Class: Parser::Source::Rewriter

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# File 'lib/parser/source/rewriter.rb', line 24

class Rewriter
  attr_reader :source_buffer
  attr_reader :diagnostics

  ##
  # @param [Source::Buffer] source_buffer
  #
  def initialize(source_buffer)
    @diagnostics = Diagnostic::Engine.new
    @diagnostics.consumer = lambda do |diag|
      $stderr.puts diag.render
    end

    @source_buffer = source_buffer
    @queue         = []
    @clobber       = 0
  end

  ##
  # Removes the source range.
  #
  # @param [Range] range
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def remove(range)
    append Rewriter::Action.new(range, '')
  end

  ##
  # Inserts new code before the given source range.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def insert_before(range, content)
    append Rewriter::Action.new(range.begin, content)
  end

  ##
  # Inserts new code after the given source range.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def insert_after(range, content)
    append Rewriter::Action.new(range.end, content)
  end

  ##
  # Replaces the code of the source range `range` with `content`.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def replace(range, content)
    append Rewriter::Action.new(range, content)
  end

  ##
  # Applies all scheduled changes to the `source_buffer` and returns
  # modified source as a new string.
  #
  # @return [String]
  #
  def process
    if in_transaction?
      raise "Do not call #{self.class}##{__method__} inside a transaction"
    end

    adjustment = 0
    source     = @source_buffer.source.dup

    sorted_queue = @queue.sort_by.with_index do |action, index|
      [action.range.begin_pos, index]
    end

    sorted_queue.each do |action|
      begin_pos = action.range.begin_pos + adjustment
      end_pos   = begin_pos + action.range.length

      source[begin_pos...end_pos] = action.replacement

      adjustment += (action.replacement.length - action.range.length)
    end

    source
  end

  ##
  # Provides a protected block where a sequence of multiple rewrite actions
  # are handled atomic. If any of the action failed by clobbering,
  # all the actions are rolled back.
  #
  # @example
  #  begin
  #    rewriter.transaction do
  #      rewriter.insert_before(range_of_something, '(')
  #      rewriter.insert_after(range_of_something, ')')
  #    end
  #  rescue Parser::ClobberingError
  #  end
  #
  # @raise [RuntimeError] when no block is passed
  # @raise [RuntimeError] when already in a transaction
  #
  def transaction
    unless block_given?
      raise "#{self.class}##{__method__} requires block"
    end

    if in_transaction?
      raise 'Nested transaction is not supported'
    end

    @pending_queue = @queue.dup
    @pending_clobber = @clobber

    yield

    @queue = @pending_queue
    @clobber = @pending_clobber

    self
  ensure
    @pending_queue = nil
    @pending_clobber = nil
  end

  private

  def append(action)
    if (clobber_action = clobbered?(action.range))
      # cannot replace 3 characters with "foobar"
      diagnostic = Diagnostic.new(:error,
                                  :invalid_action,
                                  { :action => action },
                                  action.range)
      @diagnostics.process(diagnostic)

      # clobbered by: remove 3 characters
      diagnostic = Diagnostic.new(:note,
                                  :clobbered,
                                  { :action => clobber_action },
                                  clobber_action.range)
      @diagnostics.process(diagnostic)

      raise ClobberingError, "Parser::Source::Rewriter detected clobbering"
    else
      clobber(action.range)

      active_queue << action
    end

    self
  end

  def clobber(range)
    self.active_clobber = active_clobber | (2 ** range.size - 1) << range.begin_pos
  end

  def clobbered?(range)
    if active_clobber & ((2 ** range.size - 1) << range.begin_pos) != 0
      active_queue.find do |action|
        action.range.to_a & range.to_a
      end
    end
  end

  def in_transaction?
    !@pending_queue.nil?
  end

  def active_queue
    @pending_queue || @queue
  end

  def active_clobber
    @pending_clobber || @clobber
  end

  def active_clobber=(value)
    if @pending_clobber
      @pending_clobber = value
    else
      @clobber = value
    end
  end
end