require 'fcntl'
require 'socket'
require 'stringio'

require 'nack/builder'
require 'nack/error'
require 'nack/netstring'

module Nack
  class Server
    def self.run(*args)
      new(*args).start
    end

    attr_accessor :config, :app, :file
    attr_accessor :ppid, :server, :heartbeat

    def initialize(config, options = {})
      self.config = config
      self.file   = options[:file]
      self.ppid   = Process.ppid

      at_exit { close }

      self.server = UNIXServer.open(file)
      self.server.fcntl(Fcntl::F_SETFD, Fcntl::FD_CLOEXEC)

      readable, _ = IO.select([self.server], nil, nil, 3)

      if readable && readable.first == self.server
        self.heartbeat = server.accept_nonblock
        self.heartbeat.fcntl(Fcntl::F_SETFD, Fcntl::FD_CLOEXEC)
      else
        warn "No heartbeat connected"
        exit 1
      end

      trap('TERM') { exit }
      trap('INT')  { exit }
      trap('QUIT') { close }

      self.app = load_config
      require 'nack/json'
    rescue Exception => e
      require 'nack/json'
      handle_exception(e)
    end

    def load_config
      cfgfile = File.read(config)
      eval("Nack::Builder.new {( #{cfgfile}\n )}.to_app", TOPLEVEL_BINDING, config)
    end

    def close
      server.close if server && !server.closed?
      heartbeat.close if heartbeat && !heartbeat.closed?
      File.unlink(file) if file && File.exist?(file)
    end

    def start
      heartbeat.write "#{$$}\n"
      heartbeat.flush

      clients = []
      buffers = {}

      loop do
        listeners = clients + [heartbeat]
        listeners << server unless server.closed?

        readable, writable = nil
        begin
          readable, writable = IO.select(listeners, nil, nil, 60)
        rescue Errno::EBADF
        end

        if (server.closed? || heartbeat.closed?) && clients.empty?
          return close
        end

        if ppid != Process.ppid
          return close
        end

        next unless readable

        readable.each do |sock|
          if sock == heartbeat && heartbeat.eof?
            return close
          elsif sock == server
            client = server.accept_nonblock
            client.fcntl(Fcntl::F_SETFD, Fcntl::FD_CLOEXEC)
            clients << client
          else
            client, buf = sock, buffers[sock] ||= ''

            begin
              buf << client.read_nonblock(1024)
            rescue EOFError
              handle sock, StringIO.new(buf)
              buffers.delete(client)
              clients.delete(client)
            end
          end
        end
      end

      nil
    rescue SystemExit, Errno::EINTR
      # Ignore
    rescue Exception => e
      handle_exception(e)
    end

    def handle(sock, buf)
      status  = 500
      headers = { 'Content-Type' => 'text/html' }
      body    = ["Internal Server Error"]

      env, input = nil, StringIO.new
      input.set_encoding('ASCII-8BIT') if input.respond_to?(:set_encoding)

      NetString.read(buf) do |data|
        if env.nil?
          env = JSON.decode(data)
        elsif data.length > 0
          input.write(data)
        else
          break
        end
      end

      sock.close_read
      input.rewind

      env = {
        "rack.version" => Rack::VERSION,
        "rack.input" => input,
        "rack.errors" => $stderr,
        "rack.multithread" => false,
        "rack.multiprocess" => true,
        "rack.run_once" => false,
        "rack.url_scheme" => ["yes", "on", "1"].include?(env["HTTPS"]) ? "https" : "http"
      }.merge(env)

      status, headers, body = app.call(env)

      begin
        NetString.write(sock, status.to_s)
        NetString.write(sock, JSON.encode(headers))

        body.each do |part|
          NetString.write(sock, part) if part.length > 0
        end
        NetString.write(sock, "")
      ensure
        body.close if body.respond_to?(:close)
      end
    rescue Exception => e
      NetString.write(sock, JSON.encode({
        'name'    => e.class.name,
        'message' => e.message,
        'stack'   => e.backtrace.join("\n")
      }))
    ensure
      sock.close_write
    end

    def handle_exception(e)
      if heartbeat && !heartbeat.closed?
        error = JSON.encode({
          'name'    => e.class.name,
          'message' => e.message,
          'stack'   => e.backtrace.join("\n")
        })
        heartbeat.write("#{error}\n")
        heartbeat.flush
        heartbeat.close
        exit 1
      else
        raise e
      end
    end
  end
end