feat: Modernize LCS Internals

Simplified string enumerable sequence handling.

Signed-off-by: Austin Ziegler <austin@zieglers.ca>

Author: halostatue

lib/diff/lcs/internals.rb

@@ -1,22 +1,31 @@
 # frozen_string_literal: true
 
 class << Diff::LCS
+  def callbacks_for(callbacks) # :nodoc:
+    callbacks.new
+  rescue
+    callbacks
+  end
+  private :callbacks_for
+
   def diff_traversal(method, seq1, seq2, callbacks, &block)
     callbacks = callbacks_for(callbacks)
+
     case method
     when :diff
       traverse_sequences(seq1, seq2, callbacks)
     when :sdiff
       traverse_balanced(seq1, seq2, callbacks)
     end
+
     callbacks.finish if callbacks.respond_to? :finish
 
     if block
       callbacks.diffs.map do |hunk|
         if hunk.is_a? Array
-          hunk.map { |hunk_block| block[hunk_block] }
+          hunk.map { block.call(_1) }
         else
-          block[hunk]
+          block.call(hunk)
         end
       end
     else
@@ -27,18 +36,16 @@ def diff_traversal(method, seq1, seq2, callbacks, &block)
 end
 
 module Diff::LCS::Internals # :nodoc:
-end
-
-class << Diff::LCS::Internals
-  # Compute the longest common subsequence between the sequenced
-  # Enumerables +a+ and +b+. The result is an array whose contents is such
-  # that
+  # Compute the longest common subsequence between the sequenced enumerable values `a` and
+  # `b`. The result is an array whose contents is such that
   #
-  #     result = Diff::LCS::Internals.lcs(a, b)
-  #     result.each_with_index do |e, i|
-  #       assert_equal(a[i], b[e]) unless e.nil?
-  #     end
-  def lcs(a, b)
+  # ```ruby
+  # result = Diff::LCS::Internals.lcs(a, b)
+  # result.each_with_index do |e, i|
+  #   assert_equal(a[i], b[e]) unless e.nil?
+  # end
+  # ```
+  def self.lcs(a, b)
     a_start = b_start = 0
     a_finish = a.size - 1
     b_finish = b.size - 1
@@ -58,21 +65,20 @@ def lcs(a, b)
       b_finish -= 1
     end
 
-    # Now, compute the equivalence classes of positions of elements.
-    # An explanation for how this works: https://codeforces.com/topic/92191
+    # Now, compute the equivalence classes of positions of elements. An explanation for
+    # how this works: https://codeforces.com/topic/92191
     b_matches = position_hash(b, b_start..b_finish)
 
     thresh = []
     links = []
-    string = a.is_a?(String)
 
     (a_start..a_finish).each do |i|
-      ai = string ? a[i, 1] : a[i]
+      ai = a[i]
       bm = b_matches[ai]
       k = nil
       bm.reverse_each do |j|
-        # Although the threshold check is not mandatory for this to work,
-        # it may have an optimization purpose
+        # Although the threshold check is not mandatory for this to work, it may have an
+        # optimization purpose.
         # An attempt to remove it: https://github.com/halostatue/diff-lcs/pull/72
         # Why it is reintroduced: https://github.com/halostatue/diff-lcs/issues/78
         if k && (thresh[k] > j) && (thresh[k - 1] < j)
@@ -95,11 +101,10 @@ def lcs(a, b)
     vector
   end
 
-  # This method will analyze the provided patchset to provide a single-pass
-  # normalization (conversion of the array form of Diff::LCS::Change objects to
-  # the object form of same) and detection of whether the patchset represents
-  # changes to be made.
-  def analyze_patchset(patchset, depth = 0)
+  # This method will analyze the provided patchset to provide a single-pass normalization
+  # (conversion of the array form of Diff::LCS::Change objects to the object form of same)
+  # and detection of whether the patchset represents changes to be made.
+  def self.analyze_patchset(patchset, depth = 0)
     fail "Patchset too complex" if depth > 1
 
     has_changes = false
@@ -137,24 +142,22 @@ def analyze_patchset(patchset, depth = 0)
     [has_changes, new_patchset]
   end
 
