Stats: GitHub-style watch-time heatmap

- api/stats gains by_day: local-date -> seconds (same watch-time
  heuristic as by_weekday)
- ?stats renders a Mon..Sun x week grid (30d window, matches the
  page header) with 4 intensity levels + tooltip per cell + legend;
  replaces the by-weekday bar chart the heatmap subsumes
- test_stats covers by_day (sums, slug-scoped, empty case)

server/app.py

@@ -281,6 +281,7 @@ def api_stats(request: Request, days: int = Query(30, ge=1, le=365),
     # viewing; a backward jump >60s within an ep counts as a rewatch
     eps = {}
     watch_sec = [0.0] * 7  # Mon..Sun
+    by_day = {}  # local YYYY-MM-DD -> seconds
     for ts, payload in positions:
         e = json.loads(payload)
         k = (str(e.get("slug_id")), e.get("season_id"), e.get("ep_id"))
@@ -299,9 +300,13 @@ def api_stats(request: Request, days: int = Query(30, ge=1, le=365),
         if e.get("total"):
             s["total"] = e["total"]
         if s["pos"] is not None and 0 < p - s["pos"] <= 90:
-            s["secs"] += p - s["pos"]
-            s["eng" if e.get("lang") == "eng" else "jpn"] += p - s["pos"]
-            watch_sec[datetime.fromtimestamp(ts).weekday()] += p - s["pos"]
+            d = p - s["pos"]
+            s["secs"] += d
+            s["eng" if e.get("lang") == "eng" else "jpn"] += d
+            dt = datetime.fromtimestamp(ts)
+            watch_sec[dt.weekday()] += d
+            k = dt.strftime("%Y-%m-%d")
+            by_day[k] = by_day.get(k, 0) + d
         elif s["pos"] is not None and p < s["pos"] - 60:
             s["rewinds"] += 1
         s["pos"] = p
@@ -362,6 +367,7 @@ def api_stats(request: Request, days: int = Query(30, ge=1, le=365),
         "plays": len(plays),
         "errors": n_errors,
         "by_weekday": [int(x) for x in watch_sec],  # seconds, Mon..Sun
+        "by_day": {k: int(v) for k, v in by_day.items()},  # seconds per local day
         "top_anime": top,
         "top_searches": [q for q, _ in Counter(searches).most_common(5) if q],
         "sub_dub": {"jpn": plays_by_lang.get("jpn", 0), "eng": plays_by_lang.get("eng", 0)},

static/app.js

@@ -482,24 +482,44 @@ function histBoard(items, limit = 0) {
   return [chips, grid];
 }
 
+function heatMap(byDay, days) {
+  const today = new Date(); today.setHours(12, 0, 0, 0);
+  const win = new Date(today); win.setDate(win.getDate() - (days - 1));
+  const start = new Date(win);
+  start.setDate(start.getDate() - (start.getDay() + 6) % 7);  // back to Monday
+  const max = Math.max(1, ...Object.values(byDay || {}));
+  const box = el("div", "heat");
+  for (let d = new Date(start); d <= today; d.setDate(d.getDate() + 1)) {
+    const k = `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, "0")}-${String(d.getDate()).padStart(2, "0")}`;
+    const v = (byDay || {})[k] || 0;
+    const c = el("i");
+    if (d < win) c.className = "none";
+    else if (v) {
+      c.className = "l" + Math.min(4, Math.ceil(v / max * 4));
+      c.title = k + " \u00b7 " + fmtMin(v / 60);
+    }
+    box.append(c);
+  }
+  const lg = el("div", "heat-lg");
+  lg.append(el("span", "muted", "less"));
+  for (const cls of ["", "l1", "l2", "l3", "l4"]) {
+    const s = el("i");
+    if (cls) s.className = cls;
+    lg.append(s);
+  }
+  lg.append(el("span", "muted", "more"));
+  return [box, lg];
+}
+
 async function showStats() {
   skel(5);
   const d = await api("/api/stats?days=30");
   main.innerHTML = "";
   main.append(el("h2", null, "Stats \u2014 last 30 days"));
   main.append(statsCards(d));
-  const WD = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"];
-  const mx = Math.max(1, ...d.by_weekday);
-  const wk = el("div", "wk");
-  d.by_weekday.forEach((s, i) => {
-    const col = el("div", "wk-col");
-    const b = el("div", "wk-bar");
-    b.style.height = Math.max(3, Math.round(s / mx * 50)) + "px";
-    b.title = fmtMin(s / 60);
-    col.append(b, el("div", "wk-day", WD[i]));
-    wk.append(col);
-  });
-  main.append(wk);
+  const hm = el("section", null);
+  hm.append(el("h2", null, "Watch time by day"), ...heatMap(d.by_day, d.days));
+  main.append(hm);
   const ta = topAnime(d);
   if (ta) main.append(ta);
   if (d.top_searches.length) {

