WIP: Initial release

Fixes #1

inc/class-url.php

+<?php
+/**
+ * URL Building
+ *
+ * @package Camo_Image_Proxy
+ */
+
+namespace Camo_Image_Proxy;
+
+/**
+ * Class URL
+ */
+class URL {
+	use Singleton;
+
+	/**
+	 * Can URLs be rewritten to use Camo?
+	 *
+	 * @return bool
+	 */
+	public function can_rewrite() : bool {
+		// Never rewrite in admin.
+		if ( is_admin() ) {
+			return false;
+		}
+
+		$host = Options::instance()->get( 'host' );
+		$key  = Options::instance()->get( 'key' );
+
+		$can_rewrite = true;
+
+		// Validate host.
+		if ( ! $this->is_valid_url( $host ) ) {
+			$can_rewrite = false;
+		}
+
+		// Validate key.
+		// TODO: make sure it's an HMAC or something?
+		if ( empty( $key ) || ! is_string( $key ) ) {
+			$can_rewrite = false;
+		}
+
+		return apply_filters( 'camo_image_proxy_can_rewrite', $can_rewrite, $host, $key );
+	}
+
+	/**
+	 * Encode image URL
+	 *
+	 * @param string $url Image URL to encode.
+	 * @return string|bool
+	 */
+	public function encode( string $url ) : string {
+		if ( ! $this->can_rewrite() || ! $this->is_valid_url( $url ) ) {
+			return false;
+		}
+
+		$key         = hash_hmac( 'sha1', $url, Options::instance()->get( 'key' ) );
+		$url_encoded = bin2hex( $url );
+
+		$url_encoded = sprintf( '%1$s/%2$s/%3$s', Options::instance()->get( 'host' ), $key, $url_encoded );
+		$url_encoded = set_url_scheme( $url_encoded, 'https' );
+
+		return $url_encoded;
+	}
+
+	/**
+	 * Decode encoded URL
+	 *
+	 * @param string $url Camo URL to decode.
+	 * @return string|bool
+	 */
+	public function decode( string $url ) : string {
+		return false;
+	}
+
+	/**
+	 * Can we encode this URL?
+	 *
+	 * @param string $url URL to validate.
+	 * @return bool
+	 */
+	private function is_valid_url( string $url ) : bool {
+		if ( empty( $url ) ) {
+			return false;
+		}
+
+		if ( false === filter_var( $url, FILTER_VALIDATE_URL ) && false === filter_var( $url, FILTER_VALIDATE_IP ) ) {
+			return false;
+		}
+
+		return true;
+	}
+}