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+# This class implements a pretty printing algorithm. It finds line breaks and
+# nice indentations for grouped structure.
+#
+# By default, the class assumes that primitive elements are strings and each
+# byte in the strings have single column in width. But it can be used for
+# other situations by giving suitable arguments for some methods:
+# * newline object and space generation block for PrettyPrint.new
+# * optional width argument for PrettyPrint#text
+# * PrettyPrint#breakable
+#
+# There are several candidate uses:
+# * text formatting using proportional fonts
+# * multibyte characters which has columns different to number of bytes
+# * non-string formatting
+#
+# == Bugs
+# * Box based formatting?
+# * Other (better) model/algorithm?
+#
+# Report any bugs at http://bugs.ruby-lang.org
+#
+# == References
+# Christian Lindig, Strictly Pretty, March 2000,
+# http://www.st.cs.uni-sb.de/~lindig/papers/#pretty
+#
+# Philip Wadler, A prettier printer, March 1998,
+# http://homepages.inf.ed.ac.uk/wadler/topics/language-design.html#prettier
+#
+# == Author
+# Tanaka Akira <akr@fsij.org>
+#
+class PrettyPrint
+
+  # This is a convenience method which is same as follows:
+  #
+  #   begin
+  #     q = PrettyPrint.new(output, maxwidth, newline, &genspace)
+  #     ...
+  #     q.flush
+  #     output
+  #   end
+  #
+  def PrettyPrint.format(output='', maxwidth=79, newline="\n", genspace=lambda {|n| ' ' * n})
+    q = PrettyPrint.new(output, maxwidth, newline, &genspace)
+    yield q
+    q.flush
+    output
+  end
+
+  # This is similar to PrettyPrint::format but the result has no breaks.
+  #
+  # +maxwidth+, +newline+ and +genspace+ are ignored.
+  #
+  # The invocation of +breakable+ in the block doesn't break a line and is
+  # treated as just an invocation of +text+.
+  #
+  def PrettyPrint.singleline_format(output='', maxwidth=nil, newline=nil, genspace=nil)
+    q = SingleLine.new(output)
+    yield q
+    output
+  end
+
+  # Creates a buffer for pretty printing.
+  #
+  # +output+ is an output target. If it is not specified, '' is assumed. It
+  # should have a << method which accepts the first argument +obj+ of
+  # PrettyPrint#text, the first argument +sep+ of PrettyPrint#breakable, the
+  # first argument +newline+ of PrettyPrint.new, and the result of a given
+  # block for PrettyPrint.new.
+  #
+  # +maxwidth+ specifies maximum line length. If it is not specified, 79 is
+  # assumed. However actual outputs may overflow +maxwidth+ if long
+  # non-breakable texts are provided.
+  #
+  # +newline+ is used for line breaks. "\n" is used if it is not specified.
+  #
+  # The block is used to generate spaces. {|width| ' ' * width} is used if it
+  # is not given.
+  #
+  def initialize(output='', maxwidth=79, newline="\n", &genspace)
+    @output = output
+    @maxwidth = maxwidth
+    @newline = newline
+    @genspace = genspace || lambda {|n| ' ' * n}
+
+    @output_width = 0
+    @buffer_width = 0
+    @buffer = []
+
+    root_group = Group.new(0)
+    @group_stack = [root_group]
+    @group_queue = GroupQueue.new(root_group)
+    @indent = 0
+  end
+
+  # The output object.
+  #
+  # This defaults to '', and should accept the << method
+  attr_reader :output
+
+  # The maximum width of a line, before it is separated in to a newline
+  #
+  # This defaults to 79, and should be a Fixnum
+  attr_reader :maxwidth
+
+  # The value that is appended to +output+ to add a new line.
+  #
+  # This defaults to "\n", and should be String
+  attr_reader :newline
+
+  # A lambda or Proc, that takes one argument, of a Fixnum, and returns
+  # the corresponding number of spaces.
+  #
+  # By default this is:
+  #   lambda {|n| ' ' * n}
+  attr_reader :genspace
+
+  # The number of spaces to be indented
+  attr_reader :indent
+
+  # The PrettyPrint::GroupQueue of groups in stack to be pretty printed
+  attr_reader :group_queue
+
+  # Returns the group most recently added to the stack.
