Add prototype model for GemTypo

app/models/gem_typo.rb

@@ -0,0 +1,46 @@
+require 'rubygems/text'
+
+class GemTypo
+  PROTECTED_GEMS = [
+    'rspec-core',
+    'diff-lcs',
+    'rspec-expectations',
+    'rspec-mocks',
+    'rspec',
+    'bundler',
+    'rspec-support',
+    'multi_json',
+    'rack',
+    'rake'
+  ].freeze
+
+  DISTANCE_THRESHOLD = 1
+
+  GEM_EXCEPTIONS = [
+    'rspec-coreZ'
+    # Add exceptions here to manage gems which share a close distance,
+    # but are manually reviewed and accepted by rubygems team
+  ].freeze
+
+  include Gem::Text
+
+  def initialize(rubygem_name, opts = {})
+    @rubygem_name = rubygem_name
+    @protected_gems = opts[:protected_gems] || GemTypo::PROTECTED_GEMS
+    @distance_threshold = opts[:distance_threshold] || GemTypo::DISTANCE_THRESHOLD
+    @gem_exceptions = opts[:gem_exceptions] || GemTypo::GEM_EXCEPTIONS
+  end
+
+  def protected_typo?
+    @protected_gems.each do |protected_gem|
+      return false if @rubygem_name == protected_gem
+      distance = levenshtein_distance(@rubygem_name, protected_gem)
+      if distance <= @distance_threshold &&
+          !@gem_exceptions.include?(@rubygem_name)
+        return true
+      end
+    end
+
+    false
+  end
+end

test/unit/gem_typo_test.rb

@@ -0,0 +1,78 @@
+require 'test_helper'
+require 'gem_typo'
+
+class GemTypoTest < ActiveSupport::TestCase
+  teardown do
+    Rails.cache.clear
+  end
+
+  should 'return false for exact match' do
+    gem_typo = GemTypo.new('rspec-core')
+    assert_equal false, gem_typo.protected_typo?
+  end
+
+  should 'return true for 1 char distance match' do
+    gem_typo = GemTypo.new('rspec-core2')
+    assert_equal true, gem_typo.protected_typo?
+  end
+
+  should 'return false for 2 char distance match' do
+    gem_typo = GemTypo.new('rspec-core12')
+    assert_equal false, gem_typo.protected_typo?
+  end
+
+  should 'return false for 3 char distance match' do
+    gem_typo = GemTypo.new('rspec-core123')
+    assert_equal false, gem_typo.protected_typo?
+  end
+
+  should 'return false for 1 char distance match on the exception list' do
+    gem_typo = GemTypo.new('rspec-coreZ')
+    assert_equal false, gem_typo.protected_typo?
+  end
+
+  should 'allow customized protected_gems' do
+    opts = {
+      protected_gems: ["hello"]
+    }
+
+    gem_typo = GemTypo.new('hello', opts)
+    assert_equal false, gem_typo.protected_typo?
+
+    gem_typo = GemTypo.new('hello1', opts)
+    assert_equal true, gem_typo.protected_typo?
+  end
+
+  should 'allow customized distance_threshold' do
+    opts = {
+      distance_threshold: 3
+    }
+
+    gem_typo = GemTypo.new('rack', opts)
+    assert_equal false, gem_typo.protected_typo?
+
+    gem_typo = GemTypo.new('rack1', opts)
+    assert_equal true, gem_typo.protected_typo?
+
+    gem_typo = GemTypo.new('rack12', opts)
+    assert_equal true, gem_typo.protected_typo?
+
+    gem_typo = GemTypo.new('rack123', opts)
+    assert_equal true, gem_typo.protected_typo?
+
+    gem_typo = GemTypo.new('rack1234', opts)
+    assert_equal false, gem_typo.protected_typo?
+  end
+
+  should 'allow customized protected_gem_exceptions' do
+    opts = {
+      gem_exceptions: ["rake1"]
+    }
+
+    gem_typo = GemTypo.new('rake', opts)
+    assert_equal false, gem_typo.protected_typo?
+
+    gem_typo = GemTypo.new('rake1', opts)
+    assert_equal false, gem_typo.protected_typo?
+  end
+end