<?php

/* Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
/* Licensed under the Apache License, Version 2.0. */

// Put your Secret Key in place of **********
$serviceName="ProductAdvertisingAPI";
$region="eu-west-1";
$accessKey="XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
$secretKey="**********";
$payload="{"
        ." \"ItemIds\": ["
        ."  \"ASINXXXX\""
        ." ],"
        ." \"Resources\": ["
        ."  \"Images.Primary.Small\","
        ."  \"Images.Primary.Medium\","
        ."  \"Images.Primary.Large\","
        ."  \"Images.Variants.Small\","
        ."  \"Images.Variants.Medium\","
        ."  \"Images.Variants.Large\","
        ."  \"ItemInfo.ByLineInfo\","
        ."  \"ItemInfo.ContentInfo\","
        ."  \"ItemInfo.ContentRating\","
        ."  \"ItemInfo.Classifications\","
        ."  \"ItemInfo.ExternalIds\","
        ."  \"ItemInfo.Features\","
        ."  \"ItemInfo.ManufactureInfo\","
        ."  \"ItemInfo.ProductInfo\","
        ."  \"ItemInfo.TechnicalInfo\","
        ."  \"ItemInfo.Title\","
        ."  \"ItemInfo.TradeInInfo\","
        ."  \"Offers.Listings.DeliveryInfo.IsFreeShippingEligible\","
        ."  \"Offers.Listings.DeliveryInfo.IsPrimeEligible\","
        ."  \"Offers.Listings.MerchantInfo\","
        ."  \"Offers.Listings.Price\""
        ." ],"
        ." \"PartnerTag\": \"XXXXXXXXXXXXXXXXXXXXXXX-21\","
        ." \"PartnerType\": \"Associates\","
        ." \"Marketplace\": \"www.amazon.it\""
        ."}";
$host="webservices.amazon.it";
$uriPath="/paapi5/getitems";
$awsv4 = new AwsV4 ($accessKey, $secretKey);
$awsv4->setRegionName($region);
$awsv4->setServiceName($serviceName);
$awsv4->setPath ($uriPath);
$awsv4->setPayload ($payload);
$awsv4->setRequestMethod ("POST");
$awsv4->addHeader ('content-encoding', 'amz-1.0');
$awsv4->addHeader ('content-type', 'application/json; charset=utf-8');
$awsv4->addHeader ('host', $host);
$awsv4->addHeader ('x-amz-target', 'com.amazon.paapi5.v1.ProductAdvertisingAPIv1.GetItems');
$headers = $awsv4->getHeaders ();
$headerString = "";
foreach ( $headers as $key => $value ) {
    $headerString .= $key . ': ' . $value . "\r\n";
}
$params = array (
        'http' => array (
            'header' => $headerString,
            'method' => 'POST',
            'content' => $payload
        )
    );
$stream = stream_context_create ( $params );

$fp = @fopen ( 'https://'.$host.$uriPath, 'rb', false, $stream );

if (! $fp) {
    throw new Exception ( "Exception Occured" );
}
$response = @stream_get_contents ( $fp );
if ($response === false) {
    throw new Exception ( "Exception Occured" );
}
echo $response;

class AwsV4 {

    private $accessKey = null;
    private $secretKey = null;
    private $path = null;
    private $regionName = null;
    private $serviceName = null;
    private $httpMethodName = null;
    private $queryParametes = array ();
    private $awsHeaders = array ();
    private $payload = "";

    private $HMACAlgorithm = "AWS4-HMAC-SHA256";
    private $aws4Request = "aws4_request";
    private $strSignedHeader = null;
    private $xAmzDate = null;
    private $currentDate = null;

    public function __construct($accessKey, $secretKey) {
        $this->accessKey = $accessKey;
        $this->secretKey = $secretKey;
        $this->xAmzDate = $this->getTimeStamp ();
        $this->currentDate = $this->getDate ();
    }

