pdga-rating/public/js/chart.js

function createRatingChart(container, history) {
    if (!history || history.length === 0) {
        container.textContent = '';
        var empty = document.createElement('div');
        empty.className = 'loading-chart';
        empty.textContent = 'No rating history available';
        container.appendChild(empty);
        return;
    }

    var W = 880, H = 240;
    var pad = { left: 44, right: 16, top: 20, bottom: 32 };
    var chartW = W - pad.left - pad.right;
    var chartH = H - pad.top - pad.bottom;

    var ratings = history.map(function(h) { return h.rating; });
    var minR = Math.min.apply(null, ratings) - 5;
    var maxR = Math.max.apply(null, ratings) + 5;
    var range = maxR - minR || 1;

    function xOf(i) {
        return pad.left + (i / Math.max(history.length - 1, 1)) * chartW;
    }
    function yOf(r) {
        return pad.top + ((maxR - r) / range) * chartH;
    }

    var pts = history.map(function(h, i) {
        return { x: xOf(i), y: yOf(h.rating), rating: h.rating, date: h.date };
    });

    var linePath = pts.map(function(p, i) {
        return (i === 0 ? 'M' : 'L') + ' ' + p.x.toFixed(1) + ' ' + p.y.toFixed(1);
    }).join(' ');

    var last = pts[pts.length - 1];
    var bottomY = (pad.top + chartH).toFixed(1);
    var areaPath = linePath +
        ' L ' + last.x.toFixed(1) + ' ' + bottomY +
        ' L ' + pad.left.toFixed(1) + ' ' + bottomY + ' Z';

    // Build SVG using DOM API to avoid innerHTML on user-supplied content
    var ns = 'http://www.w3.org/2000/svg';

    function el(tag, attrs) {
        var e = document.createElementNS(ns, tag);
        Object.keys(attrs).forEach(function(k) { e.setAttribute(k, attrs[k]); });
        return e;
    }

    function txt(tag, attrs, text) {
        var e = el(tag, attrs);
        e.textContent = text;
        return e;
    }

    var svg = el('svg', {
        viewBox: '0 0 ' + W + ' ' + H,
        width: '100%',
        style: 'display:block;overflow:visible',
        'aria-hidden': 'true'
    });

    // Grid lines + y-axis labels (4 ticks)
    var tickCount = 4;
    for (var i = 0; i <= tickCount; i++) {
        var gy = pad.top + (i / tickCount) * chartH;
        var gr = Math.round(maxR - (i / tickCount) * range);
        svg.appendChild(el('line', {
            x1: pad.left, y1: gy.toFixed(1),
            x2: pad.left + chartW, y2: gy.toFixed(1),
            stroke: 'var(--line)', 'stroke-width': '1', 'stroke-dasharray': '2 4'
        }));
        svg.appendChild(txt('text', {
            x: pad.left - 8, y: (gy + 4).toFixed(1),
            'text-anchor': 'end', 'font-size': '10',
            'font-family': "'JetBrains Mono', monospace",
            fill: 'var(--ink-3)'
        }, String(gr)));
    }

    // Area fill (8% opacity)
    svg.appendChild(el('path', {
        d: areaPath, fill: 'var(--accent)', 'fill-opacity': '0.08'
    }));

    // Line
    svg.appendChild(el('path', {
        d: linePath, stroke: 'var(--accent)', 'stroke-width': '2',
        fill: 'none', 'stroke-linejoin': 'round', 'stroke-linecap': 'round'
    }));

    // Dots
    pts.forEach(function(p, i) {
        var isLast = i === pts.length - 1;
        if (isLast) {
            svg.appendChild(el('circle', {
                cx: p.x.toFixed(1), cy: p.y.toFixed(1),
                r: '4', fill: 'var(--accent)', stroke: 'var(--paper)', 'stroke-width': '2'
            }));
        } else {
            svg.appendChild(el('circle', {
                cx: p.x.toFixed(1), cy: p.y.toFixed(1),
                r: '3', fill: 'var(--accent)'
            }));
        }
    });

    // X-axis labels (5 evenly spaced)
    var labelCount = Math.min(5, history.length);
    var labelIndices = [];
    if (labelCount <= 1) {
        labelIndices.push(0);
    } else {
        for (var k = 0; k < labelCount; k++) {
            labelIndices.push(Math.round(k * (history.length - 1) / (labelCount - 1)));
        }
    }

    var seen = {};
    labelIndices.forEach(function(idx) {
        if (seen[idx]) return;
        seen[idx] = true;
        var p = pts[idx];
        var d = new Date(history[idx].date);
        var label = d.toLocaleDateString('en-US', { month: 'short', year: '2-digit' });
        svg.appendChild(txt('text', {
            x: p.x.toFixed(1),
            y: (pad.top + chartH + 16).toFixed(1),
            'text-anchor': 'middle', 'font-size': '10',
            'font-family': "'JetBrains Mono', monospace",
            fill: 'var(--ink-3)'
        }, label));
    });

    container.textContent = '';
    container.appendChild(svg);
}