Method: Diff::LCS.__diff_direction

Defined in:
lib/gems/diff-lcs-1.1.2/lib/diff/lcs.rb

.__diff_direction(src, patchset, limit = nil) ⇒ Object

Examine the patchset and the source to see in which direction the patch should be applied.

WARNING: By default, this examines the whole patch, so this could take some time. This also works better with Diff::LCS::ContextChange or Diff::LCS::Change as its source, as an array will cause the creation of one of the above.



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# File 'lib/gems/diff-lcs-1.1.2/lib/diff/lcs.rb', line 939

def __diff_direction(src, patchset, limit = nil)
  count = left = left_miss = right = right_miss = 0
  string = src.kind_of?(String)

  patchset.each do |change|
    count += 1

    case change
    when Diff::LCS::Change
        # With a simplistic change, we can't tell the difference between
        # the left and right on '!' actions, so we ignore those. On '='
        # actions, if there's a miss, we miss both left and right.
      element = string ? src[change.position, 1] : src[change.position]

      case change.action
      when '-'
        if element == change.element
          left += 1
        else
          left_miss += 1
        end
      when '+'
        if element == change.element
          right += 1
        else
          right_miss += 1
        end
      when '='
        if element != change.element
          left_miss += 1
          right_miss += 1
        end
      end
    when Diff::LCS::ContextChange
      case change.action
      when '-' # Remove details from the old string
        element = string ? src[change.old_position, 1] : src[change.old_position]
        if element == change.old_element
          left += 1
        else
          left_miss += 1
        end
      when '+'
        element = string ? src[change.new_position, 1] : src[change.new_position]
        if element == change.new_element
          right += 1
        else
          right_miss += 1
        end
      when '='
        le = string ? src[change.old_position, 1] : src[change.old_position]
        re = string ? src[change.new_position, 1] : src[change.new_position]

        left_miss += 1 if le != change.old_element
        right_miss += 1 if re != change.new_element
      when '!'
        element = string ? src[change.old_position, 1] : src[change.old_position]
        if element == change.old_element
          left += 1
        else
          element = string ? src[change.new_position, 1] : src[change.new_position]
          if element == change.new_element
            right += 1
          else
            left_miss += 1
            right_miss += 1
          end
        end
      end
    end

    break if not limit.nil? and count > limit
  end

  no_left = (left == 0) and (left_miss >= 0)
  no_right = (right == 0) and (right_miss >= 0)

  case [no_left, no_right]
  when [false, true]
    return :patch
  when [true, false]
    return :unpatch
  else
    raise "The provided patchset does not appear to apply to the provided value as either source or destination value."
  end
end