#! /usr/env/bin ruby
#--
# Copyright 2004 Austin Ziegler <diff-lcs@halostatue.ca>
#   adapted from:
#     Algorithm::Diff (Perl) by Ned Konz <perl@bike-nomad.com>
#     Smalltalk by Mario I. Wolczko <mario@wolczko.com>
#   implements McIlroy-Hunt diff algorithm
#
# This program is free software. It may be redistributed and/or modified under
# the terms of the GPL version 2 (or later), the Perl Artistic licence, or the
# Ruby licence.
# 
# $Id: hunk.rb,v 1.2 2004/08/08 20:33:09 austin Exp $
#++
# Contains Diff::LCS::Hunk for bin/ldiff.

require 'diff/lcs/block'

  # A Hunk is a group of Blocks which overlap because of the context
  # surrounding each block. (So if we're not using context, every hunk will
  # contain one block.) Used in the diff program (bin/diff).
class Diff::LCS::Hunk
    # Create a hunk using references to both the old and new data, as well as
    # the piece of data
  def initialize(data_old, data_new, piece, context, file_length_difference)
      # At first, a hunk will have just one Block in it
    @blocks = [ Diff::LCS::Block.new(piece) ]
    @data_old = data_old
    @data_new = data_new

    before = after = file_length_difference
    after += @blocks[0].diff_size
    @file_length_difference = after # The caller must get this manually

      # Save the start & end of each array. If the array doesn't exist
      # (e.g., we're only adding items in this block), then figure out the
      # line number based on the line number of the other file and the
      # current difference in file lengths.
    if @blocks[0].remove.empty?
      a1 = a2 = nil
    else
      a1 = @blocks[0].remove[0].position
      a2 = @blocks[0].remove[-1].position
    end

    if @blocks[0].insert.empty?
      b1 = b2 = nil
    else
      b1 = @blocks[0].insert[0].position
      b2 = @blocks[0].insert[-1].position
    end

    @start_old = a1 || (b1 - before)
    @start_new = b1 || (a1 + before)
    @end_old   = a2 || (b2 - after)
    @end_new   = b2 || (a2 + after)

    self.flag_context = context
  end

  attr_reader :blocks
  attr_reader :start_old, :start_new
  attr_reader :end_old, :end_new
  attr_reader :file_length_difference

    # Change the "start" and "end" fields to note that context should be added
    # to this hunk
  attr_accessor :flag_context
  def flag_context=(context) #:nodoc:
    return if context.nil? or context.zero?

    add_start = (context > @start_old) ? @start_old : context
    @start_old -= add_start
    @start_new -= add_start

    if (@end_old + context) > @data_old.size
      add_end = @data_old.size - @end_old
    else
      add_end = context
    end
    @end_old += add_end
    @end_new += add_end
  end

  def unshift(hunk)
    @start_old = hunk.start_old
    @start_new = hunk.start_new
    blocks.unshift(*hunk.blocks)
  end

    # Is there an overlap between hunk arg0 and old hunk arg1? Note: if end
    # of old hunk is one less than beginning of second, they overlap
  def overlaps?(hunk = nil)
    return nil if hunk.nil?

    a = (@start_old - hunk.end_old) <= 1
    b = (@start_new - hunk.end_new) <= 1
    return (a or b)
  end

  def diff(format)
    case format
    when :old
      old_diff
    when :unified
      unified_diff
    when :context
      context_diff
    when :ed
      self
    when :reverse_ed, :ed_finish
      ed_diff(format)
    else
      raise "Unknown diff format #{format}."
    end
  end

  def each_old(block)
    @data_old[@start_old .. @end_old].each { |e| yield e }
  end

  private
    # Note that an old diff can't have any context. Therefore, we know that
    # there's only one block in the hunk.
  def old_diff
    warn "Expecting only one block in an old diff hunk!" if @blocks.size > 1
    op_act = { "+" => 'a', "-" => 'd', "!" => "c" }

    block = @blocks[0]

