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require "socket"

# Namespace everything under DND
module DND
  Users = {
    'simone' => 'secretpassword',
    'carl'   => 'whatever',
  }

  Delimiter = "\r\n"

  class Server
    attr_reader :socket, :server_thread, :clients

    def initialize(host='0.0.0.0', port=20_000)
      puts "[I] Initialising server"
      @keep_running  = true
      @host          = host
      @port          = port
      @socket        = TCPServer.new(@host, @port)
      @clients       = []
      @connection_id = 0
    end

    def stop
      @keep_running = false
    end

    # blocks
    def run
      @keep_running  = true
      puts "Listening on #{@host}:#{@port}"
      accept_connection while @keep_running
    end

    def accept_connection
      return unless IO.select([@socket], nil, nil, 0.1)
      socket        = @socket.accept
      connection_id = new_connection_id # you could just use the socket's object-id or something...
      puts("[Connection]\tAccepted connection with ID: #{connection_id}")
      client        = Client.new(self, socket, connection_id)
      if client.login then
        puts("[Connection]\tConnection ID #{connection_id} logged in as #{client.username}")
        client.welcome
        @clients << client
        client.run_thread
      else
        client.disconnect
      end
    end

    def new_connection_id
      @connection_id += 1 # the last expression's value is the return value already
    end

    def disconnect(client)
      @clients.delete(client)
    end
  end

  class Client
    attr_reader :socket, :connection_id, :username

    def initialize(server, socket, connection_id)
      @server       = server
      @socket       = socket
      @username     = nil
      @password     = nil
    end

    def login
      say("Welcome to ZombiServer v0.01")

      @username = ask("Your username: ")
      @password = ask("Password: ")

      if Users[@username] == @password then
        true
      else
        @username = nil
        @password = nil

        false
      end
    end

    def welcome
      say("You have successfully logged in as #{@username}")
    end

    def disconnect
      say("You're being disconnected")
      @socket.close
      @server.disconnect(self)
    end

    def ask(question)
      @socket.print(question)
      @socket.flush           # IO's are line buffered, you have to flush if you want to emit an incomplete line
      @socket.gets.chomp      # chomp removes the trailing newline
    end

    def say(line)
      @socket.print(line, Delimiter)
    end

    def run_thread
      Thread.new do
        while line = @socket.gets # gets returns nil at eof
          process(line.chomp)
        end
      end
    end

    def process(line)
      puts "[Command] User wrote: #{line}"
      case line
        when /\Aquit\z/i
          disconnect
        when /\Ausers\z/i
          say("There are currently #{@server.clients.size} connected users")
        else
          say("Unknown command: #{line.inspect}")
          say("Known commands are: users, quit")
      end
    end
  end
end

server = DND::Server.new
trap("SIGINT") { # handle ctrl-C
  trap("SIGINT", "SYSTEM_DEFAULT") # restore original signal handler
  server.stop
}
server.run
puts "","Server terminated"