-  # Examine the patchset and the source to see in which direction the
-  # patch should be applied.
+  # 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.
-  def intuit_diff_direction(src, patchset, limit = nil)
-    string = src.is_a?(String)
+  # 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.
+  def self.intuit_diff_direction(src, patchset, limit = nil)
     count = left_match = left_miss = right_match = right_miss = 0
 
     patchset.each do |change|
       count += 1
 
       case change
       when Diff::LCS::ContextChange
-        le = string ? src[change.old_position, 1] : src[change.old_position]
-        re = string ? src[change.new_position, 1] : src[change.new_position]
+        le = src[change.old_position]
+        re = src[change.new_position]
 
         case change.action
         when "-" # Remove details from the old string
@@ -183,10 +186,10 @@ def intuit_diff_direction(src, patchset, limit = nil)
           end
         end
       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]
+        # 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 = src[change.position]
 
         case change.action
         when "-"
@@ -235,74 +238,67 @@ def intuit_diff_direction(src, patchset, limit = nil)
           :patch
         end
       else
-        fail "The provided patchset does not appear to apply to the provided \
-enumerable as either source or destination value."
+        fail "The provided patchset does not appear to apply to the provided enumerable as either source or destination value."
       end
     end
   end
 
-  # Find the place at which +value+ would normally be inserted into the
-  # Enumerable. If that place is already occupied by +value+, do nothing
-  # and return +nil+. If the place does not exist (i.e., it is off the end
-  # of the Enumerable), add it to the end. Otherwise, replace the element
-  # at that point with +value+. It is assumed that the Enumerable's values
-  # are numeric.
-  #
-  # This operation preserves the sort order.
-  def replace_next_larger(enum, value, last_index = nil)
-    # Off the end?
-    if enum.empty? || (value > enum[-1])
-      enum << value
-      return enum.size - 1
-    end
+  class << self
+    # Find the place at which `value` would normally be inserted into the Enumerable. If
+    # that place is already occupied by `value`, do nothing and return `nil`. If the place
+    # does not exist (i.e., it is off the end of the Enumerable), add it to the end.
+    # Otherwise, replace the element at that point with `value`. It is assumed that the
+    # Enumerable's values are numeric.
+    #
+    # This operation preserves the sort order.
+    def replace_next_larger(enum, value, last_index = nil)
+      # Off the end?
+      if enum.empty? || (value > enum[-1])
+        enum << value
+        return enum.size - 1
+      end
 
-    # Binary search for the insertion point
-    last_index ||= enum.size - 1
-    first_index = 0
-    while first_index <= last_index
-      i = (first_index + last_index) >> 1
+      # Binary search for the insertion point
+      last_index ||= enum.size - 1
+      first_index = 0
+      while first_index <= last_index
+        i = (first_index + last_index) >> 1
 
-      found = enum[i]
+        found = enum[i]
 
-      return nil if value == found
+        return nil if value == found
 
-      if value > found
-        first_index = i + 1
-      else
-        last_index = i - 1
+        if value > found
+          first_index = i + 1
+        else
+          last_index = i - 1
+        end
       end
-    end
 
-    # The insertion point is in first_index; overwrite the next larger
-    # value.
-    enum[first_index] = value
-    first_index
-  end
-  private :replace_next_larger
-
-  # If +vector+ maps the matching elements of another collection onto this
-  # Enumerable, compute the inverse of +vector+ that maps this Enumerable
-  # onto the collection. (Currently unused.)
-  def inverse_vector(a, vector)
-    inverse = a.dup
-    (0...vector.size).each do |i|
-      inverse[vector[i]] = i unless vector[i].nil?
+      # The insertion point is in first_index; overwrite the next larger value.
+      enum[first_index] = value
+      first_index
     end
-    inverse
-  end
-  private :inverse_vector
-
-  # Returns a hash mapping each element of an Enumerable to the set of
-  # positions it occupies in the Enumerable, optionally restricted to the
-  # elements specified in the range of indexes specified by +interval+.
-  def position_hash(enum, interval)
-    string = enum.is_a?(String)
-    hash = Hash.new { |h, k| h[k] = [] }
-    interval.each do |i|
-      k = string ? enum[i, 1] : enum[i]
-      hash[k] << i
+    private :replace_next_larger
+
+    # If `vector` maps the matching elements of another collection onto this Enumerable,
+    # compute the inverse of `vector` that maps this Enumerable onto the collection.
+    # (Currently unused.)
+    def inverse_vector(a, vector)
+      inverse = a.dup
+      (0...vector.size).each do
+        inverse[vector[_1]] = i unless vector[_1].nil?
+      end
+      inverse
+    end
+    private :inverse_vector
+
+    # Returns a hash mapping each element of an Enumerable to the set of positions it
+    # occupies in the Enumerable, optionally restricted to the elements specified in the
+    # range of indexes specified by `interval`.
+    def position_hash(enum, interval)
+      Hash.new { |h, k| h[k] = [] }.tap { |hash| interval.each { hash[enum[_1]] << _1 } }
     end
-    hash
+    private :position_hash
   end
-  private :position_hash
 end