/*
    * Copyright (C) 2015, Matthias Sohn <matthias.sohn@sap.com>
    * Copyright (C) 2015, Sasa Zivkov <sasa.zivkov@sap.com> and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
   */
  package org.eclipse.jgit.lfs.server.s3;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  import static org.eclipse.jgit.util.HttpSupport.HDR_AUTHORIZATION;
  
  import java.io.UnsupportedEncodingException;
  import java.net.URL;
  import java.net.URLEncoder;
  import java.security.MessageDigest;
  import java.text.MessageFormat;
  import java.text.SimpleDateFormat;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Date;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Locale;
  import java.util.Map;
  import java.util.SimpleTimeZone;
  import java.util.SortedMap;
  import java.util.TreeMap;
  
  import javax.crypto.Mac;
  import javax.crypto.spec.SecretKeySpec;
  
  import org.eclipse.jgit.lfs.lib.Constants;
  import org.eclipse.jgit.lfs.server.internal.LfsServerText;
  
  /**
   * Signing support for Amazon AWS signing V4
   * <p>
   * See
   * http://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-authenticating-requests.html
   */
  class SignerV4 {
  	static final String UNSIGNED_PAYLOAD = "UNSIGNED-PAYLOAD"; //$NON-NLS-1$
  
  	private static final String ALGORITHM = "HMAC-SHA256"; //$NON-NLS-1$
  	private static final String DATE_STRING_FORMAT = "yyyyMMdd"; //$NON-NLS-1$
  	private static final String HEX = "0123456789abcdef"; //$NON-NLS-1$
  	private static final String HMACSHA256 = "HmacSHA256"; //$NON-NLS-1$
  	private static final String ISO8601_BASIC_FORMAT = "yyyyMMdd'T'HHmmss'Z'"; //$NON-NLS-1$
  	private static final String S3 = "s3"; //$NON-NLS-1$
  	private static final String SCHEME = "AWS4"; //$NON-NLS-1$
  	private static final String TERMINATOR = "aws4_request"; //$NON-NLS-1$
  	private static final String UTC = "UTC"; //$NON-NLS-1$
  	private static final String X_AMZ_ALGORITHM = "X-Amz-Algorithm"; //$NON-NLS-1$
  	private static final String X_AMZ_CREDENTIAL = "X-Amz-Credential"; //$NON-NLS-1$
  	private static final String X_AMZ_DATE = "X-Amz-Date"; //$NON-NLS-1$
  	private static final String X_AMZ_SIGNATURE = "X-Amz-Signature"; //$NON-NLS-1$
  	private static final String X_AMZ_SIGNED_HEADERS = "X-Amz-SignedHeaders"; //$NON-NLS-1$
  
  	static final String X_AMZ_CONTENT_SHA256 = "x-amz-content-sha256"; //$NON-NLS-1$
  	static final String X_AMZ_EXPIRES = "X-Amz-Expires"; //$NON-NLS-1$
  	static final String X_AMZ_STORAGE_CLASS = "x-amz-storage-class"; //$NON-NLS-1$
  
  	/**
  	 * Create an AWSV4 authorization for a request, suitable for embedding in
  	 * query parameters.
  	 *
  	 * @param bucketConfig
  	 *            configuration of S3 storage bucket this request should be
  	 *            signed for
  	 * @param url
  	 *            HTTP request URL
  	 * @param httpMethod
  	 *            HTTP method
  	 * @param headers
  	 *            The HTTP request headers; 'Host' and 'X-Amz-Date' will be
  	 *            added to this set.
  	 * @param queryParameters
  	 *            Any query parameters that will be added to the endpoint. The
  	 *            parameters should be specified in canonical format.
  	 * @param bodyHash
  	 *            Pre-computed SHA256 hash of the request body content; this
  	 *            value should also be set as the header 'X-Amz-Content-SHA256'
  	 *            for non-streaming uploads.
  	 * @return The computed authorization string for the request. This value
  	 *         needs to be set as the header 'Authorization' on the subsequent
  	 *         HTTP request.
  	 */
  	static String createAuthorizationQuery(S3Config bucketConfig, URL url,
  			String httpMethod, Map<String, String> headers,
  			Map<String, String> queryParameters, String bodyHash) {
  		addHostHeader(url, headers);
  
  		queryParameters.put(X_AMZ_ALGORITHM, SCHEME + "-" + ALGORITHM); //$NON-NLS-1$
  
  		Date now = new Date();
 		String dateStamp = dateStamp(now);
 		String scope = scope(bucketConfig.getRegion(), dateStamp);
 		queryParameters.put(X_AMZ_CREDENTIAL,
 				bucketConfig.getAccessKey() + "/" + scope); //$NON-NLS-1$
 