      # Calculate item number range. Old diff range is just like a context
      # diff range, except the ranges are on one line with the action between
      # them.
    s = "#{context_range(:old)}#{op_act[block.op]}#{context_range(:new)}\n"
      # If removing anything, just print out all the remove lines in the hunk
      # which is just all the remove lines in the block.
    @data_old[@start_old .. @end_old].each { |e| s << "< #{e}\n" } unless block.remove.empty?
    s << "---\n" if block.op == "!"
    @data_new[@start_new .. @end_new].each { |e| s << "> #{e}\n" } unless block.insert.empty?
    s
  end

  def unified_diff
      # Calculate item number range.
    s = "@@ -#{unified_range(:old)} +#{unified_range(:new)} @@\n"

      # Outlist starts containing the hunk of the old file. Removing an item
      # just means putting a '-' in front of it. Inserting an item requires
      # getting it from the new file and splicing it in. We splice in
      # +num_added+ items. Remove blocks use +num_added+ because splicing
      # changed the length of outlist.
      #
      # We remove +num_removed+ items. Insert blocks use +num_removed+
      # because their item numbers -- corresponding to positions in the NEW
      # file -- don't take removed items into account.
    lo, hi, num_added, num_removed = @start_old, @end_old, 0, 0

    outlist = @data_old[lo .. hi].collect { |e| e.gsub(/^/, ' ') }

    @blocks.each do |block|
      block.remove.each do |item|
        op = item.action.to_s # -
        offset = item.position - lo + num_added
        outlist[offset].gsub!(/^ /, op.to_s)
        num_removed += 1
      end
      block.insert.each do |item|
        op = item.action.to_s # +
        offset = item.position - @start_new + num_removed
        outlist[offset, 0] = "#{op}#{@data_new[item.position]}"
        num_added += 1
      end
    end

    s << outlist.join("\n")
  end

  def context_diff
    s = "***************\n"
    s << "*** #{context_range(:old)} ****\n"
    r = context_range(:new)

      # Print out file 1 part for each block in context diff format if there
      # are any blocks that remove items
    lo, hi = @start_old, @end_old
    removes = @blocks.select { |e| not e.remove.empty? }
    if removes
      outlist = @data_old[lo .. hi].collect { |e| e.gsub(/^/, '  ') }
      removes.each do |block|
        block.remove.each do |item|
          outlist[item.position - lo].gsub!(/^ /) { block.op } # - or !
        end
      end
      s << outlist.join("\n")
    end

    s << "\n--- #{r} ----\n"
    lo, hi = @start_new, @end_new
    inserts = @blocks.select { |e| not e.insert.empty? }
    if inserts
      outlist = @data_new[lo .. hi].collect { |e| e.gsub(/^/, '  ') }
      inserts.each do |block|
        block.insert.each do |item|
          outlist[item.position - lo].gsub!(/^ /) { block.op } # + or !
        end
      end
      s << outlist.join("\n")
    end
    s
  end

  def ed_diff(format)
    op_act = { "+" => 'a', "-" => 'd', "!" => "c" }
    warn "Expecting only one block in an old diff hunk!" if @blocks.size > 1

    if format == :reverse_ed
      s = "#{op_act[@blocks[0].op]}#{context_range(:old)}\n"
    else
      s = "#{context_range(:old).gsub(/,/, ' ')}#{op_act[@blocks[0].op]}\n"
    end

    unless @blocks[0].insert.empty?
      @data_new[@start_new .. @end_new].each { |e| s << "#{e}\n" }
      s << ".\n"
    end
    s
  end

    # Generate a range of item numbers to print. Only print 1 number if the
    # range has only one item in it. Otherwise, it's 'start,end'
  def context_range(mode)
    case mode
    when :old
      s, e = (@start_old + 1), (@end_old + 1)
    when :new
      s, e = (@start_new + 1), (@end_new + 1)
    end

    (s < e) ? "#{s},#{e}" : "#{e}"
  end

    # Generate a range of item numbers to print for unified diff. Print
    # number where block starts, followed by number of lines in the block
    # (don't print number of lines if it's 1)
  def unified_range(mode)
    case mode
    when :old
      s, e = (@start_old + 1), (@end_old + 1)
    when :new
      s, e = (@start_new + 1), (@end_new + 1)
    end

    length = e - s + 1
    first = (length < 2) ? e : s # "strange, but correct"
    (length == 1) ? "#{first}" : "#{first},#{length}"
  end
end
