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use std::ops::Deref;
use std::ops::DerefMut;
use std::fmt::{self, Debug};
#[cfg(any(feature = "serialize", feature="ecs"))]
use serde_derive::{Serialize, Deserialize};


/// A value cache that tracks changes in the value since the
/// last update
#[derive(Clone, Copy)]
#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
pub struct ValueCache<T>{
    has_changed: bool,
    value: T,
}

// pub enum ValueChanged<T>{
//     New(T),
//     Old(T)
// }

// impl<T> ValueChanged<T>{
//     pub fn map<F,U>(self, f: F) -> ValueChanged<U>
//     where F: Fn(T) -> U
//     {
//         match self{
//             ValueChanged::New(t) => ValueChanged::New(f(t)),
//             ValueChanged::Old(t) => ValueChanged::Old(f(t)),
//         }
//     }

//     pub fn as_ref(&self) -> ValueChanged<&T>{
//         match self{
//             ValueChanged::New(t) => ValueChanged::New(&t),
//             ValueChanged::Old(t) => ValueChanged::Old(&t),
//         }
//     }

//     pub fn is_new(&self) -> bool {
//         match self{
//             ValueChanged::New(_) => true,
//             ValueChanged::Old(_) => false,
//         }
//     }

//     pub fn is_old(&self) -> bool {
//         match self{
//             ValueChanged::New(_) => false,
//             ValueChanged::Old(_) => true,
//         }
//     }

//     pub fn value(&self) -> &T{
//         self.deref()
//     }

//     pub fn into_inner(self) -> T{
//         match self{
//             ValueChanged::New(t) | ValueChanged::Old(t) => t,
//         }
//     }
// }

// impl<T> Deref for ValueChanged<T>{
//     type Target = T;
//     #[inline]
//     fn deref(&self) -> &T{
//         match self{
//             ValueChanged::New(t) | ValueChanged::Old(t) => t,
//         }
//     }
// }

// impl<T> DerefMut for ValueChanged<T>{
//     #[inline]
//     fn deref_mut(&mut self) -> &mut T{
//         match self{
//             ValueChanged::New(t) | ValueChanged::Old(t) => t,
//         }
//     }
// }

impl<T: Default> Default for ValueCache<T>{
    fn default() -> ValueCache<T>{
        ValueCache{
            has_changed: true,
            value: T::default()
        }
    }
}

impl<T: Debug> Debug for ValueCache<T>{
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result{
        fmt.debug_struct("ValueCache")
            .field("has_changed", &self.has_changed)
            .field("value", &self.value)
            .finish()
    }
}

impl<T> ValueCache<T>{
    #[inline]
    pub fn new(t: T) -> ValueCache<T>{
        ValueCache{
            has_changed: true,
            value: t
        }
    }

    #[inline]
    pub fn set(&mut self, t: T){
        self.has_changed = true;
        self.value = t;
    }

    #[inline]
    pub fn as_ref(&self) -> &T{
        &self.value
    }

    #[inline]
    pub fn as_mut(&mut self) -> &mut T{
        self.has_changed = true;
        &mut self.value
    }

    #[inline]
    pub fn has_changed(&self) -> bool{
        self.has_changed
    }

    // #[inline]
    // pub fn as_changed(&self) -> ValueChanged<&T>{
    //     if self.has_changed {
    //         ValueChanged::New(&self.value)
    //     }else{
    //         ValueChanged::Old(&self.value)
    //     }
    // }

    #[inline]
    pub fn update(&mut self){
        self.has_changed = false;
    }
}

impl<T> Deref for ValueCache<T>{
    type Target = T;
    #[inline]
    fn deref(&self) -> &T{
        self.as_ref()
    }
}

impl<T> DerefMut for ValueCache<T>{
    #[inline]
    fn deref_mut(&mut self) -> &mut T{
        self.as_mut()
    }
}