From afccef718c01f02c14e977d1b7c28dc7afd78172 Mon Sep 17 00:00:00 2001
From: David Craig <david@silverstripe.com>
Date: Mon, 22 Feb 2016 14:13:35 +1300
Subject: [PATCH 1/5] Initial Form Field Schema implementation

- Adds FormSchema class
- Adds FormSchema dependency to LeftAndMain via Injector
- Adds schema allowed_action method to LeftAndMain for generating Form schemas
- Adds FormFieldSchemaTrait to for schema getters and setters on FormFields
---
 _config/config.yml             |  3 ++
 admin/code/LeftAndMain.php     | 20 ++++++++-
 forms/FormField.php            | 21 ++++++++-
 forms/FormFieldSchemaTrait.php | 81 ++++++++++++++++++++++++++++++++++
 forms/FormSchema.php           | 56 +++++++++++++++++++++++
 tests/forms/FormFieldTest.php  | 37 ++++++++++++++++
 tests/forms/FormSchemaTest.php | 62 ++++++++++++++++++++++++++
 7 files changed, 276 insertions(+), 4 deletions(-)
 create mode 100644 forms/FormFieldSchemaTrait.php
 create mode 100644 forms/FormSchema.php
 create mode 100644 tests/forms/FormSchemaTest.php

diff --git a/_config/config.yml b/_config/config.yml
index 42dc3103c..77ff116b9 100644
--- a/_config/config.yml
+++ b/_config/config.yml
@@ -1,6 +1,9 @@
 ---
 Name: coreconfig
 ---
+Injector:
+  FormSchema:
+    class: SilverStripe\Forms\Schema\FormSchema
 Upload:
   # Replace an existing file rather than renaming the new one.
   replaceFile: false
diff --git a/admin/code/LeftAndMain.php b/admin/code/LeftAndMain.php
index b651ac957..ec4c09145 100644
--- a/admin/code/LeftAndMain.php
+++ b/admin/code/LeftAndMain.php
@@ -5,6 +5,8 @@
  * @subpackage admin
  */
 
+use SilverStripe\Forms\Schema\FormSchema;
+
 /**
  * LeftAndMain is the parent class of all the two-pane views in the CMS.
  * If you are wanting to add more areas to the CMS, you can do it by subclassing LeftAndMain.
@@ -84,7 +86,7 @@ class LeftAndMain extends Controller implements PermissionProvider {
 	/**
 	 * @var array
 	 */
-	private static $allowed_actions = array(
+	private static $allowed_actions = [
 		'index',
 		'save',
 		'savetreenode',
@@ -97,7 +99,12 @@ class LeftAndMain extends Controller implements PermissionProvider {
 		'AddForm',
 		'batchactions',
 		'BatchActionsForm',
-	);
+		'schema',
+	];
+
+	private static $dependencies = [
+		'schema' => '%$FormSchema'
+	];
 
 	/**
 	 * @config
@@ -169,6 +176,15 @@ class LeftAndMain extends Controller implements PermissionProvider {
 	 */
 	protected $responseNegotiator;
 
+	/**
+	 * Gets a JSON schema representing the current edit form.
+	 *
+	 * @return SS_HTTPResponse
+	 */
+	public function schema() {
+		return $this->schema->getSchema($this->getEditForm());
+	}
+
 	/**
 	 * @param Member $member
 	 * @return boolean
diff --git a/forms/FormField.php b/forms/FormField.php
index f041af1f8..239dba2cb 100644
--- a/forms/FormField.php
+++ b/forms/FormField.php
@@ -25,6 +25,8 @@
  */
 class FormField extends RequestHandler {
 
+	use SilverStripe\Forms\Schema\FormFieldSchemaTrait;
+
 	/**
 	 * @var Form
 	 */
@@ -80,7 +82,7 @@ class FormField extends RequestHandler {
 	 * @config
 	 * @var array $default_classes The default classes to apply to the FormField
 	 */
-	private static $default_classes = array();
+	private static $default_classes = [];
 
 
 	/**
@@ -162,7 +164,22 @@ class FormField extends RequestHandler {
 	 *
 	 * @var array
 	 */
-	protected $attributes = array();
+	protected $attributes = [];
+
+	/**
+	 * The type of front-end component to render the FormField as.
+	 *
+	 * @var string
+	 */
+	protected $schemaComponent;
+
+	/**
+	 * Structured schema data representing the FormField.
+	 * Used to render the FormField as a ReactJS Component on the front-end.
+	 *
+	 * @var array
+	 */
+	protected $schemaData = [];
 