+  #
+  # Contrived example:
+  #   out = ""
+  #   => ""
+  #   q = PrettyPrint.new(out)
+  #   => #<PrettyPrint:0x82f85c0 @output="", @maxwidth=79, @newline="\n", @genspace=#<Proc:0x82f8368@/home/vbatts/.rvm/rubies/ruby-head/lib/ruby/2.0.0/prettyprint.rb:82 (lambda)>, @output_width=0, @buffer_width=0, @buffer=[], @group_stack=[#<PrettyPrint::Group:0x82f8138 @depth=0, @breakables=[], @break=false>], @group_queue=#<PrettyPrint::GroupQueue:0x82fb7c0 @queue=[[#<PrettyPrint::Group:0x82f8138 @depth=0, @breakables=[], @break=false>]]>, @indent=0>
+  #   q.group {
+  #     q.text q.current_group.inspect
+  #     q.text q.newline
+  #     q.group(q.current_group.depth + 1) {
+  #       q.text q.current_group.inspect
+  #       q.text q.newline
+  #       q.group(q.current_group.depth + 1) {
+  #         q.text q.current_group.inspect
+  #         q.text q.newline
+  #         q.group(q.current_group.depth + 1) {
+  #           q.text q.current_group.inspect
+  #           q.text q.newline
+  #         }
+  #       }
+  #     }
+  #   }
+  #   => 284
+  #    puts out
+  #   #<PrettyPrint::Group:0x8354758 @depth=1, @breakables=[], @break=false>
+  #   #<PrettyPrint::Group:0x8354550 @depth=2, @breakables=[], @break=false>
+  #   #<PrettyPrint::Group:0x83541cc @depth=3, @breakables=[], @break=false>
+  #   #<PrettyPrint::Group:0x8347e54 @depth=4, @breakables=[], @break=false>
+  def current_group
+    @group_stack.last
+  end
+
+  # Breaks the buffer into lines that are shorter than #maxwidth
+  def break_outmost_groups
+    while @maxwidth < @output_width + @buffer_width
+      return unless group = @group_queue.deq
+      until group.breakables.empty?
+        data = @buffer.shift
+        @output_width = data.output(@output, @output_width)
+        @buffer_width -= data.width
+      end
+      while !@buffer.empty? && Text === @buffer.first
+        text = @buffer.shift
+        @output_width = text.output(@output, @output_width)
+        @buffer_width -= text.width
+      end
+    end
+  end
+
+  # This adds +obj+ as a text of +width+ columns in width.
+  #
+  # If +width+ is not specified, obj.length is used.
+  #
+  def text(obj, width=obj.length)
+    if @buffer.empty?
+      @output << obj
+      @output_width += width
+    else
+      text = @buffer.last
+      unless Text === text
+        text = Text.new
+        @buffer << text
+      end
+      text.add(obj, width)
+      @buffer_width += width
+      break_outmost_groups
+    end
+  end
+
+  # This is similar to #breakable except
+  # the decision to break or not is determined individually.
+  #
+  # Two #fill_breakable under a group may cause 4 results:
+  # (break,break), (break,non-break), (non-break,break), (non-break,non-break).
+  # This is different to #breakable because two #breakable under a group
+  # may cause 2 results:
+  # (break,break), (non-break,non-break).
+  #
+  # The text +sep+ is inserted if a line is not broken at this point.
+  #
+  # If +sep+ is not specified, " " is used.
+  #
+  # If +width+ is not specified, +sep.length+ is used. You will have to
+  # specify this when +sep+ is a multibyte character, for example.
+  #
+  def fill_breakable(sep=' ', width=sep.length)
+    group { breakable sep, width }
+  end
+
+  # This says "you can break a line here if necessary", and a +width+\-column
+  # text +sep+ is inserted if a line is not broken at the point.
+  #
+  # If +sep+ is not specified, " " is used.
+  #
+  # If +width+ is not specified, +sep.length+ is used. You will have to
+  # specify this when +sep+ is a multibyte character, for example.
+  #
+  def breakable(sep=' ', width=sep.length)
+    group = @group_stack.last
+    if group.break?
+      flush
+      @output << @newline
+      @output << @genspace.call(@indent)
+      @output_width = @indent
+      @buffer_width = 0
+    else
+      @buffer << Breakable.new(sep, width, self)
+      @buffer_width += width
+      break_outmost_groups
+    end
+  end
+
+  # Groups line break hints added in the block. The line break hints are all
+  # to be used or not.