 		String dateTimeStampISO8601 = dateTimeStampISO8601(now);
 		queryParameters.put(X_AMZ_DATE, dateTimeStampISO8601);
 
 		String canonicalizedHeaderNames = canonicalizeHeaderNames(headers);
 		queryParameters.put(X_AMZ_SIGNED_HEADERS, canonicalizedHeaderNames);
 
 		String canonicalizedQueryParameters = canonicalizeQueryString(
 				queryParameters);
 		String canonicalizedHeaders = canonicalizeHeaderString(headers);
 		String canonicalRequest = canonicalRequest(url, httpMethod,
 				canonicalizedQueryParameters, canonicalizedHeaderNames,
 				canonicalizedHeaders, bodyHash);
 		byte[] signature = createSignature(bucketConfig, dateTimeStampISO8601,
 				dateStamp, scope, canonicalRequest);
 		queryParameters.put(X_AMZ_SIGNATURE, toHex(signature));
 
 		return formatAuthorizationQuery(queryParameters);
 	}
 
 	private static String formatAuthorizationQuery(
 			Map<String, String> queryParameters) {
 		StringBuilder s = new StringBuilder();
 		for (String key : queryParameters.keySet()) {
 			appendQuery(s, key, queryParameters.get(key));
 		}
 		return s.toString();
 	}
 
 	private static void appendQuery(StringBuilder s, String key,
 			String value) {
 		if (s.length() != 0) {
 			s.append("&"); //$NON-NLS-1$
 		}
 		s.append(key).append("=").append(value); //$NON-NLS-1$
 	}
 
 	/**
 	 * Sign headers for given bucket, url and HTTP method and add signature in
 	 * Authorization header.
 	 *
 	 * @param bucketConfig
 	 *            configuration of S3 storage bucket this request should be
 	 *            signed for
 	 * @param url
 	 *            HTTP request URL
 	 * @param httpMethod
 	 *            HTTP method
 	 * @param headers
 	 *            HTTP headers to sign
 	 * @param bodyHash
 	 *            Pre-computed SHA256 hash of the request body content; this
 	 *            value should also be set as the header 'X-Amz-Content-SHA256'
 	 *            for non-streaming uploads.
 	 * @return HTTP headers signd by an Authorization header added to the
 	 *         headers
 	 */
 	static Map<String, String> createHeaderAuthorization(
 			S3Config bucketConfig, URL url, String httpMethod,
 			Map<String, String> headers, String bodyHash) {
 		addHostHeader(url, headers);
 
 		Date now = new Date();
 		String dateTimeStamp = dateTimeStampISO8601(now);
 		headers.put(X_AMZ_DATE, dateTimeStamp);
 
 		String canonicalizedHeaderNames = canonicalizeHeaderNames(headers);
 		String canonicalizedHeaders = canonicalizeHeaderString(headers);
 		String canonicalRequest = canonicalRequest(url, httpMethod, "", //$NON-NLS-1$
 				canonicalizedHeaderNames, canonicalizedHeaders, bodyHash);
 		String dateStamp = dateStamp(now);
 		String scope = scope(bucketConfig.getRegion(), dateStamp);
 
 		byte[] signature = createSignature(bucketConfig, dateTimeStamp,
 				dateStamp, scope, canonicalRequest);
 
 		headers.put(HDR_AUTHORIZATION, formatAuthorizationHeader(bucketConfig,
 				canonicalizedHeaderNames, scope, signature)); // $NON-NLS-1$
 
