Hammerspoon script for "timed mute"

timed-mute.lua

do
   local log = hs.logger.new('mutation', 'info')
   local cmd_shift = {"cmd", "shift"}

   -- Mute or unmute the speaker according to the truth of t.
   local function mute(t)
      return string.format("set volume %s output muted",
			   t and "with" or "without")
   end

   -- Run the specified thunk and report how long it took in seconds.
   local function time(fn)
      local start = hs.timer:absoluteTime()
      fn()
      local stop = hs.timer:absoluteTime()
      return (stop - start) / 1e9 -- nanoseconds to seconds
   end

   -- Run script via the AppleScript interpreter.
   local function run(script)
      return time(function () hs.osascript.applescript(script) end)
   end

   --[[
      Mute the speakers for sec seconds. If the speakers are already muted, add
      sec to the amount of time they will remain muted.

      To allow mutes to "stack", keep a persistent timer, and add the designated
      value to what is already there. Since hammerspoon is single threaded we do
      not have to worry about races.
   ]]
   local timer = hs.timer.new(0, function ()
     run(mute(false))
     log.f('Sound unmuted')
   end)
   local function silence(sec)
      -- Always mute, in case the user manually unmuted.
      local delta = run(mute(true))
      if not timer:running() then log.f('Sound muted') end

      -- Pin the timer at 0, since a stopped timer will have a next trigger
      -- sometime in the past.
      local left = timer:setNextTrigger(
	 math.max(timer:nextTrigger(), 0) + sec - delta):nextTrigger()
      log.f('Time remaining now: %.1f sec', left)
   end

   -- Error correction when an interstitial turns out to be a full.
   hs.hotkey.bind(cmd_shift, '8', function () silence(10) end)
   -- Interstitials after a manual skip.
   hs.hotkey.bind(cmd_shift, '9', function () silence(15) end)
   -- Normal random interval.
   hs.hotkey.bind(cmd_shift, '0', function () silence(59.5) end)
end