<?php
/* is_valid_email is dual licensed under the GNU GPL v3 (or later) and
 * under the MIT license.
 *
 * is_valid_email is available from http://rumkin.com/software/email/
 *
 * is_valid_email is a function that determines if the email address
 * passed in appears to be valid.
 */
function is_valid_email($email) {
    $email = trim($email);

    // Some quick checks
    if (strpos($email, "\t") !== false || strpos($email, "\r") !== false || strpos($email, "\n") !== false) {
        return false;
    }

    if ($email == '') {
        return true;
    }

    if (strlen($email) > 320) {
        return false;
    }

    /* TODO:  Write some code here to check the normal cases.
     * 1 @ symbol, explode, if left <= 64 characters, right doesn't have ..,
     * -., .-, leading . or -, ending . or -, both have only a-zA-Z0-9, then
     * it is good.  No need for the complex stuff. */

    /**
     * The rules for parsing a domain are easier to grok than the rules for
     * parsing the localpart of an email address.  Thus, we will work
     * backwards.
     *
     * We are either looking for a domain that consists of labels separated
     * by periods or a domain surrounded by [ and ].
     *
     * If we are using the label version, we want to only allow the following
     * characters:
     * abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!#$%&'*+-/=?^_`{|}~
     * Additionally, labels must be less than 64 characters long, and must not
     * start or end with a hyphen.  No label can be blank.  No leading or
     * trailing . at the start or end of the domain.
     *
     * For bracketed domains, we look for characters with the decimal values
     * 1-9, 11, 12, 14-90, 94-127
     * If a character is preceded with a \, we allow any 7-bit character to
     * follow.
     *
     * The entire domain must be at most 253 characters long for DNS to work.
     * The top level domain must be all alphabetic.
     */
    $atIndex = strlen($email) - 1;  // We want this on the @ when done
    if (substr($email, $atIndex, 1) == ']') {
        // Bracketed domain
        $atIndex --;
        $curr = substr($email, $atIndex, 1);
        $prev = substr($email, $atIndex - 1, 1);
        $domain = '';

        while ($curr != '[' && $atIndex) {
            $currOrd = ord($curr);

            if ($prev == '\\') {
                if ($currOrd >= 128 || $currOrd < 1) {
                    return false;
                }

                $domain = $curr . $domain;
                $atIndex -= 2;
                $curr = substr($email, $atIndex, 1);
                $prev = substr($email, $atIndex - 1, 1);
            } else {
                if (($currOrd <= 127 && $currOrd >= 94) || ($currOrd <= 90 && $currOrd >= 14) || ($currOrd <= 9 && $currOrd >= 1) || $currOrd == 11 || $currOrd == 12) {
                    $domain = $curr . $domain;
                    $atIndex --;
                    $curr = $prev;
                    $prev = substr($email, $atIndex - 1, 1);
                } else {
                    // Invalid unquoted character
                    return false;
                }
            }
        }

        if ($atIndex < 1) {
            // We need at least one character to the left of the @ symbol
            return false;
        }

        if ($prev != '@') {
            // Improper escaping
            return false;
        }

        if (! is_valid_email_domain($domain, true)) {
            return false;
        }

        $atIndex --;
    } else {
        // Labels with dots; ":" is a special thing for IPv6
        $allowed = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!#$%&\'*+-/=?^_`{|}~.:';

        while (strpos($allowed, substr($email, $atIndex, 1)) !== false && $atIndex) {
            $atIndex --;
        }

        if ($atIndex < 1) {
            // Must have at least 1 character to the left of the @ symbol
            return false;
        }

        if (substr($email, $atIndex, 1) != '@') {
            // Invalid
            return false;
        }

        $domain = substr($email, $atIndex + 1);

        if (! is_valid_email_domain($domain, false)) {
            return false;
        }
    }

    /**
     * Whew!  We made it through that mess and we determined that the domain
     * portion seems valid.  Now for the rules with the local part:
     *
     * Emails can contain labels separated by dots.
     * No label can start or end with a dot.
     * Labels can be unquoted or surrounded by quotes.
     * Unquoted text must have at least one character.  (Quoted text doesn't.)
     * Unquoted characters allowed:  !#$%&'*+-/0123456789=?ABCDEFGHIJKLMNOPQRSTUVWXYZ^_`abcdefghijklmnopqrstuvwxyz{|}~
     * Quoted text allowed: 1-8, 11, 12, 14-33, 35-90, 94-127
     * Quoted text allowed escaped (preceded by backslash):  all except 10, 13
     * Maximum length for the local part is 64 characters
     */
    $localPart = substr($email, 0, $atIndex);

    if (strlen($localPart) > 64) {
        return false;
    }

    $allowedLocal = '!#$%&\'*+-/0123456789=?ABCDEFGHIJKLMNOPQRSTUVWXYZ^_`abcdefghijklmnopqrstuvwxyz{|}~';

