loro/crates/delta/src/text_delta.rs

use crate::{
    delta_trait::{DeltaAttr, DeltaValue},
    DeltaItem, DeltaRope,
};
use arrayvec::ArrayString;
use generic_btree::rle::{HasLength, Mergeable, Sliceable, TryInsert};

#[cfg(test)]
const MAX_STRING_SIZE: usize = 8;
#[cfg(not(test))]
const MAX_STRING_SIZE: usize = 128;

#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub struct TextChunk(ArrayString<MAX_STRING_SIZE>);
pub type TextDelta<Attr = ()> = DeltaRope<TextChunk, Attr>;

impl<Attr: DeltaAttr> TextDelta<Attr> {
    pub fn insert_str(&mut self, index: usize, s: &str) {
        if s.is_empty() || index == self.len() {
            self.push_str_insert(s);
            return;
        }

        self.insert_values(
            index,
            TextChunk::from_long_str(s).map(|chunk| DeltaItem::Replace {
                value: chunk,
                attr: Default::default(),
                delete: 0,
            }),
        );
    }

    pub fn push_str_insert(&mut self, s: &str) -> &mut Self {
        self.push_str_insert_with_attr(s, Default::default())
    }

    pub fn push_str_insert_with_attr(&mut self, s: &str, attr: Attr) -> &mut Self {
        if s.is_empty() {
            return self;
        }

        if s.len() <= MAX_STRING_SIZE {
            self.push_insert(TextChunk(ArrayString::from(s).unwrap()), attr);
            return self;
        }

        let mut split_end = 128;
        let mut split_start = 0;
        while split_end != s.len() {
            while !s.is_char_boundary(split_end) {
                split_end -= 1;
            }

            let chunk = TextChunk(ArrayString::from(&s[split_start..split_end]).unwrap());
            self.push_insert(chunk, attr.clone());
            split_start = split_end;
            split_end = (split_end + 128).min(s.len());
        }

        self
    }

    pub fn try_to_string(&self) -> Option<String> {
        let mut ans = String::with_capacity(self.len());
        for item in self.iter() {
            match item {
                crate::DeltaItem::Retain { .. } => return None,
                crate::DeltaItem::Replace { value, .. } => {
                    ans.push_str(&value.0);
                }
            }
        }

        Some(ans)
    }
}

impl TextChunk {
    pub(crate) fn try_insert(&mut self, pos: usize, s: &str) -> Result<(), ()> {
        if self.0.len() + s.len() > MAX_STRING_SIZE {
            return Err(());
        }

        assert!(self.0.is_char_boundary(pos));
        let new_len = self.0.len() + s.len();
        unsafe {
            let ptr = self.0.as_mut_ptr().add(pos);
            ptr.copy_to(ptr.add(s.len()), self.0.len() - pos);
            ptr.copy_from_nonoverlapping(s.as_ptr(), s.len());
            self.0.set_len(new_len);
        }

        Ok(())
    }

    pub fn try_from_str(s: &str) -> Option<Self> {
        Some(TextChunk(ArrayString::from(s).ok()?))
    }

    pub fn from_long_str(s: &str) -> impl Iterator<Item = Self> + '_ {
        let mut text_iter = s.chars();
        std::iter::from_fn(move || {
            let mut chunk = Self::default();
            for c in text_iter.by_ref() {
                let mut bytes = [0, 0, 0, 0];
                chunk.0.push_str(c.encode_utf8(&mut bytes));
                if chunk.0.is_full() {
                    break;
                }
            }

            if chunk.0.is_empty() {
                return None;
            }

            Some(chunk)
        })
    }
}

impl HasLength for TextChunk {
    fn rle_len(&self) -> usize {
        self.0.len()
    }
}

impl Mergeable for TextChunk {
    fn can_merge(&self, rhs: &Self) -> bool {
        MAX_STRING_SIZE >= self.0.len() + rhs.0.len()
    }

    fn merge_right(&mut self, rhs: &Self) {
        self.0.push_str(&rhs.0)
    }

    fn merge_left(&mut self, left: &Self) {
        let ptr = self.0.as_mut_ptr();
        // Safety: `self.0` is a valid `ArrayString` and `left.0` is a valid `ArrayString`.
        unsafe {
            ptr.copy_to(ptr.add(left.0.len()), self.0.len());
            ptr.copy_from_nonoverlapping(left.0.as_ptr(), left.0.len());
            self.0.set_len(self.0.len() + left.0.len());
        }
    }
}

impl Sliceable for TextChunk {
    fn _slice(&self, range: std::ops::Range<usize>) -> Self {
        let mut new = ArrayString::new();
        new.push_str(&self.0.as_str()[range]);
        TextChunk(new)
    }

    fn split(&mut self, pos: usize) -> Self {
        let mut right = ArrayString::new();
        right.push_str(&self.0.as_str()[pos..]);
        self.0.truncate(pos);
        TextChunk(right)
    }
}

impl TryInsert for TextChunk {
    fn try_insert(&mut self, pos: usize, elem: Self) -> Result<(), Self>
    where
        Self: Sized,
    {
        match self.try_insert(pos, elem.0.as_str()) {
            Ok(_) => Ok(()),
            Err(_) => Err(elem),
        }
    }
}

impl DeltaValue for TextChunk {}