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pub trait Undo {
type Undo;
fn undo(&self) -> Self::Undo;
}
pub struct History<T: Undo> {
events: Vec<T>,
len: usize
}
impl<T: Undo> History<T> {
pub fn new() -> Self {
Self {
events: Vec::new(),
len: 0
}
}
pub fn len(&self) -> usize {
self.len
}
pub fn undone(&self) -> usize {
self.events.len().saturating_sub(self.len)
}
pub fn record(&mut self, event: T) {
self.events.truncate(self.len);
self.events.push(event);
self.len = self.events.len();
}
pub fn undo(&mut self) -> Result<T::Undo, ()> {
if self.len > 0 {
self.len -= 1;
let undo = self.events[self.len].undo();
Ok(undo)
} else {
Err(())
}
}
}
impl<T: Undo + Clone> History<T> {
pub fn redo(&mut self) -> Result<T, ()> {
if self.len < self.events.len() {
let redo = self.events[self.len].clone();
self.len += 1;
Ok(redo)
} else {
Err(())
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[derive(PartialEq, Clone)]
enum Event {
Forward,
Backward
}
impl Undo for Event {
type Undo = Event;
fn undo(&self) -> Self::Undo {
match *self {
Event::Forward => Event::Backward,
Event::Backward => Event::Forward
}
}
}
#[test]
fn main() {
let mut hist = History::new();
assert!(hist.undo().is_err());
assert!(hist.redo().is_err());
assert_eq!(0, hist.len());
assert_eq!(0, hist.undone());
hist.record(Event::Forward);
assert_eq!(1, hist.len());
assert_eq!(0, hist.undone());
hist.record(Event::Backward);
assert_eq!(2, hist.len());
assert_eq!(0, hist.undone());
assert!(match hist.undo() {
Result::Ok(Event::Forward) => true,
_ => false
});
assert!(match hist.undo() {
Result::Ok(Event::Backward) => true,
_ => false
});
assert!(hist.undo().is_err());
assert!(match hist.redo() {
Result::Ok(Event::Forward) => true,
_ => false
});
assert!(match hist.redo() {
Result::Ok(Event::Backward) => true,
_ => false
});
assert!(hist.redo().is_err());
}
}