Lists (#5703)

* Add structure for lists

* Add list timeline streaming API

* Add list APIs, bind list-account relation to follow relation

* Add API for adding/removing accounts from lists

* Add pagination to lists API

* Add pagination to list accounts API

* Adjust scopes for new APIs

- Creating and modifying lists merely requires "write" scope
- Fetching information about lists merely requires "read" scope

* Add test for wrong user context on list timeline

* Clean up tests

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

@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+class Api::V1::Lists::AccountsController < Api::BaseController
+  before_action -> { doorkeeper_authorize! :read },    only: [:show]
+  before_action -> { doorkeeper_authorize! :write }, except: [:show]
+
+  before_action :require_user!
+  before_action :set_list
+
+  after_action :insert_pagination_headers, only: :show
+
+  def show
+    @accounts = @list.accounts.paginate_by_max_id(limit_param(DEFAULT_ACCOUNTS_LIMIT), params[:max_id], params[:since_id])
+    render json: @accounts, each_serializer: REST::AccountSerializer
+  end
+
+  def create
+    ApplicationRecord.transaction do
+      list_accounts.each do |account|
+        @list.accounts << account
+      end
+    end
+
+    render_empty
+  end
+
+  def destroy
+    ListAccount.where(list: @list, account_id: account_ids).destroy_all
+    render_empty
+  end
+
+  private
+
+  def set_list
+    @list = List.where(account: current_account).find(params[:list_id])
+  end
+
+  def list_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
+    if records_continue?
+      api_v1_list_accounts_url pagination_params(max_id: pagination_max_id)
+    end
+  end
+
+  def prev_path
+    unless @accounts.empty?
+      api_v1_list_accounts_url pagination_params(since_id: pagination_since_id)
+    end
+  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.permit(:limit).merge(core_params)
+  end
+end