Add RenderStack

This is a special configurable that can be used to alter the
Renderable[] AST before output.

src/Configurables/RenderStack.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace Erusev\Parsedown\Configurables;
+
+use Erusev\Parsedown\Configurable;
+use Erusev\Parsedown\Html\Renderable;
+
+final class RenderStack implements Configurable
+{
+    /** @var list<\Closure(Renderable[]):Renderable[]> */
+    private $stack;
+
+    /**
+     * @param list<\Closure(Renderable[]):Renderable[]> $stack
+     */
+    private function __construct($stack = [])
+    {
+        $this->stack = $stack;
+    }
+
+    /** @return self */
+    public static function initial()
+    {
+        return new self;
+    }
+
+    /**
+     * @param \Closure(Renderable[]):Renderable[] $RenderMap
+     * @return self
+     */
+    public function push(\Closure $RenderMap): self
+    {
+        return new self(\array_merge($this->stack, [$RenderMap]));
+    }
+
+    /** @return list<\Closure(Renderable[]):Renderable[]> */
+    public function getStack(): array
+    {
+        return $this->stack;
+    }
+}

src/Parsedown.php

@@ -14,6 +14,7 @@ use Erusev\Parsedown\Components\StateUpdatingBlock;
 use Erusev\Parsedown\Configurables\BlockTypes;
 use Erusev\Parsedown\Configurables\InlineTypes;
 use Erusev\Parsedown\Configurables\RecursionLimiter;
+use Erusev\Parsedown\Configurables\RenderStack;
 use Erusev\Parsedown\Html\Renderable;
 use Erusev\Parsedown\Parsing\Excerpt;
 use Erusev\Parsedown\Parsing\Line;
@@ -44,7 +45,18 @@ final class Parsedown
             $this->State->isolatedCopy()
         );
 
-        $Renderables = $State->applyTo($StateRenderables);
+        $Renderables = \array_reduce(
+            \array_reverse($State->get(RenderStack::class)->getStack()),
+            /**
+             * @param Renderable[] $Renderables
+             * @param \Closure(Renderable[]):Renderable[] $RenderMap
+             * @return Renderable[]
+             */
+            function (array $Renderables, \Closure $RenderMap): array {
+                return $RenderMap($Renderables);
+            },
+            $State->applyTo($StateRenderables)
+        );
 
         $html = self::render($Renderables);
 

tests/src/Configurables/RenderStackTest.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace Erusev\Parsedown\Tests\Configurables;
+
+use Erusev\Parsedown\Configurables\RenderStack;
+use Erusev\Parsedown\Html\Renderable;
+use Erusev\Parsedown\Html\Renderables\Text;
+use Erusev\Parsedown\Parsedown;
+use Erusev\Parsedown\State;
+use PHPUnit\Framework\TestCase;
+
+final class RenderStackTest extends TestCase
+{
+    /**
+     * @return void
+     * @throws \PHPUnit\Framework\ExpectationFailedException
+     * @throws \SebastianBergmann\RecursionContext\InvalidArgumentException
+     */
+    public function testRenderStack()
+    {
+        $State = new State;
+        $RenderStack = $State->get(RenderStack::class)
+            ->push(
+                /**
+                 * @param Renderable[] $Rs
+                 * return Renderable[]
+                 */
+                function ($Rs) { return \array_merge($Rs, [new Text('baz')]); }
+            )
+            ->push(
+                /**
+                 * @param Renderable[] $Rs
+                 * return Renderable[]
+                 */
+                function ($Rs) { return \array_merge($Rs, [new Text('bar')]); }
+            )
+        ;
+
+        $State = $State->setting($RenderStack);
+
+        $this->assertSame(
+            "<p>foo</p>\nbar\nbaz",
+            (new Parsedown($State))->toHtml('foo')
+        );
+    }
+}