better seek bar

src/components/waveformScrubDetents.test.mts

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+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {
+  SCRUB_DETENT_SPACING_DP,
+  SCRUB_TICK_ACTIVATION_DISTANCE_DP,
+  SCRUB_TICK_MIN_INTERVAL_MS,
+  beginScrubDetents,
+  updateScrubDetents,
+} from './waveformScrubDetents.ts';
+
+test('begins silently and stays silent within one detent or while stationary', () => {
+  const initial = beginScrubDetents(4, 120);
+  assert.deepEqual(initial, {
+    detentIndex: 0,
+    lastTickAtMs: null,
+    startPositionDp: 4,
+    activated: false,
+  });
+
+  const movedInside = updateScrubDetents(initial, 11, 120, 1_000);
+  assert.equal(movedInside.shouldTick, false);
+  const held = updateScrubDetents(movedInside.state, 11, 120, 10_000);
+  assert.equal(held.shouldTick, false);
+});
+
+test('keeps tap jitter silent even when it crosses a detent boundary', () => {
+  const initial = beginScrubDetents(11, 120);
+  const jitter = updateScrubDetents(
+    initial,
+    11 + SCRUB_TICK_ACTIVATION_DISTANCE_DP - 1,
+    120,
+    1_000
+  );
+  assert.equal(jitter.state.detentIndex, 1);
+  assert.equal(jitter.state.activated, false);
+  assert.equal(jitter.shouldTick, false);
+
+  const held = updateScrubDetents(jitter.state, 16, 120, 10_000);
+  assert.equal(held.shouldTick, false);
+});
+
+test('emits one step whenever slow movement crosses a spatial detent', () => {
+  const initial = beginScrubDetents(0, 120);
+  const first = updateScrubDetents(initial, SCRUB_DETENT_SPACING_DP, 120, 1_000);
+  assert.equal(first.shouldTick, true);
+  const second = updateScrubDetents(
+    first.state,
+    SCRUB_DETENT_SPACING_DP * 2,
+    120,
+    1_000 + SCRUB_TICK_MIN_INTERVAL_MS
+  );
+  assert.equal(second.shouldTick, true);
+});
+
+test('rate-limits fast crossings without queuing a catch-up tick', () => {
+  const initial = beginScrubDetents(0, 120);
+  const first = updateScrubDetents(initial, SCRUB_DETENT_SPACING_DP, 120, 1_000);
+  const skipped = updateScrubDetents(
+    first.state,
+    SCRUB_DETENT_SPACING_DP * 3,
+    120,
+    1_020
+  );
+
+  assert.equal(skipped.shouldTick, false);
+  assert.equal(skipped.state.detentIndex, 3);
+
+  const heldAfterLimit = updateScrubDetents(
+    skipped.state,
+    SCRUB_DETENT_SPACING_DP * 3,
+    120,
+    2_000
+  );
+  assert.equal(heldAfterLimit.shouldTick, false);
+
+  const nextMovement = updateScrubDetents(
+    heldAfterLimit.state,
+    SCRUB_DETENT_SPACING_DP * 4,
+    120,
+    2_001
+  );
+  assert.equal(nextMovement.shouldTick, true);
+});
+
+test('direction reversals tick only when they cross a different detent', () => {
+  const initial = beginScrubDetents(30, 120);
+  const forward = updateScrubDetents(initial, 48, 120, 1_000);
+  assert.equal(forward.shouldTick, true);
+
+  const sameDetent = updateScrubDetents(forward.state, 49, 120, 1_100);
+  assert.equal(sameDetent.shouldTick, false);
+
+  const reverse = updateScrubDetents(sameDetent.state, 35, 120, 1_100);
+  assert.equal(reverse.shouldTick, true);
+});
+
+test('clamps out-of-bounds and invalid positions to the waveform', () => {
+  const beforeStart = beginScrubDetents(-100, 120);
+  assert.equal(beforeStart.detentIndex, 0);
+
+  const pastEnd = updateScrubDetents(beforeStart, 999, 120, 1_000);
+  assert.equal(pastEnd.state.detentIndex, Math.floor(120 / SCRUB_DETENT_SPACING_DP));
+  assert.equal(pastEnd.shouldTick, true);
+
+  const invalid = beginScrubDetents(Number.NaN, 0);
+  assert.deepEqual(invalid, {
+    detentIndex: 0,
+    lastTickAtMs: null,
+    startPositionDp: 0,
+    activated: false,
+  });
+});