    function setPath($path) {
        $this->path = $path;
    }

    function setServiceName($serviceName) {
        $this->serviceName = $serviceName;
    }

    function setRegionName($regionName) {
        $this->regionName = $regionName;
    }

    function setPayload($payload) {
        $this->payload = $payload;
    }

    function setRequestMethod($method) {
        $this->httpMethodName = $method;
    }

    function addHeader($headerName, $headerValue) {
        $this->awsHeaders [$headerName] = $headerValue;
    }

    private function prepareCanonicalRequest() {
        $canonicalURL = "";
        $canonicalURL .= $this->httpMethodName . "\n";
        $canonicalURL .= $this->path . "\n" . "\n";
        $signedHeaders = '';
        foreach ( $this->awsHeaders as $key => $value ) {
            $signedHeaders .= $key . ";";
            $canonicalURL .= $key . ":" . $value . "\n";
        }
        $canonicalURL .= "\n";
        $this->strSignedHeader = substr ( $signedHeaders, 0, - 1 );
        $canonicalURL .= $this->strSignedHeader . "\n";
        $canonicalURL .= $this->generateHex ( $this->payload );
        return $canonicalURL;
    }

    private function prepareStringToSign($canonicalURL) {
        $stringToSign = '';
        $stringToSign .= $this->HMACAlgorithm . "\n";
        $stringToSign .= $this->xAmzDate . "\n";
        $stringToSign .= $this->currentDate . "/" . $this->regionName . "/" . $this->serviceName . "/" . $this->aws4Request . "\n";
        $stringToSign .= $this->generateHex ( $canonicalURL );
        return $stringToSign;
    }

    private function calculateSignature($stringToSign) {
        $signatureKey = $this->getSignatureKey ( $this->secretKey, $this->currentDate, $this->regionName, $this->serviceName );
        $signature = hash_hmac ( "sha256", $stringToSign, $signatureKey, true );
        $strHexSignature = strtolower ( bin2hex ( $signature ) );
        return $strHexSignature;
    }

    public function getHeaders() {
        $this->awsHeaders ['x-amz-date'] = $this->xAmzDate;
        ksort ( $this->awsHeaders );

        // Step 1: CREATE A CANONICAL REQUEST
        $canonicalURL = $this->prepareCanonicalRequest ();

        // Step 2: CREATE THE STRING TO SIGN
        $stringToSign = $this->prepareStringToSign ( $canonicalURL );

        // Step 3: CALCULATE THE SIGNATURE
        $signature = $this->calculateSignature ( $stringToSign );

        // Step 4: CALCULATE AUTHORIZATION HEADER
        if ($signature) {
            $this->awsHeaders ['Authorization'] = $this->buildAuthorizationString ( $signature );
            return $this->awsHeaders;
        }
    }

    private function buildAuthorizationString($strSignature) {
        return $this->HMACAlgorithm . " " . "Credential=" . $this->accessKey . "/" . $this->getDate () . "/" . $this->regionName . "/" . $this->serviceName . "/" . $this->aws4Request . "," . "SignedHeaders=" . $this->strSignedHeader . "," . "Signature=" . $strSignature;
    }

    private function generateHex($data) {
        return strtolower ( bin2hex ( hash ( "sha256", $data, true ) ) );
    }

    private function getSignatureKey($key, $date, $regionName, $serviceName) {
        $kSecret = "AWS4" . $key;
        $kDate = hash_hmac ( "sha256", $date, $kSecret, true );
        $kRegion = hash_hmac ( "sha256", $regionName, $kDate, true );
        $kService = hash_hmac ( "sha256", $serviceName, $kRegion, true );
        $kSigning = hash_hmac ( "sha256", $this->aws4Request, $kService, true );

        return $kSigning;
    }

    private function getTimeStamp() {
        return gmdate ( "Ymd\THis\Z" );
    }

    private function getDate() {
        return gmdate ( "Ymd" );
    }
}
?>