-- Calendar: the current month, and the week's appointments below it.
--
-- Events come from a cache file written by bin/calendar-sample.sh, because
-- conky's Lua cannot run a process and khal costs ~200ms of Python startup,
-- which is two orders of magnitude over the frame budget.

local card = require 'lib.card'
local data = require 'lib.data'

local CACHE = (os.getenv('XDG_CACHE_HOME') or (os.getenv('HOME') .. '/.cache'))
  .. '/udt/calendar.txt'

-- khal's colour names mapped onto the board's palette roles, so the card
-- follows a scheme switch instead of pinning three literal hues that stop
-- matching the rest of the dashboard.
--
-- The palette has no green/magenta/blue as such; it has roles. `ok` is the
-- green-ish one in every UDT scheme, `critical` the red/magenta one and
-- `highlight` the blue/accent one, which is why the mapping reads as it does.
-- A calendar whose colour is not listed falls back to `value`, so an added
-- calendar is visible and unstyled rather than invisible.
local COLOUR_ROLE = {
  ['light green']   = 'ok',        ['green']   = 'ok',
  ['light magenta'] = 'critical',  ['magenta'] = 'critical',
  ['light red']     = 'critical',  ['red']     = 'critical',
  ['light blue']    = 'highlight', ['blue']    = 'highlight',
  ['light cyan']    = 'highlight', ['cyan']    = 'highlight',
  ['light yellow']  = 'warning',   ['yellow']  = 'warning',
  ['brown']         = 'warning',
}

local WEEKDAYS = { 'L', 'M', 'M', 'G', 'V', 'S', 'D' }

local M = {}

local function clamp(v, lo, hi) return math.max(lo, math.min(hi, v)) end

-- The palette colour for a calendar name, via khal's declared colour.
local function cal_colour(name, colors, khal_colors)
  local role = COLOUR_ROLE[tostring(khal_colors[name] or ''):lower()]
  return colors[role] or colors.value
end

-- 'Dentist' on 24 September at 13:00 -> '24/09 13:00', an all-day event ->
-- '26/09 all day'. Never '00:00' for an all-day event: midnight is a
-- legitimate start time and the two must not read the same.
--
-- Day/month, no year: the grid above already names the month, and the window
-- is a week, so a year would be three characters of the row spent on the one
-- field that cannot vary.
local function when(e)
  return string.format('%02d/%02d %s', e.d, e.m, e.start or 'all day')
end

-- The legend: one coloured dot and name per calendar, along the card's bottom.
-- Wraps to a second line when the names do not fit, and drops any that still
-- do not: a legend spilling off the card is worse than a short one, since the
-- colours are also readable from the grid above.
local function draw_legend(cr, inner, y, size, names, colors, khal_colors)
  card.font(cr, card.FONT_MONO, size, false)
  local r = size * 0.30
  local x = inner.x
  local right = inner.x + inner.w
  for _, name in ipairs(names) do
    local w = r * 2 + size * 0.45 + card.advance(cr, name)
    if x + w > right then
      -- Next line, if the card has one to give.
      x = inner.x
      y = y + size * 1.5
      if y > inner.y + inner.h then return end
    end
    card.rgba(cr, cal_colour(name, colors, khal_colors))
    cairo_new_path(cr)
    cairo_arc(cr, x + r, y - size * 0.32, r, 0, math.pi * 2)
    cairo_fill(cr)
    card.rgba(cr, colors.label, 0.85)
    card.text(cr, x + r * 2 + size * 0.45, y, name)
    x = x + w + size * 0.9
  end
end

function M.draw(cr, rect, colors)
  local inner = card.card(cr, rect, colors)
  local LABEL_F = 0.30

  local cal = data.calendar_parse(data.slurp(CACHE) or '')
  if not cal then
    card.notice(cr, inner, colors, 'CALENDAR', 'no calendar data',
      'bin/calendar-sample.sh')
    return
  end

  -- The cache's own date, not os.date: they agree while the sampler is
  -- running, and when it has stopped the grid should show the month the data
  -- describes rather than silently drifting to a month with no marks in it.
  local today = cal.today or { tonumber(os.date('%Y')), tonumber(os.date('%m')),
                               tonumber(os.date('%d')) }
  local year, month, day = today[1], today[2], today[3]
  local ndays, first_wd = data.month_shape(year, month)
  local marked = data.calendar_month_days(cal.events, year, month)