 	/**
 	 * Takes a field name and converts camelcase to spaced words. Also resolves combined field
diff --git a/forms/FormFieldSchemaTrait.php b/forms/FormFieldSchemaTrait.php
new file mode 100644
index 000000000..f78209f5f
--- /dev/null
+++ b/forms/FormFieldSchemaTrait.php
@@ -0,0 +1,81 @@
+<?php
+
+namespace SilverStripe\Forms\Schema;
+
+trait FormFieldSchemaTrait {
+
+	/**
+	 * Sets the component type the FormField will be rendered as on the front-end.
+	 *
+	 * @param string $componentType
+	 * @return FormField
+	 */
+	public function setSchemaComponent($componentType) {
+		$this->schemaComponent = $componentType;
+		return $this;
+	}
+
+	/**
+	 * Gets the type of front-end component the FormField will be rendered as.
+	 *
+	 * @return string
+	 */
+	public function getSchemaComponent() {
+		return $this->schemaComponent;
+	}
+
+	/**
+	 * Sets the schema data used for rendering the field on the front-end.
+	 * Merges the passed array with the current `$schemaData` or {@link getSchemaDataDefaults()}.
+	 * Any passed keys that are not defined in {@link getSchemaDataDefaults()} are ignored.
+	 * If you want to pass around ad hoc data use the `data` array e.g. pass `['data' => ['myCustomKey' => 'yolo']]`.
+	 *
+	 * @param array $schemaData - The data to be merged with $this->schemaData.
+	 * @return FormField
+	 *
+	 * @todo Add deep merging of arrays like `data` and `attributes`.
+	 */
+	public function setSchemaData($schemaData = []) {
+		$current = $this->getSchemaData();
+
+		$this->schemaData = array_merge($current, array_intersect_key($schemaData, $current));
+		return $this;
+	}
+
+	/**
+	 * Gets the schema data used to render the FormField on the front-end.
+	 *
+	 * @return array
+	 */
+	public function getSchemaData() {
+		return array_merge($this->getSchemaDataDefaults(), $this->schemaData);
+	}
+
+	/**
+	 * Gets the defaults for $schemaData.
+	 * The keys defined here are immutable, meaning undefined keys passed to {@link setSchemaData()} are ignored.
+	 * Instead the `data` array should be used to pass around ad hoc data.
+	 *
+	 * @return array
+	 */
+	function getSchemaDataDefaults() {
+		return [
+			'type' => $this->class,
+			'component' => $this->getSchemaComponent(),
+			'id' => $this->ID,
+			'holder_id' => null,
+			'name' => $this->getName(),
+			'title' => $this->Title(),
+			'source' => null,
+			'extraClass' => $this->ExtraClass(),
+			'description' => $this->getDescription(),
+			'rightTitle' => $this->RightTitle(),
+			'leftTitle' => $this->LeftTitle(),
+			'readOnly' => $this->isReadOnly(),
+			'disabled' => $this->isDisabled(),
+			'customValidationMessage' => $this->getCustomValidationMessage(),
+			'attributes' => [],
+			'data' => [],
+		];
+	}
+}
diff --git a/forms/FormSchema.php b/forms/FormSchema.php
new file mode 100644
index 000000000..b3d61a44e
--- /dev/null
+++ b/forms/FormSchema.php
@@ -0,0 +1,56 @@
+<?php
+
+namespace SilverStripe\Forms\Schema;
+
+use Convert;
+use Form;
+
+class FormSchema {
+
+	/**
+	 * Gets the schema for this form as a nested array.
+	 *
+	 * @param Form $form
+	 * @return string
+	 */
+	public function getSchema(Form $form) {
+		$request = $form->controller()->getRequest();
+		$params = $request->AllParams();
+
+		$schema = [
+			'name' => $form->getName(),
+			'id' => isset($params['ID']) ? $params['ID'] : null,
+			'action' => isset($params['Action']) ? $params['Action'] : null,
+			'method' => $form->controller()->getRequest()->HttpMethod(),
+			'schema_url' => $request->getUrl(),
+			'attributes' => $form->getAttributes(),
+			'data' => [],
+			'fields' => [],
+			'actions' => []
+		];
+
+		foreach ($form->Actions() as $action) {
+			$schema['actions'][] = $action->getSchemaData();
+		}
+
+		foreach ($form->Fields() as $fieldList) {
+			foreach ($fieldList->getForm()->fields()->dataFields() as $field) {
+				$schema['fields'][] = $field->getSchemaData();
+			}
+		}
+
+		return Convert::raw2json($schema);
+	}
+
+	/**
+	 * Gets the current state of this form as a nested array.
+	 *
+	 * @param From $form
+	 * @return string
+	 */
+	public function getState(Form $form) {
+		$state = ['state' => []];
+
+		return Convert::raw2json($state);
+	}
+}
diff --git a/tests/forms/FormFieldTest.php b/tests/forms/FormFieldTest.php
index 221091dad..7ab132327 100644
--- a/tests/forms/FormFieldTest.php
+++ b/tests/forms/FormFieldTest.php
@@ -241,6 +241,43 @@ class FormFieldTest extends SapphireTest {
 		$this->assertArrayHasKey('extended', $field->getAttributes());
 	}
 
+	public function testSetSchemaComponent() {
+		$field = new FormField('MyField');
+		$field = $field->setSchemaComponent('MyComponent');
+		$component = $field->getSchemaComponent();
+		$this->assertEquals('MyComponent', $component);
+	}
+
+	public function testGetSchemaDataDefaults() {
+		$field = new FormField('MyField');
+		$schema = $field->getSchemaDataDefaults();
+		$this->assertInternalType('array', $schema);
+	}
+
+	public function testGetSchemaData() {
+		$field = new FormField('MyField');
+		$schema = $field->getSchemaData();
+		$this->assertEquals('MyField', $schema['name']);
+
+		// Make sure the schema data is up-to-date with object properties.
+		$field->setName('UpdatedField');
+		$schema = $field->getSchemaData();
+		$this->assertEquals($field->getName(), $schema['name']);
+	}
+
+	public function testSetSchemaData() {
+		$field = new FormField('MyField');
+
+		// Make sure the user can update values.
+		$field = $field->setSchemaData(['name' => 'MyUpdatedField']);
+		$schema = $field->getSchemaData();
+		$this->assertEquals($schema['name'], 'MyUpdatedField');
+
+		// Make user the user can't define custom keys on the schema.
+		$field = $field->setSchemaData(['myCustomKey' => 'yolo']);
+		$schema = $field->getSchemaData();
+		$this->assertEquals(array_key_exists('myCustomKey', $schema), false);
+	}
 }
 
