Add UpdateComponent mutation to allow components to be modified (#162)

Example:

```
mutation {
  updateComponent(input: {
    id: "Z2lkOi8vYXBwL0NvbXBvbmVudC81MTcyZjk2NC1mNjVlLTRkZDgtOGY1ZC1lODdjZTZlMzU2MzA"
    name: "mainB",
    extension: "py",
    content: "",
    default: false,
  }) {
          component {
            id
          }
      }
}
```

closes #150

---------

Co-authored-by: chrisruk <chrisruk@users.noreply.github.com>
Co-authored-by: chrisruk <christopher.richardson@raspberrypi.org>

Author: create-issue-branch[bot]

app/graphql/mutations/update_component.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module Mutations
+  class UpdateComponent < BaseMutation
+    description 'A mutation to update an existing component'
+
+    input_object_class Types::UpdateComponentInputType
+
+    field :component, Types::ComponentType, description: 'The component that has been updated'
+
+    def resolve(**input)
+      component = GlobalID.find(input[:id])
+      raise GraphQL::ExecutionError, 'Component not found' unless component
+
+      unless context[:current_ability].can?(:update, component)
+        raise GraphQL::ExecutionError,
+              'You are not permitted to update this component'
+      end
+
+      return { component: } if component.update(input.slice(:content, :name, :extension, :default))
+
+      raise GraphQL::ExecutionError, component.errors.full_messages.join(', ')
+    end
+
+    def ready?(**_args)
+      return true if context[:current_ability]&.can?(:update, Component, user_id: context[:current_user_id])
+
+      raise GraphQL::ExecutionError, 'You are not permitted to update a component'
+    end
+  end
+end

app/graphql/types/mutation_type.rb

@@ -7,6 +7,7 @@ class MutationType < Types::BaseObject
     field :create_project, mutation: Mutations::CreateProject, description: 'Create a project, complete with components'
     field :delete_project, mutation: Mutations::DeleteProject, description: 'Delete an existing project'
     field :remix_project, mutation: Mutations::RemixProject, description: 'Remix a project'
+    field :update_component, mutation: Mutations::UpdateComponent, description: 'Update fields on an existing component'
     field :update_project, mutation: Mutations::UpdateProject, description: 'Update fields on an existing project'
     # rubocop:enable GraphQL/ExtractType
   end

app/graphql/types/update_component_input_type.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module Types
+  class UpdateComponentInputType < Types::BaseInputObject
+    description 'Represents a project during an update'
+
+    argument :content, String, required: false, description: 'The text content of the component'
+    argument :default, Boolean, required: false, description: 'If this is the default component on a project'
+    argument :extension, String, required: false, description: 'The file extension of the component, e.g. html, csv, py'
+    argument :id, String, required: true, description: 'The ID of the component to update'
+    argument :name, String, required: false, description: 'The name of the file'
+  end
+end

db/schema.graphql

@@ -309,6 +309,16 @@ type Mutation {
     input: RemixProjectInput!
   ): RemixProjectPayload
 
+  """
+  Update fields on an existing component
+  """
+  updateComponent(
+    """
+    Parameters for UpdateComponent
+    """
+    input: UpdateComponentInput!
+  ): UpdateComponentPayload
+
   """
   Update fields on an existing project
   """
@@ -627,6 +637,56 @@ type RemixProjectPayload {
   project: Project
 }
 
+"""
+Represents a project during an update
+"""
+input UpdateComponentInput {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  The text content of the component
+  """
+  content: String
+
+  """
+  If this is the default component on a project
+  """
+  default: Boolean
+
+  """
+  The file extension of the component, e.g. html, csv, py
+  """
+  extension: String
+
+  """
+  The ID of the component to update
+  """
+  id: String!
+
+  """
+  The name of the file
+  """
+  name: String
+}
+
+"""
+Autogenerated return type of UpdateComponent.
+"""
+type UpdateComponentPayload {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  The component that has been updated
+  """
+  component: Component
+}
+
 """
 Represents a project during an update
 """

spec/graphql/mutations/update_component_mutation_spec.rb

@@ -0,0 +1,100 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'mutation UpdateComponent() { ... }' do
+  subject(:result) { execute_query(query: mutation, variables:) }
+
+  let(:mutation) { 'mutation UpdateComponent($component: UpdateComponentInput!) { updateComponent(input: $component) { component { id } } }' }
+  let(:component_id) { 'dummy-id' }
+  let(:variables) do
+    {
+      component: {
+        id: component_id,
+        name: 'main2',
+        extension: 'py',
+        content: '',
+        default: false
+      }
+    }
+  end
+
+  it { expect(mutation).to be_a_valid_graphql_query }
+
+  context 'with an existing component' do
+    let(:component) { create(:component, name: 'bob', extension: 'html', content: 'new', default: true) }
+    let(:component_id) { component.to_gid_param }
+
+    before do
+      # Instantiate component
+      component
+    end
+
+    context 'when unauthenticated' do
+      it 'does not update a component' do
+        expect { result }.not_to change { component.reload.name }
+      end
+
+      it 'returns an error' do
+        expect(result.dig('errors', 0, 'message')).not_to be_blank
+      end
+    end
+
+    context 'when the graphql context is unset' do
+      let(:graphql_context) { nil }
+
+      it 'does not update a component' do
+        expect { result }.not_to change { component.reload.name }
+      end
+    end
+
+    context 'when authenticated' do
+      let(:current_user_id) { component.project.user_id }
+
+      it 'updates the component name' do
+        expect { result }.to change { component.reload.name }.from(component.name).to(variables.dig(:component, :name))
+      end
+
+      it 'updates the component content' do
+        expect { result }.to change { component.reload.content }.from(component.content).to(variables.dig(:component, :content))
+      end
+
+      it 'updates the component extension' do
+        expect { result }.to change { component.reload.extension }.from(component.extension).to(variables.dig(:component, :extension))
+      end
+
+      it 'updates the component default' do
+        expect { result }.to change { component.reload.default }.from(component.default).to(variables.dig(:component, :default))
+      end
+
+      context 'when the component cannot be found' do
+        let(:component_id) { 'dummy' }
+
+        it 'returns an error' do
+          expect(result.dig('errors', 0, 'message')).to match(/not found/)
+        end
+      end
+
+      context 'with another users component' do
+        let(:current_user_id) { SecureRandom.uuid }
+
+        it 'returns an error' do
+          expect(result.dig('errors', 0, 'message')).to match(/not permitted/)
+        end
+      end
+
+      context 'when component update fails' do
+        before do
+          errors = instance_double(ActiveModel::Errors, full_messages: ['An error message'])
+          allow(component).to receive(:save).and_return(false)
+          allow(component).to receive(:errors).and_return(errors)
+          allow(GlobalID).to receive(:find).and_return(component)
+        end
+
+        it 'returns an error' do
+          expect(result.dig('errors', 0, 'message')).to match(/An error message/)
+        end
+      end
+    end
+  end
+end