mirror of https://github.com/helix-editor/helix
OT: changeset: Implement compose and apply.
Blaž Hrastnik
5 years ago
parent
44ff4d3c1f
commit
23109f1512
@ -1,25 +1,293 @@
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pub struct Change {
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from: usize,
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to: usize,
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insert: Option<String>,
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// pub struct Change {
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// from: usize,
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// to: usize,
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// insert: Option<String>,
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// }
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// 40 bytes (8 + 24 + 8) -> strings are really big 24 as String, 16 as &str
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// pub struct Change {
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// /// old extent
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// old_extent: usize,
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// /// inserted text, new extent equal to insert length
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// insert: Option<String>,
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// /// distance from the previous change
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// distance: usize,
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// }
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use crate::{Buffer, Selection};
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use ropey::Rope;
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use tendril::StrTendril as Tendril;
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// TODO: divided into three different operations, I sort of like having just
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// Splice { extent, Option<text>, distance } better.
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// insert: Splice { extent: 0, text: Some("a"), distance: 2 }
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// delete: Splice { extent: 2, text: None, distance: 2 }
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// replace: Splice { extent: 2, text: Some("abc"), distance: 2 }
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// unchanged?: Splice { extent: 0, text: None, distance: 2 }
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// harder to compose though.
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#[derive(Debug, Clone, PartialEq, Eq)]
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pub enum Change {
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/// Move cursor by n characters.
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Retain(usize),
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/// Delete n characters.
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Delete(usize),
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/// Insert text at position.
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Insert(Tendril),
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}
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impl Change {
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pub fn new(from: usize, to: usize, insert: Option<String>) {
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pub fn new(from: usize, to: usize, insert: Option<Tendril>) {
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// old_extent, new_extent, insert
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}
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}
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pub struct Transaction {}
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// ChangeSpec = Change | ChangeSet | Vec<Change>
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// ChangeDesc as a ChangeSet without text: can't be applied, cheaper to store.
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// ChangeSet = ChangeDesc with Text
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#[derive(Debug)]
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pub struct ChangeSet {
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// basically Vec<ChangeDesc> where ChangeDesc = (current len, replacement len?)
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// (0, n>0) for insertion, (n>0, 0) for deletion, (>0, >0) for replacement
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sections: Vec<(usize, isize)>,
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// sections: Vec<(usize, isize)>,
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changes: Vec<Change>,
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/// The required document length. Will refuse to apply changes unless it matches.
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len: usize,
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}
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impl ChangeSet {
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pub fn new(buf: &Buffer) -> Self {
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let len = buf.contents.len_chars();
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Self {
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changes: vec![Change::Retain(len)],
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len,
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}
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}
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// TODO: from iter
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/// Combine two changesets together.
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/// In other words, If `this` goes `docA` → `docB` and `other` represents `docB` → `docC`, the
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/// returned value will represent the change `docA` → `docC`.
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pub fn compose(self, other: ChangeSet) -> Result<Self, ()> {
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if self.len != other.len {
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// length mismatch
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return Err(());
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}
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let len = self.changes.len();
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let mut changes_a = self.changes.into_iter();
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let mut changes_b = other.changes.into_iter();
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let mut head_a = changes_a.next();
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let mut head_b = changes_b.next();
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let mut changes: Vec<Change> = Vec::with_capacity(len); // TODO: max(a, b), shrink_to_fit() afterwards
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loop {
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use std::cmp::Ordering;
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use Change::*;
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match (head_a, head_b) {
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// we are done
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(None, None) => {
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break;
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}
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// deletion in A
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(Some(change @ Delete(..)), b) => {
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changes.push(change);
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head_a = changes_a.next();
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head_b = b;
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}
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// insertion in B
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(a, Some(change @ Insert(..))) => {
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changes.push(change);
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head_a = a;
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head_b = changes_b.next();
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}
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(None, _) => return Err(()),
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(_, None) => return Err(()),
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(Some(Retain(i)), Some(Retain(j))) => match i.cmp(&j) {
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Ordering::Less => {
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changes.push(Retain(i));
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head_a = changes_a.next();
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head_b = Some(Retain(j - i));
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}
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Ordering::Equal => {
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changes.push(Retain(i));
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head_a = changes_a.next();
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head_b = changes_b.next();
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}
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Ordering::Greater => {
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changes.push(Retain(j));
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head_a = Some(Retain(i - j));
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head_b = changes_b.next();
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}
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},
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(Some(Insert(mut s)), Some(Delete(j))) => {
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let len = s.chars().count();
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match len.cmp(&j) {
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Ordering::Less => {
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head_a = changes_a.next();
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head_b = Some(Delete(j - len));
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}
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Ordering::Equal => {
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head_a = changes_a.next();
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head_b = changes_b.next();
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}