 /**
diff --git a/tests/forms/FormSchemaTest.php b/tests/forms/FormSchemaTest.php
new file mode 100644
index 000000000..11b7f3697
--- /dev/null
+++ b/tests/forms/FormSchemaTest.php
@@ -0,0 +1,62 @@
+<?php
+
+use SilverStripe\Forms\Schema\FormSchema;
+
+class FormSchemaTest extends SapphireTest {
+
+	public function testGetSchema() {
+		$form = new Form(new Controller(), 'TestForm', new FieldList(), new FieldList());
+		$formSchema = new FormSchema();
+		$expectedJSON = json_encode([
+			'name' => 'TestForm',
+			'id' => null,
+			'action' => null,
+			'method' => '',
+			'schema_url' => '',
+			'attributes' => [
+				'id' => 'Form_TestForm',
+				'action' => 'Controller/TestForm',
+				'method' => 'POST',
+				'enctype' => 'application/x-www-form-urlencoded',
+				'target' => null,
+				'class' => ''
+			],
+			'data' => [],
+			'fields' => [
+				[
+					'type' => "HiddenField",
+					'component' => null,
+					'id' => null,
+					'holder_id' => null,
+					'name' => 'SecurityID',
+					'title' => 'Security ID',
+					'source' => null,
+					'extraClass' => 'hidden',
+					'description' => null,
+					'rightTitle' => null,
+					'leftTitle' => null,
+					'readOnly' => false,
+					'disabled' => false,
+					'customValidationMessage' => '',
+					'attributes' => [],
+					'data' => []
+				],
+			],
+			'actions' => []
+		]);
+
+		$schema = $formSchema->getSchema($form);
+
+		$this->assertJsonStringEqualsJsonString($expectedJSON, $schema);
+	}
+
+	public function testGetState() {
+		$form = new Form(new Controller(), 'TestForm', new FieldList(), new FieldList());
+		$formSchema = new FormSchema();
+		$expectedJSON = json_encode(['state' => []]);
+
+		$state = $formSchema->getState($form);
+
+		$this->assertJsonStringEqualsJsonString($expectedJSON, $state);
+	}
+}

From 404ac4ae43d15e957510f5f4764273d3433dea51 Mon Sep 17 00:00:00 2001
From: David Craig <david@silverstripe.com>
Date: Mon, 29 Feb 2016 13:50:59 +1300
Subject: [PATCH 2/5] Initial schemaState implementation

---
 admin/code/LeftAndMain.php     | 38 +++++++++++++++++++++++++++++++++-
 forms/FormSchema.php           | 14 ++++++++-----
 tests/forms/FormSchemaTest.php | 18 +++++++++-------
 3 files changed, 57 insertions(+), 13 deletions(-)

diff --git a/admin/code/LeftAndMain.php b/admin/code/LeftAndMain.php
index ec4c09145..a64dac490 100644
--- a/admin/code/LeftAndMain.php
+++ b/admin/code/LeftAndMain.php
@@ -182,7 +182,43 @@ class LeftAndMain extends Controller implements PermissionProvider {
 	 * @return SS_HTTPResponse
 	 */
 	public function schema() {
-		return $this->schema->getSchema($this->getEditForm());
+		$req = $this->getRequest();
+		$res = $this->getResponse();
+		$schemaParts = [];
+
+		// Valid values for the "X-Formschema-Request" header are "schema" and "state".
+		// If either of these values are set they will be stored in the $schemaParst array
+		// and used to construct the response body.
+		if ($schemaHeader = $req->getHeader('X-Formschema-Request')) {
+			$schemaParts = array_filter(explode(',', $schemaHeader), function($value) {
+				$validHeaderValues = ['schema', 'state'];
+				return in_array(trim($value), $validHeaderValues);
+			});
+		}
+
+		// Make sure it's an AJAX GET request with a valid "X-Formschema-Request" header value.
+		if (!$req->isAjax() || !$req->isGET() || !count($schemaParts)) {
+			throw new SS_HTTPResponse_Exception(
+				'Invalid request. Check you\'ve set a "X-Formschema-Request" header with "schema" or "state" values.',
+				400
+			);
+		}
+
+		$form = $this->getEditForm();
+		$responseBody = ['id' => $form->getName()];
+
+		if (in_array('schema', $schemaParts)) {
+			$responseBody['schema'] = $this->schema->getSchema($form);
+		}
+
+		if (in_array('state', $schemaParts)) {
+			$responseBody['state'] = $this->schema->getState($form);
+		}
+
+		$res->addHeader('Content-Type', 'application/json');
+		$res->setBody(Convert::raw2json($responseBody));
+
+		return $res;
 	}
 
 	/**
diff --git a/forms/FormSchema.php b/forms/FormSchema.php
index b3d61a44e..2b7335b70 100644
--- a/forms/FormSchema.php
+++ b/forms/FormSchema.php
@@ -11,7 +11,7 @@ class FormSchema {
 	 * Gets the schema for this form as a nested array.
 	 *
 	 * @param Form $form
-	 * @return string
+	 * @return array
 	 */
 	public function getSchema(Form $form) {
 		$request = $form->controller()->getRequest();
@@ -39,18 +39,22 @@ class FormSchema {
 			}
 		}
 
-		return Convert::raw2json($schema);
+		return $schema;
 	}
 
 	/**
 	 * Gets the current state of this form as a nested array.
 	 *
 	 * @param From $form
-	 * @return string
+	 * @return array
 	 */
 	public function getState(Form $form) {
-		$state = ['state' => []];
+		$state = [
+			'id' => $form->getName(),
+			'fields' => [],
+			'messages' => []
+		];
 
