1 files changed, 46 insertions, 0 deletions
diff --git a/lib/did_you_mean/spell_checker.rb b/lib/did_you_mean/spell_checker.rb
new file mode 100644
index 0000000000..e5106abba2
--- /dev/null
+++ b/lib/did_you_mean/spell_checker.rb
@@ -0,0 +1,46 @@
+# frozen-string-literal: true
+
+require_relative "levenshtein"
+require_relative "jaro_winkler"
+
+module DidYouMean
+  class SpellChecker
+    def initialize(dictionary:)
+      @dictionary = dictionary
+    end
+
+    def correct(input)
+      input     = normalize(input)
+      threshold = input.length > 3 ? 0.834 : 0.77
+
+      words = @dictionary.select { |word| JaroWinkler.distance(normalize(word), input) >= threshold }
+      words.reject! { |word| input == word.to_s }
+      words.sort_by! { |word| JaroWinkler.distance(word.to_s, input) }
+      words.reverse!
+
+      # Correct mistypes
+      threshold   = (input.length * 0.25).ceil
+      corrections = words.select { |c| Levenshtein.distance(normalize(c), input) <= threshold }
+
+      # Correct misspells
+      if corrections.empty?
+        corrections = words.select do |word|
+          word   = normalize(word)
+          length = input.length < word.length ? input.length : word.length
+
+          Levenshtein.distance(word, input) < length
+        end.first(1)
+      end
+
+      corrections
+    end
+
+    private
+
+    def normalize(str_or_symbol) #:nodoc:
+      str = str_or_symbol.to_s.downcase
+      str.tr!("@", "")
+      str
+    end
+  end
+end