# -*- coding: binary -*-
module PacketGen
  # StructFu, a nifty way to leverage Ruby's built in Struct class
  # to create meaningful binary data.
  #
  # Copied from PacketFu:
  #
  # Copyright (c) 2008-2014, Tod Beardsley
  # All rights reserved.
  #
  # Redistribution and use in source and binary forms, with or without
  # modification, are permitted provided that the following conditions are met:
  # 
  #     * Redistributions of source code must retain the above copyright
  #       notice, this list of conditions and the following disclaimer.
  #     * Redistributions in binary form must reproduce the above copyright
  #       notice, this list of conditions and the following disclaimer in the
  #       documentation and/or other materials provided with the distribution.
  #     * Neither the name of Tod Beardsley nor the
  #       names of its contributors may be used to endorse or promote products
  #       derived from this software without specific prior written permission.
  #
  # THIS SOFTWARE IS PROVIDED BY TOD BEARDSLEY ''AS IS'' AND ANY
  # EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  # WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  # DISCLAIMED. IN NO EVENT SHALL TOD BEARDSLEY BE LIABLE FOR ANY
  # DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  # (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  # LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  # ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  module StructFu
  
    # Normally, self.size and self.length will refer to the Struct
    # size as an array. It's a hassle to redefine, so this introduces some
    # shorthand to get at the size of the resultant string.
    def sz
      self.to_s.size
    end

    alias len sz

    # Typecast is used mostly by packet header classes, such as IPHeader,
    # TCPHeader, and the like. It takes an argument, and casts it to the
    # expected type for that element. 
    def typecast(i)
      c = caller[0].match(/.*`([^']+)='/)[1]
      self[c.intern].read i
    end

    # Used like typecast(), but specifically for casting Strings to StructFu::Strings.
    def body=(i)
      if i.kind_of? ::String
        typecast(i)
      elsif i.kind_of? StructFu
        self[:body] = i
      elsif i.nil?
        self[:body] = StructFu::String.new.read("")
      else
        raise ArgumentError, "Can't cram a #{i.class} into a StructFu :body"
      end
    end

    # Handle deep copies correctly.
    def clone
      Marshal.load(Marshal.dump(self))
    end

    # Set the endianness for the various Int classes handled by self
    # @param [:little, :big] e
    # @return [:little, :big] returns e
    def set_endianness(e)
      unless [:little, :big].include? e
        raise ArgumentError, "unknown endianness for #{self.class}"
      end
      @int64 = e == :little ? Int64le : Int64be
      @int32 = e == :little ? Int32le : Int32be
      @int16 = e == :little ? Int16le : Int16be
      e
    end

    # Get binary string
    # @return [String]
    def to_s
      to_a.map { |field| field.to_s }.join
    end

    # Ints all have a value, an endianness, and a default value.
    # Note that the signedness of Int values are implicit as
    # far as the subclasses are concerned; to_i and to_f will 
    # return Integer/Float versions of the input value, instead
    # of attempting to unpack the pack value. (This can be a useful
    # hint to other functions).
    #
    # ==== Header Definition
    #
    #   Fixnum  :value
    #   Symbol  :endian
    #   Fixnum  :width
    #   Fixnum  :default
    class Int < Struct.new(:value, :endian, :width, :default)
      alias :v= :value=
      alias :v :value
      alias :e= :endian=
      alias :e :endian
      alias :w= :width=
      alias :w :width
      alias :d= :default=
      alias :d :default

      # This is a parent class definition and should not be used directly.
      def to_s
        raise StandardError, "StructFu::Int#to_s accessed, must be redefined."
      end

      # Returns the Int as an Integer.
      def to_i
        (self.v || self.d).to_i
      end

      # Returns the Int as a Float.
      def to_f
        (self.v || self.d).to_f
      end
    
      def initialize(value=nil, endian=nil, width=nil, default=nil)
        super(value,endian,width,default=0)
      end

      # Reads either an Integer or a packed string, and populates the value accordingly.
      def read(i)
        self.v = i.kind_of?(Integer) ? i.to_i : i.to_s.unpack(@packstr).first
        self
      end
    end

    # Int8 is a one byte value.
    class Int8 < Int

      def initialize(v=nil)
        super(v,nil,w=1)
        @packstr = "C"
      end

      # Returns a one byte value as a packed string.
      def to_s
        [(self.v || self.d)].pack("C")
      end
    end

    # Int16 is a two byte value.
    class Int16 < Int
      def initialize(v=nil, e=:big)
        super(v,e,w=2)
        @packstr = (self.e == :big) ? "n" : "v"
      end

      # Returns a two byte value as a packed string.
      def to_s
        @packstr = (self.e == :big) ? "n" : "v"
        [(self.v || self.d)].pack(@packstr)
      end
    end
  
    # Int16be is a two byte value in big-endian format. The endianness cannot be altered.
    class Int16be < Int16
      undef :endian=
    end

    # Int16le is a two byte value in little-endian format. The endianness cannot be altered.
    class Int16le < Int16
      undef :endian=
      def initialize(v=nil, e=:little)
        super(v,e)
        @packstr = (self.e == :big) ? "n" : "v"
      end
    end

