/// Normalize the given character name in place according to UAX44-LM2.
///
/// See: http://unicode.org/reports/tr44/#UAX44-LM2
pub fn character_name_normalize(string: &mut String) {
    let bytes = unsafe {
        // SAFETY: `character_name_normalize_bytes` guarantees that
        // `bytes[..len]` is valid UTF-8.
        string.as_mut_vec()
    };
    let len = character_name_normalize_bytes(bytes).len();
    bytes.truncate(len);
}

/// Normalize the given character name in place according to UAX44-LM2.
///
/// The slice returned is guaranteed to be valid UTF-8 for all possible values
/// of `slice`.
///
/// See: http://unicode.org/reports/tr44/#UAX44-LM2
fn character_name_normalize_bytes(slice: &mut [u8]) -> &mut [u8] {
    // According to Unicode 4.8, character names consist only of Latin
    // capital letters A to Z, ASCII digits, ASCII space or ASCII hypen.
    // Therefore, we can do very simplistic case folding and operate on the
    // raw bytes, since everything is ASCII. Note that we don't actually know
    // whether `slice` is all ASCII or not, so we drop all non-ASCII bytes.
    let mut next_write = 0;
    let mut prev_letter = false;
    // let mut prev_space = true;
    for i in 0..slice.len() {
        // SAFETY ARGUMENT: To guarantee that the resulting slice is valid
        // UTF-8, we ensure that the slice contains only ASCII bytes. In
        // particular, we drop every non-ASCII byte from the normalized string.
        let b = slice[i];
        if b == b' ' {
            // Drop spaces.
        } else if b == b'_' {
            // Drop the underscore.
        } else if b == b'-' {
            let medial = prev_letter
                && slice.get(i+1).map_or(false, |b| b.is_ascii_alphabetic());
            let mut keep_hyphen = !medial;
            // We want to keep the hypen only if it isn't medial. However,
            // there is one exception. We need to keep the hypen in the
            // character (U+1180) named `HANGUL JUNGSEONG O-E`. So we check for
            // that here.
            let next_e = slice
                .get(i+1)
                .map_or(false, |&b| b == b'E' || b == b'e');
            // More characters after the final E are fine, as long as they are
            // underscores and spaces.
            let rest_empty = i+2 >= slice.len()
                || slice[i+2..].iter().all(|&b| b == b' ' || b == b'_');
            if !keep_hyphen && next_e && rest_empty {
                keep_hyphen = slice[..next_write] == b"hanguljungseongo"[..];
            }
            if keep_hyphen {
                slice[next_write] = b;
                next_write += 1;
            }
        } else if b'A' <= b && b <= b'Z' {
            slice[next_write] = b + (b'a' - b'A');
            next_write += 1;
        } else if b <= 0x7F {
            slice[next_write] = b;
            next_write += 1;
        }
        // prev_space = false;
        prev_letter = b.is_ascii_alphabetic();
    }
    &mut slice[..next_write]
}

/// Normalize the given symbolic name in place according to UAX44-LM3.
///
/// A "symbolic name" typically corresponds to property names and property
/// value aliases. Note, though, that it should not be applied to property
/// string values.
///
/// See: http://unicode.org/reports/tr44/#UAX44-LM2
pub fn symbolic_name_normalize(string: &mut String) {
    let bytes = unsafe {
        // SAFETY: `symbolic_name_normalize_bytes` guarantees that
        // `bytes[..len]` is valid UTF-8.
        string.as_mut_vec()
    };
    let len = symbolic_name_normalize_bytes(bytes).len();
    bytes.truncate(len);
}

