Federated reports (#6570)

* Fix #2176: Federated reports

* UI for federated reports

* Add spec for ActivityPub Flag handler

* Add spec for ReportService

app/services/report_service.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+class ReportService < BaseService
+  def call(source_account, target_account, options = {})
+    @source_account = source_account
+    @target_account = target_account
+    @status_ids     = options.delete(:status_ids) || []
+    @comment        = options.delete(:comment) || ''
+    @options        = options
+
+    create_report!
+    notify_staff!
+    forward_to_origin! if !@target_account.local? && ActiveModel::Type::Boolean.new.cast(@options[:forward])
+
+    @report
+  end
+
+  private
+
+  def create_report!
+    @report = @source_account.reports.create!(
+      target_account: @target_account,
+      status_ids: @status_ids,
+      comment: @comment
+    )
+  end
+
+  def notify_staff!
+    User.staff.includes(:account).each do |u|
+      AdminMailer.new_report(u.account, @report).deliver_later
+    end
+  end
+
+  def forward_to_origin!
+    ActivityPub::DeliveryWorker.perform_async(
+      payload,
+      some_local_account.id,
+      @target_account.inbox_url
+    )
+  end
+
+  def payload
+    Oj.dump(ActiveModelSerializers::SerializableResource.new(
+      @report,
+      serializer: ActivityPub::FlagSerializer,
+      adapter: ActivityPub::Adapter,
+      account: some_local_account
+    ).as_json)
+  end
+
+  def some_local_account
+    @some_local_account ||= Account.local.where(suspended: false).first
+  end
+end