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use frappe::{Sink, Stream};
pub trait Inverse {
fn inverse(self) -> Self;
}
pub struct History<T: Inverse> {
events: Vec<T>,
events_inv: Vec<T>,
event_sink: Sink<T>
}
impl<T: Inverse> History<T> {
pub fn new() -> Self {
Self {
events: Vec::new(),
events_inv: Vec::new(),
event_sink: Sink::new()
}
}
pub fn len(&self) -> usize {
self.events.len()
}
pub fn len_redo(&self) -> usize {
self.events_inv.len()
}
pub fn events(&self) -> Stream<T> {
self.event_sink.stream()
}
pub fn record(&mut self, event: T) {
self.event_sink.send_ref(&event);
self.events.push(event);
}
pub fn undo(&mut self) -> bool {
if let Some(event) = self.events.pop() {
let event = event.inverse();
self.event_sink.send_ref(&event);
self.events_inv.push(event);
true
} else {
false
}
}
pub fn redo(&mut self) -> bool {
if let Some(event) = self.events_inv.pop() {
let event = event.inverse();
self.event_sink.send_ref(&event);
self.events.push(event);
true
} else {
false
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[derive(PartialEq, Clone, Debug)]
enum Event {
Forward,
Backward
}
impl Inverse for Event {
fn inverse(self) -> Self {
match &self {
&Event::Forward => Event::Backward,
&Event::Backward => Event::Forward
}
}
}
#[test]
fn main() {
let mut hist = History::new();
let last_event = hist.events().hold(Event::Forward);
assert!(!hist.undo());
assert!(!hist.redo());
hist.record(Event::Forward);
assert_eq!(Event::Forward, last_event.sample());
hist.record(Event::Backward);
assert_eq!(Event::Backward, last_event.sample());
assert!(hist.undo());
assert_eq!(Event::Forward, last_event.sample());
assert!(hist.undo());
assert_eq!(Event::Backward, last_event.sample());
assert!(!hist.undo());
assert!(hist.redo());
assert_eq!(Event::Forward, last_event.sample());
assert!(hist.redo());
assert_eq!(Event::Backward, last_event.sample());
assert!(!hist.redo());
}
}