/// Normalize the given symbolic name in place according to UAX44-LM3.
///
/// A "symbolic name" typically corresponds to property names and property
/// value aliases. Note, though, that it should not be applied to property
/// string values.
///
/// The slice returned is guaranteed to be valid UTF-8 for all possible values
/// of `slice`.
///
/// See: http://unicode.org/reports/tr44/#UAX44-LM3
fn symbolic_name_normalize_bytes(slice: &mut [u8]) -> &mut [u8] {
    // I couldn't find a place in the standard that specified that property
    // names/aliases had a particular structure (unlike character names), but
    // we assume that it's ASCII only and drop anything that isn't ASCII.
    let mut start = 0;
    let mut starts_with_is = false;
    if slice.len() >= 2 {
        // Ignore any "is" prefix.
        starts_with_is =
            slice[0..2] == b"is"[..]
            || slice[0..2] == b"IS"[..]
            || slice[0..2] == b"iS"[..]
            || slice[0..2] == b"Is"[..];
        if starts_with_is {
            start = 2;
        }
    }
    let mut next_write = 0;
    for i in start..slice.len() {
        // SAFETY ARGUMENT: To guarantee that the resulting slice is valid
        // UTF-8, we ensure that the slice contains only ASCII bytes. In
        // particular, we drop every non-ASCII byte from the normalized string.
        let b = slice[i];
        if b == b' ' || b == b'_' || b == b'-' {
            continue;
        } else if b'A' <= b && b <= b'Z' {
            slice[next_write] = b + (b'a' - b'A');
            next_write += 1;
        } else if b <= 0x7F {
            slice[next_write] = b;
            next_write += 1;
        }
    }
    // Special case: ISO_Comment has a 'isc' abbreviation. Since we generally
    // ignore 'is' prefixes, the 'isc' abbreviation gets caught in the cross
    // fire and ends up creating an alias for 'c' to 'ISO_Comment', but it
    // is actually an alias for the 'Other' general category.
    if starts_with_is && next_write == 1 && slice[0] == b'c' {
        slice[0] = b'i';
        slice[1] = b's';
        slice[2] = b'c';
        next_write = 3;
    }
    &mut slice[..next_write]
}

#[cfg(test)]
mod tests {
    use super::{
        character_name_normalize, character_name_normalize_bytes,
        symbolic_name_normalize, symbolic_name_normalize_bytes,
    };

    fn char_norm(s: &str) -> String {
        let mut s = s.to_string();
        character_name_normalize(&mut s);
        s
    }

    fn sym_norm(s: &str) -> String {
        let mut s = s.to_string();
        symbolic_name_normalize(&mut s);
        s
    }

    #[test]
    fn char_normalize() {
        assert_eq!(char_norm("HANGUL JUNGSEONG O-E"), "hanguljungseongo-e");
        assert_eq!(char_norm("HANGUL JUNGSEONG O-E _"), "hanguljungseongo-e");
        assert_eq!(char_norm("zero-width space"), "zerowidthspace");
        assert_eq!(char_norm("zerowidthspace"), "zerowidthspace");
        assert_eq!(char_norm("ZERO WIDTH SPACE"), "zerowidthspace");
        assert_eq!(char_norm("TIBETAN MARK TSA -PHRU"), "tibetanmarktsa-phru");
        assert_eq!(char_norm("tibetan_letter_-a"), "tibetanletter-a");
    }

    #[test]
    fn sym_normalize() {
        assert_eq!(sym_norm("Line_Break"), "linebreak");
        assert_eq!(sym_norm("Line-break"), "linebreak");
        assert_eq!(sym_norm("linebreak"), "linebreak");
        assert_eq!(sym_norm("BA"), "ba");
        assert_eq!(sym_norm("ba"), "ba");
        assert_eq!(sym_norm("Greek"), "greek");
        assert_eq!(sym_norm("isGreek"), "greek");
        assert_eq!(sym_norm("IS_Greek"), "greek");
        assert_eq!(sym_norm("isc"), "isc");
        assert_eq!(sym_norm("is c"), "isc");
        assert_eq!(sym_norm("is_c"), "isc");
    }

    #[test]
    fn valid_utf8_character() {
        let mut x = b"abc\xFFxyz".to_vec();
        let y = character_name_normalize_bytes(&mut x);
        assert_eq!(y, b"abcxyz");
    }

    #[test]
    fn valid_utf8_symbolic() {
        let mut x = b"abc\xFFxyz".to_vec();
        let y = symbolic_name_normalize_bytes(&mut x);
        assert_eq!(y, b"abcxyz");
    }
}