feat(calendar): list due tasks from a task vdir beside the events

The sampler reads open VTODOs with a due date from
~/.local/share/tasks/<list>/*.ics (a vdirsyncer filesystem storage,
override with UDT_TASKS_DIR) and writes them to the cache as ISO
'task' lines. The card merges them into the week's rows by date, with
a checkbox before the title and an urgency colour: overdue critical,
due today warning, later label. Overdue tasks stay until done, so they
lead the table. Tasks never mark the month grid.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 32 insertions, 2 deletions

diff --git a/lib/data.lua b/lib/data.lua
index dca039a..75dedcd 100644
--- a/lib/data.lua
+++ b/lib/data.lua
@@ -36,7 +36,8 @@ end
 -- The calendar cache written by bin/calendar-sample.sh.
 --
 -- Returns { today = { y, m, d }, colors = { <calendar> = <khal colour name> },
--- events = { { y, m, d, start, finish, calendar, title }, ... } }, or nil when
+-- events = { { y, m, d, start, finish, calendar, title }, ... },
+-- tasks = { { y, m, d, start, title, task = true }, ... } }, or nil when
 -- the cache is absent or carries no 'generated' key. nil means "the sampler
 -- never ran", which the card names; an empty events list means "nothing in the
 -- next week", which is a different and equally valid state.
@@ -50,7 +51,7 @@ end
 function M.calendar_parse(text)
   if type(text) ~= 'string' then return nil end
 
-  local out = { colors = {}, events = {} }
+  local out = { colors = {}, events = {}, tasks = {} }
   local generated = false
 
   for line in text:gmatch('[^\n]+') do
@@ -77,6 +78,16 @@ function M.calendar_parse(text)
           title = title,
         }
       end
+    elseif kind == 'task' then
+      -- Written by the sampler from the task vdir, so the date is ISO: no
+      -- positional guessing as for khal's events.
+      local y, m, d, st, title = rest:match('^(%d+)-(%d+)-(%d+)|([^|]*)|(.*)$')
+      if y then
+        out.tasks[#out.tasks + 1] = {
+          y = tonumber(y), m = tonumber(m), d = tonumber(d),
+          start = st ~= '' and st or nil, title = title, task = true,
+        }
+      end
     end
   end
 
@@ -146,6 +157,25 @@ function M.calendar_upcoming(events, today, days)
   return out
 end
 
+-- The card's table: the week's events and the open tasks due in it, as one
+-- list by date. Overdue tasks pass calendar_upcoming's window (a negative day
+-- offset is under any limit), so they lead the list, which is where they
+-- belong. Within a day an all-day row ('' start) sorts before a timed one.
+function M.calendar_agenda(cal, today, days)
+  local rows = M.calendar_upcoming(cal.events, today, days)
+  for _, t in ipairs(M.calendar_upcoming(cal.tasks, today, days)) do
+    rows[#rows + 1] = t
+  end
+  -- The index breaks ties, since table.sort is not stable.
+  local key = {}
+  for i, e in ipairs(rows) do
+    key[e] = string.format('%04d%02d%02d %-5s %04d', e.y, e.m, e.d,
+      e.start or '', i)
+  end
+  table.sort(rows, function(a, b) return key[a] < key[b] end)
+  return rows
+end
+
 -- Days in a month, and the weekday its 1st falls on.
 --
 -- os.time/os.date rather than a leap-year rule: the C library already knows,