  -- === Type ===============================================================
  -- The grid's cell width is what actually constrains this card: seven columns
  -- of two digits plus gaps. The event rows then take what is left.
  local weeks = math.ceil((first_wd - 1 + ndays) / 7)
  local grid_w = inner.w
  local cell_w = grid_w / 7
  -- Day numbers sized to the column, with a ceiling so a wide card does not
  -- grow the digits past the event type below them.
  local day_size = clamp(cell_w * 0.46, 7, 26)

  local header_h = inner.h * 0.16
  local label_size = clamp(header_h * LABEL_F * 2.2, 9, 22)
  local big_size = clamp(header_h * 0.46, 11, 28)

  -- === Header =============================================================
  -- The month name is the card's big value, top-right, per DESIGN.md.
  local title = os.date('%B', os.time({ year = year, month = month, day = 1,
                                        hour = 12 })):upper()
  card.font(cr, card.FONT_HEAVY, big_size, false)
  card.rgba(cr, colors.heading)
  card.text_right(cr, inner.x + inner.w, inner.y + big_size, title)

  card.font(cr, card.FONT_MONO, label_size, false)
  card.title(cr, inner.x, inner.y + label_size, card.ICON.calendar, 'CALENDAR', colors)

  -- === Month grid =========================================================
  -- 2.3, not 1.5: the weekday row sat close enough to the header that the
  -- initials read as part of it rather than as the top of the grid.
  local gy = inner.y + big_size * 2.3
  local row_h = day_size * 1.55

  -- Weekday initials. Monday-first, matching khal's firstweekday = 0.
  card.font(cr, card.FONT_MONO, day_size * 0.72, false)
  card.rgba(cr, colors.label, 0.7)
  for i = 1, 7 do
    local w = card.measure(cr, WEEKDAYS[i])
    card.text(cr, inner.x + (i - 0.5) * cell_w - w / 2, gy, WEEKDAYS[i])
  end

  gy = gy + day_size * 0.9
  local col = first_wd
  local gy_row = gy
  for d = 1, ndays do
    local s = tostring(d)
    local cx = inner.x + (col - 0.5) * cell_w
    local baseline = gy_row + day_size

    -- Today gets a filled pill behind the number, so the eye finds it before
    -- reading any digits.
    if d == day then
      -- The pill takes the day's calendar colour when there is an event, so
      -- today reads as both 'today' and 'busy' without the number having to
      -- carry two codes at once.
      card.rgba(cr, marked[d] and cal_colour(marked[d], colors, cal.colors)
        or colors.highlight, 0.30)
      card.rounded_path(cr, cx - cell_w * 0.40, baseline - day_size * 0.95,
        cell_w * 0.80, day_size * 1.25, day_size * 0.3)
      cairo_fill(cr)
    end

    -- A day with an event takes its calendar's colour; the rest stay in the
    -- body colour, so colour on this grid always means "something is on".
    local owner = marked[d]

    card.font(cr, card.FONT_MONO, day_size, owner ~= nil or d == day)
    if d == day then
      -- Over the pill the calendar colour loses too much contrast, so today's
      -- number stays in the heading colour and the pill behind it carries the
      -- calendar code.
      card.rgba(cr, colors.heading)
    elseif owner then
      card.rgba(cr, cal_colour(owner, colors, cal.colors))
    else
      -- A past day dims: the month grid is mostly about what is still coming.
      card.rgba(cr, colors.body, d < day and 0.45 or 0.85)
    end
    local w = card.measure(cr, s)
    card.text(cr, cx - w / 2, baseline, s)

    col = col + 1
    if col > 7 then col = 1; gy_row = gy_row + row_h end
  end

  local grid_bottom = gy + weeks * row_h

  -- === Event table ========================================================
  -- Everything below the grid, however much that is. A card too short for even
  -- one row draws the grid alone rather than a clipped half-row.
  local ev_size = clamp(day_size * 0.78, 7, 18)
  local ev_step = ev_size * 1.75

