Add more accurate account search (#11537)

* Add more accurate account search

When ElasticSearch is available, a more accurate search is implemented:

- Using edge n-gram index for acct and display name
- Using asciifolding and cjk width normalization on display names
- Using Gaussian decay on account activity for additional scoring (recency)
- Using followers/friends ratio for additional scoring (spamminess)
- Using followers number for additional scoring (size)

The exact match precedence only takes effect when the input conforms
to the username format and the username part of it is complete, i.e.
when the user started typing the domain part.

* Support single-letter usernames

* Fix tests

* Fix not picking up account updates

* Add weights and normalization for scores, skip zero terms queries

* Use local counts for accounts index, adjust search parameters

* Fix mistakes

* Using updated_at of accounts is inadequate for remote accounts

app/chewy/accounts_index.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+class AccountsIndex < Chewy::Index
+  settings index: { refresh_interval: '5m' }, analysis: {
+    analyzer: {
+      content: {
+        tokenizer: 'whitespace',
+        filter: %w(lowercase asciifolding cjk_width),
+      },
+
+      edge_ngram: {
+        tokenizer: 'edge_ngram',
+        filter: %w(lowercase asciifolding cjk_width),
+      },
+    },
+
+    tokenizer: {
+      edge_ngram: {
+        type: 'edge_ngram',
+        min_gram: 1,
+        max_gram: 15,
+      },
+    },
+  }
+
+  define_type ::Account.searchable.includes(:account_stat), delete_if: ->(account) { account.destroyed? || !account.searchable? } do
+    root date_detection: false do
+      field :id, type: 'long'
+      field :display_name, type: 'text', analyzer: 'edge_ngram', search_analyzer: 'content'
+      field :acct, type: 'text', analyzer: 'edge_ngram', search_analyzer: 'content', value: ->(account) { [account.username, account.domain].compact.join('@') }
+      field :following_count, type: 'long', value: ->(account) { account.active_relationships.count }
+      field :followers_count, type: 'long', value: ->(account) { account.passive_relationships.count }
+      field :last_status_at, type: 'date', value: ->(account) { account.last_status_at || account.created_at }
+    end
+  end
+end

app/models/account.rb

@@ -127,6 +127,8 @@ class Account < ApplicationRecord
 
   delegate :chosen_languages, to: :user, prefix: false, allow_nil: true
 
+  update_index('accounts#account', :self) if Chewy.enabled?
+
   def local?
     domain.nil?
   end
@@ -169,6 +171,10 @@ class Account < ApplicationRecord
     subscription_expires_at.present?
   end
 
+  def searchable?
+    !(suspended? || moved?)
+  end
+
   def possibly_stale?
     last_webfingered_at.nil? || last_webfingered_at <= 1.day.ago
   end

app/models/account_stat.rb

@@ -16,6 +16,8 @@
 class AccountStat < ApplicationRecord
   belongs_to :account, inverse_of: :account_stat
 
+  update_index('accounts#account', :account) if Chewy.enabled?
+
   def increment_count!(key)
     update(attributes_for_increment(key))
   end

app/services/account_search_service.rb

@@ -4,105 +4,134 @@ class AccountSearchService < BaseService
   attr_reader :query, :limit, :offset, :options, :account
 
   def call(query, account = nil, options = {})
-    @query   = query.strip
+    @acct_hint = query.start_with?('@')
+    @query     = query.strip.gsub(/\A@/, '')
     @limit     = options[:limit].to_i
     @offset    = options[:offset].to_i
     @options   = options
     @account   = account
 
-    search_service_results
+    search_service_results.compact.uniq
   end
 
   private
 
   def search_service_results
-    return [] if query_blank_or_hashtag? || limit < 1
+    return [] if query.blank? || limit < 1
 
-    if resolving_non_matching_remote_account?
-      [ResolveAccountService.new.call("#{query_username}@#{query_domain}")].compact
-    else
-      search_results_and_exact_match.compact.uniq
-    end
-  end
-
-  def resolving_non_matching_remote_account?
-    offset.zero? && options[:resolve] && !exact_match? && !domain_is_local?
+    [exact_match] + search_results
   end
 
-  def search_results_and_exact_match
-    return search_results.to_a unless offset.zero?
-
-    results = [exact_match]
+  def exact_match
+    return unless offset.zero? && username_complete?
 
-    return results if exact_match? && limit == 1
+    return @exact_match if defined?(@exact_match)
 
-    results + search_results.to_a
+    @exact_match = begin
+      if options[:resolve]
+        ResolveAccountService.new.call(query)
+      elsif domain_is_local?
+        Account.find_local(query_username)
+      else
+        Account.find_remote(query_username, query_domain)
       end
-
-  def query_blank_or_hashtag?
-    query.blank? || query.start_with?('#')
     end
-
-  def split_query_string
-    @split_query_string ||= query.gsub(/\A@/, '').split('@')
   end
 
-  def query_username
-    @query_username ||= split_query_string.first || ''
-  end
+  def search_results
+    return [] if limit_for_non_exact_results.zero?
 