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Ordering::Greater => {
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// figure out the byte index of the truncated string end
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let (pos, _) = s.char_indices().nth(len - j).unwrap();
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// calculate the difference
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let to_drop = s.len() - pos;
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s.pop_back(to_drop as u32);
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head_a = Some(Insert(s));
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head_b = changes_b.next();
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}
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}
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}
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(Some(Insert(mut s)), Some(Retain(j))) => {
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let len = s.chars().count();
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match len.cmp(&j) {
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Ordering::Less => {
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changes.push(Insert(s));
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head_a = changes_a.next();
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head_b = Some(Retain(j - len));
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}
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Ordering::Equal => {
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changes.push(Insert(s));
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head_a = changes_a.next();
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head_b = changes_b.next();
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}
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Ordering::Greater => {
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// figure out the byte index of the truncated string end
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let (pos, _) = s.char_indices().nth(j).unwrap();
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// calculate the difference
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let to_drop = s.len() - pos;
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s.pop_back(to_drop as u32);
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head_a = Some(Insert(s));
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head_b = changes_b.next();
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}
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}
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}
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(Some(Retain(i)), Some(Delete(j))) => match i.cmp(&j) {
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Ordering::Less => {
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changes.push(Delete(i));
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head_a = changes_a.next();
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head_b = Some(Delete(j - i));
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}
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Ordering::Equal => {
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changes.push(Delete(j));
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head_a = changes_a.next();
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head_b = changes_b.next();
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}
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Ordering::Greater => {
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changes.push(Delete(j));
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head_a = Some(Retain(i - j));
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head_b = changes_b.next();
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}
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},
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};
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}
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Ok(Self {
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len: self.len,
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changes,
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})
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}
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/// Given another change set starting in the same document, maps this
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/// change set over the other, producing a new change set that can be
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/// applied to the document produced by applying `other`. When
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/// `before` is `true`, order changes as if `this` comes before
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/// `other`, otherwise (the default) treat `other` as coming first.
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///
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/// Given two changes `A` and `B`, `A.compose(B.map(A))` and
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/// `B.compose(A.map(B, true))` will produce the same document. This
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/// provides a basic form of [operational
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/// transformation](https://en.wikipedia.org/wiki/Operational_transformation),
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/// and can be used for collaborative editing.
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pub fn map(self, other: Self) -> Self {
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unimplemented!()
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}
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/// Returns a new changeset that reverts this one. Useful for `undo` implementation.
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pub fn invert(self) -> Self {
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unimplemented!()
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}
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pub fn apply(&self, text: &mut Rope) {
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// TODO: validate text.chars() == self.len
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let mut pos = 0;
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for change in self.changes.iter() {
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use Change::*;
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match change {
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Retain(n) => {
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pos += n;
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}
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Delete(n) => {
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text.remove(pos..pos + *n);
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// pos += n;
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}
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Insert(s) => {
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text.insert(pos, s);
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pos += s.len();
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}
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}
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}
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}
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// iter over changes
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}
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//
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// trait Transaction
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// trait StrictTransaction
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/// Transaction represents a single undoable unit of changes. Several changes can be grouped into
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/// a single transaction.
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pub struct Transaction {
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/// Changes made to the buffer.
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changes: ChangeSet,
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/// When set, explicitly updates the selection.
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selection: Option<Selection>,
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// effects, annotations
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// scroll_into_view
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}
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#[cfg(test)]
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mod test {
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use super::*;
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#[test]
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fn composition() {
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use Change::*;
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let a = ChangeSet {
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changes: vec![
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Retain(5),
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Insert("!".into()),
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Retain(1),
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Delete(2),
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Insert("ab".into()),
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],
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len: 7,
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};
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let b = ChangeSet {
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changes: vec![Delete(5), Insert("world".into()), Retain(4)],
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len: 7,
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};
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let mut text = Rope::from("hello xz");
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// should probably return cloned text
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a.compose(b).unwrap().apply(&mut text);
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unimplemented!("{:?}", text);
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}
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#[test]
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fn map() {}
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}
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