-		return Convert::raw2json($state);
+		return $state;
 	}
 }
diff --git a/tests/forms/FormSchemaTest.php b/tests/forms/FormSchemaTest.php
index 11b7f3697..3aaf36533 100644
--- a/tests/forms/FormSchemaTest.php
+++ b/tests/forms/FormSchemaTest.php
@@ -7,7 +7,7 @@ class FormSchemaTest extends SapphireTest {
 	public function testGetSchema() {
 		$form = new Form(new Controller(), 'TestForm', new FieldList(), new FieldList());
 		$formSchema = new FormSchema();
-		$expectedJSON = json_encode([
+		$expected = [
 			'name' => 'TestForm',
 			'id' => null,
 			'action' => null,
@@ -43,20 +43,24 @@ class FormSchemaTest extends SapphireTest {
 				],
 			],
 			'actions' => []
-		]);
+		];
 
 		$schema = $formSchema->getSchema($form);
-
-		$this->assertJsonStringEqualsJsonString($expectedJSON, $schema);
+		$this->assertInternalType('array', $schema);
+		$this->assertJsonStringEqualsJsonString(json_encode($expected), json_encode($schema));
 	}
 
 	public function testGetState() {
 		$form = new Form(new Controller(), 'TestForm', new FieldList(), new FieldList());
 		$formSchema = new FormSchema();
-		$expectedJSON = json_encode(['state' => []]);
+		$expected = [
+			'id' => 'TestForm',
+			'fields' => [],
+			'messages' => []
+		];
 
 		$state = $formSchema->getState($form);
-
-		$this->assertJsonStringEqualsJsonString($expectedJSON, $state);
+		$this->assertInternalType('array', $state);
+		$this->assertJsonStringEqualsJsonString(json_encode($expected), json_encode($state));
 	}
 }

From 746322a9f18365bff554e72faa9789d890e1512d Mon Sep 17 00:00:00 2001
From: Ingo Schommer <ingo@silverstripe.com>
Date: Tue, 1 Mar 2016 16:15:15 +1300
Subject: [PATCH 3/5] Replace CMSForm use with new
 setValidationResponseCallback() API

Preparing for form schema API, see https://github.com/silverstripe/silverstripe-framework/issues/4938
---
 admin/code/CMSForm.php       | 52 ------------------------------------
 admin/code/LeftAndMain.php   | 24 +++++++++++++----
 admin/code/ModelAdmin.php    |  3 +--
 admin/code/SecurityAdmin.php |  3 +--
 forms/Form.php               | 36 ++++++++++++++++++++++++-
 5 files changed, 56 insertions(+), 62 deletions(-)
 delete mode 100644 admin/code/CMSForm.php

diff --git a/admin/code/CMSForm.php b/admin/code/CMSForm.php
deleted file mode 100644
index 563a2d821..000000000
--- a/admin/code/CMSForm.php
+++ /dev/null
@@ -1,52 +0,0 @@
-<?php
-
-/**
- * Deals with special form handling in CMS, mainly around
- * {@link PjaxResponseNegotiator}
- *
- * @package framework
- * @subpackage admin
- */
-class CMSForm extends Form {
-	
-	/**
-	 * Route validation error responses through response negotiator,
-	 * so they return the correct markup as expected by the requesting client.
-	 */
-	protected function getValidationErrorResponse() {
-		$request = $this->getRequest();
-		$negotiator = $this->getResponseNegotiator();
-
-		if($request->isAjax() && $negotiator) {
-			$this->setupFormErrors();
-			$result = $this->forTemplate();
-
-			return $negotiator->respond($request, array(
-				'CurrentForm' => function() use($result) {
-					return $result;
-				}
-			));
-		} else {
-			return parent::getValidationErrorResponse();
-		}
-	}
-
-	/**
-	 * Sets the response negotiator
-	 * @param ResponseNegotiator $negotiator The response negotiator to use
-	 * @return Form The current form
-	 */
-	public function setResponseNegotiator($negotiator) {
-		$this->responseNegotiator = $negotiator;
-		return $this;
-	}
-
-	/**
-	 * Gets the current response negotiator
-	 * @return ResponseNegotiator|null
-	 */
-	public function getResponseNegotiator() {
-		return $this->responseNegotiator;
-	}
-
-}
diff --git a/admin/code/LeftAndMain.php b/admin/code/LeftAndMain.php
index a64dac490..f20e5aceb 100644
--- a/admin/code/LeftAndMain.php
+++ b/admin/code/LeftAndMain.php
@@ -13,6 +13,8 @@ use SilverStripe\Forms\Schema\FormSchema;
  *
  * This is essentially an abstract class which should be subclassed.
  * See {@link CMSMain} for a good example.
+ *
+ * @property FormSchema $schema
  */
 class LeftAndMain extends Controller implements PermissionProvider {
 
@@ -197,7 +199,7 @@ class LeftAndMain extends Controller implements PermissionProvider {
 		}
 
 		// Make sure it's an AJAX GET request with a valid "X-Formschema-Request" header value.
-		if (!$req->isAjax() || !$req->isGET() || !count($schemaParts)) {
+		if (!$req->isGET() || !count($schemaParts)) {
 			throw new SS_HTTPResponse_Exception(
 				'Invalid request. Check you\'ve set a "X-Formschema-Request" header with "schema" or "state" values.',
 				400
@@ -1312,14 +1314,27 @@ class LeftAndMain extends Controller implements PermissionProvider {
 			$actionsFlattened = $actions->dataFields();
 			if($actionsFlattened) foreach($actionsFlattened as $action) $action->setUseButtonTag(true);
 
