class Diff::LCS::Hunk

def context_diff
  s = encode("***************\n")
  s << encode("*** #{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].map { |e| e.insert(0, encode(' ')) }
    removes.each do |block|
      block.remove.each do |item|
        outlist[item.position - lo][0, 1] = encode(block.op) # - or !
      end
    end
    s << outlist.join("\n")
  end
  s << encode("\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.insert(0, encode(' ')) }
    inserts.each do |block|
      block.insert.each do |item|
        outlist[item.position - lo][0, 1] = encode(block.op) # + or !
      end
    end
    s << outlist.join("\n")
  end
  s
end

def context_range(mode, op = ',')
  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}#{op}#{e}" : "#{e}"
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 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 = encode("#{op_act[@blocks[0].op]}#{context_range(:old)}\n")
  else
    s = encode("#{context_range(:old, ' ')}#{op_act[@blocks[0].op]}\n")
  end
  unless @blocks[0].insert.empty?
    @data_new[@start_new .. @end_new].each { |e| s << e + encode("\n") }
    s << encode(".\n")
  end
  s
end

def encode(literal, target_encoding = @preferred_data_encoding)
  literal.encode target_encoding
end

def encode(literal, target_encoding = nil)
  literal
end

def encode_as(string, *args)
  args.map { |arg| arg.encode(string.encoding) }
end

def encode_as(string, *args)
  args
end

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 initialize(data_old, data_new, piece, flag_context, file_length_difference)
  # At first, a hunk will have just one Block in it
  @blocks = [ Diff::LCS::Block.new(piece) ]
  if String.method_defined?(:encoding)
    @preferred_data_encoding = data_old.fetch(0, data_new.fetch(0,'') ).encoding
  end
  @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 = flag_context
end

def merge(hunk)
  if overlaps?(hunk)
    @start_old = hunk.start_old
    @start_new = hunk.start_new
    blocks.unshift(*hunk.blocks)
  else
    nil
  end
end

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 = encode("#{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 << encode("< ") + e + encode("\n") } unless block.remove.empty?
  s << encode("---\n") if block.op == "!"
  @data_new[@start_new .. @end_new].each { |e| s << encode("> ") + e + encode("\n") } unless block.insert.empty?
  s
end

def overlaps?(hunk)
  hunk and (((@start_old - hunk.end_old) <= 1) or
            ((@start_new - hunk.end_new) <= 1))
end

def unified_diff
  # Calculate item number range.
  s = encode("@@ -#{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].map { |e| e.insert(0, encode(' ')) }
  @blocks.each do |block|
    block.remove.each do |item|
      op     = item.action.to_s # -
      offset = item.position - lo + num_added
      outlist[offset][0, 1] = encode(op)
      num_removed += 1
    end
    block.insert.each do |item|
      op     = item.action.to_s # +
      offset = item.position - @start_new + num_removed
      outlist[offset, 0] = encode(op) + @data_new[item.position]
      num_added += 1
    end
  end
  s << outlist.join(encode("\n"))
end

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