gpx-vis/gpx-vis-frontend/js/elevation.js

const Elevation = (() => {
  const CHART_MAX_PTS = 500;
  const PAD = { top: 20, right: 16, bottom: 28, left: 46 };

  let canvas = null;
  let tooltip = null;
  let points = null;    // full-res flat [{lat,lon,ele,time,dist}]
  let chartPts = null;  // downsampled
  let bounds = null;    // computed after draw: {cw,ch,minE,eRange,totDist}

  // ===== Public API =====

  function init() {
    canvas  = document.getElementById('elevation-canvas');
    tooltip = document.getElementById('elevation-tooltip');
    if (!canvas) return;
    canvas.addEventListener('mousemove', onChartMove);
    canvas.addEventListener('mouseleave', onChartLeave);
    window.addEventListener('resize', () => { if (points) raf(draw); });
  }

  function setTrack(pts) {
    points   = pts;
    chartPts = downsample(pts, CHART_MAX_PTS);
    bounds   = null;
    raf(draw);
  }

  function clear() {
    points = chartPts = bounds = null;
    hideTooltip();
    if (canvas) {
      canvas.width = canvas.width; // reset context
    }
  }

  // Called by MapView when hovering a point that belongs to the current track
  function onMapHover(point) {
    if (!bounds || !canvas) return;
    drawIndicator(point);
    const x = PAD.left + (point.dist / bounds.totDist) * bounds.cw;
    positionTooltip(point, x, PAD.top + bounds.ch / 2);
  }

  // Called by MapView when hover leaves the current track
  function onMapLeave() {
    hideTooltip();
    if (bounds) draw();
  }

  // Shared tooltip formatter used by MapView for the Leaflet map tooltip
  function formatTooltip(p) {
    const dist = p.dist >= 1000
      ? (p.dist / 1000).toFixed(2) + ' km'
      : Math.round(p.dist) + ' m';
    let html = `<div><b>Dist:</b> ${dist}</div>`;
    if (p.ele != null) html += `<div><b>Ele:</b> ${Math.round(p.ele)} m</div>`;
    if (p.time) {
      const t = new Date(p.time);
      if (!isNaN(t)) {
        html += `<div><b>Time:</b> ${t.toLocaleTimeString(undefined,
          { hour: '2-digit', minute: '2-digit', second: '2-digit' })}</div>`;
      }
    }
    html += `<div style="color:rgba(255,255,255,0.6)">${p.lat.toFixed(5)}, ${p.lon.toFixed(5)}</div>`;
    return html;
  }

  // ===== Internal =====

  function raf(fn) {
    requestAnimationFrame(() => requestAnimationFrame(fn));
  }

  function downsample(pts, max) {
    if (pts.length <= max) return pts;
    const out = [];
    const step = (pts.length - 1) / (max - 1);
    for (let i = 0; i < max; i++) out.push(pts[Math.round(i * step)]);
    return out;
  }

  // ===== Chart drawing =====

  function draw() {
    if (!canvas || !chartPts || chartPts.length === 0) return;
    const rect = canvas.getBoundingClientRect();
    if (!rect.width || !rect.height) return;

    const dpr = window.devicePixelRatio || 1;
    canvas.width  = rect.width  * dpr;
    canvas.height = rect.height * dpr;
    const ctx = canvas.getContext('2d');
    ctx.scale(dpr, dpr);               // from here on, all coords are CSS pixels
    ctx.clearRect(0, 0, rect.width, rect.height);

    const hasEle = chartPts.some(p => p.ele != null);
    if (!hasEle) {
      ctx.fillStyle = '#95a5a6';
      ctx.font = '11px sans-serif';
      ctx.textAlign = 'center';
      ctx.fillText('No elevation data', rect.width / 2, rect.height / 2);
      bounds = null;
      return;
    }

    const cw = rect.width  - PAD.left - PAD.right;
    const ch = rect.height - PAD.top  - PAD.bottom;
    const eles   = chartPts.map(p => p.ele).filter(e => e != null);
    const minE   = Math.min(...eles);
    const maxE   = Math.max(...eles);
    const eRange = maxE - minE || 1;
    const totDist = chartPts[chartPts.length - 1].dist;

    drawGrid(ctx, rect, cw, ch, minE, maxE, eRange, totDist);
    drawProfile(ctx, cw, ch, minE, eRange, totDist);

    bounds = { cw, ch, minE, maxE, eRange, totDist };
  }

  function drawGrid(ctx, rect, cw, ch, minE, maxE, eRange, totDist) {
    ctx.strokeStyle = '#e8e8e8';
    ctx.lineWidth   = 1;
    ctx.fillStyle   = '#999';
    ctx.font        = '10px sans-serif';

    // Horizontal grid + elevation labels
    for (let i = 0; i <= 4; i++) {
      const y = PAD.top + ch * i / 4;
      ctx.beginPath();
      ctx.moveTo(PAD.left, y);
      ctx.lineTo(PAD.left + cw, y);
      ctx.stroke();
      ctx.textAlign = 'right';
      ctx.fillText(Math.round(maxE - eRange * i / 4) + 'm', PAD.left - 4, y + 3);
    }

