feat: add a calendar card reading khal

The month grid with the week's appointments below it, colour-coded by
calendar. Events come from a cache file rather than a live call: khal
costs about 200ms of Python startup, which is two orders of magnitude
over the 2-second draw budget, so bin/calendar-sample.sh writes the
cache on a 5-minute execi and the widget only parses.

Calendar colours are read out of khal's own config by the sampler and
mapped onto the board's palette roles, so the card follows a scheme
change instead of pinning three literal hues.

khal will not emit an ISO date: {start-date} uses the user's dateformat,
which carries no year here, and a strftime spec inside the field raises.
The sampler asks for {start-date-long} and data.calendar_date recovers
the numbers by position, resolving day/month by magnitude and reading a
genuinely ambiguous pair day-first. A 2-digit year is refused rather
than guessed at.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 61 insertions, 0 deletions

diff --git a/test/test_data.lua b/test/test_data.lua
index 34021c5..00616d6 100644
--- a/test/test_data.lua
+++ b/test/test_data.lua
@@ -322,4 +322,65 @@ assert(data.iface_addr_parse('5: br0: <BROADCAST,MULTICAST> mtu 1500 state DOWN\
 assert(data.iface_addr_parse('') == nil, 'empty gives nil')
 assert(data.iface_addr_parse(nil) == nil, 'nil gives nil')
 
+-- === Calendar =============================================================
+-- The fixture uses generic event titles. This repository is public: a real
+-- appointment names a real person or a real appointment, and neither belongs
+-- in a committed file.
+local cal = data.calendar_parse(read('test/fixtures/calendar_cache'))
+assert(cal, 'calendar cache parses')
+assert(cal.today[1] == 2026 and cal.today[2] == 9 and cal.today[3] == 18,
+  'today parses')
+assert(cal.colors.personal == 'light green', 'calendar colour, got '
+  .. tostring(cal.colors.personal))
+assert(#cal.events == 5, 'event count, got ' .. tostring(#cal.events))
+
+-- A timed event keeps its times; an all-day one has neither, and the card
+-- shows 'all day' rather than an invented 00:00.
+assert(cal.events[1].start == '13:00' and cal.events[1].finish == '13:30',
+  'timed event keeps its times')
+assert(cal.events[2].start == nil and cal.events[2].finish == nil,
+  'all-day event has no times')
+
+-- A title containing a pipe survives: only the first four separators split.
+assert(cal.events[3].title == 'Team sync | notes',
+  'title keeps its pipe, got ' .. tostring(cal.events[3].title))
+
+-- No 'generated' key means the sampler never ran, which is not the same as
+-- having run and found nothing.
+assert(data.calendar_parse('today 2026-09-18\n') == nil, 'no generated key: nil')
+assert(data.calendar_parse('') == nil, 'empty cache: nil')
+assert(data.calendar_parse(nil) == nil, 'nil cache: nil')
+local empty = data.calendar_parse('generated 1\ntoday 2026-09-18\n')
+assert(empty and #empty.events == 0, 'ran with no events: empty list, not nil')
+
+-- calendar_date: the year is the 4-digit group wherever it sits, and the
+-- day/month pair is resolved by magnitude.
+local function ymd(s)
+  local t = data.calendar_date(s)
+  return t and table.concat(t, '-') or nil
+end
+assert(ymd('18.09.2026') == '2026-9-18', 'day-first, got ' .. tostring(ymd('18.09.2026')))
+assert(ymd('09/18/2026') == '2026-9-18', 'month-first resolved by magnitude')
+assert(ymd('2026-09-18') == '2026-9-18', 'ISO, year leading')
+-- Genuinely ambiguous: both below 13. Day-first, matching khal's defaults.
+assert(ymd('03.04.2026') == '2026-4-3', 'ambiguous reads day-first')
+assert(ymd('18.09.26') == nil, 'two-digit year is refused, not guessed')
+assert(ymd('nonsense') == nil, 'unparseable date: nil')
+assert(ymd('18.13.2026') == nil, 'impossible month: nil')
+
+-- month_days: first calendar of a day wins, and only the asked-for month.
+local days = data.calendar_month_days(cal.events, 2026, 9)
+assert(days[18] == 'personal', 'first event of the day owns it, got '
+  .. tostring(days[18]))
+assert(days[24] == 'work' and days[26] == 'birthdays', 'later days marked')
+assert(days[2] == nil, 'October event does not mark September')
+
+-- month_shape: September 2026 has 30 days and starts on a Tuesday.
+-- Monday = 1, so Tuesday = 2.
+local ndays, first = data.month_shape(2026, 9)
+assert(ndays == 30 and first == 2, 'september 2026, got ' .. ndays .. '/' .. first)
+-- February in a leap year, and a December that must roll into January.
+assert((data.month_shape(2024, 2)) == 29, 'leap february has 29 days')
+assert((data.month_shape(2026, 12)) == 31, 'december rolls over correctly')
+
 print('test_data: all assertions passed')