#+TITLE: Comprehensive Statistics Dashboard for org-drill — v0 design spec
#+AUTHOR: Craig Jennings
#+DATE: 2026-05-27

* Status

*Ratified 2026-05-27* — all 10 open decisions accepted as recommended.
The companion todo entry is =todo.org=:20 [#A] "Comprehensive
Statistics Dashboard".  No implementation has started; the spec is now
the implementation gate.

See =Ratified decisions= at the bottom of this file for the locked
choice on each question; inline =Decided:= blocks repeat the choice
next to the section it affects.

* Context and motivation

org-drill's end-of-session report is =org-drill-final-report=
(=org-drill.el=:3128) — a minibuffer prompt with the pass percentage,
qualities histogram, and the new/mature/failed counts for the *single
just-completed session*.  Nothing about that report persists.  Once the
user presses a key to dismiss it, the only retained learning data is
what each card carries in its own =DRILL_*= properties.

The currently-retained per-card data is real and usable:

| Property | Source |
|----------+--------|
| =DRILL_LAST_INTERVAL= | scheduler output, updated every review |
| =DRILL_REPEATS_SINCE_FAIL= | review counter resetting on a lapse |
| =DRILL_TOTAL_REPEATS= | lifetime review count for the card |
| =DRILL_FAILURE_COUNT= | lifetime lapses |
| =DRILL_AVERAGE_QUALITY= | running mean of the 0–5 quality scale |
| =DRILL_EASE= | SM-family easiness factor |
| =DRILL_LAST_QUALITY= | quality at the most recent review |
| =DRILL_LAST_REVIEWED= | inactive timestamp of the most recent review |
| =DATE_ADDED= | inactive timestamp of card creation |

What's missing is the *temporal axis*: there's no record that the user
reviewed N cards on a given day, or that the pass percentage trended
upward over the last month, or that a particular card has been failed
three times in the last two weeks.  Those questions need a per-review
or per-session event log that survives Emacs restarts.

This spec sketches a dashboard that combines (a) per-card aggregates
read live from existing properties (no new storage) with (b) a new
persisted session/review history (org-persist, separate file) that
gives the time-series view.

* Goals

- New command =org-drill-statistics= opens an interactive dashboard
  buffer summarizing review history across all known drill files.
- Per-card aggregates read live from the existing =DRILL_*= properties
  — no migration, no new per-card properties.
- A new persisted session log records, at the end of every session,
  what landed (date, files scoped, cards reviewed, qualities histogram,
  duration, pass percentage).  Survives Emacs restarts.
- Dashboard renders trends, distributions, and "needs attention" lists
  by reading the session log + the per-card properties.
- CSV export for users who want to bring the data into a spreadsheet
  or a notebook.
- No-op for users who don't open the dashboard — collection cost on
  session end is bounded (single =persist-save= write), and the
  dashboard command is lazy-loaded.

* Non-goals (v1)

- *No graphical charting.*  The dashboard renders in plain org-mode
  text — tables, unicode-block sparklines, and minibuffer summaries.
  A Vega/SVG/PNG output stays out of v1; users who want charts use
  CSV export.
- *No per-review event log.*  The persisted record is per-session, not
  per-card-review.  A full per-review log is more expensive to write,
  more expensive to read, and crosses the line into "we are now a
  learning-analytics platform."  Per-card lifetime aggregates already
  cover most card-level questions.
- *No multi-machine sync.*  The persist file is local; users who want
  cross-machine continuity sync it themselves (org-roam-style,
  Syncthing, whatever).  Defining a sync protocol is out of scope.
- *No retroactive backfill.*  Sessions before this feature lands have
  no history; the dashboard starts from the first session after the
  upgrade.  Per-card properties carry their own retroactive baseline.
- *No forecasting.*  "How many cards will be due tomorrow" is one of
  the dashboard's panels (cheap — sum over SCHEDULED dates), but
  predictive forecasting of retention or workload is FSRS territory
  and stays there.

* Data model

** Live (no new storage)

Read at dashboard-open time, no persistence:

- Per-card aggregates by walking =org-map-entries= over the user's
  configured =org-drill-scope= or an explicit scope argument.  For each
  drill entry, the existing accessors (=org-drill-entry-total-repeats=,
  =-failure-count=, =-average-quality=, =-last-reviewed=, =-last-interval=,
  =-ease=, =-last-quality=, =-days-since-creation=) yield the per-card
  view without touching disk beyond reading the file.
- Card status counts (new / young-mature / old-mature / overdue /
  lapsed / due-tomorrow) by reusing =org-drill-entry-status= over the
  scope.  This is what the session opener already does in =org-drill=
  for the initial counts.

