Add REST API for managing and posting to circles

Circles are the conceptual opposite of lists. A list is a subdivision
of your follows, a circle is a subdivision of your followers. Posting
to a circle means making content available to only some of your
followers. Circles have been internally supported in Mastodon for
the purposes of federation since #8950, this adds the REST API
necessary for making use of them in Mastodon itsef.

app/controllers/api/v1/accounts/circles_controller.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class Api::V1::Accounts::CirclesController < Api::BaseController
+  before_action -> { doorkeeper_authorize! :read, :'read:circles' }
+  before_action :require_user!
+  before_action :set_account
+
+  def index
+    @circles = @account.circles.where(account: current_account)
+    render json: @circles, each_serializer: REST::CircleSerializer
+  end
+
+  private
+
+  def set_account
+    @account = Account.find(params[:account_id])
+  end
+end

app/controllers/api/v1/circles/accounts_controller.rb

@@ -0,0 +1,93 @@
+# frozen_string_literal: true
+
+class Api::V1::Circles::AccountsController < Api::BaseController
+  before_action -> { doorkeeper_authorize! :read, :'read:circles' }, only: [:show]
+  before_action -> { doorkeeper_authorize! :write, :'write:circles' }, except: [:show]
+
+  before_action :require_user!
+  before_action :set_circle
+
+  after_action :insert_pagination_headers, only: :show
+
+  def show
+    @accounts = load_accounts
+    render json: @accounts, each_serializer: REST::AccountSerializer
+  end
+
+  def create
+    ApplicationRecord.transaction do
+      circle_accounts.each do |account|
+        @circle.accounts << account
+      end
+    end
+
+    render_empty
+  end
+
+  def destroy
+    CircleAccount.where(circle: @circle, account_id: account_ids).destroy_all
+    render_empty
+  end
+
+  private
+
+  def set_circle
+    @circle = current_account.owned_circles.find(params[:circle_id])
+  end
+
+  def load_accounts
+    if unlimited?
+      @circle.accounts.includes(:account_stat).all
+    else
+      @circle.accounts.includes(:account_stat).paginate_by_max_id(limit_param(DEFAULT_ACCOUNTS_LIMIT), params[:max_id], params[:since_id])
+    end
+  end
+
+  def circle_accounts
+    Account.find(account_ids)
+  end
+
+  def account_ids
+    Array(resource_params[:account_ids])
+  end
+
+  def resource_params
+    params.permit(account_ids: [])
+  end
+
+  def insert_pagination_headers
+    set_pagination_headers(next_path, prev_path)
+  end
+
+  def next_path
+    return if unlimited?
+
+    api_v1_circle_accounts_url(pagination_params(max_id: pagination_max_id)) if records_continue?
+  end
+
+  def prev_path
+    return if unlimited?
+
+    api_v1_circle_accounts_url(pagination_params(since_id: pagination_since_id)) unless @accounts.empty?
+  end
+
+  def pagination_max_id
+    @accounts.last.id
+  end
+
+  def pagination_since_id
+    @accounts.first.id
+  end
+
+  def records_continue?
+    @accounts.size == limit_param(DEFAULT_ACCOUNTS_LIMIT)
+  end
+
+  def pagination_params(core_params)
+    params.slice(:limit).permit(:limit).merge(core_params)
+  end
+
+  def unlimited?
+    params[:limit] == '0'
+  end
+end

app/controllers/api/v1/circles_controller.rb

@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+class Api::V1::CirclesController < Api::BaseController
+  before_action -> { doorkeeper_authorize! :read, :'read:circles' }, only: [:index, :show]
+  before_action -> { doorkeeper_authorize! :write, :'write:circles' }, except: [:index, :show]
+
+  before_action :require_user!
+  before_action :set_circle, except: [:index, :create]
+
+  after_action :insert_pagination_headers, only: :index
+
+  def index
+    @circles = current_account.owned_circles.paginate_by_max_id(limit_param(DEFAULT_ACCOUNTS_LIMIT), params[:max_id], params[:since_id])
+    render json: @circles, each_serializer: REST::CircleSerializer
+  end
+
+  def show
+    render json: @circle, serializer: REST::CircleSerializer
+  end
+
+  def create
+    @circle = current_account.owned_circles.create!(circle_params)
+    render json: @circle, serializer: REST::CircleSerializer
+  end
+
+  def update
+    @circle.update!(circle_params)
+    render json: @circle, serializer: REST::CircleSerializer
+  end
+
+  def destroy
+    @circle.destroy!
+    render_empty
+  end
+
+  private
+
+  def set_circle
+    @circle = current_account.owned_circles.find(params[:id])
+  end
+
+  def circle_params
+    params.permit(:title)
+  end
+
+  def insert_pagination_headers
+    set_pagination_headers(next_path, prev_path)
+  end
+
+  def next_path
+    api_v1_circles_url(pagination_params(max_id: pagination_max_id)) if records_continue?
+  end
+
+  def prev_path
+    api_v1_circles_url(pagination_params(since_id: pagination_since_id)) unless @circles.empty?
+  end
+
+  def pagination_max_id
+    @circles.last.id
+  end
+
+  def pagination_since_id
+    @circles.first.id
+  end
+
+  def records_continue?
+    @circles.size == limit_param(DEFAULT_ACCOUNTS_LIMIT)
+  end
+
+  def pagination_params(core_params)
+    params.slice(:limit).permit(:limit).merge(core_params)
+  end
+end

app/controllers/api/v1/statuses_controller.rb

@@ -8,6 +8,7 @@ class Api::V1::StatusesController < Api::BaseController
   before_action :require_user!, except:  [:show, :context]
   before_action :set_status, only:       [:show, :context]
   before_action :set_thread, only:       [:create]
+  before_action :set_circle, only:       [:create]
 
   override_rate_limit_headers :create, family: :statuses
 
@@ -38,6 +39,7 @@ class Api::V1::StatusesController < Api::BaseController
     @status = PostStatusService.new.call(current_user.account,
                                          text: status_params[:status],
                                          thread: @thread,
+                                         circle: @circle,
                                          media_ids: status_params[:media_ids],
                                          sensitive: status_params[:sensitive],
                                          spoiler_text: status_params[:spoiler_text],
@@ -76,10 +78,17 @@ class Api::V1::StatusesController < Api::BaseController
     render json: { error: I18n.t('statuses.errors.in_reply_not_found') }, status: 404
   end
 
+  def set_circle
+    @circle = status_params[:circle_id].blank? ? nil : current_account.owned_circles.find(status_params[:circle_id])
+  rescue ActiveRecord::RecordNotFound
+    render json: { error: I18n.t('statuses.errors.circle_not_found') }, status: 404
+  end
+
   def status_params
     params.permit(
       :status,
       :in_reply_to_id,
+      :circle_id,
       :sensitive,
       :spoiler_text,
       :visibility,