Introduce interfaces for codecs

Author: alcaeus

src/Codec/Codec.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace MongoDB\Codec;
+
+/**
+ * @api
+ *
+ * @psalm-template B
+ * @psalm-template T
+ * @template-extends Decoder<B, T>
+ * @template-extends Encoder<B, T>
+ */
+interface Codec extends Decoder, Encoder
+{
+}

src/Codec/Decoder.php

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+<?php
+
+namespace MongoDB\Codec;
+
+/**
+ * @api
+ *
+ * @psalm-template B
+ * @psalm-template T
+ */
+interface Decoder
+{
+    /**
+     * @param mixed $value
+     * @psalm-assert-if-true B $value
+     */
+    public function canDecode($value): bool;
+
+    /**
+     * @param mixed $value
+     * @psalm-param B $value
+     * @return mixed
+     * @psalm-return T
+     */
+    public function decode($value);
+}

src/Codec/Encoder.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace MongoDB\Codec;
+
+/**
+ * @api
+ *
+ * @psalm-template B
+ * @psalm-template T
+ */
+interface Encoder
+{
+    /**
+     * @param mixed $value
+     * @psalm-assert-if-true T $value
+     */
+    public function canEncode($value): bool;
+
+    /**
+     * @param mixed $value
+     * @psalm-param T $value
+     * @return mixed
+     * @psalm-return B
+     */
+    public function encode($value);
+}