/*
 * Copyright (c) 2011-2013 GoPivotal, Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package reactor.function.support;

import reactor.util.Assert;

import java.io.ByteArrayOutputStream;
import java.io.UnsupportedEncodingException;
import java.util.BitSet;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Utility class for URI encoding and decoding based on RFC 3986. Offers encoding methods for
 * the various URI components.
 * <p/>
 * All {@code encode*(String, String} methods in this class operate in a similar way:
 * <ul>
 *   <li>Valid characters for the specific URI component as defined in RFC 3986 stay the same.
 *   <li>All other characters are converted into one or more bytes in the given encoding scheme.
 *       Each of the resulting bytes is written as a hexadecimal string in the
 *       "<code>%<i>xy</i></code>" format.
 * </ul>
 *
 * @author Arjen Poutsma
 *
 * @see <a href="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986</a>
 */
public abstract class UriUtils {

	private static final BitSet SCHEME;

	private static final BitSet USER_INFO;

	private static final BitSet HOST;

	private static final BitSet PORT;

	private static final BitSet PATH;

	private static final BitSet SEGMENT;

	private static final BitSet QUERY;

	private static final BitSet QUERY_PARAM;

	private static final BitSet FRAGMENT;

	private static final String SCHEME_PATTERN = "([^:/?#]+):";

	private static final String HTTP_PATTERN = "(http|https):";

	private static final String USERINFO_PATTERN = "([^@/]*)";

	private static final String HOST_PATTERN = "([^/?#:]*)";

	private static final String PORT_PATTERN = "(\\d*)";

	private static final String PATH_PATTERN = "([^?#]*)";

	private static final String QUERY_PATTERN = "([^#]*)";

	private static final String LAST_PATTERN = "(.*)";

	// Regex patterns that matches URIs. See RFC 3986, appendix B
	private static final Pattern URI_PATTERN = Pattern.compile(
			"^(" + SCHEME_PATTERN + ")?" + "(//(" + USERINFO_PATTERN + "@)?" + HOST_PATTERN + "(:" + PORT_PATTERN +
					")?" + ")?" + PATH_PATTERN + "(\\?" + QUERY_PATTERN + ")?" + "(#" + LAST_PATTERN + ")?");

	private static final Pattern HTTP_URL_PATTERN = Pattern.compile(
			"^" + HTTP_PATTERN + "(//(" + USERINFO_PATTERN + "@)?" + HOST_PATTERN + "(:" + PORT_PATTERN + ")?" +
					")?" + PATH_PATTERN + "(\\?" + LAST_PATTERN + ")?");


	static {
		// variable names refer to RFC 3986, appendix A
		BitSet alpha = new BitSet(256);
		for (int i = 'a'; i <= 'z'; i++) {
			alpha.set(i);
		}
		for (int i = 'A'; i <= 'Z'; i++) {
			alpha.set(i);
		}
		BitSet digit = new BitSet(256);
		for (int i = '0'; i <= '9'; i++) {
			digit.set(i);
		}

		BitSet gendelims = new BitSet(256);
		gendelims.set(':');
		gendelims.set('/');
		gendelims.set('?');
		gendelims.set('#');
		gendelims.set('[');
		gendelims.set(']');
		gendelims.set('@');

		BitSet subdelims = new BitSet(256);
		subdelims.set('!');
		subdelims.set('$');
		subdelims.set('&');
		subdelims.set('\'');
		subdelims.set('(');
		subdelims.set(')');
		subdelims.set('*');
		subdelims.set('+');
		subdelims.set(',');
		subdelims.set(';');
		subdelims.set('=');

		BitSet reserved = new BitSet(256);
		reserved.or(gendelims);
		reserved.or(subdelims);

		BitSet unreserved = new BitSet(256);
		unreserved.or(alpha);
		unreserved.or(digit);
		unreserved.set('-');
		unreserved.set('.');
		unreserved.set('_');
		unreserved.set('~');

		SCHEME = new BitSet(256);
		SCHEME.or(alpha);
		SCHEME.or(digit);
		SCHEME.set('+');
		SCHEME.set('-');
		SCHEME.set('.');

		USER_INFO = new BitSet(256);
		USER_INFO.or(unreserved);
		USER_INFO.or(subdelims);
		USER_INFO.set(':');

		HOST = new BitSet(256);
		HOST.or(unreserved);
		HOST.or(subdelims);

		PORT = new BitSet(256);
		PORT.or(digit);

		BitSet pchar = new BitSet(256);
		pchar.or(unreserved);
		pchar.or(subdelims);
		pchar.set(':');
		pchar.set('@');

		SEGMENT = new BitSet(256);
		SEGMENT.or(pchar);

		PATH = new BitSet(256);
		PATH.or(SEGMENT);
		PATH.set('/');

