class Parser::Source::Buffer

def self.recognize_encoding(string)
  return if string.empty?
  # extract the first two lines in an efficient way
  string =~ /\A(.*)\n?(.*\n)?/
  first_line, second_line = $1, $2
  if first_line =~ /\A\xef\xbb\xbf/ # BOM
    return Encoding::UTF_8
  elsif first_line[0, 2] == '#!'
    encoding_line = second_line
  else
    encoding_line = first_line
  end
  if (result = ENCODING_RE.match(encoding_line))
    Encoding.find(result[2] || result[3] || result[5])
  else
    nil
  end
end

def self.reencode_string(string)
  original_encoding = string.encoding
  detected_encoding = recognize_encoding(string.force_encoding(Encoding::BINARY))
  if detected_encoding.nil?
    string.force_encoding(original_encoding)
  elsif detected_encoding == Encoding::BINARY
    string
  else
    string.
      force_encoding(detected_encoding).
      encode(Encoding::UTF_8)
  end
end

def decompose_position(position)
  line_no, line_begin = line_for(position)
  [ @first_line + line_no, position - line_begin ]
end

def initialize(name, first_line = 1)
  @name        = name
  @source      = nil
  @first_line  = first_line
  @lines       = nil
  @line_begins = nil
end

def line_begins
  unless @line_begins
    @line_begins, index = [ [ 0, 0 ] ], 1
    @source.each_char do |char|
      if char == "\n"
        @line_begins.unshift [ @line_begins.length, index ]
      end
      index += 1
    end
  end
  @line_begins
end

def line_for(position)
  if line_begins.respond_to? :bsearch
    # Fast O(log n) variant for Ruby >=2.0.
    line_begins.bsearch do |line, line_begin|
      line_begin <= position
    end
  else
    # Slower O(n) variant for Ruby <2.0.
    line_begins.find do |line, line_begin|
      line_begin <= position
    end
  end
end

def raw_source=(source)
  if @source
    raise ArgumentError, 'Source::Buffer is immutable'
  end
  @source = source.gsub(/\r\n/, "\n").freeze
end

def read
  File.open(@name, 'rb') do |io|
    self.source = io.read
  end
  self
end

def source
  if @source.nil?
    raise RuntimeError, 'Cannot extract source from uninitialized Source::Buffer'
  end
  @source
end

def source=(source)
  if defined?(Encoding)
    source = source.dup if source.frozen?
    source = self.class.reencode_string(source)
  end
  self.raw_source = source
end

def source_line(lineno)
  unless @lines
    @lines = @source.lines.to_a
    @lines.each { |line| line.gsub!(/\n$/, '') }
    # Lexer has an "infinite stream of EOF symbols" after the
    # actual EOF, so in some cases (e.g. EOF token of ruby-parse -E)
    # tokens will refer to one line past EOF.
    @lines << ""
  end
  @lines[lineno - @first_line].dup
end