** Persisted (new storage)

A single new persisted variable, the session log:

#+begin_src elisp
(persist-defvar org-drill-session-log nil
  "List of completed-session records, newest first.

Each entry is an `org-drill-session-record' struct.")
#+end_src

=org-drill-session-record= is a =cl-defstruct=:

| Slot | Type | Meaning |
|------+------+---------|
| =start-time= | float | =float-time= at session start |
| =end-time= | float | =float-time= at session end |
| =scope= | symbol or list | =org-drill-scope= value at session start |
| =algorithm= | symbol | =org-drill-spaced-repetition-algorithm= at start |
| =qualities= | vector of int | every quality 0–5 entered, in order |
| =pass-percent= | int | qualities > =org-drill-failure-quality=, / total |
| =new-count= | int | size of =(oref session new-entries)= at end |
| =mature-count= | int | =young-mature= + =old-mature= entries at end |
| =failed-count= | int | =failed-entries= at end |
| =cram-mode= | bool | =cram-mode= at session start |

A single record is small (a few hundred bytes).  At one session per
day, the log holds a year of history in well under 100 KB.  At three
sessions per day for ten years, still under 4 MB.  No pruning needed
for v1.

=Decided:= persistence shape = =persist-defvar=.  Integrates with the
=persist= dependency already in =Package-Requires=, lives at
=~/.emacs.d/persist/org-drill-session-log= by default, mirrors the
=org-drill-sm5-optimal-factor-matrix= precedent including its
=condition-case= wrapper for corrupt-load recovery.  Plain elisp file
and org-mode log file declined — the former is what =persist-defvar=
already is under the hood, the latter trades structured I/O for
parse-and-rewrite failure modes.

=Decided:= corrupted-load recovery = log a single warning, start with
a fresh empty log, rename the corrupt file to =.corrupt-YYYY-MM-DD=
before next save so it isn't overwritten.  Mirrors the SM5-matrix
path verbatim.  History loss is bounded; the precedent makes this
consistent.

** Out-of-scope storage

Explicit non-storage to keep scope tight:

- No per-review event log (a row per card-rating).
- No per-card review history (a list of past timestamps + qualities
  per card).  =DRILL_AVERAGE_QUALITY= and =DRILL_LAST_REVIEWED= cover
  the dashboard's needs; full per-card history is what FSRS would
  need, and FSRS owns that question.
- No per-deck (per-file) aggregate cache.  Walking org files on
  dashboard open is fast enough for the file counts org-drill users
  actually have; if a user has 10 000 files this becomes an issue —
  cross that bridge if it shows up.

* UI shell

The dashboard is a single command =org-drill-statistics= that opens a
read-only org-mode buffer named =*Org Drill Statistics*= with the
sections below.  =Decided:= keymap = =q= bury, =g= refresh, =e=
export-csv, =s= scope, =r= range, =a= algorithm-filter, =RET= follow
the card link at point.  None conflict with read-only org-mode
bindings.

** Section 1 — Overview

A four-column summary table:

#+begin_example
| Total cards | New | Mature | Lapsed |
|-------------+-----+--------+--------|
|         412 |  18 |    367 |     27 |
#+end_example

Plus a one-line "last session" recap reading the most recent record
from =org-drill-session-log= (date, duration, cards reviewed, pass %).

** Section 2 — Trends

Two unicode-block sparklines:

- Reviews per day (last 90 days).  X axis = day, Y axis = card count.
- Pass rate per day (last 90 days).  Same X axis, Y axis = 0..100.

Range and bar count are defcustoms.  Default 90 days = roughly a
quarter, fits on one line at 1 cell/day.

Below the sparklines, a small table of weekly aggregates for the last
12 weeks (reviews, pass %, average duration).

=Decided:= sparkline character set = quadrant blocks (▁▂▃▄▅▆▇█),
8 levels.  Emacs renders them fine by default; users on a font without
them are rare enough to handle by documentation rather than a runtime
fallback.

** Section 3 — Distribution

Quality histogram across all sessions in the log (or scoped — see the
range filter below).  A horizontal bar per quality 0..5 with the
absolute count and the percentage.

