util.shn

import Fiber from "async.fiber"
import yield from "async"
import Queue from 'data.queue'

class Semaphore

   self(count = 1)
      self.count = count
      self.queue = Queue()
   end
   up()
      self.count += 1
      if self.count > 0 and self.queue.count() > 0 then
         wait = self.queue.dequeue()
         wait.ready()
      end
   end
   down()
      if self.count > 0 then
         self.count -= 1
         return
      end
      curr = Fiber::current
      self.queue.enqueue(curr)
      while self.count < 1 do
         curr.pause()
         yield
      end
      self.count -= 1
   end
   release()
      self.count = 1
      while not self.queue.empty() do
         wait = self.queue.dequeue()
         wait.ready()
         self.count += 1
      end
   end
   try_down()
      if self.count > 0 then
         self.down()
         return true
      end
      return false
   end
end

class Channel
   self(size = math.huge)
      self.wput = Semaphore(size)
      self.wget = Semaphore(0)
      self.data = Queue()
   end
   put(data)
      self.wput.down()
      self.data.enqueue(data)
      self.wget.up()
   end
   get()
      self.wget.down()
      if self.wput.queue.count() > 0 then
         self.wput.up()
      end
      return self.data.dequeue()
   end
   join(that)
      src, dst = that.wput.queue, self.wput.queue
      while src.count() > 0 do
         dst.enqueue(src.dequeue())
      end
      src, dst = that.wget.queue, self.wget.queue
      while src.count() > 0 do
         dst.enqueue(src.dequeue())
      end
      src, dst = that.data, self.data
      while src.count() > 0 do
         dst.enqueue(src.dequeue())
      end
      self.wput.count += that.wput.count
      self.wget.count += that.wget.count
      return self
   end
end