static/style.css

@@ -56,10 +56,14 @@ h2 { margin: 0.4rem 0; }
 .grid.stats { grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); }
 .card.stat { padding: .8rem; gap: .2rem; }
 .stat-value { font-size: 1.3rem; font-weight: 700; }
-.wk { display: flex; gap: .5rem; align-items: flex-end; margin: .4rem 0 .8rem; }
-.wk-col { display: flex; flex-direction: column; align-items: center; gap: .2rem; }
-.wk-bar { width: 26px; background: var(--acc); border-radius: 4px; }
-.wk-day { font-size: .7rem; color: var(--muted); }
+.heat { display: grid; grid-auto-flow: column; grid-template-rows: repeat(7, 11px); gap: 3px; width: fit-content; margin: .5rem 0 .3rem; }
+.heat i, .heat-lg i { width: 11px; height: 11px; border-radius: 2px; background: var(--bd); }
+.heat i.none { background: transparent; }
+.heat i.l1, .heat-lg i.l1 { background: color-mix(in srgb, var(--acc) 30%, var(--bd)); }
+.heat i.l2, .heat-lg i.l2 { background: color-mix(in srgb, var(--acc) 55%, var(--bd)); }
+.heat i.l3, .heat-lg i.l3 { background: color-mix(in srgb, var(--acc) 78%, var(--bd)); }
+.heat i.l4, .heat-lg i.l4 { background: var(--acc); }
+.heat-lg { display: flex; align-items: center; gap: 3px; font-size: .75rem; color: var(--muted); }
 .chip { font-size: .7rem; padding: .1rem .5rem; border-radius: 99px; border: 1px solid var(--bd);
   color: var(--muted); white-space: nowrap; }
 .chip.on { color: var(--acc); border-color: var(--acc); }

tests/test_api.py

@@ -198,6 +198,7 @@ def test_stats(base=BASE):
     assert d["days_active"] == 1 and d["best_streak"] == 1
     assert d["on_hold"] == 0
     assert sum(d["by_weekday"]) == 250  # seconds, Mon..Sun
+    assert sum(d["by_day"].values()) == 250 and all(isinstance(v, int) and v > 0 for v in d["by_day"].values())
     a0 = d["top_anime"][0]
     assert a0["title"] == "Stat Show" and a0["status"] == "ongoing", a0
     assert a0["cur_ep"] == "2" and a0["total"] == 24 and a0["poster"] == "https://p/1.jpg"
@@ -207,8 +208,9 @@ def test_stats(base=BASE):
     # slug filter scopes to one anime
     ds = _json("GET", "/api/stats?days=7&slug=stat-a", jar=jar, base=base)
     assert len(ds["top_anime"]) == 1 and ds["watch_minutes"] == 4
+    assert sum(ds["by_day"].values()) == 250
     dn = _json("GET", "/api/stats?days=7&slug=none", jar=jar, base=base)
-    assert dn["top_anime"] == [] and dn["watch_minutes"] == 0
+    assert dn["top_anime"] == [] and dn["watch_minutes"] == 0 and dn["by_day"] == {}
     # per-user isolation: alice never watched stat-a
     a = login("alice", "alicepw12345", base)
     da = _json("GET", "/api/stats?days=7", jar=a, base=base)