-  def query_domain
-    @query_domain ||= query_without_split? ? nil : split_query_string.last
+    @search_results ||= begin
+      if Chewy.enabled?
+        from_elasticsearch
+      else
+        from_database
+      end
     end
-
-  def query_without_split?
-    split_query_string.size == 1
   end
 
-  def domain_is_local?
-    @domain_is_local ||= TagManager.instance.local_domain?(query_domain)
+  def from_database
+    if account
+      advanced_search_results
+    else
+      simple_search_results
+    end
   end
 
-  def search_from
-    options[:following] && account ? account.following : Account
+  def advanced_search_results
+    Account.advanced_search_for(terms_for_query, account, limit_for_non_exact_results, options[:following], offset)
   end
 
-  def exact_match?
-    exact_match.present?
+  def simple_search_results
+    Account.search_for(terms_for_query, limit_for_non_exact_results, offset)
   end
 
-  def exact_match
-    return @exact_match if defined?(@exact_match)
+  def from_elasticsearch
+    must_clauses   = [{ multi_match: { query: terms_for_query, fields: likely_acct? ? %w(acct) : %w(acct^2 display_name), type: 'best_fields' } }]
+    should_clauses = []
 
-    @exact_match = begin
-      if domain_is_local?
-        search_from.without_suspended.find_local(query_username)
-      else
-        search_from.without_suspended.find_remote(query_username, query_domain)
-      end
+    if account
+      return [] if options[:following] && following_ids.empty?
+
+      if options[:following]
+        must_clauses << { terms: { id: following_ids } }
+      elsif following_ids.any?
+        should_clauses << { terms: { id: following_ids, boost: 100 } }
       end
     end
 
-  def search_results
-    @search_results ||= begin
-      if account
-        advanced_search_results
-      else
-        simple_search_results
+    query     = { bool: { must: must_clauses, should: should_clauses } }
+    functions = [reputation_score_function, followers_score_function, time_distance_function]
+
+    records = AccountsIndex.query(function_score: { query: query, functions: functions, boost_mode: 'multiply', score_mode: 'avg' })
+                           .limit(limit_for_non_exact_results)
+                           .offset(offset)
+                           .objects
+                           .compact
+
+    ActiveRecord::Associations::Preloader.new.preload(records, :account_stat)
+
+    records
   end
+
+  def reputation_score_function
+    {
+      script_score: {
+        script: {
+          source: "(doc['followers_count'].value + 0.0) / (doc['followers_count'].value + doc['following_count'].value + 1)",
+        },
+      },
+    }
   end
+
+  def followers_score_function
+    {
+      field_value_factor: {
+        field: 'followers_count',
+        modifier: 'log2p',
+        missing: 1,
+      },
+    }
   end
 
-  def advanced_search_results
-    Account.advanced_search_for(terms_for_query, account, limit_for_non_exact_results, options[:following], offset)
+  def time_distance_function
+    {
+      gauss: {
+        last_status_at: {
+          scale: '30d',
+          offset: '30d',
+          decay: 0.3,
+        },
+      },
+    }
   end
 
-  def simple_search_results
-    Account.search_for(terms_for_query, limit_for_non_exact_results, offset)
+  def following_ids
+    @following_ids ||= account.active_relationships.pluck(:target_account_id)
   end
 
   def limit_for_non_exact_results
-    if offset.zero? && exact_match?
+    if exact_match?
       limit - 1
     else
       limit
@@ -113,7 +142,39 @@ class AccountSearchService < BaseService
     if domain_is_local?
       query_username
     else
-      "#{query_username} #{query_domain}"
+      query
+    end
   end
+
+  def split_query_string
+    @split_query_string ||= query.split('@')
+  end
+
+  def query_username
+    @query_username ||= split_query_string.first || ''
+  end
+
+  def query_domain
+    @query_domain ||= query_without_split? ? nil : split_query_string.last
+  end
+
+  def query_without_split?
+    split_query_string.size == 1
+  end
+
+  def domain_is_local?
+    @domain_is_local ||= TagManager.instance.local_domain?(query_domain)
+  end
+
+  def exact_match?
+    exact_match.present?
+  end
+
+  def username_complete?
+    query.include?('@') && "@#{query}" =~ Account::MENTION_RE
+  end
+
+  def likely_acct?
+    @acct_hint || username_complete?
   end
 end

spec/services/account_search_service_spec.rb

@@ -1,110 +1,38 @@
 require 'rails_helper'
 
 describe AccountSearchService, type: :service do
-  describe '.call' do
-    describe 'with a query to ignore' do
+  describe '#call' do
+    context 'with a query to ignore' do
       it 'returns empty array for missing query' do
         results = subject.call('', nil, limit: 10)
 
         expect(results).to eq []
       end
-      it 'returns empty array for hashtag query' do
-        results = subject.call('#tag', nil, limit: 10)
 
