Extract Rails::Command::Spellchecker

1 files changed, 53 insertions, 0 deletions

diff --git a/railties/lib/rails/command/spellchecker.rb b/railties/lib/rails/command/spellchecker.rb
new file mode 100644
index 0000000000..59ccab4ea2
--- /dev/null
+++ b/railties/lib/rails/command/spellchecker.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+module Rails
+  module Command
+    module Spellchecker # :nodoc:
+      class << self
+        def suggest(word, from:, count: 3)
+          from.sort_by { |w| levenshtein_distance(word, w) }.take(count)
+        end
+
+        private
+          # This code is based directly on the Text gem implementation.
+          # Copyright (c) 2006-2013 Paul Battley, Michael Neumann, Tim Fletcher.
+          #
+          # Returns a value representing the "cost" of transforming str1 into str2.
+          def levenshtein_distance(str1, str2) # :doc:
+            s = str1
+            t = str2
+            n = s.length
+            m = t.length
+
+            return m if (0 == n)
+            return n if (0 == m)
+
+            d = (0..m).to_a
+            x = nil
+
+            # avoid duplicating an enumerable object in the loop
+            str2_codepoint_enumerable = str2.each_codepoint
+
+            str1.each_codepoint.with_index do |char1, i|
+              e = i + 1
+
+              str2_codepoint_enumerable.with_index do |char2, j|
+                cost = (char1 == char2) ? 0 : 1
+                x = [
+                  d[j + 1] + 1, # insertion
+                  e + 1,        # deletion
+                  d[j] + cost   # substitution
+                ].min
+                d[j] = e
+                e = x
+              end
+
+              d[m] = x
+            end
+
+            x
+          end
+      end
+    end
+  end
+end