feat(pure): summary with today/week counts and per-day rate

src/pure.js

@@ -65,3 +65,41 @@ export function pruneHistory(entries, now = Date.now()) {
   const cutoff = now - THIRTY_DAYS_MS;
   return entries.filter((e) => e.ts > cutoff);
 }
+
+/**
+ * Summarise training history.
+ *
+ * @param {{ts:number, delta:number}[]} entries
+ * @param {number} [now] Reference time in ms (defaults to Date.now()).
+ * @returns {{trainsToday:number, sevenDayAvgPerDay:number, perDay:number}}
+ */
+export function summary(entries, now = Date.now()) {
+  if (entries.length === 0) {
+    return { trainsToday: 0, sevenDayAvgPerDay: 0, perDay: 0 };
+  }
+
+  const ONE_DAY = MS_PER_DAY;
+  const SEVEN_DAYS = 7 * MS_PER_DAY;
+
+  const todayCutoff = now - ONE_DAY;
+  const weekCutoff = now - SEVEN_DAYS;
+
+  let trainsToday = 0;
+  let trainsWeek = 0;
+  let latestDelta = 0;
+  let latestTs = -Infinity;
+
+  for (const e of entries) {
+    if (e.ts >= todayCutoff) trainsToday++;
+    if (e.ts >= weekCutoff) trainsWeek++;
+    if (e.ts > latestTs) {
+      latestTs = e.ts;
+      latestDelta = e.delta;
+    }
+  }
+
+  const sevenDayAvgPerDay = trainsWeek / 7;
+  const perDay = latestDelta > 0 ? Math.floor(sevenDayAvgPerDay * latestDelta) : 0;
+
+  return { trainsToday, sevenDayAvgPerDay, perDay };
+}

tests/pure.test.js

@@ -1,6 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { parseTarget, computeEstimate, pruneHistory, MS_PER_DAY } from '../src/pure.js';
+import { parseTarget, computeEstimate, pruneHistory, summary, MS_PER_DAY } from '../src/pure.js';
 
 const DAY = MS_PER_DAY;
 const NOW = 1_700_000_000_000; // fixed reference
@@ -94,3 +94,48 @@ test('pruneHistory: does not mutate input', () => {
 test('pruneHistory: empty input', () => {
   assert.deepEqual(pruneHistory([], NOW), []);
 });
+
+test('summary: empty history returns zeros', () => {
+  const s = summary([], NOW);
+  assert.equal(s.trainsToday, 0);
+  assert.equal(s.sevenDayAvgPerDay, 0);
+  assert.equal(s.perDay, 0);
+});
+
+test('summary: counts trains within last 24h', () => {
+  const entries = [
+    { ts: NOW - 1 * 60_000, delta: 100 },   // 1 min ago
+    { ts: NOW - 12 * 3_600_000, delta: 100 }, // 12h ago
+    { ts: NOW - 23 * 3_600_000, delta: 100 }, // 23h ago
+    { ts: NOW - 25 * 3_600_000, delta: 100 }, // 25h ago (not today)
+  ];
+  const s = summary(entries, NOW);
+  assert.equal(s.trainsToday, 3);
+});
+
+test('summary: 7-day average is total/7', () => {
+  // 14 entries in last 7 days (spaced 12h apart, all within window)
+  const entries = [];
+  for (let i = 0; i < 14; i++) {
+    entries.push({ ts: NOW - (i / 2) * DAY, delta: 100 });
+  }
+  const s = summary(entries, NOW);
+  assert.equal(s.sevenDayAvgPerDay, 2);
+});
+
+test('summary: perDay uses most recent delta when available', () => {
+  const entries = [
+    { ts: NOW - 1 * 60_000, delta: 247 },
+    { ts: NOW - 12 * 3_600_000, delta: 300 },
+  ];
+  const s = summary(entries, NOW);
+  // 2 trains in last 7 days → 2/7 avg
+  // perDay = avg * most recent delta = (2/7) * 247 = ~70.57
+  assert.equal(s.perDay, Math.floor((2 / 7) * 247));
+});
+
+test('summary: perDay is 0 when no recent delta', () => {
+  const entries = [{ ts: NOW - 31 * DAY, delta: 100 }];
+  const s = summary(entries, NOW);
+  assert.equal(s.perDay, 0);
+});