-        expect(results).to eq []
-      end
       it 'returns empty array for limit zero' do
         Fabricate(:account, username: 'match')
+
         results = subject.call('match', nil, limit: 0)
 
         expect(results).to eq []
       end
     end
 
-    describe 'searching for a simple term that is not an exact match' do
+    context 'searching for a simple term that is not an exact match' do
       it 'does not return a nil entry in the array for the exact match' do
-        match = Fabricate(:account, username: 'matchingusername')
-
+        account = Fabricate(:account, username: 'matchingusername')
         results = subject.call('match', nil, limit: 5)
-        expect(results).to eq [match]
-      end
-    end
-
-    describe 'searching local and remote users' do
-      describe "when only '@'" do
-        before do
-          allow(Account).to receive(:find_local)
-          allow(Account).to receive(:search_for)
-          subject.call('@', nil, limit: 10)
-        end
-
-        it 'uses find_local with empty query to look for local accounts' do
-          expect(Account).to have_received(:find_local).with('')
-        end
-      end
-
-      describe 'when no domain' do
-        before do
-          allow(Account).to receive(:find_local)
-          allow(Account).to receive(:search_for)
-          subject.call('one', nil, limit: 10)
-        end
-
-        it 'uses find_local to look for local accounts' do
-          expect(Account).to have_received(:find_local).with('one')
-        end
-
-        it 'uses search_for to find matches' do
-          expect(Account).to have_received(:search_for).with('one', 10, 0)
-        end
-      end
-
-      describe 'when there is a domain' do
-        before do
-          allow(Account).to receive(:find_remote)
-        end
-
-        it 'uses find_remote to look for remote accounts' do
-          subject.call('two@example.com', nil, limit: 10)
-          expect(Account).to have_received(:find_remote).with('two', 'example.com')
-        end
-
-        describe 'and there is no account provided' do
-          it 'uses search_for to find matches' do
-            allow(Account).to receive(:search_for)
-            subject.call('two@example.com', nil, limit: 10, resolve: false)
 
-            expect(Account).to have_received(:search_for).with('two example.com', 10, 0)
+        expect(results).to eq [account]
       end
     end
 
-        describe 'and there is an account provided' do
-          it 'uses advanced_search_for to find matches' do
-            account = Fabricate(:account)
-            allow(Account).to receive(:advanced_search_for)
-            subject.call('two@example.com', account, limit: 10, resolve: false)
-
-            expect(Account).to have_received(:advanced_search_for).with('two example.com', account, 10, nil, 0)
-          end
-        end
-      end
-    end
-
-    describe 'with an exact match' do
-      it 'returns exact match first, and does not return duplicates' do
-        partial = Fabricate(:account, username: 'exactness')
-        exact = Fabricate(:account, username: 'exact')
-
-        results = subject.call('exact', nil, limit: 10)
-        expect(results.size).to eq 2
-        expect(results).to eq [exact, partial]
-      end
-    end
-
-    describe 'when there is a local domain' do
+    context 'when there is a local domain' do
       around do |example|
         before = Rails.configuration.x.local_domain
+
         example.run
+
         Rails.configuration.x.local_domain = before
       end
 
@@ -112,15 +40,17 @@ describe AccountSearchService, type: :service do
         remote     = Fabricate(:account, username: 'a', domain: 'remote', display_name: 'e')
         remote_too = Fabricate(:account, username: 'b', domain: 'remote', display_name: 'e')
         exact      = Fabricate(:account, username: 'e')
+
         Rails.configuration.x.local_domain = 'example.com'
 
         results = subject.call('e@example.com', nil, limit: 2)
+
         expect(results.size).to eq 2
         expect(results).to eq([exact, remote]).or eq([exact, remote_too])
       end
     end
 
-    describe 'when there is a domain but no exact match' do
+    context 'when there is a domain but no exact match' do
       it 'follows the remote account when resolve is true' do
         service = double(call: nil)
         allow(ResolveAccountService).to receive(:new).and_return(service)
@@ -138,23 +68,21 @@ describe AccountSearchService, type: :service do
       end
     end
 
-    describe 'should not include suspended accounts' do
     it 'returns the fuzzy match first, and does not return suspended exacts' do
       partial = Fabricate(:account, username: 'exactness')
       exact   = Fabricate(:account, username: 'exact', suspended: true)
-
       results = subject.call('exact', nil, limit: 10)
+
       expect(results.size).to eq 1
       expect(results).to eq [partial]
     end
 
     it "does not return suspended remote accounts" do
       remote  = Fabricate(:account, username: 'a', domain: 'remote', display_name: 'e', suspended: true)
-
       results = subject.call('a@example.com', nil, limit: 2)
+
       expect(results.size).to eq 0
       expect(results).to eq []
     end
   end
-  end
 end