require "uri"

# Class representing one patch operation.
class PatchObj
  attr_accessor :start1, :start2
  attr_accessor :length1, :length2
  attr_accessor :diffs

  def initialize
    # Initializes with an empty list of diffs.
    @start1 = nil
    @start2 = nil
    @length1 = 0
    @length2 = 0
    @diffs = []
  end

  OPERATOR_TO_CHAR = {insert: "+", delete: "-", equal: " "}
  private_constant :OPERATOR_TO_CHAR

  ENCODE_REGEX = /[^0-9A-Za-z_.;!~*'(),\/?:@&=+$\#-]/
  private_constant :ENCODE_REGEX

  PATCH_PARSER = URI::RFC2396_Parser.new

  # Emulate GNU diff's format
  # Header: @@ -382,8 +481,9 @@
  # Indices are printed as 1-based, not 0-based.
  def to_s
    coords1 = get_coords(length1, start1)
    coords2 = get_coords(length2, start2)

    text = ["@@ -", coords1, " +", coords2, " @@\n"].join

    # Encode the body of the patch with %xx notation.
    text += diffs.map { |op, data|
      [OPERATOR_TO_CHAR[op], PATCH_PARSER.escape(data, ENCODE_REGEX), "\n"].join
    }.join.gsub("%20", " ")

    text
  end

  def get_coords(length, start)
    if length == 0
      start.to_s + ",0"
    elsif length == 1
      (start + 1).to_s
    else
      (start + 1).to_s + "," + length.to_s
    end
  end

  private :get_coords
end