#
# Fluentd
#
#    Licensed under the Apache License, Version 2.0 (the "License");
#    you may not use this file except in compliance with the License.
#    You may obtain a copy of the License at
#
#        http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS,
#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#    See the License for the specific language governing permissions and
#    limitations under the License.
#

module Fluent
  class DetachProcessManager
    require 'singleton'
    include Singleton

    class Broker
      def initialize
      end

      def engine
        Engine
      end
    end

    def initialize
      require 'drb'
      DRb.start_service(create_drb_uri, Broker.new)
      @parent_uri = DRb.uri
    end

    def fork(delegate_object)
      ipr, ipw = IO.pipe  # child Engine.emit_stream -> parent Engine.emit_stream
      opr, opw = IO.pipe  # parent target.emit -> child target.emit

      pid = Process.fork
      if pid
        # parent process
        ipw.close
        opr.close
        forward_thread = process_parent(ipr, opw, pid, delegate_object)
        return pid, forward_thread
      end

      # child process
      ipr.close
      opw.close
      forward_thread = process_child(ipw, opr, delegate_object)
      return nil, forward_thread
    end

    private
    def read_header(ipr)
      sz = ipr.read(4).unpack('N')[0]
      ipr.read(sz)
    end

    def send_header(ipw, data)
      ipw.write [data.bytesize].pack('N')
      ipw.write data
      ipw.flush
    end

    def create_drb_uri
      "drbunix:"  # TODO
    end

    private
    def process_child(ipw, opr, delegate_object)
      DRb.start_service(create_drb_uri, delegate_object)
      child_uri = DRb.uri

      send_header(ipw, child_uri)

      # override target.emit_stream to write event stream to the pipe
      fwd = new_forwarder(ipw, 0.5)  # TODO interval
      Engine.define_singleton_method(:emit_stream) do |tag,es|
        fwd.emit(tag, es)
      end

      # read event stream from the pipe and forward to target.emit
      forward_thread = Thread.new(opr, delegate_object, &method(:output_forward_main))

      # override global methods to call parent process
      override_shared_methods(@parent_uri)

      return forward_thread
    end

    def override_shared_methods(parent_uri)
      broker = DRbObject.new_with_uri(parent_uri)
      shared_methods.each {|(broker_accessor,target,name)|
        remote = broker.send(broker_accessor)
        target.define_singleton_method(name) do |*args,&block|
          remote.send(name, *args, &block)
        end
      }
    end

    def shared_methods
      [
        #[:engine, Engine, :flush!],
        #[:engine, Engine, :stop],
      ]
    end

    def process_parent(ipr, opw, pid, delegate_object)
      child_uri = read_header(ipr)

      # read event stream from the pipe and forward to Engine.emit_stream
      forward_thread = Thread.new(ipr, pid, &method(:input_forward_main))

      # note: don't override methods in parent process
      #       because another process may fork after overriding
      #override_delegate_methods(delegate_object, child_uri)

      # return forwarder for DetachProcessMixin to
      # override target.emit and write event stream to the pipe
      fwd = new_forwarder(opw, 0.5)  # TODO interval
      # note: override emit method on DetachProcessMixin
      forward_thread.define_singleton_method(:forwarder) do
        fwd
      end

      return forward_thread
    end

    #def override_delegate_methods(target, child_uri)
    #  remote = DRbObject.new_with_uri(child_uri)
    #  delegate_methods(target).each {|name|
    #    target.define_singleton_method(name) do |*args,&block|
    #      remote.send(name, *args, &block)
    #    end
    #  }
    #end
    #
    #def delegate_methods(target)
    #  target.methods - Object.public_instance_methods
    #end

    def output_forward_main(opr, target)
      read_event_stream(opr) {|tag,es|
        # FIXME error handling
        begin
          target.emit(tag, es, NullOutputChain.instance)
        rescue
          $log.warn "failed to emit", :error=>$!.to_s, :pid=>Process.pid
          $log.warn_backtrace
        end
      }
    rescue
      $log.error "error on output process forwarding thread", :error=>$!.to_s, :pid=>Process.pid
      $log.error_backtrace
      raise
    end

    def input_forward_main(ipr, pid)
      read_event_stream(ipr) {|tag,es|
        # FIXME error handling
        begin
          Engine.emit_stream(tag, es)
        rescue
          $log.warn "failed to emit", :error=>$!.to_s, :pid=>Process.pid
          $log.warn_backtrace
        end
      }
    rescue
      $log.error "error on input process forwarding thread", :error=>$!.to_s, :pid=>Process.pid
      $log.error_backtrace
      raise
    end

    def read_event_stream(r, &block)
      u = MessagePack::Unpacker.new(r)
      begin
        #buf = ''
        #map = {}
        #while true
        #  r.readpartial(64*1024, buf)
        #  u.feed_each(buf) {|tag,ms|
        #    if msbuf = map[tag]
        #      msbuf << ms
        #    else
        #      map[tag] = ms
        #    end
        #  }
        #  unless map.empty?
        #    map.each_pair {|tag,ms|
        #      es = MessagePackEventStream.new(ms)
        #      block.call(tag, es)
        #    }
        #    map.clear
        #  end
        #end
        u.each {|tag,ms|
          es = MessagePackEventStream.new(ms)
          block.call(tag, es)
        }
      rescue EOFError
      ensure
        r.close
      end
    end