-			$form = CMSForm::create(
+			$negotiator = $this->getResponseNegotiator();
+			$form = Form::create(
 				$this, "EditForm", $fields, $actions
 			)->setHTMLID('Form_EditForm');
-			$form->setResponseNegotiator($this->getResponseNegotiator());
 			$form->addExtraClass('cms-edit-form');
 			$form->loadDataFrom($record);
 			$form->setTemplate($this->getTemplatesWithSuffix('_EditForm'));
 			$form->setAttribute('data-pjax-fragment', 'CurrentForm');
+			$form->setValidationResponseCallback(function() use ($negotiator, $form) {
+				$request = $this->getRequest();
+				if($request->isAjax() && $negotiator) {
+					$form->setupFormErrors();
+					$result = $form->forTemplate();
+
+					return $negotiator->respond($request, array(
+						'CurrentForm' => function() use($result) {
+							return $result;
+						}
+					));
+				}
+			});
 
 			// Announce the capability so the frontend can decide whether to allow preview or not.
 			if(in_array('CMSPreviewable', class_implements($record))) {
@@ -1368,7 +1383,7 @@ class LeftAndMain extends Controller implements PermissionProvider {
 	 * @return Form
 	 */
 	public function EmptyForm() {
-		$form = CMSForm::create(
+		$form = Form::create(
 			$this,
 			"EditForm",
 			new FieldList(
@@ -1387,7 +1402,6 @@ class LeftAndMain extends Controller implements PermissionProvider {
 			),
 			new FieldList()
 		)->setHTMLID('Form_EditForm');
-		$form->setResponseNegotiator($this->getResponseNegotiator());
 		$form->unsetValidator();
 		$form->addExtraClass('cms-edit-form');
 		$form->addExtraClass('root-form');
diff --git a/admin/code/ModelAdmin.php b/admin/code/ModelAdmin.php
index cc41d7bce..3ff8ef89c 100644
--- a/admin/code/ModelAdmin.php
+++ b/admin/code/ModelAdmin.php
@@ -138,13 +138,12 @@ abstract class ModelAdmin extends LeftAndMain {
 			$listField->getConfig()->getComponentByType('GridFieldDetailForm')->setValidator($detailValidator);
 		}
 
-		$form = CMSForm::create(
+		$form = Form::create(
 			$this,
 			'EditForm',
 			new FieldList($listField),
 			new FieldList()
 		)->setHTMLID('Form_EditForm');
-		$form->setResponseNegotiator($this->getResponseNegotiator());
 		$form->addExtraClass('cms-edit-form cms-panel-padded center');
 		$form->setTemplate($this->getTemplatesWithSuffix('_EditForm'));
 		$editFormAction = Controller::join_links($this->Link($this->sanitiseClassName($this->modelClass)), 'EditForm');
diff --git a/admin/code/SecurityAdmin.php b/admin/code/SecurityAdmin.php
index cfbf4fe3d..923f9d4f9 100755
--- a/admin/code/SecurityAdmin.php
+++ b/admin/code/SecurityAdmin.php
@@ -177,13 +177,12 @@ class SecurityAdmin extends LeftAndMain implements PermissionProvider {
 
 		$actions = new FieldList();
 
-		$form = CMSForm::create(
+		$form = Form::create(
 			$this,
 			'EditForm',
 			$fields,
 			$actions
 		)->setHTMLID('Form_EditForm');
-		$form->setResponseNegotiator($this->getResponseNegotiator());
 		$form->addExtraClass('cms-edit-form');
 		$form->setTemplate($this->getTemplatesWithSuffix('_EditForm'));
 		// Tab nav in CMS is rendered through separate template
diff --git a/forms/Form.php b/forms/Form.php
index 112d8b3b7..0523c14a4 100644
--- a/forms/Form.php
+++ b/forms/Form.php
@@ -79,6 +79,11 @@ class Form extends RequestHandler {
 	 */
 	protected $validator;
 
+	/**
+	 * @var callable {@see setValidationResponseCallback()}
+	 */
+	protected $validationResponseCallback;
+
 	/**
 	 * @var string
 	 */
@@ -479,16 +484,45 @@ class Form extends RequestHandler {
 		);
 	}
 
+	/**
+	 * @return callable
+	 */
+	public function getValidationResponseCallback() {
+		return $this->validationResponseCallback;
+	}
+
+	/**
+	 * Overrules validation error behaviour in {@link httpSubmission()}
+	 * when validation has failed. Useful for optional handling of a certain accepted content type.
+	 *
+	 * The callback can opt out of handling specific responses by returning NULL,
+	 * in which case the default form behaviour will kick in.
+	 *
+	 * @param $callback
+	 * @return self
+	 */
+	public function setValidationResponseCallback($callback) {
+		$this->validationResponseCallback = $callback;
+
+		return $this;
+	}
+
 	/**
 	 * Returns the appropriate response up the controller chain
 	 * if {@link validate()} fails (which is checked prior to executing any form actions).
 	 * By default, returns different views for ajax/non-ajax request, and
 	 * handles 'application/json' requests with a JSON object containing the error messages.
-	 * Behaviour can be influenced by setting {@link $redirectToFormOnValidationError}.
+	 * Behaviour can be influenced by setting {@link $redirectToFormOnValidationError},
+	 * and can be overruled by setting {@link $validationResponseCallback}.
 	 *
 	 * @return SS_HTTPResponse|string
 	 */
 	protected function getValidationErrorResponse() {
+		$callback = $this->getValidationResponseCallback();
+		if($callback && $callbackResponse = $callback()) {
+			return $callbackResponse;
+		}
+
 		$request = $this->getRequest();
 		if($request->isAjax()) {
 				// Special case for legacy Validator.js implementation

From e1fcc64c41c6e2c44f7a088b72f0c0fb5577f12f Mon Sep 17 00:00:00 2001
From: Ingo Schommer <ingo@silverstripe.com>
Date: Tue, 1 Mar 2016 16:15:47 +1300
Subject: [PATCH 4/5] Form field schema state