    # Int32 is a four byte value.
    class Int32 < Int
      def initialize(v=nil, e=:big)
        super(v,e,w=4)
        @packstr = (self.e == :big) ? "N" : "V"
      end

      # Returns a four byte value as a packed string.
      def to_s
        @packstr = (self.e == :big) ? "N" : "V"
        [(self.v || self.d)].pack(@packstr)
      end
    end

    # Int32be is a four byte value in big-endian format. The endianness cannot be altered.
    class Int32be < Int32
      undef :endian=
    end

    # Int32le is a four byte value in little-endian format. The endianness cannot be altered.
    class Int32le < Int32
      undef :endian=
      def initialize(v=nil, e=:little)
        super(v,e)
      end
    end

    # Int64 is a eight byte value.
    class Int64 < Int
      def initialize(v=nil, e=:big)
        super(v, e, w=4)
        @packstr = (self.e == :big) ? 'Q>' : 'Q<'
      end

      # Returns a eight byte value as a packed string.
      def to_s
        @packstr = (self.e == :big) ? 'Q>' : 'Q<'
        [(self.v || self.d)].pack(@packstr)
      end
    end

    # Int64be is a eight byte value in big-endian format. The endianness cannot be altered.
    class Int64be < Int64
      undef :endian=
    end

    # Int64le is a eight byte value in little-endian format. The endianness cannot be altered.
    class Int64le < Int64
      undef :endian=
      def initialize(v=nil, e=:little)
        super(v,e)
      end
    end

    # Strings are just like regular strings, except it comes with a read() function
    # so that it behaves like other StructFu elements.
    class String < ::String
      def read(str)
        str = str.to_s
        self.replace str
        self
      end

      # @author Sylvain Daubert
      # Added for consistency with Struct classes
      alias :sz :length
    end

    # Provides a primitive for creating strings, preceeded by
    # an Int type of length. By default, a string of length zero with
    # a one-byte length is presumed.  
    #
    # Note that IntStrings aren't used for much, but it seemed like a good idea at the time.
    class IntString < Struct.new(:int, :string, :mode)

      def initialize(string='',int=Int8,mode=nil)
        if int < Int
          super(int.new,string,mode)
          calc
        else
          raise "IntStrings need a StructFu::Int for a length."
        end
      end

      # Calculates the size of a string, and sets it as the value.
      def calc
        int.v = string.to_s.size
        self.to_s
      end

      # Returns the object as a string, depending on the mode set upon object creation.
      def to_s
        if mode == :parse
          "#{int}" + [string].pack("a#{len}")
        elsif mode == :fix
          self.int.v = string.size
          "#{int}#{string}"
        else
          "#{int}#{string}"
        end
      end

      # By redefining #string=, we can ensure the correct value
      # is calculated upon assignment. If you'd prefer to have
      # an incorrect value, use the syntax, obj[:string]="value"
      # instead. Note, by using the alternate form, you must
      # #calc before you can trust the int's value. Think of the = 
      # assignment as "set to equal," while the []= assignment
      # as "boxing in" the value. Maybe.
      def string=(s)
        self[:string] = s
        calc
      end

      # Shorthand for querying a length. Note that the usual "length"
      # and "size" refer to the number of elements of this struct.
      def len
        self[:int].value
      end

      # Override the size, if you must.
      def len=(i)
        self[:int].value=i
      end

      # Read takes a string, assumes an int width as previously
      # defined upon initialization, but makes no guarantees
      # the int value isn't lying. You're on your own to test
      # for that (or use parse() with a :mode set).
      def read(s)
        unless s[0,int.width].size == int.width
          raise StandardError, "String is too short for type #{int.class}"
        else
          int.read(s[0,int.width])
          self[:string] = s[int.width,s.size]
        end
        self.to_s
      end

      # parse() is like read(), except that it interprets the string, either
      # based on the declared length, or the actual length. Which strategy
      # is used is dependant on which :mode is set (with self.mode).
      #
      # :parse : Read the length, and then read in that many bytes of the string. 
      # The string may be truncated or padded out with nulls, as dictated by the value.
      #
      # :fix   : Skip the length, read the rest of the string, then set the length 
      # to what it ought to be.
      #
      # else   : If neither of these modes are set, just perfom a normal read().
      # This is the default.
      def parse(s)
        unless s[0,int.width].size == int.width
          raise StandardError, "String is too short for type #{int.class}"
        else
          case mode 
          when :parse
            int.read(s[0,int.width])
            self[:string] = s[int.width,int.value]
            if string.size < int.value
              self[:string] += ("\x00" * (int.value - self[:string].size))
            end
          when :fix
            self.string = s[int.width,s.size]
          else
            return read(s)
          end
        end
        self.to_s
      end
    end
  end
end

class Struct
  # Monkeypatch for Struct to include some string safety -- anything that uses
  # Struct is going to presume binary strings anyway.
  # Modified by S. Daubert to not call PacketFu.force_binary
  def force_binary(str)
    str.force_encoding Encoding::BINARY
  end
end