#
#
#            Nim's Runtime Library
#        (c) Copyright 2014 Dominik Picheta
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

# TODO: Docs.

import tables, os, unsigned, hashes

when defined(linux): 
  import posix, epoll
elif defined(windows): 
  import winlean
else: 
  import posix

proc hash*(x: SocketHandle): THash {.borrow.}
proc `$`*(x: SocketHandle): string {.borrow.}

type
  Event* = enum
    EvRead, EvWrite

  SelectorKey* = ref object
    fd*: SocketHandle
    events*: set[Event] ## The events which ``fd`` listens for.
    data*: RootRef ## User object.

  ReadyInfo* = tuple[key: SelectorKey, events: set[Event]]

when defined(nimdoc):
  type
    Selector* = ref object
      ## An object which holds file descripters to be checked for read/write
      ## status.
      fds: Table[SocketHandle, SelectorKey]

  proc register*(s: Selector, fd: SocketHandle, events: set[Event],
                 data: RootRef): SelectorKey {.discardable.} =
    ## Registers file descriptor ``fd`` to selector ``s`` with a set of TEvent
    ## ``events``.

  proc update*(s: Selector, fd: SocketHandle,
               events: set[Event]): SelectorKey {.discardable.} =
    ## Updates the events which ``fd`` wants notifications for.

  proc select*(s: Selector, timeout: int): seq[ReadyInfo] =
    ## The ``events`` field of the returned ``key`` contains the original events
    ## for which the ``fd`` was bound. This is contrary to the ``events`` field
    ## of the ``TReadyInfo`` tuple which determines which events are ready
    ## on the ``fd``.

  proc contains*(s: Selector, fd: SocketHandle): bool =
    ## Determines whether selector contains a file descriptor.

  proc `[]`*(s: Selector, fd: SocketHandle): SelectorKey =
    ## Retrieves the selector key for ``fd``.


elif defined(linux):
  type
    Selector* = ref object
      epollFD: cint
      events: array[64, epoll_event]
      fds: Table[SocketHandle, SelectorKey]
  
  proc createEventStruct(events: set[Event], fd: SocketHandle): epoll_event =
    if EvRead in events:
      result.events = EPOLLIN
    if EvWrite in events:
      result.events = result.events or EPOLLOUT
    result.events = result.events or EPOLLRDHUP
    result.data.fd = fd.cint
  
  proc register*(s: Selector, fd: SocketHandle, events: set[Event],
      data: RootRef): SelectorKey {.discardable.} =
    ## Registers file descriptor ``fd`` to selector ``s`` with a set of TEvent
    ## ``events``.
    var event = createEventStruct(events, fd)
    if events != {}:
      if epoll_ctl(s.epollFD, EPOLL_CTL_ADD, fd, addr(event)) != 0:
        raiseOSError(osLastError())

    var key = SelectorKey(fd: fd, events: events, data: data)
  
    s.fds[fd] = key
    result = key
  
  proc update*(s: Selector, fd: SocketHandle,
      events: set[Event]): SelectorKey {.discardable.} =
    ## Updates the events which ``fd`` wants notifications for.
    if s.fds[fd].events != events:
      if events == {}:
        # This fd is idle -- it should not be registered to epoll.
        # But it should remain a part of this selector instance.
        # This is to prevent epoll_wait from returning immediately
        # because its got fds which are waiting for no events and
        # are therefore constantly ready. (leading to 100% CPU usage).
        if epoll_ctl(s.epollFD, EPOLL_CTL_DEL, fd, nil) != 0:
          raiseOSError(osLastError())
        s.fds[fd].events = events
      else:
        var event = createEventStruct(events, fd)
        if s.fds[fd].events == {}:
          # This fd is idle. It's not a member of this epoll instance and must
          # be re-registered.
          if epoll_ctl(s.epollFD, EPOLL_CTL_ADD, fd, addr(event)) != 0:
            raiseOSError(osLastError())
        else:
          if epoll_ctl(s.epollFD, EPOLL_CTL_MOD, fd, addr(event)) != 0:
            raiseOSError(osLastError())
        s.fds[fd].events = events
      
