/src/main/java/ac/simons/autolinker/EmailAddressAutoLinker.java

/*
 * Copyright 2014-2018 michael-simons.eu.
 *
 * 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 ac.simons.autolinker;

import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.jsoup.nodes.Element;
import org.jsoup.nodes.Node;
import org.jsoup.nodes.TextNode;
import org.jsoup.parser.Tag;

/**
 * Turns valid ASCII email adresses into anchor text. The label can be
 * obsfuscated, the email address can be encoded to hex.
 *
 * @author Michael J. Simons, 2014-12-27
 */
public final class EmailAddressAutoLinker implements AutoLinker {

	/**
	 * Regex according to http://www.w3.org/Protocols/rfc822/, Originally
	 * written by Cal Henderson
	 * (http://iamcal.com/publish/articles/php/parsing_email/), Translated to
	 * Ruby by Tim Fletcher, with changes suggested by Dan Kubb. Translated to
	 * Java by Michael J. Simons
	 */
	private static final String VALID_EMAIL_ADDRESS_REGEX = "(?:[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-\\x3c\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+|\\x22(?:[^\\x0d\\x22\\x5c\\x80-\\xff]|\\x5c[\\x00-\\x7f])*\\x22)(?:\\x2e(?:[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-\\x3c\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+|\\x22(?:[^\\x0d\\x22\\x5c\\x80-\\xff]|\\x5c[\\x00-\\x7f])*\\x22))*\\x40(?:[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-\\x3c\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+|\\x5b(?:[^\\x0d\\x5b-\\x5d\\x80-\\xff]|\\x5c[\\x00-\\x7f])*\\x5d)(?:\\x2e(?:[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-\\x3c\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+|\\x5b(?:[^\\x0d\\x5b-\\x5d\\x80-\\xff]|\\x5c[\\x00-\\x7f])*\\x5d))*";
	public static final Pattern VALID_EMAIL_ADDRESS = Pattern.compile(String.format("\\A%s\\z", VALID_EMAIL_ADDRESS_REGEX));
	public static final Pattern VALID_EMAIL_ADRESS_ML = Pattern.compile(String.format("(?m)(?<![^\\s])%s", VALID_EMAIL_ADDRESS_REGEX));
	public static final Pattern AT_SIGNS = Pattern.compile("[@\uFF20\\x40]");

	/**
	 * A flag if the addresses in the mailto: protocoll should be hex-encoded
	 */
	private final boolean hexEncodeEmailAddress;
	/**
	 * A flag if the labels should be obfuscated
	 */
	private final boolean obfuscateEmailAddress;

	/**
	 * Instantiates a new email address autolinker.
	 *
	 * @param hexEncodeEmailAddress Should mailto: Addresses be hex-encoded?
	 * @param obfuscateEmailAddress Should labels be obfuscated?
	 */
	public EmailAddressAutoLinker(
		final boolean hexEncodeEmailAddress,
		final boolean obfuscateEmailAddress
	) {
		this.hexEncodeEmailAddress = hexEncodeEmailAddress;
		this.obfuscateEmailAddress = obfuscateEmailAddress;
	}

	@Override
	public List<Node> createLinks(final TextNode textNode) {

		final List<Node> rv = new ArrayList<>();

		int start = 0;

		final String nodeText = textNode.getWholeText();
		final String baseUri = textNode.baseUri();

		final Matcher matcher = VALID_EMAIL_ADRESS_ML.matcher(nodeText);

		while (matcher.find()) {
			final String emailAddress = matcher.group();

			if (!(new String(emailAddress.getBytes(), StandardCharsets.US_ASCII)).equals(emailAddress)) {
				continue;
			}

			final String textBefore = nodeText.substring(start, matcher.start());
			if (!textBefore.isEmpty()) {
				rv.add(new TextNode(textBefore));
			}
			final Element newAnchor = new Element(Tag.valueOf("a"), baseUri);
			newAnchor.attr("href", String.format("%s%s", "mailto:", hexEncodeEmailAddress ? hexEncodeEmailAddress(emailAddress) : emailAddress));
			newAnchor.appendChild(new TextNode(obfuscateEmailAddress ? obfuscateEmailAddress(emailAddress) : emailAddress));
			rv.add(newAnchor);
			start = matcher.end();
		}
		// Add a new textnode for everything after
		final String textAfter = nodeText.substring(start);
		if (!textAfter.isEmpty()) {
			rv.add(new TextNode(textAfter));
		}
		return rv;
	}

	/**
	 * Obfuscates an email address. @ will be replaced throught " [AT] " and .
	 * through " [DOT] ". The email address is lowercased before processing.
	 *
	 * @param emailAddress The email address to obfuscate
	 * @return An obfuscated email address
	 */
	public String obfuscateEmailAddress(final String emailAddress) {
		return AT_SIGNS.matcher(emailAddress.toLowerCase()).replaceAll(" [AT] ").replaceAll("\\.", " [DOT] ");
	}

	/**
	 * Hex encodes an email addess, leaving the '@' intact. Browsers are able to
	 * decode this and maybe it's stops spammers from using emails like that.
	 * The email address is lowercased before processing.
	 *
	 * @param emailAddress The email address that should be encoded to
	 *                     hexadecimal
	 * @return An hexadecimal encoded email adresse
	 */
	public String hexEncodeEmailAddress(final String emailAddress) {
		final String emailAddressLc = emailAddress.toLowerCase();
		final StringBuilder rv = new StringBuilder();
		for (int i = 0; i < emailAddressLc.length(); ++i) {
			char c = emailAddressLc.charAt(i);
			rv.append(c == '@' ? c : String.format("%%%x", (int) c));
		}
		return rv.toString();
	}

}