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helix/helix-core/src/transaction.rs

291 lines
9.7 KiB
Rust

// pub struct Change {
// from: usize,
// to: usize,
// insert: Option<String>,
// }
// 40 bytes (8 + 24 + 8) -> strings are really big 24 as String, 16 as &str
// pub struct Change {
// /// old extent
// old_extent: usize,
// /// inserted text, new extent equal to insert length
// insert: Option<String>,
// /// distance from the previous change
// distance: usize,
// }
use crate::{Buffer, Rope, Selection, Tendril};
// TODO: divided into three different operations, I sort of like having just
// Splice { extent, Option<text>, distance } better.
// insert: Splice { extent: 0, text: Some("a"), distance: 2 }
// delete: Splice { extent: 2, text: None, distance: 2 }
// replace: Splice { extent: 2, text: Some("abc"), distance: 2 }
// unchanged?: Splice { extent: 0, text: None, distance: 2 }
// harder to compose though.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Change {
/// Move cursor by n characters.
Retain(usize),
/// Delete n characters.
Delete(usize),
/// Insert text at position.
Insert(Tendril),
}
impl Change {
pub fn new(from: usize, to: usize, insert: Option<Tendril>) {
// old_extent, new_extent, insert
}
}
// ChangeSpec = Change | ChangeSet | Vec<Change>
// ChangeDesc as a ChangeSet without text: can't be applied, cheaper to store.
// ChangeSet = ChangeDesc with Text
#[derive(Debug)]
pub struct ChangeSet {
// basically Vec<ChangeDesc> where ChangeDesc = (current len, replacement len?)
// (0, n>0) for insertion, (n>0, 0) for deletion, (>0, >0) for replacement
// sections: Vec<(usize, isize)>,
changes: Vec<Change>,
/// The required document length. Will refuse to apply changes unless it matches.
len: usize,
}
impl ChangeSet {
#[must_use]
pub fn new(buf: &Buffer) -> Self {
let len = buf.contents.len_chars();
Self {
changes: vec![Change::Retain(len)],
len,
}
}
// TODO: from iter
/// Combine two changesets together.
/// In other words, If `this` goes `docA` → `docB` and `other` represents `docB` → `docC`, the
/// returned value will represent the change `docA` → `docC`.
pub fn compose(self, other: ChangeSet) -> Result<Self, ()> {
if self.len != other.len {
// length mismatch
return Err(());
}
let len = self.changes.len();
let mut changes_a = self.changes.into_iter();
let mut changes_b = other.changes.into_iter();
let mut head_a = changes_a.next();
let mut head_b = changes_b.next();
let mut changes: Vec<Change> = Vec::with_capacity(len); // TODO: max(a, b), shrink_to_fit() afterwards
loop {
use std::cmp::Ordering;
use Change::*;
match (head_a, head_b) {
// we are done
(None, None) => {
break;
}
// deletion in A
(Some(change @ Delete(..)), b) => {
changes.push(change);
head_a = changes_a.next();
head_b = b;
}
// insertion in B
(a, Some(change @ Insert(..))) => {
changes.push(change);
head_a = a;
head_b = changes_b.next();
}
(None, _) | (_, None) => return Err(()),
(Some(Retain(i)), Some(Retain(j))) => match i.cmp(&j) {
Ordering::Less => {
changes.push(Retain(i));
head_a = changes_a.next();
head_b = Some(Retain(j - i));
}
Ordering::Equal => {
changes.push(Retain(i));
head_a = changes_a.next();
head_b = changes_b.next();
}
Ordering::Greater => {
changes.push(Retain(j));
head_a = Some(Retain(i - j));
head_b = changes_b.next();
}
},
(Some(Insert(mut s)), Some(Delete(j))) => {
let len = s.chars().count();
match len.cmp(&j) {
Ordering::Less => {
head_a = changes_a.next();
head_b = Some(Delete(j - len));
}
Ordering::Equal => {
head_a = changes_a.next();
head_b = changes_b.next();
}
Ordering::Greater => {
// figure out the byte index of the truncated string end
let (pos, _) = s.char_indices().nth(len - j).unwrap();
// calculate the difference
let to_drop = s.len() - pos;
s.pop_back(to_drop as u32);
head_a = Some(Insert(s));
head_b = changes_b.next();
}
}
}
(Some(Insert(mut s)), Some(Retain(j))) => {
let len = s.chars().count();
match len.cmp(&j) {
Ordering::Less => {
changes.push(Insert(s));
head_a = changes_a.next();
head_b = Some(Retain(j - len));
}
Ordering::Equal => {
changes.push(Insert(s));
head_a = changes_a.next();
head_b = changes_b.next();
}
Ordering::Greater => {
// figure out the byte index of the truncated string end
let (pos, _) = s.char_indices().nth(j).unwrap();
// calculate the difference
let to_drop = s.len() - pos;
s.pop_back(to_drop as u32);
head_a = Some(Insert(s));
head_b = changes_b.next();
}
}
}
(Some(Retain(i)), Some(Delete(j))) => match i.cmp(&j) {
Ordering::Less => {
changes.push(Delete(i));
head_a = changes_a.next();
head_b = Some(Delete(j - i));
}
Ordering::Equal => {
changes.push(Delete(j));
head_a = changes_a.next();
head_b = changes_b.next();
}
Ordering::Greater => {
changes.push(Delete(j));
head_a = Some(Retain(i - j));
head_b = changes_b.next();
}
},
};
}
Ok(Self {
len: self.len,
changes,
})
}
/// Given another change set starting in the same document, maps this
/// change set over the other, producing a new change set that can be
/// applied to the document produced by applying `other`. When
/// `before` is `true`, order changes as if `this` comes before
/// `other`, otherwise (the default) treat `other` as coming first.
///
/// Given two changes `A` and `B`, `A.compose(B.map(A))` and
/// `B.compose(A.map(B, true))` will produce the same document. This
/// provides a basic form of [operational
/// transformation](https://en.wikipedia.org/wiki/Operational_transformation),
/// and can be used for collaborative editing.
pub fn map(self, other: Self) -> Self {
unimplemented!()
}
/// Returns a new changeset that reverts this one. Useful for `undo` implementation.
pub fn invert(self) -> Self {
unimplemented!()
}
pub fn apply(&self, text: &mut Rope) {
// TODO: validate text.chars() == self.len
let mut pos = 0;
for change in &self.changes {
use Change::*;
match change {
Retain(n) => {
pos += n;
}
Delete(n) => {
text.remove(pos..pos + *n);
// pos += n;
}
Insert(s) => {
text.insert(pos, s);
pos += s.len();
}
}
}
}
// iter over changes
}
// trait Transaction
// trait StrictTransaction
/// Transaction represents a single undoable unit of changes. Several changes can be grouped into
/// a single transaction.
pub struct Transaction {
/// Changes made to the buffer.
changes: ChangeSet,
/// When set, explicitly updates the selection.
selection: Option<Selection>,
// effects, annotations
// scroll_into_view
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn composition() {
use Change::*;
let a = ChangeSet {
changes: vec![
Retain(5),
Insert("!".into()),
Retain(1),
Delete(2),
Insert("ab".into()),
],
len: 7,
};
let b = ChangeSet {
changes: vec![Delete(5), Insert("world".into()), Retain(4)],
len: 7,
};
let mut text = Rope::from("hello xz");
// should probably return cloned text
a.compose(b).unwrap().apply(&mut text);
unimplemented!("{:?}", text);
}
#[test]
fn map() {}
}