added countdown widget recipe (#91)

recipes.mdwn

@@ -12,6 +12,7 @@ The recipes section is where you can find useful snippets and tutorials on how t
 
 * [Lain Widget Library](https://github.com/copycat-killer/lain)
 * [Vicious](https://github.com/Mic92/vicious)
+* [[Countdown|recipes/countdown]]
 * [[MPD current song|recipes/mpc]]
 
 ## Libraries

recipes/countdown.mdwn

@@ -0,0 +1,67 @@
+# Countdown widget
+
+Add the following in your `rc.lua`:
+
+```lua
+local countdown = {
+    widget   = wibox.widget.textbox(),
+    checkbox = wibox.widget {
+        checked      = false,
+        check_color  = beautiful.fg_focus,  -- customize
+        border_color = beautiful.fg_normal, -- customize
+        border_width = 2,                   -- customize
+        shape        = gears.shape.circle,
+        widget       = wibox.widget.checkbox
+    }
+}
+
+function countdown.set()
+    awful.prompt.run {
+        prompt       = "Countdown minutes: ", -- floats accepted
+        textbox      = awful.screen.focused().mypromptbox.widget,
+        exe_callback = function(timeout)
+            countdown.seconds = tonumber(timeout)
+            if not countdown.seconds then return end
+            countdown.checkbox.checked = false
+            countdown.minute_t = countdown.seconds > 1 and "minutes" or "minute"
+            countdown.seconds = countdown.seconds * 60
+            countdown.timer = gears.timer({ timeout = 1 })
+            countdown.timer:connect_signal("timeout", function()
+                if countdown.seconds > 0 then
+                    local minutes = math.floor(countdown.seconds / 60)
+                    local seconds = math.fmod(countdown.seconds, 60)
+                    countdown.widget:set_markup(string.format("%d:%02d", minutes, seconds))
+                    countdown.seconds = countdown.seconds - 1
+                else
+                    naughty.notify({
+                        title = "Countdown",
+                        text  = string.format("%s %s timeout", timeout, countdown.minute_t)
+                    })
+                    countdown.widget:set_markup("")
+                    countdown.checkbox.checked = true
+                    countdown.timer:stop()
+                end
+            end)
+            countdown.timer:start()
+        end
+    }
+end
+
+countdown.checkbox:buttons(awful.util.table.join(
+    awful.button({}, 1, function() countdown.set() end), -- left click
+    awful.button({}, 3, function() -- right click
+        if countdown.timer and countdown.timer.started then
+            countdown.widget:set_markup("")
+            countdown.checkbox.checked = false
+            countdown.timer:stop()
+            naughty.notify({ title = "Countdown", text  = "Timer stopped" })
+        end
+    end)
+))
+```
+
+then, add `countdown.widget` and `countdown.checkbox` to your favourite `wibox`.
+
+Left clicking on the `checkbox` will prompt for a countdown, right clicking will stop the timer.
+
+The `widget` will display the countdown.