See https://github.com/silverstripe/silverstripe-framework/issues/4938
---
 forms/FormField.php            | 15 ------
 forms/FormFieldSchemaTrait.php | 84 +++++++++++++++++++++++++++++++++-
 forms/FormSchema.php           | 13 +++++-
 tests/forms/FormFieldTest.php  | 31 +++++++++++++
 tests/forms/FormSchemaTest.php | 78 ++++++++++++++++++++++++++++++-
 5 files changed, 203 insertions(+), 18 deletions(-)

diff --git a/forms/FormField.php b/forms/FormField.php
index 239dba2cb..e324ff78a 100644
--- a/forms/FormField.php
+++ b/forms/FormField.php
@@ -166,21 +166,6 @@ class FormField extends RequestHandler {
 	 */
 	protected $attributes = [];
 
-	/**
-	 * The type of front-end component to render the FormField as.
-	 *
-	 * @var string
-	 */
-	protected $schemaComponent;
-
-	/**
-	 * Structured schema data representing the FormField.
-	 * Used to render the FormField as a ReactJS Component on the front-end.
-	 *
-	 * @var array
-	 */
-	protected $schemaData = [];
-
 	/**
 	 * Takes a field name and converts camelcase to spaced words. Also resolves combined field
 	 * names with dot syntax to spaced words.
diff --git a/forms/FormFieldSchemaTrait.php b/forms/FormFieldSchemaTrait.php
index f78209f5f..ab9e40115 100644
--- a/forms/FormFieldSchemaTrait.php
+++ b/forms/FormFieldSchemaTrait.php
@@ -4,6 +4,29 @@ namespace SilverStripe\Forms\Schema;
 
 trait FormFieldSchemaTrait {
 
+	/**
+	 * The type of front-end component to render the FormField as.
+	 *
+	 * @var string
+	 */
+	protected $schemaComponent;
+
+	/**
+	 * Structured schema data representing the FormField.
+	 * Used to render the FormField as a ReactJS Component on the front-end.
+	 *
+	 * @var array
+	 */
+	protected $schemaData = [];
+
+	/**
+	 * Structured schema state representing the FormField's current data and validation.
+	 * Used to render the FormField as a ReactJS Component on the front-end.
+	 *
+	 * @var array
+	 */
+	protected $schemaState = [];
+
 	/**
 	 * Sets the component type the FormField will be rendered as on the front-end.
 	 *
@@ -58,7 +81,7 @@ trait FormFieldSchemaTrait {
 	 *
 	 * @return array
 	 */
-	function getSchemaDataDefaults() {
+	public function getSchemaDataDefaults() {
 		return [
 			'type' => $this->class,
 			'component' => $this->getSchemaComponent(),
@@ -78,4 +101,63 @@ trait FormFieldSchemaTrait {
 			'data' => [],
 		];
 	}
+
+	/**
+	 * Sets the schema data used for rendering the field on the front-end.
+	 * Merges the passed array with the current `$schemaData` or {@link getSchemaDataDefaults()}.
+	 * Any passed keys that are not defined in {@link getSchemaDataDefaults()} are ignored.
+	 * If you want to pass around ad hoc data use the `data` array e.g. pass `['data' => ['myCustomKey' => 'yolo']]`.
+	 *
+	 * @param array $schemaData - The data to be merged with $this->schemaData.
+	 * @return FormField
+	 *
+	 * @todo Add deep merging of arrays like `data` and `attributes`.
+	 */
+	public function setSchemaState($schemaState = []) {
+		$current = $this->getSchemaState();
+
+		$this->schemaState = array_merge($current, array_intersect_key($schemaState, $current));
+		return $this;
+	}
+
+	/**
+	 * Gets the schema state used to render the FormField on the front-end.
+	 *
+	 * @return array
+	 */
+	public function getSchemaState() {
+		return array_merge($this->getSchemaStateDefaults(), $this->schemaState);
+	}
+
+	/**
+	 * Gets the defaults for $schemaState.
+	 * The keys defined here are immutable, meaning undefined keys passed to {@link setSchemaState()} are ignored.
+	 * Instead the `data` array should be used to pass around ad hoc data.
+	 * Includes validation data if the field is associated to a {@link Form},
+	 * and {@link Form->validate()} has been called.
+	 *
+	 * @return array
+	 */
+	public function getSchemaStateDefaults() {
+		$field = $this;
+		$form = $this->getForm();
+		$validator = $form ? $form->getValidator() : null;
+		$errors = $validator ? (array)$validator->getErrors() : [];
+		$messages = array_filter(array_map(function($error) use ($field) {
+			if($error['fieldName'] === $field->getName()) {
+				return [
+					'value' => $error['message'],
+					'type' => $error['messageType']
+				];
+			}
+		}, $errors));
+
+		return [
+			'id' => $this->ID(),
+			'value' => $this->Value(),
+			'valid' => (count($messages) === 0),
+			'messages' => (array)$messages,
+			'data' => [],
+		];
+	}
 }
diff --git a/forms/FormSchema.php b/forms/FormSchema.php
index 2b7335b70..17307193f 100644
--- a/forms/FormSchema.php
+++ b/forms/FormSchema.php
@@ -45,7 +45,7 @@ class FormSchema {
 	/**
 	 * Gets the current state of this form as a nested array.
 	 *
-	 * @param From $form
+	 * @param Form $form
 	 * @return array
 	 */
 	public function getState(Form $form) {
@@ -55,6 +55,17 @@ class FormSchema {
 			'messages' => []
 		];
 
