Add /api/v1/admin/domain_allows (#18668)

- `GET /api/v1/admin/domain_allows` lists allowed domains
- `GET /api/v1/admin/domain_allows/:id` shows one by ID
- `DELETE /api/v1/admin/domain_allows/:id` deletes a given domain from the list
  of allowed domains
- `POST /api/v1/admin/domain_allows` to allow a new domain:
  if that domain is already allowed, the existing DomainAllow will be returned

app/controllers/api/v1/admin/domain_allows_controller.rb

@@ -0,0 +1,95 @@
+# frozen_string_literal: true
+
+class Api::V1::Admin::DomainAllowsController < Api::BaseController
+  include Authorization
+  include AccountableConcern
+
+  LIMIT = 100
+
+  before_action -> { authorize_if_got_token! :'admin:read', :'admin:read:domain_allows' }, only: [:index, :show]
+  before_action -> { authorize_if_got_token! :'admin:write', :'admin:write:domain_allows' }, except: [:index, :show]
+  before_action :require_staff!
+  before_action :set_domain_allows, only: :index
+  before_action :set_domain_allow, only: [:show, :destroy]
+
+  after_action :insert_pagination_headers, only: :index
+
+  PAGINATION_PARAMS = %i(limit).freeze
+
+  def create
+    authorize :domain_allow, :create?
+
+    @domain_allow = DomainAllow.find_by(resource_params)
+
+    if @domain_allow.nil?
+      @domain_allow = DomainAllow.create!(resource_params)
+      log_action :create, @domain_allow
+    end
+
+    render json: @domain_allow, serializer: REST::Admin::DomainAllowSerializer
+  end
+
+  def index
+    authorize :domain_allow, :index?
+    render json: @domain_allows, each_serializer: REST::Admin::DomainAllowSerializer
+  end
+
+  def show
+    authorize @domain_allow, :show?
+    render json: @domain_allow, serializer: REST::Admin::DomainAllowSerializer
+  end
+
+  def destroy
+    authorize @domain_allow, :destroy?
+    UnallowDomainService.new.call(@domain_allow)
+    log_action :destroy, @domain_allow
+    render json: @domain_allow, serializer: REST::Admin::DomainAllowSerializer
+  end
+
+  private
+
+  def set_domain_allows
+    @domain_allows = filtered_domain_allows.order(id: :desc).to_a_paginated_by_id(limit_param(LIMIT), params_slice(:max_id, :since_id, :min_id))
+  end
+
+  def set_domain_allow
+    @domain_allow = DomainAllow.find(params[:id])
+  end
+
+  def filtered_domain_allows
+    # TODO: no filtering yet
+    DomainAllow.all
+  end
+
+  def insert_pagination_headers
+    set_pagination_headers(next_path, prev_path)
+  end
+
+  def next_path
+    api_v1_admin_domain_allows_url(pagination_params(max_id: pagination_max_id)) if records_continue?
+  end
+
+  def prev_path
+    api_v1_admin_domain_allows_url(pagination_params(min_id: pagination_since_id)) unless @domain_allows.empty?
+  end
+
+  def pagination_max_id
+    @domain_allows.last.id
+  end
+
+  def pagination_since_id
+    @domain_allows.first.id
+  end
+
+  def records_continue?
+    @domain_allows.size == limit_param(LIMIT)
+  end
+
+  def pagination_params(core_params)
+    params.slice(*PAGINATION_PARAMS).permit(*PAGINATION_PARAMS).merge(core_params)
+  end
+
+  def resource_params
+    params.permit(:domain)
+  end
+end