      result = s.fds[fd]
  
  proc unregister*(s: Selector, fd: SocketHandle): SelectorKey {.discardable.} =
    if epoll_ctl(s.epollFD, EPOLL_CTL_DEL, fd, nil) != 0:
      let err = osLastError()
      if err.cint notin {ENOENT, EBADF}: # TODO: Why do we sometimes get an EBADF? Is this normal?
        raiseOSError(err)
    result = s.fds[fd]
    s.fds.del(fd)

  proc close*(s: Selector) =
    if s.epollFD.close() != 0: raiseOSError(osLastError())
    dealloc(addr s.events) # TODO: Test this
  
  proc epollHasFd(s: Selector, fd: SocketHandle): bool =
    result = true
    var event = createEventStruct(s.fds[fd].events, fd)
    if epoll_ctl(s.epollFD, EPOLL_CTL_MOD, fd, addr(event)) != 0:
      let err = osLastError()
      if err.cint in {ENOENT, EBADF}:
        return false
      raiseOSError(osLastError())
  
  proc select*(s: Selector, timeout: int): seq[ReadyInfo] =
    ##
    ## The ``events`` field of the returned ``key`` contains the original events
    ## for which the ``fd`` was bound. This is contrary to the ``events`` field
    ## of the ``TReadyInfo`` tuple which determines which events are ready
    ## on the ``fd``.
    result = @[]
    let evNum = epoll_wait(s.epollFD, addr s.events[0], 64.cint, timeout.cint)
    if evNum < 0: raiseOSError(osLastError())
    if evNum == 0: return @[]
    for i in 0 .. <evNum:
      let fd = s.events[i].data.fd.SocketHandle
    
      var evSet: set[Event] = {}
      if (s.events[i].events and EPOLLIN) != 0: evSet = evSet + {EvRead}
      if (s.events[i].events and EPOLLOUT) != 0: evSet = evSet + {EvWrite}
      let selectorKey = s.fds[fd]
      assert selectorKey != nil
      result.add((selectorKey, evSet))

      #echo("Epoll: ", result[i].key.fd, " ", result[i].events, " ", result[i].key.events)
  
  proc newSelector*(): Selector =
    new result
    result.epollFD = epoll_create(64)
    #result.events = cast[array[64, epoll_event]](alloc0(sizeof(epoll_event)*64))
    result.fds = initTable[SocketHandle, SelectorKey]()
    if result.epollFD < 0:
      raiseOSError(osLastError())

  proc contains*(s: Selector, fd: SocketHandle): bool =
    ## Determines whether selector contains a file descriptor.
    if s.fds.hasKey(fd):
      # Ensure the underlying epoll instance still contains this fd.
      if s.fds[fd].events != {}:
        result = epollHasFd(s, fd)
      else:
        result = true
    else:
      return false

  proc `[]`*(s: Selector, fd: SocketHandle): SelectorKey =
    ## Retrieves the selector key for ``fd``.
    return s.fds[fd]

elif not defined(nimdoc):
  # TODO: kqueue for bsd/mac os x.
  type
    Selector* = ref object
      fds: Table[SocketHandle, SelectorKey]

  proc register*(s: Selector, fd: SocketHandle, events: set[Event],
      data: RootRef): SelectorKey {.discardable.} =
    if s.fds.hasKey(fd):
      raise newException(ValueError, "File descriptor already exists.")
    var sk = SelectorKey(fd: fd, events: events, data: data)
    s.fds[fd] = sk
    result = sk

  proc update*(s: Selector, fd: SocketHandle,
      events: set[Event]): SelectorKey {.discardable.} =
    ## Updates the events which ``fd`` wants notifications for.
    if not s.fds.hasKey(fd):
      raise newException(ValueError, "File descriptor not found.")

    s.fds[fd].events = events
    result = s.fds[fd]

  proc unregister*(s: Selector, fd: SocketHandle): SelectorKey {.discardable.} =
    result = s.fds[fd]
    s.fds.del(fd)

  proc close*(s: Selector) = discard

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