		QUERY = new BitSet(256);
		QUERY.or(pchar);
		QUERY.set('/');
		QUERY.set('?');

		QUERY_PARAM = new BitSet(256);
		QUERY_PARAM.or(pchar);
		QUERY_PARAM.set('/');
		QUERY_PARAM.set('?');
		QUERY_PARAM.clear('=');
		QUERY_PARAM.clear('+');
		QUERY_PARAM.clear('&');

		FRAGMENT = new BitSet(256);
		FRAGMENT.or(pchar);
		FRAGMENT.set('/');
		FRAGMENT.set('?');
	}


	/**
	 * Encodes the given source URI into an encoded String. All various URI components are encoded according to their
	 * respective valid character sets.
	 *
	 * @param uri      the URI to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded URI
	 * @throws IllegalArgumentException     when the given uri parameter is not a valid URI
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeUri(String uri, String encoding) throws UnsupportedEncodingException {
		Assert.notNull(uri, "'uri' must not be null");
		Assert.notNull(encoding, "'encoding' must not be empty");
		Matcher m = URI_PATTERN.matcher(uri);
		if (m.matches()) {
			String scheme = m.group(2);
			String authority = m.group(3);
			String userinfo = m.group(5);
			String host = m.group(6);
			String port = m.group(8);
			String path = m.group(9);
			String query = m.group(11);
			String fragment = m.group(13);

			return encodeUriComponents(scheme, authority, userinfo, host, port, path, query, fragment, encoding);
		} else {
			throw new IllegalArgumentException("[" + uri + "] is not a valid URI");
		}
	}

	/**
	 * Encodes the given HTTP URI into an encoded String. All various URI components are encoded according to their
	 * respective valid character sets. <p><strong>Note</strong> that this method does not support fragments ({@code #}),
	 * as these are not supposed to be sent to the server, but retained by the client.
	 *
	 * @param httpUrl  the HTTP URL to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded URL
	 * @throws IllegalArgumentException     when the given uri parameter is not a valid URI
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeHttpUrl(String httpUrl, String encoding) throws UnsupportedEncodingException {
		Assert.notNull(httpUrl, "'httpUrl' must not be null");
		Assert.notNull(encoding, "'encoding' must not be empty");
		Matcher m = HTTP_URL_PATTERN.matcher(httpUrl);
		if (m.matches()) {
			String scheme = m.group(1);
			String authority = m.group(2);
			String userinfo = m.group(4);
			String host = m.group(5);
			String portString = m.group(7);
			String path = m.group(8);
			String query = m.group(10);

			return encodeUriComponents(scheme, authority, userinfo, host, portString, path, query, null, encoding);
		} else {
			throw new IllegalArgumentException("[" + httpUrl + "] is not a valid HTTP URL");
		}
	}

	/**
	 * Encodes the given source URI components into an encoded String. All various URI components are optional, but encoded
	 * according to their respective valid character sets.
	 *
	 * @param scheme    the scheme
	 * @param authority the authority
	 * @param userinfo  the user info
	 * @param host      the host
	 * @param port      the port
	 * @param path      the path
	 * @param query     the query
	 * @param fragment  the fragment
	 * @param encoding  the character encoding to encode to
	 * @return the encoded URI
	 * @throws IllegalArgumentException     when the given uri parameter is not a valid URI
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeUriComponents(String scheme,
																					 String authority,
																					 String userinfo,
																					 String host,
																					 String port,
																					 String path,
																					 String query,
																					 String fragment,
																					 String encoding)
			throws UnsupportedEncodingException {

		Assert.notNull(encoding, "'encoding' must not be empty");
		StringBuilder sb = new StringBuilder();

		if (scheme != null) {
			sb.append(encodeScheme(scheme, encoding));
			sb.append(':');
		}

		if (authority != null) {
			sb.append("//");
			if (userinfo != null) {
				sb.append(encodeUserInfo(userinfo, encoding));
				sb.append('@');
			}
			if (host != null) {
				sb.append(encodeHost(host, encoding));
			}
			if (port != null) {
				sb.append(':');
				sb.append(encodePort(port, encoding));
			}
		}

		sb.append(encodePath(path, encoding));

		if (query != null) {
			sb.append('?');
			sb.append(encodeQuery(query, encoding));
		}

		if (fragment != null) {
			sb.append('#');
			sb.append(encodeFragment(fragment, encoding));
		}

		return sb.toString();
	}

	/**
	 * Encodes the given URI scheme.
	 *
	 * @param scheme   the scheme to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded scheme
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeScheme(String scheme, String encoding) throws UnsupportedEncodingException {
		return encode(scheme, encoding, SCHEME);
	}

	/**
	 * Encodes the given URI user info.
	 *
	 * @param userInfo the user info to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded user info
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeUserInfo(String userInfo, String encoding) throws UnsupportedEncodingException {
		return encode(userInfo, encoding, USER_INFO);
	}

