// Copyright 2016  Jonas Me
// See the 'AUTHORS' file at the top-level directory for a full list of authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

use ascii_utils;

use errors::*;

// https://tools.ietf.org/html/rfc5321#section-4.5.3.1
//
// The maximum total length of a user name or other local-part is 64 octets.
// The maximum total length of a domain name or number is 255 octets.
const MAX_LOCAL_PART: usize = 64;
const MAX_DOMAIN_PART: usize = 255;
const MAX_LABEL: usize = 63;

/// `is_valid_email` checks wheter an email address is valid.
pub fn is_valid_email(address: &str) -> bool {
    parse_email(address).is_ok()
}

/// `parse_email` scans an email address to check wheter it is correct.
pub fn parse_email(address: &str) -> Result<(), ParseError> {
    if address.starts_with('@') {
        return Err(ParseError::NoLocalPart);
    }
    if address.ends_with('@') {
        return Err(ParseError::NoDomainPart);
    }

    // https://tools.ietf.org/html/rfc5321#section-4.1.2
    //
    // Systems MUST NOT define mailboxes in such a way as to require the use in
    // SMTP of non-ASCII characters (octets with the high order bit set to one)
    // or ASCII "control characters" (decimal value 0-31 and 127).
    ascii_utils::check_ascii_printable(address)?;

    let mut address_iter = address.split('@');
    let local = address_iter.next().unwrap();
    let domain = address_iter.next().ok_or(ParseError::NoSignAt)?;
    if address_iter.next().is_some() {
        return Err(ParseError::TooAt);
    }

    // == Local part

    // https://tools.ietf.org/html/rfc3696#section-3
    //
    // Period (".") may also appear, but may not be used to start or end
    // the local part, nor may two or more consecutive periods appear.

    if local.len() > MAX_LOCAL_PART {
        return Err(ParseError::LocalTooLong);
    }
    if local.starts_with('.') {
        return Err(ParseError::LocalStartPeriod);
    }
    if local.ends_with('.') {
        return Err(ParseError::LocalEndPeriod);
    }

    let mut last_period: bool = false;
    for ch in local.chars() {
        if ascii_utils::Check::is_letter(ch) || ascii_utils::Check::is_digit(ch) {
            if last_period {
                last_period = false;
            }
            continue;
        }

        match ch {
            // atom :: https://tools.ietf.org/html/rfc5322#section-3.2.3
            '!' | '#' | '$' | '%' | '&' | '\'' | '*' | '+' | '-' | '/' | '=' | '?' | '^' |
            '_' | '`' | '{' | '|' | '}' | '~' => {
                if last_period {
                    last_period = false;
                }
            }
            '.' => {
                if last_period {
                    return Err(ParseError::ConsecutivePeriod);
                }
                last_period = true;
            }
            _ => return Err(ParseError::WrongCharLocal(ch)),
        }
    }

    // == Domain part

    // https://tools.ietf.org/html/rfc5321#section-4.1.2
    //
    // characters outside the set of alphabetic characters, digits, and hyphen
    // MUST NOT appear in domain name labels for SMTP clients or servers.  In
    // particular, the underscore character is not permitted.

    // https://tools.ietf.org/html/rfc1034#section-3.5
    //
    // The labels must follow the rules for ARPANET host names.  They must start
    // with a letter, end with a letter or digit, and have as interior
    // characters only letters, digits, and hyphen.  There are also some
    // restrictions on the length.  Labels must be 63 characters or less.

    // https://tools.ietf.org/html/rfc3696#section-2
    //
    // It is likely that the better strategy has now become to make the "at
    // least one period" test, to verify LDH conformance (including verification
    // that the apparent TLD name is not all-numeric), and then to use the DNS
    // to determine domain name validity, rather than trying to maintain a local
    // list of valid TLD names.

    if domain.len() > MAX_DOMAIN_PART {
        return Err(ParseError::DomainTooLong);
    }
    if domain.starts_with('.') {
        return Err(ParseError::DomainStartPeriod);
    }
    if domain.ends_with('.') {
        return Err(ParseError::DomainEndPeriod);
    }

    let labels: Vec<&str> = domain.split('.').collect();
    if labels.len() == 1 {
        return Err(ParseError::NoPeriodDomain);
    }

    // label = let-dig [ [ ldh-str ] let-dig ]
	// limited to a length of 63 characters by RFC 1034 section 3.5
	//
	// <let-dig> ::= <letter> | <digit>
	// <ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str>
	// <let-dig-hyp> ::= <let-dig> | "-"
    for label in labels {
        if label.is_empty() {
            return Err(ParseError::ConsecutivePeriod);
        }
        if label.len() > MAX_LABEL {
            return Err(ParseError::LabelTooLong);
        }

        if let Some(ch) = label.chars().find(|&x| {
            !ascii_utils::Check::is_letter(x) && !ascii_utils::Check::is_digit(x) && x != '-'
        }) {
            return Err(ParseError::WrongCharDomain(ch));
        }

        let label_bytes = label.as_bytes();

        let first_char = label_bytes[0];
        if !ascii_utils::Check::is_letter(first_char) && !ascii_utils::Check::is_digit(first_char) {
            return Err(ParseError::WrongStartLabel(label_bytes[0] as char));
        }
        let last_char = label_bytes[label_bytes.len() - 1];
        if !ascii_utils::Check::is_letter(last_char) && !ascii_utils::Check::is_digit(last_char) {
            return Err(ParseError::WrongEndLabel(last_char as char));
        }
    }

    Ok(())
}

// == Tests
//

#[test]
fn test_length() {
    let local_part = "a".repeat(MAX_LOCAL_PART);

    let label = format!("{}.", "x".repeat(MAX_LABEL));
    let all_labels = format!("{}", label.repeat(3));
    let last_label = "y".repeat(MAX_DOMAIN_PART - all_labels.len());

    let input_ok = format!("{}@{}{}", local_part, all_labels, last_label);
    assert_eq!(parse_email(&input_ok), Ok(()));

    // == Errors

    let mut input_err = format!("a{}@{}{}", local_part, all_labels, last_label);
    assert_eq!(parse_email(&input_err), Err(ParseError::LocalTooLong));

    input_err = format!("{}@{}{}z", local_part, all_labels, last_label);
    assert_eq!(parse_email(&input_err), Err(ParseError::DomainTooLong));

    input_err = format!("{}@{}x{}", local_part, label, last_label);
    assert_eq!(parse_email(&input_err), Err(ParseError::LabelTooLong));
}