feat: add the org-drill statistics dashboard renderer

Step 1 shipped the session-log data layer. This is the renderer on top of it.

org-drill-statistics opens a read-only dashboard with five sections: an overview (card counts plus a last-session recap), trends (reviews-per-day and pass-rate-per-day quadrant-block sparklines over the trend window, plus a 12-week table), a quality histogram, a needs-attention view (leech candidates, long-overdue, and forgotten-new cards), and a 7-day forecast counted from SCHEDULED dates. A buffer-wide filter (scope, range, algorithm) sits in the header and cycles with s/r/a. The other keys are q to bury, g to refresh, e for the CSV-export hook that lands next, and RET to follow the card link at point.

The aggregation math lives in pure helpers (day-bucketing, sparkline scaling, weekly aggregates, the histogram, the attention selectors, forecast bucketing). The render helpers are thin string formatters over them, so the logic is unit-tested independently of the UI. New defcustoms tune the views: org-drill-statistics-trend-days, -forecast-days, -attention-row-limit, and -leech-quality-threshold.

I added require 'calendar for the Monday week-start arithmetic in the weekly aggregates. CSV export and the manual and README entries are the step-3 follow-on.

1 files changed, 111 insertions, 0 deletions

diff --git a/tests/test-org-drill-statistics-reviews-by-day.el b/tests/test-org-drill-statistics-reviews-by-day.el
new file mode 100644
index 0000000..94b5aa2
--- /dev/null
+++ b/tests/test-org-drill-statistics-reviews-by-day.el
@@ -0,0 +1,111 @@
+;;; test-org-drill-statistics-reviews-by-day.el --- Tests for reviews-by-day statistics  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; ERT tests for the org-drill statistics dashboard reviews-by-day block.
+
+;;; Code:
+
+(require 'ert)
+(require 'org-drill)
+(require 'cl-lib)
+(require 'org)
+
+;; Shared fixture: build a session record whose start day is a fixed
+;; offset from today, so `org-drill-statistics--record-day' maps it
+;; back to the intended absolute day without depending on a literal
+;; date.  The start-time is noon local time on that calendar day, which
+;; keeps `time-to-days' off any DST or midnight boundary.
+
+(defun org-drill-statistics-test--record-at (day-offset n-qualities)
+  "Build a session record starting DAY-OFFSET days before today.
+The start-time is noon local time on that calendar day, so
+`org-drill-statistics--record-day' maps it back to the intended day.
+N-QUALITIES sets the length of the qualities vector, the review count
+the record contributes; 0 yields an empty vector."
+  (let* ((target-day (- (org-drill-statistics--today-day) day-offset))
+         (greg (calendar-gregorian-from-absolute target-day))
+         (ts (encode-time 0 0 12 (nth 1 greg) (nth 0 greg) (nth 2 greg))))
+    (make-org-drill-session-record
+     :start-time (float-time ts)
+     :qualities (make-vector n-qualities 3))))
+
+;; Normal cases
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-normal-counts-per-day ()
+  "Reviews land in the correct oldest-to-newest slots by start day."
+  (let ((v (org-drill-statistics--reviews-by-day
+            (list (org-drill-statistics-test--record-at 0 2)
+                  (org-drill-statistics-test--record-at 1 3)
+                  (org-drill-statistics-test--record-at 6 1))
+            7)))
+    (should (= (length v) 7))
+    (should (= (aref v 6) 2))
+    (should (= (aref v 5) 3))
+    (should (= (aref v 0) 1))
+    (should (= (apply #'+ (append v nil)) 6))))
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-normal-same-day-accumulates ()
+  "Multiple records on the same day sum their quality counts."
+  (let ((v (org-drill-statistics--reviews-by-day
+            (list (org-drill-statistics-test--record-at 0 2)
+                  (org-drill-statistics-test--record-at 0 3))
+            3)))
+    (should (= (aref v 2) 5))))
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-normal-default-days ()
+  "Omitting DAYS uses `org-drill-statistics-trend-days' for the length."
+  (let ((org-drill-statistics-trend-days 30))
+    (should (= (length (org-drill-statistics--reviews-by-day nil)) 30))))
+
+;; Boundary cases
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-boundary-empty-log ()
+  "An empty log yields an all-zero vector of the requested length."
+  (let ((v (org-drill-statistics--reviews-by-day nil 5)))
+    (should (= (length v) 5))
+    (should (= (apply #'+ (append v nil)) 0))))
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-boundary-single-day ()
+  "DAYS of 1 yields a one-slot vector holding today's count."
+  (let ((v (org-drill-statistics--reviews-by-day
+            (list (org-drill-statistics-test--record-at 0 4)) 1)))
+    (should (= (length v) 1))
+    (should (= (aref v 0) 4))))
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-boundary-edges-of-window ()
+  "The oldest in-window day fills slot 0; one day older is dropped."
+  (let ((v (org-drill-statistics--reviews-by-day
+            (list (org-drill-statistics-test--record-at 6 2)
+                  (org-drill-statistics-test--record-at 7 9))
+            7)))
+    (should (= (aref v 0) 2))
+    (should (= (apply #'+ (append v nil)) 2))))
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-boundary-empty-qualities ()
+  "A record with an empty qualities vector contributes zero."
+  (let ((v (org-drill-statistics--reviews-by-day
+            (list (org-drill-statistics-test--record-at 0 0)) 3)))
+    (should (= (apply #'+ (append v nil)) 0))))
+
+;; Error cases
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-error-future-record-ignored ()
+  "A record dated in the future falls outside the window and is ignored."
+  (let ((v (org-drill-statistics--reviews-by-day
+            (list (org-drill-statistics-test--record-at -3 5)) 7)))
+    (should (= (apply #'+ (append v nil)) 0))))
+
+(ert-deftest test-org-drill-statistics-reviews-by-day-error-nonpositive-days-clamped ()
+  "DAYS of 0 or negative is clamped to a single today slot."
+  (let ((v0 (org-drill-statistics--reviews-by-day
+             (list (org-drill-statistics-test--record-at 0 2)) 0))
+        (vn (org-drill-statistics--reviews-by-day
+             (list (org-drill-statistics-test--record-at 0 3)) -5)))
+    (should (= (length v0) 1))
+    (should (= (aref v0 0) 2))
+    (should (= (length vn) 1))
+    (should (= (aref vn 0) 3))))
+
+(provide 'test-org-drill-statistics-reviews-by-day)
+
+;;; test-org-drill-statistics-reviews-by-day.el ends here