 		return headers;
 	}
 
 	private static String formatAuthorizationHeader(
 			S3Config bucketConfig, String canonicalizedHeaderNames,
 			String scope, byte[] signature) {
 		StringBuilder s = new StringBuilder();
 		s.append(SCHEME).append("-").append(ALGORITHM).append(" "); //$NON-NLS-1$ //$NON-NLS-2$
 		s.append("Credential=").append(bucketConfig.getAccessKey()).append("/") //$NON-NLS-1$//$NON-NLS-2$
 				.append(scope).append(","); //$NON-NLS-1$
 		s.append("SignedHeaders=").append(canonicalizedHeaderNames).append(","); //$NON-NLS-1$ //$NON-NLS-2$
 		s.append("Signature=").append(toHex(signature)); //$NON-NLS-1$
 		return s.toString();
 	}
 
 	private static void addHostHeader(URL url,
 			Map<String, String> headers) {
 		StringBuilder hostHeader = new StringBuilder(url.getHost());
 		int port = url.getPort();
 		if (port > -1) {
 			hostHeader.append(":").append(port); //$NON-NLS-1$
 		}
 		headers.put("Host", hostHeader.toString()); //$NON-NLS-1$
 	}
 
 	private static String canonicalizeHeaderNames(
 			Map<String, String> headers) {
 		List<String> sortedHeaders = new ArrayList<>();
 		sortedHeaders.addAll(headers.keySet());
 		Collections.sort(sortedHeaders, String.CASE_INSENSITIVE_ORDER);
 
 		StringBuilder buffer = new StringBuilder();
 		for (String header : sortedHeaders) {
 			if (buffer.length() > 0)
 				buffer.append(";"); //$NON-NLS-1$
 			buffer.append(header.toLowerCase(Locale.ROOT));
 		}
 
 		return buffer.toString();
 	}
 
 	private static String canonicalizeHeaderString(
 			Map<String, String> headers) {
 		if (headers == null || headers.isEmpty()) {
 			return ""; //$NON-NLS-1$
 		}
 
 		List<String> sortedHeaders = new ArrayList<>();
 		sortedHeaders.addAll(headers.keySet());
 		Collections.sort(sortedHeaders, String.CASE_INSENSITIVE_ORDER);
 
 		StringBuilder buffer = new StringBuilder();
 		for (String key : sortedHeaders) {
 			buffer.append(
 					key.toLowerCase(Locale.ROOT).replaceAll("\\s+", " ") + ":" //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 					+ headers.get(key).replaceAll("\\s+", " ")); //$NON-NLS-1$//$NON-NLS-2$
 			buffer.append("\n"); //$NON-NLS-1$
 		}
 
 		return buffer.toString();
 	}
 
 	private static String dateStamp(Date now) {
 		// TODO(ms) cache and reuse DateFormat instances
 		SimpleDateFormat dateStampFormat = new SimpleDateFormat(
 				DATE_STRING_FORMAT);
 		dateStampFormat.setTimeZone(new SimpleTimeZone(0, UTC));
 		String dateStamp = dateStampFormat.format(now);
 		return dateStamp;
 	}
 
 	private static String dateTimeStampISO8601(Date now) {
 		// TODO(ms) cache and reuse DateFormat instances
 		SimpleDateFormat dateTimeFormat = new SimpleDateFormat(
 				ISO8601_BASIC_FORMAT);
 		dateTimeFormat.setTimeZone(new SimpleTimeZone(0, UTC));
 		String dateTimeStamp = dateTimeFormat.format(now);
 		return dateTimeStamp;
 	}
 
 	private static String scope(String region, String dateStamp) {
 		String scope = String.format("%s/%s/%s/%s", dateStamp, region, S3, //$NON-NLS-1$
 				TERMINATOR);
 		return scope;
 	}
 
 	private static String canonicalizeQueryString(
 			Map<String, String> parameters) {
 		if (parameters == null || parameters.isEmpty()) {
 			return ""; //$NON-NLS-1$
 		}
 
 		SortedMap<String, String> sorted = new TreeMap<>();
 
 		Iterator<Map.Entry<String, String>> pairs = parameters.entrySet()
 				.iterator();
 		while (pairs.hasNext()) {
 			Map.Entry<String, String> pair = pairs.next();
 			String key = pair.getKey();
 			String value = pair.getValue();
 			sorted.put(urlEncode(key, false), urlEncode(value, false));
 		}
 
