feat: add url string transformer

src/Url/UrlTransformer.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace WPContentSync\Url;
+
+final class UrlTransformer {
+	public function transformString( string $value, UrlMappingCollection $mappings ): string {
+		$transformed = $value;
+
+		foreach ( $mappings->all() as $mapping ) {
+			$transformed = $this->replaceMapping( $transformed, $mapping );
+		}
+
+		return $transformed;
+	}
+
+	private function replaceMapping( string $value, UrlMapping $mapping ): string {
+		$source      = $mapping->sourceUrl();
+		$destination = $mapping->destinationUrl();
+
+		$replacements = array(
+			$source                              => $destination,
+			str_replace( '&', '&amp;', $source ) => str_replace( '&', '&amp;', $destination ),
+			$this->toProtocolRelative( $source ) => $this->toProtocolRelative( $destination ),
+		);
+
+		return strtr( $value, $replacements );
+	}
+
+	private function toProtocolRelative( string $url ): string {
+		return preg_replace( '#^https?:#', '', $url ) ?? $url;
+	}
+}