lyra-engine/lyra-game/src/change_tracker.rs

use std::ops::{DerefMut, Deref};

/// A change tracker. This tracks changes of the data it owns.
/// Tracking changes can cause false positives since it actually tracks calls to `deref_mut()`
/// If you mutably dereference this, make sure its only when you change the data.
pub struct Ct<T> {
    data: T,
    changed: bool,
}

impl<T> Ct<T> {
    pub fn new(data: T) -> Self {
        Self {
            data,
            changed: false,
        }
    }

    /// Create a new change tracker with data
    pub fn new_true(data: T) -> Self {
        Self {
            data,
            changed: true,
        }
    }

    /// Returns true if there was a change. Will reset back to false after this is called.
    pub fn changed(&mut self) -> bool {
        let before = self.changed;
        self.reset();
        before
    }

    /// Returns true if there was a change, will NOT reset back to false.
    pub fn peek_changed(&self) -> bool {
        self.changed
    }

    /// Resets the changed tracker to be false
    pub fn reset(&mut self) {
        self.changed = false;
    }
    
    /// Triggers the change tracker to be true
    pub fn trigger(&mut self) {
        self.changed = true;
    }

    /// Silently mutate the inner data, this wont be tracked
    pub fn silently_mutate(&mut self) -> &mut T {
        &mut self.data
    }

    /// Consumes self and returns the data stored inside.
    pub fn take(self) -> T {
        self.data
    }
}

impl<T> Deref for Ct<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.data
    }
}

impl<T> DerefMut for Ct<T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        self.changed = true;
        &mut self.data
    }
}

#[cfg(test)]
mod tests {
    use super::Ct;

    #[test]
    fn new() {
        let mut c = Ct::new(100);
        assert!(!c.changed());

        let mut c = Ct::new_true(100);
        assert!(c.changed());
        assert!(!c.changed()); // it should've reset itself
    }

    #[test]
    fn change_tracking() {
        let mut c = Ct::new(100);
        assert!(!c.changed());

        *c = 10;
        assert!(c.changed());
        assert!(!c.changed()); // should now be not changed
    }

    #[test]
    fn silent_mutate() {
        let mut c = Ct::new(100);
        let a = c.silently_mutate();
        *a = 10;
        assert!(!c.changed());
    }

    #[test]
    fn reset_trigger() {
        let mut c = Ct::new(100);
        *c = 10;
        c.reset();
        assert!(!c.changed()); // should not be changed because of reset

        let mut c = Ct::new(100);
        c.trigger();
        assert!(c.changed()); // should changed because of trigger
        assert!(!c.changed()); // should've reset itself
    }
}