/*
 * Copyright 2008 Les Hazlewood 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 org.codemonkey.simplejavamail;

import java.util.regex.Pattern;

/**
 * Validates an email address according to <a href="http://www.ietf.org/rfc/rfc2822.txt">RFC 2822</a>, using regular expressions.
 * <p>
 * From the original author: <br>
 * <blockquote> If you use this code, please keep the author information in tact and reference my site at <a
 * href="http://www.leshazlewood.com">leshazlewood.com</a>. Thanks! </blockquote>
 * <p>
 * Code sanitized by Benny Bottema (kept validation 100% in tact).
 * 
 * @author Les Hazlewood, Benny Bottema
 * @see EmailAddressValidationCriteria
 */
public final class EmailValidationUtil {

        /**
         * Private constructor; this is a utility class with static methods only, not designed for extension.
         */
        private EmailValidationUtil() {
                //
        }

        /**
         * Validates an e-mail with default validation flags that remains <code>true</code> to RFC 2822. This means allowing both domain
         * literals and quoted identifiers.
         * 
         * @param email A complete email address.
         * @return Whether the e-mail address is compliant with RFC 2822.
         * @see EmailAddressValidationCriteria#RFC_COMPLIANT
         */
        public static boolean isValid(final String email) {
                return isValid(email, EmailAddressValidationCriteria.RFC_COMPLIANT);
        }

        /**
         * Validates an e-mail with given validation flags.
         * 
         * @param email A complete email address.
         * @param emailAddressValidationCriteria A set of flags that restrict or relax RFC 2822 compliance.
         * @return Whether the e-mail address is compliant with RFC 2822, configured using the passed in {@link EmailAddressValidationCriteria}.
         * @see EmailAddressValidationCriteria#RFC_COMPLIANT
         */
        public static boolean isValid(final String email, final EmailAddressValidationCriteria emailAddressValidationCriteria) {
                return buildValidEmailPattern(emailAddressValidationCriteria).matcher(email).matches();
        }

        protected static Pattern buildValidEmailPattern(EmailAddressValidationCriteria parameterObject) {
                // RFC 2822 2.2.2 Structured Header Field Bodies
                final String wsp = "[ \\t]"; // space or tab
                final String fwsp = wsp + "*";
                // RFC 2822 3.2.1 Primitive tokens
                final String dquote = "\\\"";
                // ASCII Control characters excluding white space:
                final String noWsCtl = "\\x01-\\x08\\x0B\\x0C\\x0E-\\x1F\\x7F";
                // all ASCII characters except CR and LF:
                final String asciiText = "[\\x01-\\x09\\x0B\\x0C\\x0E-\\x7F]";
                // RFC 2822 3.2.2 Quoted characters:
                // single backslash followed by a text char
                final String quotedPair = "(\\\\" + asciiText + ")";
                // RFC 2822 3.2.4 Atom:
                final String atext = "[a-zA-Z0-9\\!\\#\\$\\%\\&\\'\\*\\+\\-\\/\\=\\?\\^\\_\\`\\{\\|\\}\\~]";
                final String atom = fwsp + atext + "+" + fwsp;
                final String dotAtomText = atext + "+" + "(" + "\\." + atext + "+)*";
                final String dotAtom = fwsp + "(" + dotAtomText + ")" + fwsp;
                // RFC 2822 3.2.5 Quoted strings:
                // noWsCtl and the rest of ASCII except the doublequote and backslash characters:
                final String qtext = "[" + noWsCtl + "\\x21\\x23-\\x5B\\x5D-\\x7E]";
                final String qcontent = "(" + qtext + "|" + quotedPair + ")";
                final String quotedString = dquote + "(" + fwsp + qcontent + ")*" + fwsp + dquote;
                // RFC 2822 3.2.6 Miscellaneous tokens
                final String word = "((" + atom + ")|(" + quotedString + "))";
                final String phrase = word + "+"; // one or more words.
                // RFC 1035 tokens for domain names:
                final String letter = "[a-zA-Z]";
                final String letDig = "[a-zA-Z0-9]";
                final String letDigHyp = "[a-zA-Z0-9-]";
                final String rfcLabel = letDig + "(" + letDigHyp + "{0,61}" + letDig + ")?";
                final String rfc1035DomainName = rfcLabel + "(\\." + rfcLabel + ")*\\." + letter + "{2,6}";
                // RFC 2822 3.4 Address specification
                // domain text - non white space controls and the rest of ASCII chars not including [, ], or \:
                final String dtext = "[" + noWsCtl + "\\x21-\\x5A\\x5E-\\x7E]";
                final String dcontent = dtext + "|" + quotedPair;
                final String domainLiteral = "\\[" + "(" + fwsp + dcontent + "+)*" + fwsp + "\\]";
                final String rfc2822Domain = "(" + dotAtom + "|" + domainLiteral + ")";
                final String domain = parameterObject.isAllowDomainLiterals() ? rfc2822Domain : rfc1035DomainName;
                final String localPart = "((" + dotAtom + ")|(" + quotedString + "))";
                final String addrSpec = localPart + "@" + domain;
                final String angleAddr = "<" + addrSpec + ">";
                final String nameAddr = "(" + phrase + ")?" + fwsp + angleAddr;
                final String mailbox = nameAddr + "|" + addrSpec;
                // now compile a pattern for efficient re-use:
                // if we're allowing quoted identifiers or not:
                final String patternString = parameterObject.isAllowQuotedIdentifiers() ? mailbox : addrSpec;
                return Pattern.compile(patternString);
        }
}