use crate::{Buffer, Rope, Selection, Tendril}; // TODO: divided into three different operations, I sort of like having just // Splice { extent, Option, 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) { // // old_extent, new_extent, insert // } // } #[derive(Copy, Clone, PartialEq, Eq)] pub enum Assoc { Before, After, } // ChangeSpec = Change | ChangeSet | Vec #[derive(Debug)] pub struct ChangeSet { changes: Vec, /// 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 { 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 = 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(); } } } } /// `true` when the set is empty. #[inline] pub fn is_empty(&self) -> bool { let len = self.changes.len(); len == 0 || (len == 1 && self.changes[0] == Change::Retain(self.len)) } /// Map a position through the changes. /// /// `assoc` indicates which size to associate the position with. `Before` will keep the /// position close to the character before, and will place it before insertions over that /// range, or at that point. `After` will move it forward, placing it at the end of such /// insertions. pub fn map_pos(&self, pos: usize, assoc: Assoc) -> usize { use Change::*; let mut old_pos = 0; let mut new_pos = 0; let mut iter = self.changes.iter().peekable(); while let Some(change) = iter.next() { let len = match change { Delete(i) | Retain(i) => *i, Insert(_) => 0, }; let old_end = old_pos + len; match change { Retain(_len) => { if old_end > pos { return new_pos + (pos - old_pos); } new_pos += len; } Delete(_len) => { // a subsequent ins means a replace, consume it let ins = if let Some(Insert(s)) = iter.peek() { iter.next(); s.chars().count() } else { 0 }; // in range if old_end > pos { // at point or tracking before if pos == old_pos || assoc == Assoc::Before { return new_pos; } else { // place to end of delete return new_pos + ins; } } new_pos += ins; } Insert(s) => { let ins = s.chars().count(); // at insert point if old_pos == pos { // return position before inserted text if assoc == Assoc::Before { return new_pos; } else { // after text return new_pos + ins; } } new_pos += ins; } } old_pos = old_end; } if pos > old_pos { panic!( "Position {} is out of range for changeset len {}!", pos, old_pos ) } new_pos } } // 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, // effects, annotations // scroll_into_view } impl Transaction {} #[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); // TODO: assert } #[test] fn map_pos() { use Change::*; // maps inserts let cs = ChangeSet { changes: vec![Retain(4), Insert("!!".into()), Retain(4)], len: 8, }; assert_eq!(cs.map_pos(0, Assoc::Before), 0); // before insert region assert_eq!(cs.map_pos(4, Assoc::Before), 4); // at insert, track before assert_eq!(cs.map_pos(4, Assoc::After), 6); // at insert, track after assert_eq!(cs.map_pos(5, Assoc::Before), 7); // after insert region // maps deletes let cs = ChangeSet { changes: vec![Retain(4), Delete(4), Retain(4)], len: 12, }; assert_eq!(cs.map_pos(0, Assoc::Before), 0); // at start assert_eq!(cs.map_pos(4, Assoc::Before), 4); // before a delete assert_eq!(cs.map_pos(5, Assoc::Before), 4); // inside a delete assert_eq!(cs.map_pos(5, Assoc::After), 4); // inside a delete // TODO: delete tracking // stays inbetween replacements let cs = ChangeSet { changes: vec![ Delete(2), Insert("ab".into()), Delete(2), Insert("cd".into()), ], len: 4, }; assert_eq!(cs.map_pos(2, Assoc::Before), 2); assert_eq!(cs.map_pos(2, Assoc::After), 2); } }