+		foreach ($form->Fields()->dataFields() as $field) {
+			$state['fields'][] = $field->getSchemaState();
+		}
+
+		if($form->Message()) {
+			$state['messages'][] = [
+				'value' => $form->Message(),
+				'type' => $form->MessageType(),
+			];
+		}
+
 		return $state;
 	}
 }
diff --git a/tests/forms/FormFieldTest.php b/tests/forms/FormFieldTest.php
index 7ab132327..b2f235fc5 100644
--- a/tests/forms/FormFieldTest.php
+++ b/tests/forms/FormFieldTest.php
@@ -278,6 +278,37 @@ class FormFieldTest extends SapphireTest {
 		$schema = $field->getSchemaData();
 		$this->assertEquals(array_key_exists('myCustomKey', $schema), false);
 	}
+
+	public function testGetSchemaState() {
+		$field = new FormField('MyField');
+		$field->setValue('My value');
+		$schema = $field->getSchemaState();
+		$this->assertEquals('My value', $schema['value']);
+	}
+
+	public function testSetSchemaState() {
+		$field = new FormField('MyField');
+
+		// Make sure the user can update values.
+		$field = $field->setSchemaState(['value' => 'My custom value']);
+		$schema = $field->getSchemaState();
+		$this->assertEquals($schema['value'], 'My custom value');
+
+		// Make user the user can't define custom keys on the schema.
+		$field = $field->setSchemaState(['myCustomKey' => 'yolo']);
+		$schema = $field->getSchemaState();
+		$this->assertEquals(array_key_exists('myCustomKey', $schema), false);
+	}
+
+	public function testGetSchemaStateWithFormValidation() {
+		$field = new FormField('MyField');
+		$validator = new RequiredFields('MyField');
+		$form = new Form(new Controller(), 'TestForm', new FieldList($field), new FieldList(), $validator);
+		$validator->validationError('MyField', 'Something is wrong', 'error');
+		$schema = $field->getSchemaState();
+		$this->assertEquals(count($schema['messages']), 1);
+		$this->assertEquals('Something is wrong', $schema['messages'][0]['value']);
+	}
 }
 
 /**
diff --git a/tests/forms/FormSchemaTest.php b/tests/forms/FormSchemaTest.php
index 3aaf36533..4cf1d5564 100644
--- a/tests/forms/FormSchemaTest.php
+++ b/tests/forms/FormSchemaTest.php
@@ -55,7 +55,83 @@ class FormSchemaTest extends SapphireTest {
 		$formSchema = new FormSchema();
 		$expected = [
 			'id' => 'TestForm',
-			'fields' => [],
+			'fields' => [
+				[
+					'id' => 'Form_TestForm_SecurityID',
+					'value' => $form->getSecurityToken()->getValue(),
+					'messages' => [],
+					'valid' => true,
+					'data' => []
+				]
+			],
+			'messages' => []
+		];
+
+		$state = $formSchema->getState($form);
+		$this->assertInternalType('array', $state);
+		$this->assertJsonStringEqualsJsonString(json_encode($expected), json_encode($state));
+	}
+
+	public function testGetStateWithFormMessages() {
+		$fields = new FieldList();
+		$actions = new FieldList();
+		$form = new Form(new Controller(), 'TestForm', $fields, $actions);
+		$form->sessionMessage('All saved', 'good');
+		$formSchema = new FormSchema();
+		$expected = [
+			'id' => 'TestForm',
+			'fields' => [
+				[
+					'id' => 'Form_TestForm_SecurityID',
+					'value' => $form->getSecurityToken()->getValue(),
+					'messages' => [],
+					'valid' => true,
+					'data' => []
+				]
+			],
+			'messages' => [
+				[
+					'value' => 'All saved',
+					'type' => 'good'
+				]
+			]
+		];
+
+		$state = $formSchema->getState($form);
+		$this->assertInternalType('array', $state);
+		$this->assertJsonStringEqualsJsonString(json_encode($expected), json_encode($state));
+	}
+
+	public function testGetStateWithFieldValidationErrors() {
+		$fields = new FieldList(new TextField('Title'));
+		$actions = new FieldList();
+		$validator = new RequiredFields('Title');
+		$form = new Form(new Controller(), 'TestForm', $fields, $actions, $validator);
+		$form->loadDataFrom([
+			'Title' => 'My Title'
+		]);
+		$validator->validationError('Title', 'Title is invalid', 'error');
+		$formSchema = new FormSchema();
+		$expected = [
+			'id' => 'TestForm',
+			'fields' => [
+				[
+					'id' => 'Form_TestForm_Title',
+					'value' => 'My Title',
+					'messages' => [
+						['value' => 'Title is invalid', 'type' => 'error']
+					],
+					'valid' => false,
+					'data' => []
+				],
+				[
+					'id' => 'Form_TestForm_SecurityID',
+					'value' => $form->getSecurityToken()->getValue(),
+					'messages' => [],
+					'valid' => true,
+					'data' => []
+				]
+			],
 			'messages' => []
 		];
 

From 61a8529d7622184785dea35bd6cae78215d234fd Mon Sep 17 00:00:00 2001
From: Ingo Schommer <ingo@silverstripe.com>
Date: Thu, 3 Mar 2016 12:03:38 +1300
Subject: [PATCH 5/5] More reuseable FormSchema logic, return on save