    // Distance labels
    ctx.textAlign = 'center';
    for (let i = 0; i <= 5; i++) {
      const x = PAD.left + cw * i / 5;
      const d = totDist * i / 5;
      const label = d >= 1000 ? (d / 1000).toFixed(1) + 'k' : Math.round(d) + 'm';
      ctx.fillText(label, x, rect.height - 5);
    }
  }

  function drawProfile(ctx, cw, ch, minE, eRange, totDist) {
    const toX = p => PAD.left + (p.dist / totDist) * cw;
    const toY = p => PAD.top + ch - ((p.ele - minE) / eRange) * ch;

    // Gradient fill
    const grad = ctx.createLinearGradient(0, PAD.top, 0, PAD.top + ch);
    grad.addColorStop(0, 'rgba(52,152,219,0.55)');
    grad.addColorStop(1, 'rgba(52,152,219,0.07)');

    ctx.beginPath();
    let first = true;
    for (const p of chartPts) {
      if (p.ele == null) continue;
      if (first) { ctx.moveTo(toX(p), toY(p)); first = false; }
      else ctx.lineTo(toX(p), toY(p));
    }
    ctx.lineTo(PAD.left + cw, PAD.top + ch);
    ctx.lineTo(PAD.left, PAD.top + ch);
    ctx.closePath();
    ctx.fillStyle = grad;
    ctx.fill();

    // Profile line
    ctx.beginPath();
    ctx.strokeStyle = '#3498db';
    ctx.lineWidth   = 1.5;
    first = true;
    for (const p of chartPts) {
      if (p.ele == null) continue;
      if (first) { ctx.moveTo(toX(p), toY(p)); first = false; }
      else ctx.lineTo(toX(p), toY(p));
    }
    ctx.stroke();
  }

  // Draw a vertical cursor + dot at the given point (CSS pixel coords)
  function drawIndicator(point) {
    if (!bounds || !canvas) return;
    draw(); // resets canvas and re-applies ctx.scale(dpr,dpr) — use CSS px below

    const { cw, ch, minE, eRange, totDist } = bounds;
    const ctx = canvas.getContext('2d');

    const x = PAD.left + (point.dist / totDist) * cw;
    const y = point.ele != null
      ? PAD.top + ch - ((point.ele - minE) / eRange) * ch
      : PAD.top + ch / 2;

    ctx.save();

    // Vertical dashed line
    ctx.strokeStyle = 'rgba(231,76,60,0.55)';
    ctx.lineWidth   = 1;
    ctx.setLineDash([4, 4]);
    ctx.beginPath();
    ctx.moveTo(x, PAD.top);
    ctx.lineTo(x, PAD.top + ch);
    ctx.stroke();
    ctx.setLineDash([]);

    // Dot
    ctx.fillStyle   = '#e74c3c';
    ctx.strokeStyle = 'white';
    ctx.lineWidth   = 1.5;
    ctx.beginPath();
    ctx.arc(x, y, 4, 0, Math.PI * 2);
    ctx.fill();
    ctx.stroke();

    ctx.restore();
  }

  // ===== Hover =====

  function onChartMove(e) {
    if (!bounds || !chartPts) return;
    const rect = canvas.getBoundingClientRect();
    const x = e.clientX - rect.left;

    if (x < PAD.left || x > PAD.left + bounds.cw) {
      onChartLeave();
      return;
    }

    const dist = ((x - PAD.left) / bounds.cw) * bounds.totDist;

    // Find nearest downsampled point for chart indicator
    const chartPt = findNearestByDist(chartPts, dist);
    // Find nearest full-res point for map marker
    const fullPt  = findNearestByDist(points,   dist);

    if (!chartPt) return;

    drawIndicator(chartPt);
    positionTooltip(chartPt, x, e.clientY - rect.top);

    if (fullPt && typeof MapView !== 'undefined') {
      MapView.showHoverMarker(fullPt.lat, fullPt.lon, fullPt);
    }
  }

  function onChartLeave() {
    hideTooltip();
    if (typeof MapView !== 'undefined') MapView.hideHoverMarker();
    if (bounds) draw();
  }

  function findNearestByDist(pts, targetDist) {
    if (!pts || pts.length === 0) return null;
    let nearest = null, nearestD = Infinity;
    for (const p of pts) {
      const d = Math.abs(p.dist - targetDist);
      if (d < nearestD) { nearestD = d; nearest = p; }
    }
    return nearest;
  }

  function positionTooltip(point, cx, cy) {
    if (!tooltip || !canvas) return;
    tooltip.innerHTML = formatTooltip(point);
    tooltip.classList.add('visible');
    const cRect = canvas.getBoundingClientRect();
    tooltip.style.left = Math.min(cx + 10, cRect.width  - tooltip.offsetWidth  - 4) + 'px';
    tooltip.style.top  = Math.max(4,        cy - tooltip.offsetHeight / 2)           + 'px';
  }

  function hideTooltip() {
    if (tooltip) tooltip.classList.remove('visible');
  }

  return { init, setTrack, clear, formatTooltip, onMapHover, onMapLeave };
})();