Add payloadAlertFields to HttpIntegration response

Now a `alertManagementHttpIntegrations` GraphQL query returns
`payloadAlertFields` calculated from the persisted `payload_example`.

doc/api/graphql/reference/gitlab_schema.graphql

@@ -634,6 +634,11 @@ type AlertManagementHttpIntegration implements AlertManagementIntegration {
   """
   name: String
 
+  """
+  Extract alert fields from payload example for custom mapping.
+  """
+  payloadAlertFields: [AlertManagementPayloadAlertField!]
+
   """
   The custom mapping of GitLab alert attributes to fields from the payload_example.
   """

doc/api/graphql/reference/gitlab_schema.json

@@ -1578,6 +1578,28 @@
               "isDeprecated": false,
               "deprecationReason": null
             },
+            {
+              "name": "payloadAlertFields",
+              "description": "Extract alert fields from payload example for custom mapping.",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "LIST",
+                "name": null,
+                "ofType": {
+                  "kind": "NON_NULL",
+                  "name": null,
+                  "ofType": {
+                    "kind": "OBJECT",
+                    "name": "AlertManagementPayloadAlertField",
+                    "ofType": null
+                  }
+                }
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
             {
               "name": "payloadAttributeMappings",
               "description": "The custom mapping of GitLab alert attributes to fields from the payload_example.",

doc/api/graphql/reference/index.md

@@ -274,6 +274,7 @@ An endpoint and credentials used to accept alerts for a project.
 | `apiUrl` | String | URL at which Prometheus metrics can be queried to populate the metrics dashboard. |
 | `id` | ID! | ID of the integration. |
 | `name` | String | Name of the integration. |
+| `payloadAlertFields` | AlertManagementPayloadAlertField! => Array | Extract alert fields from payload example for custom mapping. |
 | `payloadAttributeMappings` | AlertManagementPayloadAlertMappingField! => Array | The custom mapping of GitLab alert attributes to fields from the payload_example. |
 | `payloadExample` | JsonString | The example of an alert payload. |
 | `token` | String | Token used to authenticate alert notification requests. |

ee/app/graphql/ee/types/alert_management/http_integration_type.rb

@@ -15,6 +15,11 @@ module EE
                 null: true,
                 description: 'The custom mapping of GitLab alert attributes to fields from the payload_example.',
                 resolver: ::Resolvers::AlertManagement::PayloadAlertMappingFieldResolver
+
+          field :payload_alert_fields, [::Types::AlertManagement::PayloadAlertFieldType],
+                null: true,
+                description: 'Extract alert fields from payload example for custom mapping.',
+                resolver: ::Resolvers::AlertManagement::PersistedPayloadAlertFieldResolver
         end
       end
     end

ee/app/graphql/resolvers/alert_management/payload_alert_mapping_field_resolver.rb

@@ -8,8 +8,6 @@ module Resolvers
       alias_method :integration, :object
 
       def resolve
-        return [] unless integration.is_a?(::AlertManagement::HttpIntegration)
-
         integration.payload_attribute_mapping.map do |field_name, mapping|
           ::AlertManagement::AlertPayloadField.new(
             project: integration.project,

ee/app/graphql/resolvers/alert_management/persisted_payload_alert_field_resolver.rb

+# frozen_string_literal: true
+
+module Resolvers
+  module AlertManagement
+    class PersistedPayloadAlertFieldResolver < BaseResolver
+      type ::Types::AlertManagement::PayloadAlertFieldType, null: true
+
+      alias_method :integration, :object
+
+      def resolve
+        Gitlab::AlertManagement::AlertPayloadFieldExtractor
+          .new(integration.project)
+          .extract(integration.payload_example)
+      end
+    end
+  end
+end

ee/spec/graphql/ee/types/alert_management/http_integration_type_spec.rb

@@ -18,6 +18,7 @@ RSpec.describe GitlabSchema.types['AlertManagementHttpIntegration'] do
       api_url
       payload_example
       payload_attribute_mappings
+      payload_alert_fields
     ]
 
     expect(described_class).to have_graphql_fields(*expected_fields)

ee/spec/requests/api/graphql/project/alert_management/http_integrations_spec.rb

@@ -107,6 +107,18 @@ RSpec.describe 'getting Alert Management HTTP Integrations' do
                 'path' => %w(alert desc),
                 'type' => 'STRING'
               }
+            ],
+            'payloadAlertFields' => [
+              {
+                'label' => 'Name',
+                'path' => %w(alert name),
+                'type' => 'STRING'
+              },
+              {
+                'label' => 'Desc',
+                'path' => %w(alert desc),
+                'type' => 'STRING'
+              }
             ]
           },
           {
@@ -118,7 +130,8 @@ RSpec.describe 'getting Alert Management HTTP Integrations' do
             'url' => inactive_http_integration.url,
             'apiUrl' => nil,
             'payloadExample' => "{}",
-            'payloadAttributeMappings' => []
+            'payloadAttributeMappings' => [],
+            'payloadAlertFields' => []
           }
         )
       end