
            'interpolate', ['linear'], ['get', 'current_density'],
            0, 2,
            1000, 3,
            4000, 4,
            20000, 5.5,
            100000, 7.5
          ],
          'line-opacity': 0.95
        }
      });

      if (geojsonData.features.length > 0) {
        selectLine(geojsonData.features[0]);
      }

      map.on('click', 'rail-lines', (e) => {
        if (e.features.length > 0) {
          const clickedId = e.features[0].properties.id;
          const target = geojsonData.features.find(f => f.properties.id === clickedId);
          if (target) selectLine(target);
        }
      });

      map.on('mouseenter', 'rail-lines', () => { map.getCanvas().style.cursor = 'pointer'; });
      map.on('mouseleave', 'rail-lines', () => { map.getCanvas().style.cursor = ''; });

    } catch (err) {
      console.error("rail_data.json の読み込みに失敗しました:", err);
      alert("rail_data.json の読み込みに失敗しました。ローカルサーバー経由で開いてください。");
    }
  });