- Added documentation, fixed some bugs and optimized some parts of the source code while doing the doc.

docs/20-method-form.md

@@ -0,0 +1,107 @@
+# `form`(FormInterface $form, ? FormContext $formContext = null) : FormHandler
+
+The `form()` method will process a form in three steps :
+
+1. `initialize(FormContextInterface $context)` is first called on form processing.
+2. `validate(FormContextInterface $context) : bool` will execute on POST. If you define a name to the form, it will match the one found in the POST (`picea-ui-form[$context->name]`) ; if the form is not the target, it will be skipped. Also, if an error si found within the message list, the method will return `false`.
+3. `execute(FormContextInterface $context)` is the last method to run, which is usually where you save your entity and finilize your messages. The return value is accessible from the `formHandler` which `form()` returns.
+
+**[PHP]** So, using this code:
+
+in */app/controller/user.php*
+```php
+form(new \MyApp\Form\User\Create());
+```
+
+*/app/form/create.php*
+```php
+<?php
+
+namespace MyProject\Form;
+
+use MyProject\{ Lib, Entity };
+use Picea\Ui\Method\{ FormContextInterface, Message\ErrorMessage };
+
+use Psr\Http\Message\ServerRequestInterface;
+
+use function MyProject\View\{ lang };
+
+class Create implements \Picea\Ui\Method\FormInterface {
+
+    public function initialize(FormContextInterface $context) : void
+    {
+        $this->user = new Entity\User();
+        
+        # $context->{varname} will be populated by $_POST data.
+        $this->user = (string) $context->fullname;
+    }
+
+    public function validate(FormContextInterface $context) : bool
+    {
+        if ( strlen($this->user) < 3 ) {
+            # This won't allow `execute` to run because of the error message.
+            $context->pushMessage(Lib\Message::generateError(
+                lang("form.error.provide_fullName")
+            ));
+        }
+    
+        return $context->valid();
+    }
+
+    public function execute(FormContextInterface $context) : void
+    {    
+        # Saving a new user here
+        Entity\User::repository()->save($this->user);
+        
+        $context->pushMessage(Lib\Message::generateSuccess(
+            lang("form.save")
+        ));
+    }
+}
+```
+
+which implements this interface :
+
+```php
+interface FormInterface
+{
+    public function initialize(FormContextInterface $context) : void;
+
+    public function validate(FormContextInterface $context) : bool;
+    
+    public function execute(FormContextInterface $context);
+}
+```
+
+Would yield the same result such as:
+```php
+true
+true
+```
+
+Trying to access either variable before `execute` is called will return `null`.
+
+## `FormContext` object
+
+`__construct(ServerRequestInterface $request, ? string $formName = null)`
+
+Creating a form context manually allows to define the formName, which is essential if you want to use the
+Cross-Scripting Request Forgery (CSRF).
+
+It is populated with either $_POST or request's body which is json_decode. A property called `files` is also populated from PSR's `$request->getUploadedFiles()`.
+
+It's `valid() : bool` method called into a form `validate()` function is first checking every message which were pushed into, using `pushMessage(FormMessage $message)`, and returns false if an error message is found in the list.
+
+### Retrieve a form execution status / value
+
+There is two ways to get the execution status (from the `execute` return value):
+
+```php
+$formContext = new \Picea\Ui\Method\FormContext($request, 'form.user_create');
+$form = form(new \MyProject\Form\User\Create(), $formContext);
+
+if ($formContext->formExecuted) {
+    echo $form->executionStatus;
+    echo $formContext->formExecutionStatus;
+}
+```