require 'bindata/base'

module BinData
  # A BinData::BasePrimitive object is a container for a value that has a
  # particular binary representation.  A value corresponds to a primitive type
  # such as as integer, float or string.  Only one value can be contained by
  # this object.  This value can be read from or written to an IO stream.
  #
  #   require 'bindata'
  #
  #   obj = BinData::Uint8.new(initial_value: 42)
  #   obj #=> 42
  #   obj.assign(5)
  #   obj #=> 5
  #   obj.clear
  #   obj #=> 42
  #
  #   obj = BinData::Uint8.new(value: 42)
  #   obj #=> 42
  #   obj.assign(5)
  #   obj #=> 42
  #
  #   obj = BinData::Uint8.new(assert: 3)
  #   obj.read("\005") #=> BinData::ValidityError: value is '5' but expected '3'
  #
  #   obj = BinData::Uint8.new(assert: -> { value < 5 })
  #   obj.read("\007") #=> BinData::ValidityError: value not as expected
  #
  # == Parameters
  #
  # Parameters may be provided at initialisation to control the behaviour of
  # an object.  These params include those for BinData::Base as well as:
  #
  # [<tt>:initial_value</tt>]  This is the initial value to use before one is
  #                            either #read or explicitly set with #value=.
  # [<tt>:value</tt>]          The object will always have this value.
  #                            Calls to #value= are ignored when
  #                            using this param.  While reading, #value
  #                            will return the value of the data read from the
  #                            IO, not the result of the <tt>:value</tt> param.
  # [<tt>:assert</tt>]         Raise an error unless the value read or assigned
  #                            meets this criteria.  The variable +value+ is
  #                            made available to any lambda assigned to this
  #                            parameter.  A boolean return indicates success
  #                            or failure.  Any other return is compared to
  #                            the value just read in.
  # [<tt>:asserted_value</tt>] Equivalent to <tt>:assert</tt> and <tt>:value</tt>.
  #
  class BasePrimitive < BinData::Base
    unregister_self

    optional_parameters :initial_value, :value, :assert, :asserted_value
    mutually_exclusive_parameters :initial_value, :value
    mutually_exclusive_parameters :asserted_value, :value, :assert

    def initialize_shared_instance
      extend InitialValuePlugin  if has_parameter?(:initial_value)
      extend ValuePlugin         if has_parameter?(:value)
      extend AssertPlugin        if has_parameter?(:assert)
      extend AssertedValuePlugin if has_parameter?(:asserted_value)
      super
    end

    def initialize_instance
      @value = nil
    end

    def clear? #:nodoc:
      @value.nil?
    end

    def assign(val)
      raise ArgumentError, "can't set a nil value for #{debug_name}" if val.nil?

      raw_val = val.respond_to?(:snapshot) ? val.snapshot : val
      @value = begin
                 raw_val.dup
               rescue TypeError
                 # can't dup Fixnums
                 raw_val
               end
    end

    def snapshot
      _value
    end

    def value
      snapshot
    end

    def value=(val)
      assign(val)
    end

    def respond_to?(symbol, include_private = false) #:nodoc:
      child = snapshot
      child.respond_to?(symbol, include_private) || super
    end

    def method_missing(symbol, *args, &block) #:nodoc:
      child = snapshot
      if child.respond_to?(symbol)
        self.class.class_eval "def #{symbol}(*args, &block);" \
                              "  snapshot.#{symbol}(*args, &block);" \
                              "end"
        child.__send__(symbol, *args, &block)
      else
        super
      end
    end

    def <=>(other)
      snapshot <=> other
    end

    def eql?(other)
      # double dispatch
      other.eql?(snapshot)
    end

    def hash
      snapshot.hash
    end

    def do_read(io) #:nodoc:
      @value = read_and_return_value(io)
    end

    def do_write(io) #:nodoc:
      io.writebytes(value_to_binary_string(_value))
    end

    def do_num_bytes #:nodoc:
      value_to_binary_string(_value).length
    end

    #---------------
    private

    # The unmodified value of this data object.  Note that #snapshot calls this
    # method.  This indirection is so that #snapshot can be overridden in
    # subclasses to modify the presentation value.
    def _value
      @value != nil ? @value : sensible_default
    end

    # Logic for the :value parameter
    module ValuePlugin
      def assign(val)
        # Ignored
      end

      def _value
        reading? ? @value : eval_parameter(:value)
      end
    end

    # Logic for the :initial_value parameter
    module InitialValuePlugin
      def _value
        @value != nil ? @value : eval_parameter(:initial_value)
      end
    end

    # Logic for the :assert parameter
    module AssertPlugin
      def assign(val)
        super(val)
        assert!
      end

      def do_read(io) #:nodoc:
        super(io)
        assert!
      end

      def assert!
        current_value = snapshot
        expected = eval_parameter(:assert, value: current_value)

        msg = if !expected
                "value '#{current_value}' not as expected"
              elsif expected != true && current_value != expected
                "value is '#{current_value}' but expected '#{expected}'"
              else
                nil
              end

        raise ValidityError, "#{msg} for #{debug_name}" if msg
      end
    end

    # Logic for the :asserted_value parameter
    module AssertedValuePlugin
      def assign(val)
        assert_value(val)
        super(val)
      end

      def _value
        reading? ? @value : eval_parameter(:asserted_value)
      end

      def do_read(io) #:nodoc:
        super(io)
        assert!
      end

      def assert!
        assert_value(snapshot)
      end

      def assert_value(current_value)
        expected = eval_parameter(:asserted_value, value: current_value)
        if current_value != expected
          raise ValidityError,
                "value is '#{current_value}' but " \
                "expected '#{expected}' for #{debug_name}"
        end
      end
    end

    ###########################################################################
    # To be implemented by subclasses

    # Return the string representation that +val+ will take when written.
    def value_to_binary_string(val)
      raise NotImplementedError
    end

    # Read a number of bytes from +io+ and return the value they represent.
    def read_and_return_value(io)
      raise NotImplementedError
    end

    # Return a sensible default for this data.
    def sensible_default
      raise NotImplementedError
    end

    # To be implemented by subclasses
    ###########################################################################
  end
end