Re-add follow recommendations API

app/controllers/api/v1/suggestions_controller.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+class Api::V1::SuggestionsController < Api::BaseController
+  include Authorization
+
+  before_action -> { doorkeeper_authorize! :read }
+  before_action :require_user!
+  before_action :set_accounts
+
+  respond_to :json
+
+  def index
+    render json: @accounts, each_serializer: REST::AccountSerializer
+  end
+
+  private
+
+  def set_accounts
+    @accounts = PotentialFriendshipTracker.get(current_account.id, limit: limit_param(DEFAULT_ACCOUNTS_LIMIT))
+  end
+end

app/lib/potential_friendship_tracker.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+class PotentialFriendshipTracker
+  EXPIRE_AFTER = 90.days.seconds
+  MAX_ITEMS    = 80
+
+  WEIGHTS = {
+    reply: 1,
+    favourite: 10,
+    reblog: 20,
+  }.freeze
+
+  class << self
+    def record(account_id, target_account_id, action)
+      key    = "interactions:#{account_id}"
+      weight = WEIGHTS[action]
+
+      redis.zincrby(key, weight, target_account_id)
+      redis.zremrangebyrank(key, 0, -MAX_ITEMS)
+      redis.expire(key, EXPIRE_AFTER)
+    end
+
+    def remove(account_id, target_account_id)
+      redis.zrem("interactions:#{account_id}", target_account_id)
+    end
+
+    def get(account_id, limit: 20, offset: 0)
+      account_ids = redis.zrevrange("interactions:#{account_id}", offset, limit)
+      return [] if account_ids.empty?
+      Account.searchable.where(id: account_ids)
+    end
+
+    private
+
+    def redis
+      Redis.current
+    end
+  end
+end

app/models/account.rb

@@ -127,6 +127,7 @@ class Account < ApplicationRecord
   scope :matches_username, ->(value) { where(arel_table[:username].matches("#{value}%")) }
   scope :matches_display_name, ->(value) { where(arel_table[:display_name].matches("#{value}%")) }
   scope :matches_domain, ->(value) { where(arel_table[:domain].matches("%#{value}%")) }
+  scope :searchable, -> { where(suspended: false).where(moved_to_account_id: nil) }
 
   delegate :email,
            :unconfirmed_email,
@@ -309,34 +310,6 @@ def inboxes
       DeliveryFailureTracker.filter(urls)
     end
 
-    def triadic_closures(account, limit: 5, offset: 0)
-      sql = <<-SQL.squish
-        WITH first_degree AS (
-          SELECT target_account_id
-          FROM follows
-          WHERE account_id = :account_id
-        )
-        SELECT accounts.*
-        FROM follows
-        INNER JOIN accounts ON follows.target_account_id = accounts.id
-        WHERE
-          account_id IN (SELECT * FROM first_degree)
-          AND target_account_id NOT IN (SELECT * FROM first_degree)
-          AND target_account_id NOT IN (:excluded_account_ids)
-          AND accounts.suspended = false
-        GROUP BY target_account_id, accounts.id
-        ORDER BY count(account_id) DESC
-        OFFSET :offset
-        LIMIT :limit
-      SQL
-
-      excluded_account_ids = account.excluded_from_timeline_account_ids + [account.id]
-
-      find_by_sql(
-        [sql, { account_id: account.id, excluded_account_ids: excluded_account_ids, limit: limit, offset: offset }]
-      )
-    end
-
     def search_for(terms, limit = 10)
       textsearch, query = generate_query_for_search(terms)
 

app/models/concerns/account_interactions.rb

@@ -89,21 +89,27 @@ def follow!(other_account, reblogs: nil, uri: nil)
                               .find_or_create_by!(target_account: other_account)
 
     rel.update!(show_reblogs: reblogs)
+    remove_potential_friendship(other_account)
+
     rel
   end
 
   def block!(other_account, uri: nil)
+    remove_potential_friendship(other_account)
     block_relationships.create_with(uri: uri)
                        .find_or_create_by!(target_account: other_account)
   end
 
   def mute!(other_account, notifications: nil)
     notifications = true if notifications.nil?
     mute = mute_relationships.create_with(hide_notifications: notifications).find_or_create_by!(target_account: other_account)
+    remove_potential_friendship(other_account)
+
     # When toggling a mute between hiding and allowing notifications, the mute will already exist, so the find_or_create_by! call will return the existing Mute without updating the hide_notifications attribute. Therefore, we check that hide_notifications? is what we want and set it if it isn't.
     if mute.hide_notifications? != notifications
       mute.update!(hide_notifications: notifications)
     end
+
     mute
   end
 
@@ -194,4 +200,10 @@ def lists_for_local_distribution
     lists.joins(account: :user)
          .where('users.current_sign_in_at > ?', User::ACTIVE_DURATION.ago)
   end
+
+  private
+
+  def remove_potential_friendship(other_account)
+    PotentialFriendshipTracker.remove(id, other_account.id)
+  end
 end

app/services/favourite_service.rb

@@ -15,7 +15,10 @@ def call(account, status)
     return favourite unless favourite.nil?
 
     favourite = Favourite.create!(account: account, status: status)
+
     create_notification(favourite)
+    bump_potential_friendship(account, status)
+
     favourite
   end
 
