Add basic container implementation

src/Support/Container.php

@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Support;
+
+use Pest\Exceptions\ShouldNotHappen;
+use ReflectionClass;
+use ReflectionParameter;
+
+/**
+ * @internal
+ */
+final class Container
+{
+    /**
+     * @var array<string, mixed>
+     */
+    private $instances = [];
+
+    /**
+     * Gets a dependency from the container.
+     *
+     * @return object
+     */
+    public function get(string $id)
+    {
+        if (array_key_exists($id, $this->instances)) {
+            return $this->instances[$id];
+        }
+
+        $this->instances[$id] = $this->build($id);
+
+        return $this->instances[$id];
+    }
+
+    /**
+     * Adds the given instance to the container.
+     *
+     * @param mixed $instance
+     */
+    public function add(string $id, $instance): void
+    {
+        $this->instances[$id] = $instance;
+    }
+
+    /**
+     * Tries to build the given instance.
+     */
+    private function build(string $id): object
+    {
+        /** @phpstan-ignore-next-line */
+        $reflectionClass = new ReflectionClass($id);
+
+        if ($reflectionClass->isInstantiable()) {
+            $constructor = $reflectionClass->getConstructor();
+
+            if ($constructor !== null) {
+                $params = array_map(
+                    function (ReflectionParameter $param) use ($id) {
+                        $candidate = null;
+
+                        if ($param->getType() !== null && $param->getType()->isBuiltin()) {
+                            $candidate = $param->getName();
+                        } elseif ($param->getClass() !== null) {
+                            $candidate = $param->getClass()->getName();
+                        } else {
+                            throw ShouldNotHappen::fromMessage(sprintf('The type of `$%s` in `%s` cannot be determined.', $id, $param->getName()));
+                        }
+
+                        return $this->get($candidate);
+                    },
+                    $constructor->getParameters()
+                );
+
+                return $reflectionClass->newInstanceArgs($params);
+            }
+        }
+
+        throw ShouldNotHappen::fromMessage(sprintf('A dependency with the name `%s` cannot be resolved.', $id));
+    }
+}