=begin
    Copyright 2010-2013 Tasos Laskos <tasos.laskos@gmail.com>

    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.
=end

module Arachni
module Database

    #
    # Flat-file Queue implementation
    #
    # Behaves pretty much like a Ruby Queue however it transparently serializes and
    # saves its values to the file-system under the OS's temp directory.
    #
    # It's pretty useful when you want to reduce memory footprint without
    # having to refactor any code since it behaves just like Ruby's implementation.
    #
    # @author Tasos "Zapotek" Laskos
    #                                      <tasos.laskos@gmail.com>
    #                                      
    # @version 0.1
    #
    class Queue < Base

        #
        # @see Arachni::Database::Base#initialize
        #
        def initialize( *args )
            super( *args )
            @q = ::Queue.new
        end

        #
        # Adds an object to the queue.
        #
        # @param    [Object]    obj
        #
        def <<( obj )
            @q << dump( obj )
        end
        alias :push :<<
        alias :enq :<<

        #
        # Removes an object from the Queue and returns it.
        #
        # @return   [Object]
        #
        def pop
            return load_and_delete_file( @q.pop )
        end
        alias :deq :pop
        alias :shift :pop

        #
        # Size of the Queue, the number of objects it currently holds.
        #
        # @return   [Integer]
        #
        def size
            @q.size
        end
        alias :length :size

        #
        # True if the Queue if empty, false otherwise.
        #
        # @return   [Bool]
        #
        def empty?
            @q.empty?
        end

        #
        # Removes all objects from the Queue.
        #
        def clear
            while( !@q.empty? )
                path = @q.pop
                next if !path
                delete_file( path )
            end
        end

    end

end
end