+  #
+  # If +indent+ is specified, the method call is regarded as nested by
+  # nest(indent) { ... }.
+  #
+  # If +open_obj+ is specified, <tt>text open_obj, open_width</tt> is called
+  # before grouping. If +close_obj+ is specified, <tt>text close_obj,
+  # close_width</tt> is called after grouping.
+  #
+  def group(indent=0, open_obj='', close_obj='', open_width=open_obj.length, close_width=close_obj.length)
+    text open_obj, open_width
+    group_sub {
+      nest(indent) {
+        yield
+      }
+    }
+    text close_obj, close_width
+  end
+
+  # Takes a block and queues a new group that is indented 1 level further.
+  def group_sub
+    group = Group.new(@group_stack.last.depth + 1)
+    @group_stack.push group
+    @group_queue.enq group
+    begin
+      yield
+    ensure
+      @group_stack.pop
+      if group.breakables.empty?
+        @group_queue.delete group
+      end
+    end
+  end
+
+  # Increases left margin after newline with +indent+ for line breaks added in
+  # the block.
+  #
+  def nest(indent)
+    @indent += indent
+    begin
+      yield
+    ensure
+      @indent -= indent
+    end
+  end
+
+  # outputs buffered data.
+  #
+  def flush
+    @buffer.each {|data|
+      @output_width = data.output(@output, @output_width)
+    }
+    @buffer.clear
+    @buffer_width = 0
+  end
+
+  # The Text class is the means by which to collect strings from objects.
+  #
+  # This class is intended for internal use of the PrettyPrint buffers.
+  class Text # :nodoc:
+
+    # Creates a new text object.
+    #
+    # This constructor takes no arguments.
+    #
+    # The workflow is to append a PrettyPrint::Text object to the buffer, and
+    # being able to call the buffer.last() to reference it.
+    #
+    # As there are objects, use PrettyPrint::Text#add to include the objects
+    # and the width to utilized by the String version of this object.
+    def initialize
+      @objs = []
+      @width = 0
+    end
+
+    # The total width of the objects included in this Text object.
+    attr_reader :width
+
+    # Render the String text of the objects that have been added to this Text object.
+    #
+    # Output the text to +out+, and increment the width to +output_width+
+    def output(out, output_width)
+      @objs.each {|obj| out << obj}
+      output_width + @width
+    end
+
+    # Include +obj+ in the objects to be pretty printed, and increment
+    # this Text object's total width by +width+
+    def add(obj, width)
+      @objs << obj
+      @width += width
+    end
+  end
+
+  # The Breakable class is used for breaking up object information
+  #
+  # This class is intended for internal use of the PrettyPrint buffers.
+  class Breakable # :nodoc:
+
+    # Create a new Breakable object.
+    #
+    # Arguments:
+    # * +sep+ String of the separator
+    # * +width+ Fixnum width of the +sep+
+    # * +q+ parent PrettyPrint object, to base from
+    def initialize(sep, width, q)
+      @obj = sep
+      @width = width
+      @pp = q
+      @indent = q.indent
+      @group = q.current_group
+      @group.breakables.push self
+    end
+
+    # Holds the separator String
+    #
+    # The +sep+ argument from ::new
+    attr_reader :obj
+
+    # The width of +obj+ / +sep+
+    attr_reader :width
+
+    # The number of spaces to indent.
+    #
+    # This is inferred from +q+ within PrettyPrint, passed in ::new
+    attr_reader :indent
+
+    # Render the String text of the objects that have been added to this
+    # Breakable object.
+    #
+    # Output the text to +out+, and increment the width to +output_width+
+    def output(out, output_width)
+      @group.breakables.shift
+      if @group.break?
+        out << @pp.newline
+        out << @pp.genspace.call(@indent)
+        @indent
+      else
+        @pp.group_queue.delete @group if @group.breakables.empty?
+        out << @obj
+        output_width + @width
+      end
+    end
+  end
+
+  # The Group class is used for making indentation easier.
+  #
+  # While this class does neither the breaking into newlines nor indentation,
+  # it is used in a stack (as well as a queue) within PrettyPrint, to group
+  # objects.
+  #
+  # For information on using groups, see PrettyPrint#group
+  #
+  # This class is intended for internal use of the PrettyPrint buffers.