  -- The legend is pinned to the card's bottom, so the event rows end above it
  -- rather than running under it. Only calendars that khal declared a colour
  -- for appear, in the config's own order, which is why the names are sorted
  -- rather than taken from a hash walk: pairs() would reorder the legend
  -- between frames.
  local legend = {}
  for name in pairs(cal.colors) do legend[#legend + 1] = name end
  table.sort(legend)

  local legend_size = ev_size * 0.82
  local legend_h = #legend > 0 and legend_size * 2.0 or 0
  local floor_y = inner.y + inner.h - legend_h

  local avail = floor_y - grid_bottom
  if avail < ev_step then legend = {}; legend_h = 0; floor_y = inner.y + inner.h end
  if (floor_y - grid_bottom) < ev_step then return end

  local ey = grid_bottom + ev_size * 1.1

  if #cal.events == 0 then
    card.font(cr, card.FONT_UI, ev_size, false)
    card.rgba(cr, colors.label, 0.8)
    card.text(cr, inner.x, ey, 'nothing this week')
    if #legend > 0 then
      draw_legend(cr, inner, inner.y + inner.h - legend_size * 0.5, legend_size,
        legend, colors, cal.colors)
    end
    return
  end

  -- The time column is fixed-width so the titles align down the card; it is
  -- measured from the widest time actually present rather than assumed, since
  -- 'all day' is wider than '13:00'.
  card.font(cr, card.FONT_MONO, ev_size, false)
  local time_w = 0
  for _, e in ipairs(cal.events) do
    local w = card.advance(cr, when(e))
    if w > time_w then time_w = w end
  end
  local gap = ev_size * 0.6
  local title_x = inner.x + time_w + gap
  local title_w = (inner.x + inner.w) - title_x

  -- A rough characters-per-pixel budget for the title column, so a long title
  -- is cut rather than drawn over the card's edge. Measured from a digit's
  -- advance in the row font: proportional titles vary, but this is a cut
  -- point, not a layout the rest depends on.
  local char_w = card.advance(cr, '0')
  local title_chars = math.max(4, math.floor(title_w / math.max(char_w, 1)))

  -- How many rows actually fit, so the last one can say what it is hiding.
  -- A card that silently drops the rest of the week is worse than one showing
  -- fewer events and admitting it: the whole point of the card is knowing
  -- what is coming.
  --
  -- Counted from the same test the drawing loop uses (a row at `ey` fits when
  -- ey <= floor_y), not an independent division: the two disagreeing by one
  -- row is what made the overflow line vanish exactly when it was needed,
  -- since the loop cut the row the count had already spent.
  local room = 0
  local probe = ey
  while probe <= floor_y do room = room + 1; probe = probe + ev_step end

  local shown = #cal.events
  -- The overflow line costs a row, so it is only worth taking when it reports
  -- more than the row it displaces.
  if room < shown then
    shown = (room >= 2) and (room - 1) or room
  end
  local hidden = #cal.events - shown

  for i = 1, shown do
    local e = cal.events[i]
    if ey > floor_y then break end
    local colour = cal_colour(e.calendar, colors, cal.colors)

    card.font(cr, card.FONT_MONO, ev_size, false)
    card.rgba(cr, colour)
    card.text(cr, inner.x, ey, when(e))

    -- The title in the body colour, not the calendar's: colour-coding every
    -- glyph in the row makes three calendars read as three unrelated cards.
    -- The time carries the code, the title stays readable.
    card.font(cr, card.FONT_UI, ev_size, false)
    card.rgba(cr, colors.value)
    card.text(cr, title_x, ey, card.truncate(e.title, title_chars))

    ey = ey + ev_step
  end

  -- The overflow line, in the label colour so it reads as chrome rather than
  -- as another appointment.
  if hidden > 0 and ey <= floor_y then
    card.font(cr, card.FONT_UI, ev_size * 0.92, false)
    card.rgba(cr, colors.label, 0.8)
    card.text(cr, inner.x, ey, string.format('+%d more', hidden))
  end

  if #legend > 0 then
    draw_legend(cr, inner, inner.y + inner.h - legend_size * 0.5, legend_size,
      legend, colors, cal.colors)
  end
end

return M