1 files changed, 37 insertions, 0 deletions
diff --git a/viewer/js/profile.js b/viewer/js/profile.js
new file mode 100644
index 0000000..695ba29
--- /dev/null
+++ b/viewer/js/profile.js
@@ -0,0 +1,37 @@
+// profile.js — elevation profile chart model (pure): samples {d_km, z_m, water} → SVG path data + scales
+const PAD = { l: 40, r: 6, t: 8, b: 18 };
+
+export function profileModel(samples, w, h) {
+  const L = samples.at(-1).d_km || 1;
+  const zs = samples.map(s => s.z_m);
+  const lo = Math.min(0, ...zs);
+  const hi = Math.max(lo + 100, 0, ...zs);
+  const X = d => PAD.l + (d / L) * (w - PAD.l - PAD.r);
+  const Y = z => PAD.t + (1 - (z - lo) / (hi - lo)) * (h - PAD.t - PAD.b);
+  const line = samples.map((s, i) => `${i ? 'L' : 'M'}${X(s.d_km).toFixed(1)},${Y(s.z_m).toFixed(1)}`).join('');
+  const area = `${line}L${X(L).toFixed(1)},${Y(lo).toFixed(1)}L${X(0).toFixed(1)},${Y(lo).toFixed(1)}Z`;
+  const half = L / Math.max(1, samples.length - 1) / 2;
+  const water = [];
+  let start = null;
+  samples.forEach((s, i) => {
+    if (s.water && start === null) start = i;
+    const last = i === samples.length - 1;
+    if (start !== null && (!s.water || last)) {
+      const end = s.water ? i : i - 1;
+      water.push([X(Math.max(0, samples[start].d_km - half)), X(Math.min(L, samples[end].d_km + half))]);
+      start = null;
+    }
+  });
+  const xAt = px => ((px - PAD.l) / (w - PAD.l - PAD.r)) * L;
+  return { line, area, water, seaY: Y(0), lo, hi, L, X, Y, xAt };
+}
+
+export function sampleAt(samples, d) {
+  let a = 0, b = samples.length - 1;
+  while (b - a > 1) {
+    const m = (a + b) >> 1;
+    if (samples[m].d_km <= d) a = m;
+    else b = m;
+  }
+  return Math.abs(samples[a].d_km - d) <= Math.abs(samples[b].d_km - d) ? a : b;
+}