** Section 4 — Needs attention

Three tables:

- *Leech candidates* — cards with =DRILL_FAILURE_COUNT= ≥
  =org-drill-leech-failure-threshold= and =DRILL_AVERAGE_QUALITY= below
  =org-drill-statistics-leech-quality-threshold= (=Decided:= default
  *2.5*, below the Hard boundary of 3).  Link to card.
- *Long-overdue* — cards with =DRILL_LAST_REVIEWED= ≥
  =org-drill-lapse-threshold-days= ago.  Sorted most-overdue first.
- *Forgotten new* — cards with =DATE_ADDED= ≥ 14 days ago but
  =DRILL_TOTAL_REPEATS= = 0 (or absent).  Useful for catching cards
  that never got into rotation.

Each table caps at =org-drill-stats-attention-row-limit= rows
(defcustom, default 10) with a "+N more" footer.

** Section 5 — Forecast

A one-line table for the next 7 days:

#+begin_example
| Today | +1 | +2 | +3 | +4 | +5 | +6 |
|-------+----+----+----+----+----+----+
|    34 | 18 | 22 |  9 | 41 | 12 |  6 |
#+end_example

Computed from SCHEDULED timestamps across the scope.  No prediction —
just count of cards already scheduled for each day.

** Range filter

A line at the top of the buffer carrying the active filters:

#+begin_example
Scope: file (~/notes/drill.org)    Range: last 90d    Algorithm: simple8
#+end_example

Filters are interactive at the buffer header (=s= cycles scope, =r=
cycles range, =a= filters algorithm).  Defaults: =org-drill-scope=, "last
90d", "all algorithms".

=Decided:= single buffer-wide filter for v1.  Per-section filters
multiply the UI surface and most users want the same window across
sections.

* Export

=M-x org-drill-statistics-export-csv= writes one CSV per requested
view to a user-chosen directory:

- =sessions.csv= — one row per session record in the log.  Columns
  match the struct slots.
- =cards.csv= — one row per drill entry in the active scope, with
  every =DRILL_*= property plus the computed status.
- =daily.csv= — one row per day in the active range, with reviews,
  passes, fails, pass-percent, duration-minutes.

=Decided:= column delimiter = =,= (CSV) with proper quoting via
=csv-mode='s writer if available, else a hand-rolled =csv-quote=
helper.  Users who want TSV can run a one-line sed pipe.

* Performance

The expensive paths and their bounds:

| Path | Cost | Mitigation |
|------+------+------------|
| Session log save | one =persist-save= per session | already wrapped in =condition-case=; cost is a few KB write |
| Scope walk on dashboard open | =org-map-entries= over scope | same cost as a session open; cached for the dashboard's lifetime, refreshes on =g= |
| CSV export | one walk + one file write | one-off; user-triggered |
| Sparkline rendering | bucket the in-memory log by day | log is bounded; bucket-by-day is linear in log length |

The dashboard does *not* run at session open or close — only when the
user invokes =M-x org-drill-statistics=.  Session-end pays one =persist-save=
write.  Idle Emacs pays nothing.

=Decided:= sync dashboard open for v1.  =org-map-entries= over a
typical scope is well under a second.  Async refresh
(=run-with-idle-timer=, status line in the buffer) is a follow-on
ticket if anyone reports >2 s on a large scope.

* Integration points

** New code

- =org-drill-session-record= struct (=cl-defstruct=).
- =org-drill-session-log= persistent variable.
- =org-drill-record-session= — called once from the end-of-session
  finalizer (=org-drill-finalize-session= or wherever
  =org-drill-final-report= currently sits) when the session was not
  aborted.  Appends a record, =persist-save='s the log.
- =org-drill-statistics= — interactive command, opens the dashboard.
- =org-drill-statistics-mode= — minor-mode-like keymap on top of an
  org-mode buffer (=q g e s r a=).
- =org-drill-statistics--render-*= — one helper per section (overview,
  trends, distribution, attention, forecast).
- =org-drill-statistics-export-csv= — interactive command.

** Existing code touched

- =org-drill-final-report= grows a single call to =org-drill-record-session=
  before the read-char-exclusive dismisses the report (so the record
  lands even if the user dismisses immediately).
- A defcustom group =org-drill-statistics= added as a sibling group
  next to =org-drill-session= (=Decided:= sibling, not nested — the
  dashboard isn't session-state and a separate group keeps Customize's
  tree readable).

