<?

class AWSThumbnail {

	const THUMBNAIL_SIZE_SMALL = "Small";
	const THUMBNAIL_SIZE_BIG = "Large";

	private $HTTPRequestTimeout = 5;

	private $accessID, $secretKey, $lastImageUrl, $defaultImageUrl = null;

	/**
	 * Construct a new AWSThumbnail Instance
	 *
	 * @param string $accessID
	 * @param string $secretKey
	 */

	public function __construct($accessID, $secretKey) {
		$this->accessID = $accessID;
		$this->secretKey = $secretKey;
	}

	private function getSecretKey() {
		return $this->secretKey;
	}

	private function getAccessID() {
		return $this->accessID;
	}

	public function setDefaultImageUrl($url) {
		$this->defaultImageUrl = $url;
	}

	public function getDefaultImageUrl() {
		return $this->defaultImageUrl;
	}

	private function setLastImageUrl($url) {
		$this->lastImageUrl = $url;
	}

	public function getLastImageUrl() {
		return $this->lastImageUrl;
	}

	public function createThumbnail($url, $size = self::THUMBNAIL_SIZE_SMALL) {
		$ts = $this->generateTimestamp();

		$request_url =  "http://ast.amazonaws.com/xino/?"
		. "Service=".           "AlexaSiteThumbnail"
		. "&Action=".           "Thumbnail"
		. "&AWSAccessKeyId=".   $this->getAccessID()
		. "&Timestamp=" .       urlencode($ts)
		. "&Signature=" .       urlencode ($this->calculateRFC2104HMAC("AlexaSiteThumbnail" . "Thumbnail" . $ts, $this->getSecretKey()))
		. "&Size=" .            $size
		. "&Url=" .             $url;

		$result = $this->getHTTPResult($request_url);

		#echo nl2br(htmlentities($result));

		$response_doc = new DOMDocument();
		$response_doc->loadXML($result);

		$thumbnail = $response_doc->getElementsByTagName("Thumbnail")->item(0);
		if ($thumbnail != NULL) {
			if ($thumbnail->getAttribute("Exists") == "true") {
				$this->setLastImageUrl($thumbnail->firstChild->nodeValue);
				return true;
			}
			else {
				if ($this->getDefaultImageUrl()) {
					$this->setLastImageUrl($this->getDefaultImageUrl());
				}
				else {
					$this->setLastImageUrl($thumbnail->firstChild->nodeValue);
				}
				return false;
			}
		}

		throw new Exception('Error while creating the image...');
	}

	private function generateTimestamp () {
		return gmdate("Y-m-d\TH:i:s.\\0\\0\\0\\Z", time());
	}

	private function calculateRFC2104HMAC ($data, $key) {
		return base64_encode (
		pack("H*", sha1((str_pad($key, 64, chr(0x00))
		^(str_repeat(chr(0x5c), 64))) .
		pack("H*", sha1((str_pad($key, 64, chr(0x00))
		^(str_repeat(chr(0x36), 64))) . $data))))
		);
	}

	private function getHTTPResult($url) {
		$ch = curl_init($url);
		curl_setopt($ch, CURLOPT_TIMEOUT, $this->HTTPRequestTimeout);
		curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
		$result = curl_exec($ch);
		if (curl_errno($ch)) {
			throw new Exception("HTTP Request failed.");
		}
		curl_close($ch);
		return $result;
	}
}