    def new_forwarder(w, interval)
      if interval < 0.2  # TODO interval
        Forwarder.new(w)
      else
        DelayedForwarder.new(w, interval)
      end
    end

    class Forwarder
      def initialize(w)
        @w = w
      end

      def emit(tag, es)
        ms = es.to_msgpack_stream
        #[tag, ms].to_msgpack(@w)  # not thread safe
        @w.write [tag, ms].to_msgpack
      end
    end

    class DelayedForwarder
      def initialize(w, interval)
        @w = w
        @interval = interval
        @buffer = {}
        Thread.new(&method(:run))
      end

      def emit(tag, es)
        if ms = @buffer[tag]
          ms << es.to_msgpack_stream
        else
          @buffer[tag] = es.to_msgpack_stream
        end
      end

      def run
        while true
          sleep @interval
          @buffer.keys.each {|tag|
            if ms = @buffer.delete(tag)
              [tag, ms].to_msgpack(@w)
              #@w.write [tag, ms].to_msgpack
            end
          }
        end
      rescue
        $log.error "error on forwerder thread", :error=>$!.to_s
        $log.error_backtrace
        raise
      end
    end

    class MultiForwarder
      def initialize(forwarders)
        @forwarders = forwarders
        @rr = 1
      end

      def emit(tag, es)
        forwarder = @forwarders[@rr]
        @rr = (@rr + 1) % @forwarders.length
        forwarder.emit(tag, es)
      end
    end
  end


  module DetachProcessImpl
    def on_detach_process(i)
    end

    protected
    def detach_process_impl(num, &block)
      children = []

      num.times do |i|
        pid, forward_thread = DetachProcessManager.instance.fork(self)

        if pid
          # parent process
          $log.info "detached process", :class=>self.class, :pid=>pid
          children << [pid, forward_thread]
          next
        end

        # child process
        begin
          on_detach_process(i)

          block.call

          # disable Engine.stop called by signal handler
          Engine.define_singleton_method(:stop) do
            # do nothing
          end

          # override signal handlers called by parent process
          fin = FinishWait.new
          trap :INT do
            fin.stop
          end
          trap :TERM do
            fin.stop
          end
          #forward_thread.join  # TODO this thread won't stop because parent doesn't close pipe
          fin.wait

          exit! 0
        ensure
          $log.error "unknown error while shutting down this child process", :error=>$!.to_s, :pid=>Process.pid
          $log.error_backtrace
        end

        exit! 1
      end

      # parent process
      # override shutdown method to kill child processes
      define_singleton_method(:shutdown) do
        children.each {|pair|
          begin
            pid = pair[0]
            forward_thread = pair[1]
            if pid
              Process.kill(:TERM, pid)
              forward_thread.join   # wait until child closes pipe
              Process.waitpid(pid)
              pair[0] = nil
            end
          rescue
            $log.error "unknown error while shutting down remote child process", :error=>$!.to_s
            $log.error_backtrace
          end
        }
      end

      # override target.emit and write event stream to the pipe
      forwarders = children.map {|pair| pair[1].forwarder }
      if forwarders.length > 1
        # use roundrobin
        fwd = DetachProcessManager::MultiForwarder.new(forwarders)
      else
        fwd = forwarders[0]
      end
      define_singleton_method(:emit) do |tag,es,chain|
        chain.next
        fwd.emit(tag, es)
      end
    end

    class FinishWait
      def initialize
        @finished = false
        @mutex = Mutex.new
        @cond = ConditionVariable.new
      end

      def wait
        @mutex.synchronize do
          until @finished
            @cond.wait(@mutex, 1.0)
          end
        end
      end

      def stop
        return if @finished
        @finished = true
        # Creating new thread due to mutex can't lock in main thread during trap context
        Thread.new {
          @mutex.synchronize do
            @cond.broadcast
          end
        }.run
      end

      def finished?
        @finished
      end
    end
  end


  module DetachProcessMixin
    include DetachProcessImpl

    def configure(conf)
      super

      if detach_process = conf['detach_process']
        b3v = Config.bool_value(detach_process)
        case b3v
        when nil
          num = detach_process.to_i
          if num > 1
            $log.warn "'detach_process' parameter supports only 1 process on this plugin: #{conf}"
          elsif num > 0
            @detach_process = true
          elsif detach_process =~ /0+/
            @detach_process = false
          else
            @detach_process = true
          end
        when true
          @detach_process = true
        when false
          @detach_process = false
        end
      end
    end

    def detach_process(&block)
      if @detach_process
        detach_process_impl(1, &block)
      else
        block.call
      end
    end
  end


  module DetachMultiProcessMixin
    include DetachProcessImpl

    def initialize
      @detach_process_num = 2
      super
    end

    def configure(conf)
      super

      if detach_process = conf['detach_process']
        b3v = Config.bool_value(detach_process)
        case b3v
        when nil
          num = detach_process.to_i
          if num > 0
            @detach_process = true
            @detach_process_num = num
          elsif detach_process =~ /0+/
            @detach_process = false
          else
            @detach_process = true
          end
        when true
          @detach_process = true
        when false
          @detach_process = false
        end
      end
    end

    protected
    def detach_multi_process(&block)
      if @detach_process
        detach_process_impl(@detach_process_num, &block)
      else
        block.call
      end
    end
  end
end