---
 admin/code/LeftAndMain.php     | 69 ++++++++++++++++++++++++++--------
 forms/FormFieldSchemaTrait.php | 11 ++++++
 forms/FormSchema.php           |  8 ++++
 3 files changed, 73 insertions(+), 15 deletions(-)

diff --git a/admin/code/LeftAndMain.php b/admin/code/LeftAndMain.php
index f20e5aceb..cdeae2a36 100644
--- a/admin/code/LeftAndMain.php
+++ b/admin/code/LeftAndMain.php
@@ -181,46 +181,75 @@ class LeftAndMain extends Controller implements PermissionProvider {
 	/**
 	 * Gets a JSON schema representing the current edit form.
 	 *
+	 * WARNING: Experimental API.
+	 *
 	 * @return SS_HTTPResponse
 	 */
-	public function schema() {
-		$req = $this->getRequest();
-		$res = $this->getResponse();
+	public function schema($request) {
+		$response = $this->getResponse();
+		$formName = $request->param('ID');
+
+		if(!$this->hasMethod("get{$formName}")) {
+			throw new SS_HTTPResponse_Exception(
+				'Form not found',
+				400
+			);
+		}
+
+		if(!$this->hasAction($formName)) {
+			throw new SS_HTTPResponse_Exception(
+				'Form not accessible',
+				401
+			);
+		}
+
+		$form = $this->{"get{$formName}"}();
+		$response->addHeader('Content-Type', 'application/json');
+		$response->setBody(Convert::raw2json($this->getSchemaForForm($form)));
+
+		return $response;
+	}
+
+	/**
+	 * Returns a representation of the provided {@link Form} as structured data,
+	 * based on the request data.
+	 *
+	 * @param Form $form
+	 * @return array
+	 */
+	protected function getSchemaForForm(Form $form) {
+		$request = $this->getRequest();
 		$schemaParts = [];
+		$return = null;
 
 		// Valid values for the "X-Formschema-Request" header are "schema" and "state".
 		// If either of these values are set they will be stored in the $schemaParst array
 		// and used to construct the response body.
-		if ($schemaHeader = $req->getHeader('X-Formschema-Request')) {
+		if ($schemaHeader = $request->getHeader('X-Formschema-Request')) {
 			$schemaParts = array_filter(explode(',', $schemaHeader), function($value) {
 				$validHeaderValues = ['schema', 'state'];
 				return in_array(trim($value), $validHeaderValues);
 			});
 		}
 
-		// Make sure it's an AJAX GET request with a valid "X-Formschema-Request" header value.
-		if (!$req->isGET() || !count($schemaParts)) {
+		if (!count($schemaParts)) {
 			throw new SS_HTTPResponse_Exception(
 				'Invalid request. Check you\'ve set a "X-Formschema-Request" header with "schema" or "state" values.',
 				400
 			);
 		}
 
-		$form = $this->getEditForm();
-		$responseBody = ['id' => $form->getName()];
+		$return = ['id' => $form->getName()];
 
 		if (in_array('schema', $schemaParts)) {
-			$responseBody['schema'] = $this->schema->getSchema($form);
+			$return['schema'] = $this->schema->getSchema($form);
 		}
 
 		if (in_array('state', $schemaParts)) {
-			$responseBody['state'] = $this->schema->getState($form);
+			$return['state'] = $this->schema->getState($form);
 		}
 
-		$res->addHeader('Content-Type', 'application/json');
-		$res->setBody(Convert::raw2json($responseBody));
-
-		return $res;
+		return $return;
 	}
 
 	/**
@@ -1067,6 +1096,7 @@ class LeftAndMain extends Controller implements PermissionProvider {
 	 * Save  handler
 	 */
 	public function save($data, $form) {
+		$request = $this->getRequest();
 		$className = $this->stat('tree_class');
 
 		// Existing or new record?
@@ -1087,7 +1117,16 @@ class LeftAndMain extends Controller implements PermissionProvider {
 		$this->setCurrentPageID($record->ID);
 
 		$this->getResponse()->addHeader('X-Status', rawurlencode(_t('LeftAndMain.SAVEDUP', 'Saved.')));
-		return $this->getResponseNegotiator()->respond($this->getRequest());
+
+		if($request->getHeader('X-Formschema-Request')) {
+			$data = $this->getSchemaForForm($form);
+			$response = new SS_HTTPResponse(Convert::raw2json($data));
+			$response->addHeader('Content-Type', 'application/json');
+		} else {
+			$response = $this->getResponseNegotiator()->respond($request);
+		}
+
+		return $response;
 	}
 
 	public function delete($data, $form) {
diff --git a/forms/FormFieldSchemaTrait.php b/forms/FormFieldSchemaTrait.php
index ab9e40115..f4b3e09d9 100644
--- a/forms/FormFieldSchemaTrait.php
+++ b/forms/FormFieldSchemaTrait.php
@@ -2,6 +2,17 @@
 
 namespace SilverStripe\Forms\Schema;
 
+/**
+ * Class FormFieldSchemaTrait
+ * @package SilverStripe\Forms\Schema
+ *
+ * Allows {@link FormField} to be represented as structured data,
+ * including both structure (name, id, attributes, etc.) and state (field value).
+ * Can be used by {@link FormSchema} to represent a form in JSON,
+ * to be consumed by a front-end application.
+ *
+ * WARNING: Experimental API.
+ */
 trait FormFieldSchemaTrait {
 
 	/**
diff --git a/forms/FormSchema.php b/forms/FormSchema.php
index 17307193f..9f2c00dcf 100644
--- a/forms/FormSchema.php
+++ b/forms/FormSchema.php
@@ -5,6 +5,14 @@ namespace SilverStripe\Forms\Schema;
 use Convert;
 use Form;
 
+/**
+ * Class FormSchema
+ * @package SilverStripe\Forms\Schema
+ *
+ * Represents a {@link Form} as structured data which allows a frontend library to render it.
+ * Includes information about the form as well as its fields.
+ * Can create a "schema" (structure only) as well as "state" (data only).
+ */
 class FormSchema {
 
 	/**