Spec coverage and refactor for the api/v1/accounts controllers (#3451)

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

@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+class Api::V1::Accounts::FollowingAccountsController < ApiController
+  before_action -> { doorkeeper_authorize! :read }
+  before_action :set_account
+  after_action :insert_pagination_headers
+
+  respond_to :json
+
+  def index
+    @accounts = load_accounts
+    render 'api/v1/accounts/index'
+  end
+
+  private
+
+  def set_account
+    @account = Account.find(params[:account_id])
+  end
+
+  def load_accounts
+    default_accounts.merge(paginated_follows).to_a
+  end
+
+  def default_accounts
+    Account.includes(:passive_relationships).references(:passive_relationships)
+  end
+
+  def paginated_follows
+    Follow.where(account: @account).paginate_by_max_id(
+      limit_param(DEFAULT_ACCOUNTS_LIMIT),
+      params[:max_id],
+      params[:since_id]
+    )
+  end
+
+  def insert_pagination_headers
+    set_pagination_headers(next_path, prev_path)
+  end
+
+  def next_path
+    if records_continue?
+      api_v1_account_following_index_url pagination_params(max_id: pagination_max_id)
+    end
+  end
+
+  def prev_path
+    unless @accounts.empty?
+      api_v1_account_following_index_url pagination_params(since_id: pagination_since_id)
+    end
+  end
+
+  def pagination_max_id
+    @accounts.last.passive_relationships.first.id
+  end
+
+  def pagination_since_id
+    @accounts.first.passive_relationships.first.id
+  end
+
+  def records_continue?
+    @accounts.size == limit_param(DEFAULT_ACCOUNTS_LIMIT)
+  end
+
+  def pagination_params(core_params)
+    params.permit(:limit).merge(core_params)
+  end
+end