** Aborted-session handling

A session ended via =C-g= or quit doesn't reach =org-drill-final-report=.
=Decided:= record nothing for these — an =unwind-protect= path to
salvage partial sessions is deferred.  The "abort discards" semantics
matches =org-drill-on-timeout-action= =discard-current= already, and a
partial record's pass percentage misrepresents what the user
experienced.

* Defcustoms (proposed list)

#+begin_src elisp
(defcustom org-drill-statistics-trend-days 90
  "Number of days the trends section spans.")

(defcustom org-drill-statistics-forecast-days 7
  "Number of days ahead the forecast section spans.")

(defcustom org-drill-statistics-attention-row-limit 10
  "Maximum rows in each `Needs attention' table.")

(defcustom org-drill-statistics-leech-quality-threshold 2.5
  "Cards with `DRILL_AVERAGE_QUALITY' below this and at least
`org-drill-leech-failure-threshold' failures appear in `Leech candidates'.")

(defcustom org-drill-statistics-export-directory
  (expand-file-name "org-drill-stats/" user-emacs-directory)
  "Default directory for CSV exports.")
#+end_src

* Test strategy

Three test files, matching the existing file-per-area convention:

1. =tests/test-org-drill-session-record.el= — struct construction,
   round-trip through =persist-save=/=persist-load=, log appending,
   newest-first ordering, corrupted-load recovery.
2. =tests/test-org-drill-statistics-aggregates.el= — given a fixture
   session log + a fixture org file with known =DRILL_*= properties,
   each of the dashboard's section-render helpers produces the
   expected table.  Aggregation math (pass %, weekly buckets,
   sparkline buckets) is tested here with deterministic input.
3. =tests/test-org-drill-statistics-integration.el= — end-to-end:
   simulate three completed sessions via =org-drill-record-session=
   against a fixture file, open the dashboard, assert the buffer
   contents and the export-CSV output.

Normal / Boundary / Error per public function on the helpers.
Boundary cases worth pinning: empty log (no sessions yet), single
session, range filter that selects zero days, scope that contains
zero drill entries, the day-bucket histogram on the day-boundary
edge (a session that crosses midnight).

* Effort estimate

Multi-day, plausibly spanning sessions:

- Session record + persist round-trip + recording hook: 0.5 day.
- Dashboard renderer (5 sections) + minor-mode keymap + range filter:
  1.5 days.  Each section is a small helper; the time goes to layout
  polish and the sparkline math.
- CSV export: 0.5 day.
- Test coverage at parity (the three files above, ~40 tests): 1 day.
- Documentation (manual entry, README option list, defcustom
  docstrings, this spec ratified): 0.5 day.

Realistic: a session for the persist + recording layer with full
tests, a session for the dashboard renderer, a follow-up session for
the export + docs + polish.

* Ratified decisions (2026-05-27)

All 10 open questions resolved as recommended.  Implementation can
proceed against this spec.

| # | Question | Resolution |
|---+----------+------------|
| 1 | Persistence shape | =persist-defvar=, mirroring the SM5 matrix |
| 2 | Corrupted-load recovery | warn, fresh-start, rename to =.corrupt-YYYY-MM-DD= |
| 3 | Sparkline character set | quadrant blocks (▁▂▃▄▅▆▇█) |
| 4 | Filter scope | single buffer-wide filter |
| 5 | CSV delimiter | =,= with proper quoting |
| 6 | Dashboard-open mode | sync |
| 7 | Aborted-session recording | record nothing; =unwind-protect= deferred |
| 8 | Dashboard keymap | =q g e s r a RET= |
| 9 | Leech-quality threshold default | 2.5 |
| 10 | Defcustom group placement | sibling group =org-drill-statistics= |

* References

- =org-drill.el= around line 729 — the =org-drill-session= EIEIO class.
  Source of the per-session in-memory state that becomes a record.
- =org-drill.el= around line 3128 — =org-drill-final-report=.  Hook
  site for =org-drill-record-session=.
- =org-drill.el= around line 540 — the existing =persist-defvar= use
  for the SM5 matrix.  Template for the session-log persist + the
  =condition-case= wrapper for corrupt-load recovery.
- =docs/design/fsrs-spec.org= — sister v0 spec, same DECIDE-marker
  convention.