@@ -33,6 +36,11 @@ def create_notification(favourite)
     end
   end
 
+  def bump_potential_friendship(account, status)
+    return if account.following?(status.account_id)
+    PotentialFriendshipTracker.record(account.id, status.account_id, :favourite)
+  end
+
   def build_json(favourite)
     Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       favourite,

app/services/post_status_service.rb

@@ -47,6 +47,8 @@ def call(account, text, in_reply_to = nil, **options)
       redis.setex("idempotency:status:#{account.id}:#{options[:idempotency]}", 3_600, status.id)
     end
 
+    bump_potential_friendship(account, status)
+
     status
   end
 
@@ -79,4 +81,9 @@ def process_hashtags_service
   def redis
     Redis.current
   end
+
+  def bump_potential_friendship(account, status)
+    return if !status.reply? || account.following?(status.account_id)
+    PotentialFriendshipTracker.record(account.id, status.in_reply_to_account_id, :reply)
+  end
 end

app/services/reblog_service.rb

@@ -24,6 +24,8 @@ def call(account, reblogged_status)
     ActivityPub::DistributionWorker.perform_async(reblog.id)
 
     create_notification(reblog)
+    bump_potential_friendship(account, reblog)
+
     reblog
   end
 
@@ -41,6 +43,11 @@ def create_notification(reblog)
     end
   end
 
+  def bump_potential_friendship(account, reblog)
+    return if account.following?(reblog.reblog.account_id)
+    PotentialFriendshipTracker.record(account.id, reblog.reblog.account_id, :reblog)
+  end
+
   def build_json(reblog)
     Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       reblog,

config/routes.rb

@@ -246,6 +246,7 @@
 
       resources :streaming, only: [:index]
       resources :custom_emojis, only: [:index]
+      resources :suggestions, only: [:index]
 
       get '/search', to: 'search#index', as: :search
 

spec/controllers/api/v1/suggestions_controller_spec.rb

@@ -0,0 +1,35 @@
+require 'rails_helper'
+
+RSpec.describe Api::V1::SuggestionsController, type: :controller do
+  render_views
+
+  let(:user)  { Fabricate(:user) }
+  let(:token) { Fabricate(:accessible_access_token, resource_owner_id: user.id, scopes: 'read write') }
+
+  before do
+    allow(controller).to receive(:doorkeeper_token) { token }
+  end
+
+  describe 'GET #index' do
+    let(:bob) { Fabricate(:account) }
+    let(:jeff) { Fabricate(:account) }
+
+    before do
+      PotentialFriendshipTracker.record(user.account_id, bob.id, :reblog)
+      PotentialFriendshipTracker.record(user.account_id, jeff.id, :favourite)
+
+      get :index
+    end
+
+    it 'returns http success' do
+      expect(response).to have_http_status(200)
+    end
+
+    it 'returns accounts' do
+      json = body_as_json
+
+      expect(json.size).to be >= 1
+      expect(json.map { |i| i[:id] }).to include *[bob, jeff].map { |i| i.id.to_s }
+    end
+  end
+end

spec/models/account_spec.rb

@@ -454,77 +454,6 @@
     end
   end
 
-  describe '.triadic_closures' do
-    let!(:me) { Fabricate(:account) }
-    let!(:friend) { Fabricate(:account) }
-    let!(:friends_friend) { Fabricate(:account) }
-    let!(:both_follow) { Fabricate(:account) }
-
-    before do
-      me.follow!(friend)
-      friend.follow!(friends_friend)
-
-      me.follow!(both_follow)
-      friend.follow!(both_follow)
-    end
-
-    it 'finds accounts you dont follow which are followed by accounts you do follow' do
-      expect(described_class.triadic_closures(me)).to eq [friends_friend]
-    end
-
-    it 'limits by 5 with offset 0 by defualt' do
-      first_degree = 6.times.map { Fabricate(:account) }
-      matches = 5.times.map { Fabricate(:account) }
-      first_degree.each { |account| me.follow!(account) }
-      matches.each do |match|
-        first_degree.each { |account| account.follow!(match) }
-        first_degree.shift
-      end
-
-      expect(described_class.triadic_closures(me)).to eq matches
-    end
-
-    it 'accepts arbitrary limits' do
-      another_friend = Fabricate(:account)
-      higher_friends_friend = Fabricate(:account)
-      me.follow!(another_friend)
-      friend.follow!(higher_friends_friend)
-      another_friend.follow!(higher_friends_friend)
-
-      expect(described_class.triadic_closures(me, limit: 1)).to eq [higher_friends_friend]
-    end
-
-    it 'acceps arbitrary offset' do
-      another_friend = Fabricate(:account)
-      higher_friends_friend = Fabricate(:account)
-      me.follow!(another_friend)
-      friend.follow!(higher_friends_friend)
-      another_friend.follow!(higher_friends_friend)
-
-      expect(described_class.triadic_closures(me, offset: 1)).to eq [friends_friend]
-    end
-
-    context 'when you block account' do
-      before do
-        me.block!(friends_friend)
-      end
-
-      it 'rejects blocked accounts' do
-        expect(described_class.triadic_closures(me)).to be_empty
-      end
-    end
-
-    context 'when you mute account' do
-      before do
-        me.mute!(friends_friend)
-      end
-
-      it 'rejects muted accounts' do
-        expect(described_class.triadic_closures(me)).to be_empty
-      end
-    end
-  end
-
   describe '#statuses_count' do
     subject { Fabricate(:account) }