 		StringBuilder builder = new StringBuilder();
 		pairs = sorted.entrySet().iterator();
 		while (pairs.hasNext()) {
 			Map.Entry<String, String> pair = pairs.next();
 			builder.append(pair.getKey());
 			builder.append("="); //$NON-NLS-1$
 			builder.append(pair.getValue());
 			if (pairs.hasNext()) {
 				builder.append("&"); //$NON-NLS-1$
 			}
 		}
 
 		return builder.toString();
 	}
 
 	private static String canonicalRequest(URL endpoint, String httpMethod,
 			String queryParameters, String canonicalizedHeaderNames,
 			String canonicalizedHeaders, String bodyHash) {
 		return String.format("%s\n%s\n%s\n%s\n%s\n%s", //$NON-NLS-1$
 				httpMethod, canonicalizeResourcePath(endpoint),
 				queryParameters, canonicalizedHeaders, canonicalizedHeaderNames,
 				bodyHash);
 	}
 
 	private static String canonicalizeResourcePath(URL endpoint) {
 		if (endpoint == null) {
 			return "/"; //$NON-NLS-1$
 		}
 		String path = endpoint.getPath();
 		if (path == null || path.isEmpty()) {
 			return "/"; //$NON-NLS-1$
 		}
 
 		String encodedPath = urlEncode(path, true);
 		if (encodedPath.startsWith("/")) { //$NON-NLS-1$
 			return encodedPath;
 		}
 		return "/" + encodedPath; //$NON-NLS-1$
 	}
 
 	private static byte[] hash(String s) {
 		MessageDigest md = Constants.newMessageDigest();
 		md.update(s.getBytes(UTF_8));
 		return md.digest();
 	}
 
 	private static byte[] sign(String stringData, byte[] key) {
 		try {
 			byte[] data = stringData.getBytes(UTF_8);
 			Mac mac = Mac.getInstance(HMACSHA256);
 			mac.init(new SecretKeySpec(key, HMACSHA256));
 			return mac.doFinal(data);
 		} catch (Exception e) {
 			throw new RuntimeException(MessageFormat.format(
 					LfsServerText.get().failedToCalcSignature, e.getMessage()),
 					e);
 		}
 	}
 
 	private static String stringToSign(String scheme, String algorithm,
 			String dateTime, String scope, String canonicalRequest) {
 		return String.format("%s-%s\n%s\n%s\n%s", //$NON-NLS-1$
 				scheme, algorithm, dateTime, scope,
 				toHex(hash(canonicalRequest)));
 	}
 
 	private static String toHex(byte[] bytes) {
 		StringBuilder builder = new StringBuilder(2 * bytes.length);
 		for (byte b : bytes) {
 			builder.append(HEX.charAt((b & 0xF0) >> 4));
 			builder.append(HEX.charAt(b & 0xF));
 		}
 		return builder.toString();
 	}
 
 	private static String urlEncode(String url, boolean keepPathSlash) {
 		String encoded;
 		try {
 			encoded = URLEncoder.encode(url, UTF_8.name());
 		} catch (UnsupportedEncodingException e) {
 			throw new RuntimeException(LfsServerText.get().unsupportedUtf8, e);
 		}
 		if (keepPathSlash) {
 			encoded = encoded.replace("%2F", "/"); //$NON-NLS-1$ //$NON-NLS-2$
 		}
 		return encoded;
 	}
 
 	private static byte[] createSignature(S3Config bucketConfig,
 			String dateTimeStamp, String dateStamp,
 			String scope, String canonicalRequest) {
 		String stringToSign = stringToSign(SCHEME, ALGORITHM, dateTimeStamp,
 				scope, canonicalRequest);
 
 		byte[] signature = (SCHEME + bucketConfig.getSecretKey())
 				.getBytes(UTF_8);
 		signature = sign(dateStamp, signature);
 		signature = sign(bucketConfig.getRegion(), signature);
 		signature = sign(S3, signature);
 		signature = sign(TERMINATOR, signature);
 		signature = sign(stringToSign, signature);
 		return signature;
 	}
 }