	/**
	 * Encodes the given URI host.
	 *
	 * @param host     the host to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded host
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeHost(String host, String encoding) throws UnsupportedEncodingException {
		return encode(host, encoding, HOST);
	}

	/**
	 * Encodes the given URI port.
	 *
	 * @param port     the port to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded port
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodePort(String port, String encoding) throws UnsupportedEncodingException {
		return encode(port, encoding, PORT);
	}

	/**
	 * Encodes the given URI path.
	 *
	 * @param path     the path to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded path
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodePath(String path, String encoding) throws UnsupportedEncodingException {
		return encode(path, encoding, PATH);
	}

	/**
	 * Encodes the given URI path segment.
	 *
	 * @param segment  the segment to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded segment
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodePathSegment(String segment, String encoding) throws UnsupportedEncodingException {
		return encode(segment, encoding, SEGMENT);
	}

	/**
	 * Encodes the given URI query.
	 *
	 * @param query    the query to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded query
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeQuery(String query, String encoding) throws UnsupportedEncodingException {
		return encode(query, encoding, QUERY);
	}

	/**
	 * Encodes the given URI query parameter.
	 *
	 * @param queryParam the query parameter to be encoded
	 * @param encoding   the character encoding to encode to
	 * @return the encoded query parameter
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeQueryParam(String queryParam, String encoding) throws UnsupportedEncodingException {
		return encode(queryParam, encoding, QUERY_PARAM);
	}

	/**
	 * Encodes the given URI fragment.
	 *
	 * @param fragment the fragment to be encoded
	 * @param encoding the character encoding to encode to
	 * @return the encoded fragment
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 */
	public static String encodeFragment(String fragment, String encoding) throws UnsupportedEncodingException {
		return encode(fragment, encoding, FRAGMENT);
	}

	private static String encode(String source, String encoding, BitSet notEncoded)
			throws UnsupportedEncodingException {

		Assert.notNull(source, "'source' must not be null");
		Assert.notNull(encoding, "'encoding' must not be empty");

		byte[] bytes = encode(source.getBytes(encoding), notEncoded);
		return new String(bytes, "US-ASCII");
	}

	private static byte[] encode(byte[] source, BitSet notEncoded) {
		Assert.notNull(source, "'source' must not be null");
		ByteArrayOutputStream bos = new ByteArrayOutputStream(source.length * 2);
		for (int i = 0; i < source.length; i++) {
			int b = source[i];
			if (b < 0) {
				b += 256;
			}
			if (notEncoded.get(b)) {
				bos.write(b);
			} else {
				bos.write('%');
				char hex1 = Character.toUpperCase(Character.forDigit((b >> 4) & 0xF, 16));
				char hex2 = Character.toUpperCase(Character.forDigit(b & 0xF, 16));
				bos.write(hex1);
				bos.write(hex2);
			}
		}
		return bos.toByteArray();
	}

	/**
	 * Decodes the given encoded source String into an URI. Based on the following rules: <ul> <li>Alphanumeric characters
	 * {@code "a"} through {@code "z"}, {@code "A"} through {@code "Z"}, and {@code "0"} through {@code "9"} stay the same.
	 * <li>Special characters {@code "-"}, {@code "_"}, {@code "."}, and {@code "*"} stay the same. <li>All other
	 * characters are converted into one or more bytes using the given encoding scheme. Each of the resulting bytes is
	 * written as a hexadecimal string in the {@code %xy} format. <li>A sequence "<code>%<i>xy</i></code>" is interpreted
	 * as a hexadecimal representation of the character. </ul>
	 *
	 * @param source   the source string
	 * @param encoding the encoding
	 * @return the decoded URI
	 * @throws UnsupportedEncodingException when the given encoding parameter is not supported
	 * @see java.net.URLDecoder#decode(String, String)
	 */
	public static String decode(String source, String encoding) throws UnsupportedEncodingException {
		Assert.notNull(source, "'source' must not be null");
		Assert.notNull(encoding, "'encoding' must not be empty");
		int length = source.length();
		ByteArrayOutputStream bos = new ByteArrayOutputStream(length);
		boolean changed = false;
		for (int i = 0; i < length; i++) {
			int ch = source.charAt(i);
			if (ch == '%') {
				if ((i + 2) < length) {
					char hex1 = source.charAt(i + 1);
					char hex2 = source.charAt(i + 2);
					int u = Character.digit(hex1, 16);
					int l = Character.digit(hex2, 16);
					bos.write((char) ((u << 4) + l));
					i += 2;
					changed = true;
				} else {
					throw new IllegalArgumentException("Invalid encoded sequence \"" + source.substring(i) + "\"");
				}
			} else {
				bos.write(ch);
			}
		}
		return changed ? new String(bos.toByteArray(), encoding) : source;
	}

}
