msime-engine 0.1.1

//! The syllable being typed: one optional bopomofo symbol per slot, filled by Dachen keys until a tone key completes it.

use super::layout::{self, Kind};

/// The untoned syllable under construction. Each slot holds at most one symbol; a key of a kind already present replaces it (libchewing's slot rule), so the order the keys were typed in does not matter.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct PendingSyllable {
    pub initial: Option<char>,
    pub medial: Option<char>,
    pub rime: Option<char>,
}

impl PendingSyllable {
    pub fn is_empty(&self) -> bool {
        self.initial.is_none() && self.medial.is_none() && self.rime.is_none()
    }

    /// Puts `symbol` in the slot of `kind`, replacing whatever was there.
    pub fn insert(&mut self, symbol: char, kind: Kind) {
        *self.slot(kind) = Some(symbol);
    }

    /// Removes the last filled slot in syllable order (rime, then medial, then initial). Returns whether anything was removed.
    pub fn pop(&mut self) -> bool {
        for kind in [Kind::Rime, Kind::Medial, Kind::Initial] {
            if self.slot(kind).take().is_some() {
                return true;
            }
        }
        false
    }

    pub fn clear(&mut self) {
        *self = Self::default();
    }

    /// The symbols in syllable order, e.g. `ㄋㄧ`.
    pub fn bopomofo(&self) -> String {
        self.symbols().collect()
    }

    /// The Dachen keys that spell the filled slots, in syllable order, e.g. `su` for `ㄋㄧ`.
    pub fn keys(&self) -> String {
        let mut keys = String::new();
        self.append_keys(&mut keys);
        keys
    }

    /// Appends the Dachen keys without allocating an intermediate string.
    pub(super) fn append_keys(&self, target: &mut String) {
        for symbol in self.symbols() {
            if let Some((key, _, _)) = layout::DACHEN
                .iter()
                .find(|(_, dachen_symbol, _)| *dachen_symbol == symbol)
            {
                target.push(char::from(*key));
            }
        }
    }

    /// `msime-zhuyin.db` 中的带调音节：符号后接调号（一声为空）。没有符号时返回 `None`，调号本身不是音节。
    pub fn toned(&self, mark: &str) -> Option<String> {
        if self.is_empty() {
            return None;
        }
        let capacity = self.symbols().map(char::len_utf8).sum::<usize>() + mark.len();
        let mut toned = String::with_capacity(capacity);
        toned.extend(self.symbols());
        toned.push_str(mark);
        Some(toned)
    }

    fn symbols(&self) -> impl Iterator<Item = char> {
        [self.initial, self.medial, self.rime].into_iter().flatten()
    }

    fn slot(&mut self, kind: Kind) -> &mut Option<char> {
        match kind {
            Kind::Initial => &mut self.initial,
            Kind::Medial => &mut self.medial,
            Kind::Rime => &mut self.rime,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn typed(keys: &[u8]) -> PendingSyllable {
        let mut pending = PendingSyllable::default();
        for key in keys {
            let (symbol, kind) = layout::symbol(*key).unwrap();
            pending.insert(symbol, kind);
        }
        pending
    }

    #[test]
    fn slots_fill_in_syllable_order_whatever_the_key_order() {
        assert_eq!(typed(b"su").bopomofo(), "ㄋㄧ");
        assert_eq!(typed(b"us").bopomofo(), "ㄋㄧ");
        assert_eq!(typed(b"lc").bopomofo(), "ㄏㄠ");
        assert_eq!(typed(b"lc").keys(), "cl");
        assert_eq!(typed(b"ju0").keys(), "u0");
    }

    #[test]
    fn a_key_of_a_present_kind_replaces_its_slot() {
        // ㄋ then ㄌ: both initials, so ㄌ replaces ㄋ.
        assert_eq!(typed(b"sx").bopomofo(), "ㄌ");
        // ㄧ then ㄨ: both medials.
        assert_eq!(typed(b"suj").bopomofo(), "ㄋㄨ");
        // ㄠ then ㄚ: both rimes; the initial and medial stay.
        let pending = typed(b"cul8");
        assert_eq!(pending.bopomofo(), "ㄏㄧㄚ");
        assert_eq!(pending.keys(), "cu8");
    }

    #[test]
    fn pop_removes_from_the_end_of_the_syllable() {
        let mut pending = typed(b"l");
        pending.insert('ㄏ', Kind::Initial);
        pending.insert('ㄨ', Kind::Medial);
        let mut shown = vec![pending.bopomofo()];
        while pending.pop() {
            shown.push(pending.bopomofo());
        }
        assert_eq!(shown, ["ㄏㄨㄠ", "ㄏㄨ", "ㄏ", ""]);
        assert!(pending.is_empty());
        assert!(!pending.pop());
    }

    #[test]
    fn toned_appends_the_mark_and_needs_a_symbol() {
        assert_eq!(typed(b"su").toned("ˇ").as_deref(), Some("ㄋㄧˇ"));
        assert_eq!(typed(b"j0").toned("").as_deref(), Some("ㄨㄢ"));
        assert_eq!(typed(b"8").toned("˙").as_deref(), Some("ㄚ˙"));
        assert_eq!(PendingSyllable::default().toned("ˇ"), None);
        let mut pending = typed(b"su");
        pending.clear();
        assert!(pending.is_empty());
    }

    #[test]
    fn toned_three_symbol_syllables_allocate_only_the_returned_string() {
        let pending = typed(b"cj0");
        for mark in layout::TONE_MARKS {
            let expected = format!("ㄏㄨㄢ{mark}");
            let (toned, allocations) =
                crate::ime::personal_rerank::allocations::count(|| pending.toned(mark));
            assert_eq!(toned.as_deref(), Some(expected.as_str()));
            assert_eq!(allocations, 1, "带调音节不应在构造时反复扩容");
        }
    }

    #[test]
    fn toned_capacity_preserves_unicode_slots_long_marks_and_empty_syllables() {
        let pending = PendingSyllable {
            initial: Some('a'),
            medial: Some('字'),
            rime: Some('😀'),
        };
        let mark = "合成長調號ˇ";
        let (toned, allocations) =
            crate::ime::personal_rerank::allocations::count(|| pending.toned(mark));
        assert_eq!(toned.as_deref(), Some("a字😀合成長調號ˇ"));
        assert_eq!(allocations, 1);

        let (toned, allocations) = crate::ime::personal_rerank::allocations::count(|| {
            PendingSyllable::default().toned(mark)
        });
        assert_eq!(toned, None);
        assert_eq!(allocations, 0);
    }
}