Rework KeywordMute interface to use a matcher object; spec out matcher. #164.

A matcher object that builds a match from KeywordMute data and runs it
over text is, in my view, one of the easier ways to write examples for
this sort of thing.

app/lib/feed_manager.rb

@@ -138,7 +138,7 @@ class FeedManager
   end
 
   def filter_from_home?(status, receiver_id)
-    return true if KeywordMute.where(account_id: receiver_id).matches?(status.text)
+    return true if KeywordMute.matcher_for(receiver_id) =~ status.text
 
     return false if receiver_id == status.account_id
     return true  if status.reply? && (status.in_reply_to_id.nil? || status.in_reply_to_account_id.nil?)

app/models/keyword_mute.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # == Schema Information
 #
 # Table name: keyword_mutes
@@ -10,6 +11,34 @@
 #
 
 class KeywordMute < ApplicationRecord
-  def self.matches?(text)
+  belongs_to :account, required: true
+
+  validates_presence_of :keyword
+
+  def self.matcher_for(account)
+    Rails.cache.fetch("keyword_mutes:matcher:#{account}") { Matcher.new(account) }
+  end
+
+  class Matcher
+    attr_reader :regex
+
+    def initialize(account)
+      re = String.new.tap do |str|
+        scoped = KeywordMute.where(account: account)
+        keywords = scoped.select(:id, :keyword)
+        count = scoped.count
+
+        keywords.find_each.with_index do |kw, index|
+          str << Regexp.escape(kw.keyword.strip)
+          str << '|' if index < count - 1
+        end
+      end
+
+      @regex = /\b(?:#{re})\b/i unless re.empty?
+    end
+
+    def =~(str)
+      @regex ? @regex =~ str : false
+    end
   end
 end

spec/models/keyword_mute_spec.rb

@@ -1,21 +1,71 @@
 require 'rails_helper'
 
 RSpec.describe KeywordMute, type: :model do
-  describe '.matches?' do
-    let(:alice)  { Fabricate(:account, username: 'alice').tap(&:save!) }
-    let(:status) { Fabricate(:status, account: alice).tap(&:save!) }
-    let(:keyword_mute) { Fabricate(:keyword_mute, account: alice, keyword: 'take').tap(&:save!) }
+  let(:alice) { Fabricate(:account, username: 'alice').tap(&:save!) }
+  let(:bob) { Fabricate(:account, username: 'bob').tap(&:save!) }
 
-    it 'returns true if any keyword in the set matches the status text' do
-      status.update_attribute(:text, 'This is a hot take')
+  describe '.matcher_for' do
+    let(:matcher) { KeywordMute.matcher_for(alice) }
 
-      expect(KeywordMute.where(account: alice).matches?(status.text)).to be_truthy
+    describe 'with no KeywordMutes for an account' do
+      before do
+        KeywordMute.delete_all
+      end
+
+      it 'does not match' do
+        expect(matcher =~ 'This is a hot take').to be_falsy
+      end
     end
 
-    it 'returns false if no keyword in the set matches the status text'
+    describe 'with KeywordMutes for an account' do
+      it 'does not match keywords set by a different account' do
+        KeywordMute.create!(account: bob, keyword: 'take')
+
+        expect(matcher =~ 'This is a hot take').to be_falsy
+      end
+
+      it 'does not match if no keywords match the status text' do
+        KeywordMute.create!(account: alice, keyword: 'cold')
+
+        expect(matcher =~ 'This is a hot take').to be_falsy
+      end
+
+      it 'does not match substrings matching keywords' do
+        KeywordMute.create!(account: alice, keyword: 'take')
+
+        expect(matcher =~ 'This is a shiitake mushroom').to be_falsy
+      end
+
+      it 'matches keywords at the beginning of the text' do
+        KeywordMute.create!(account: alice, keyword: 'take')
+
+        expect(matcher =~ 'Take this').to be_truthy
+      end
+
+      it 'matches keywords at the beginning of the text' do
+        KeywordMute.create!(account: alice, keyword: 'take')
+
+        expect(matcher =~ 'This is a hot take').to be_truthy
+      end
+
+      it 'matches if at least one keyword case-insensitively matches the text' do
+        KeywordMute.create!(account: alice, keyword: 'hot')
+
+        expect(matcher =~ 'This is a hot take').to be_truthy
+      end
+
+      it 'uses case-folding rules appropriate for more than just English' do
+        KeywordMute.create!(account: alice, keyword: 'großeltern')
+
+        expect(matcher =~ 'besuch der grosseltern').to be_truthy
+      end
+
+      it 'matches keywords that are composed of multiple words' do
+        KeywordMute.create!(account: alice, keyword: 'a shiitake')
 
-    describe 'matching' do
-      it 'is case-insensitive'
+        expect(matcher =~ 'This is a shiitake').to be_truthy
+        expect(matcher =~ 'This is shiitake').to_not be_truthy
+      end
     end
   end
 end