+  class Group # :nodoc:
+    # Create a Group object
+    #
+    # Arguments:
+    # * +depth+ - this group's relation to previous groups
+    def initialize(depth)
+      @depth = depth
+      @breakables = []
+      @break = false
+    end
+
+    # This group's relation to previous groups
+    attr_reader :depth
+
+    # Array to hold the Breakable objects for this Group
+    attr_reader :breakables
+
+    # Makes a break for this Group, and returns true
+    def break
+      @break = true
+    end
+
+    # Boolean of whether this Group has made a break
+    def break?
+      @break
+    end
+
+    # Boolean of whether this Group has been queried for being first
+    #
+    # This is used as a predicate, and ought to be called first.
+    def first?
+      if defined? @first
+        false
+      else
+        @first = false
+        true
+      end
+    end
+  end
+
+  # The GroupQueue class is used for managing the queue of Group to be pretty
+  # printed.
+  #
+  # This queue groups the Group objects, based on their depth.
+  #
+  # This class is intended for internal use of the PrettyPrint buffers.
+  class GroupQueue # :nodoc:
+    # Create a GroupQueue object
+    #
+    # Arguments:
+    # * +groups+ - one or more PrettyPrint::Group objects
+    def initialize(*groups)
+      @queue = []
+      groups.each {|g| enq g}
+    end
+
+    # Enqueue +group+
+    #
+    # This does not strictly append the group to the end of the queue,
+    # but instead adds it in line, base on the +group.depth+
+    def enq(group)
+      depth = group.depth
+      @queue << [] until depth < @queue.length
+      @queue[depth] << group
+    end
+
+    # Returns the outer group of the queue
+    def deq
+      @queue.each {|gs|
+        (gs.length-1).downto(0) {|i|
+          unless gs[i].breakables.empty?
+            group = gs.slice!(i, 1).first
+            group.break
+            return group
+          end
+        }
+        gs.each {|group| group.break}
+        gs.clear
+      }
+      return nil
+    end
+
+    # Remote +group+ from this queue
+    def delete(group)
+      @queue[group.depth].delete(group)
+    end
+  end
+
+  # PrettyPrint::SingleLine is used by PrettyPrint.singleline_format
+  #
+  # It is passed to be similar to a PrettyPrint object itself, by responding to:
+  # * #text
+  # * #breakable
+  # * #nest
+  # * #group
+  # * #flush
+  # * #first?
+  #
+  # but instead, the output has no line breaks
+  #
+  class SingleLine
+    # Create a PrettyPrint::SingleLine object
+    #
+    # Arguments:
+    # * +output+ - String (or similar) to store rendered text. Needs to respond to '<<'
+    # * +maxwidth+ - Argument position expected to be here for compatibility.
+    #                This argument is a noop.
+    # * +newline+ - Argument position expected to be here for compatibility.
+    #               This argument is a noop.
+    def initialize(output, maxwidth=nil, newline=nil)
+      @output = output
+      @first = [true]
+    end
+
+    # Add +obj+ to the text to be output.
+    #
+    # +width+ argument is here for compatibility. It is a noop argument.
+    def text(obj, width=nil)
+      @output << obj
+    end
+
+    # Appends +sep+ to the text to be output. By default +sep+ is ' '
+    #
+    # +width+ argument is here for compatibility. It is a noop argument.
+    def breakable(sep=' ', width=nil)
+      @output << sep
+    end
+
+    # Takes +indent+ arg, but does nothing with it.
+    #
+    # Yields to a block.
+    def nest(indent) # :nodoc:
+      yield
+    end
+
+    # Opens a block for grouping objects to be pretty printed.
+    #
+    # Arguments:
+    # * +indent+ - noop argument. Present for compatibility.
+    # * +open_obj+ - text appended before the &blok. Default is ''
+    # * +close_obj+ - text appended after the &blok. Default is ''
+    # * +open_width+ - noop argument. Present for compatibility.
+    # * +close_width+ - noop argument. Present for compatibility.
+    def group(indent=nil, open_obj='', close_obj='', open_width=nil, close_width=nil)
+      @first.push true
+      @output << open_obj
+      yield
+      @output << close_obj
+      @first.pop
+    end
+
+    # Method present for compatibility, but is a noop
+    def flush # :nodoc:
+    end
+
+    # This is used as a predicate, and ought to be called first.
+    def first?
+      result = @first[-1]
+      @first[-1] = false
+      result
+    end
+  end
+end