    /**
     * Parsing mode:
     *   0 = start of a label
     *   1 = in label, normal text (unquoted)
     *   2 = in label, quoted text
     *   3 = in label, quoted and escaped (last was a backslash)
     *   4 = after quoted label (only allows a period as next char)
     */
    $mode = 0;

    for ($i = 0; $i < strlen($localPart); $i ++) {
        $c = substr($localPart, $i, 1);

        if ($mode == 0) {
            // Start of a label
            if ($c == '"') {
                $mode = 2;
            } elseif ($c == '.') {
                return false;
            } elseif (strpos($allowedLocal, $c) === false) {
                return false;
            } else {
                $mode = 1;
            }
        } elseif ($mode == 1) {
            // In unquoted label
            if ($c == '.') {
                $mode = 0;
            } elseif (strpos($allowedLocal, $c) === false) {
                return false;
            }
        } elseif ($mode == 2) {
            // In quoted label
            if ($c == '"') {
                $mode = 4;
            } elseif ($c == '\\') {
                $mode = 3;
            } else {
                $cOrd = ord($c);

                if (($cOrd > 8 && $cOrd < 11) || ($cOrd > 90 && $cOrd < 94) || $cOrd == 13 || $cOrd == 34 || $cOrd > 127) {
                    return false;
                }
            }
        } elseif ($mode == 3) {
            $cOrd = ord($c);

            if ($cOrd == 10 || $cOrd == 11 || $cOrd > 127) {
                return false;
            }

            $mode = 2;
        } elseif ($mode == 4) {
            if ($c != '.') {
                return false;
            }

            $mode = 0;
        }
    }

    if ($mode != 1 && $mode != 4) {
        return false;
    }

    return true;
}


/* This function assumes you already checked for invalid characters
 * Any escaping has been removed */
function is_valid_email_domain($domain, $isBracketed) {
    if (strlen($domain) == 0) {
        // Gotta have a domain
        return false;
    }

    if (strlen($domain) > 253) {
        // Too long for DNS to work
        return false;
    }

    if (strpos($domain, '..') !== false || substr($domain, 0, 1) == '.' || substr($domain, - 1) == '.') {
        // No empty labels allowed
        return false;
    }

    if (strpos($domain, '.-') !== false || strpos($domain, '-.') !== false || strpos($domain, '--') !== false) {
        // No leading or trailing hyphens allowed in labels.  No double hyphens
        return false;
    }

    if (substr($domain, 0, 1) == '-' || substr($domain, - 1) == '-') {
        // No leading or trailing hyphens allowed in labels.
        return false;
    }

    $labels = explode('.', $domain);
    $looksLikeIPv4 = false;
    $looksLikeIPv6 = false;

    if (count($labels) == 4) {
        $looksLikeIPv4 = true;
    } elseif (count($labels) == 1) {
        $looksLikeIPv6 = true;
        $allowedIPv6 = '0123456789abcdefABCDEF';
        $parts = explode(':', $labels[0]);

        if (count($parts) != 5 || $parts[2] != '') {
            $looksLikeIPv6 = false;
        }

        foreach ($parts as $p) {
            if (strlen($p) > 4) {
                $looksLikeIPv6 = false;
            }

            for ($i = 0; $i < strlen($p); $i ++) {
                if (strpos($allowedIPv6, substr($p, $i, 1)) === false) {
                    $looksLikeIPv6 = false;
                }
            }
        }
    }

    foreach ($labels as $l) {
        if (strlen($l) > 63) {
            return false;
        }

        if ($looksLikeIPv4) {
            if (strlen($l) > 3) {
                $looksLikeIPv4 = false;
            }

            for ($i = 0; $i < strlen($l); $i ++) {
                $c = ord(substr($l, $i, 1));

                if ($c < 0x30 || $c > 0x39) {
                    $looksLikeIPv4 = false;
                }
            }

            if ($l < 0 || $l > 255) {
                $looksLikeIPv4 = false;
            }
        }
    }

    // If we have a ":", it is only allowed for IPv6 or bracketed domains
    if (! $looksLikeIPv6 && strpos($domain, ':') !== false && ! $isBracketed) {
        return false;
    }

    // IPv6 and IPs don't have alpha-only TLDs
    if (! $looksLikeIPv4 && ! $looksLikeIPv6) {
        $tldIndex = strlen($l);
        $allowedTld = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

        while ($tldIndex) {
            $tldIndex --;

            if (strpos($allowedTld, substr($l, $tldIndex, 1)) === false) {
                return false;
            }
        }
    }

    return true;
}