Method: Diff::LCS.patch

Defined in:

lib/diff/lcs.rb

.patch(src, patchset, direction = nil) ⇒ Object

Applies a patchset to the sequence src according to the direction (:patch or :unpatch), producing a new sequence.

If the direction is not specified, Diff::LCS::patch will attempt to discover the direction of the patchset.

A patchset can be considered to apply forward (:patch) if the following expression is true:

patch(s1, diff(s1, s2)) -> s2

A patchset can be considered to apply backward (:unpatch) if the following expression is true:

patch(s2, diff(s1, s2)) -> s1

If the patchset contains no changes, the src value will be returned as either src.dup or src. A patchset can be deemed as having no changes if the following predicate returns true:

patchset.empty? or
  patchset.flatten(1).all? { |change| change.unchanged? }

Patchsets

A patchset is always an enumerable sequence of changes, hunks of changes, or a mix of the two. A hunk of changes is an enumerable sequence of changes:

[ # patchset
  # change
  [ # hunk
    # change
  ]
]

The patch method accepts patchsets that are enumerable sequences containing either Diff::LCS::Change objects (or a subclass) or the array representations of those objects. Prior to application, array representations of Diff::LCS::Change objects will be reified.

# File 'lib/diff/lcs.rb', line 624

def patch(src, patchset, direction = nil)
  # Normalize the patchset.
  has_changes, patchset = Diff::LCS::Internals.analyze_patchset(patchset)

  return src.respond_to?(:dup) ? src.dup : src unless has_changes

  string = src.kind_of?(String)
  # Start with a new empty type of the source's class
  res = src.class.new

  direction ||= Diff::LCS::Internals.intuit_diff_direction(src, patchset)

  ai = bj = 0

  patch_map = PATCH_MAP[direction]

  patchset.each do |change|
    # Both Change and ContextChange support #action
    action = patch_map[change.action]

    case change
    when Diff::LCS::ContextChange
      case direction
      when :patch
        el = change.new_element
        op = change.old_position
        np = change.new_position
      when :unpatch
        el = change.old_element
        op = change.new_position
        np = change.old_position
      end

      case action
      when '-' # Remove details from the old string
        while ai < op
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end
        ai += 1
      when '+'
        while bj < np
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end

        res << el
        bj += 1
      when '='
        # This only appears in sdiff output with the SDiff callback.
        # Therefore, we only need to worry about dealing with a single
        # element.
        res << el

        ai += 1
        bj += 1
      when '!'
        while ai < op
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end

        bj += 1
        ai += 1

        res << el
      end
    when Diff::LCS::Change
      case action
      when '-'
        while ai < change.position
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end
        ai += 1
      when '+'
        while bj < change.position
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end

        bj += 1

        res << change.element
      end
    end
  end

  while ai < src.size
    res << (string ? src[ai, 1] : src[ai])
    ai += 1
    bj += 1
  end

  res
end