Add configurable and state

src/Configurable.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Erusev\Parsedown;
+
+interface Configurable
+{
+    /** @return static */
+    public static function default();
+}

src/State.php

@@ -0,0 +1,95 @@
+<?php
+
+namespace Erusev\Parsedown;
+
+use Erusev\Parsedown\AST\StateRenderable;
+use Erusev\Parsedown\Html\Renderable;
+
+final class State
+{
+    /**
+     * @var array<class-string<Configurable>, Configurable>
+     * */
+    private $state;
+
+    /**
+     * @param Configurable[] $Configurables
+     */
+    public function __construct(array $Configurables = [])
+    {
+        $this->state = \array_combine(
+            \array_map(
+                /** @return class-string */
+                function (Configurable $C) { return \get_class($C); },
+                $Configurables
+            ),
+            $Configurables
+        );
+    }
+
+    /**
+     * @return self
+     */
+    public function setting(Configurable $C)
+    {
+        return new self([\get_class($C) => $C] + $this->state);
+    }
+
+    /**
+     * @return self
+     */
+    public function mergingWith(State $State)
+    {
+        return new self($State->state + $this->state);
+    }
+
+    /**
+     * @template T as Configurable
+     * @template-typeof T $configurableClass
+     * @param class-string<Configurable> $configurableClass
+     * @return T|null
+     * */
+    public function get($configurableClass)
+    {
+        return (isset($this->state[$configurableClass])
+            ? $this->state[$configurableClass]
+            : null
+        );
+    }
+
+    /**
+     * @template T as Configurable
+     * @template-typeof T $configurableClass
+     * @param class-string<Configurable> $configurableClass
+     * @return T
+     * */
+    public function getOrDefault($configurableClass)
+    {
+        return (isset($this->state[$configurableClass])
+            ? $this->state[$configurableClass]
+            : $configurableClass::default()
+        );
+    }
+
+    public function __clone()
+    {
+        $this->state = \array_map(
+            /** @return Configurable */
+            function (Configurable $C) { return clone($C); },
+            $this->state
+        );
+    }
+
+    /**
+     * @param StateRenderable[] $StateRenderables
+     * @return Renderable[]
+     */
+    public function applyTo(array $StateRenderables)
+    {
+        return \array_map(
+            /** @return Renderable */
+            function (StateRenderable $SR) { return $SR->renderable($this); },
+            $StateRenderables
+        );
+    }
+}