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use core::fmt::Debug;
use std::fmt;

pub struct Setting<T> {
    val: T,
    cb: Box<dyn FnMut(&T, &T)>,
}

impl<T> Debug for Setting<T>
where
    T: Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{:?}", self.val)
    }
}

impl<T> Setting<T>
where
    T: Default + Clone,
{
    fn new(f: impl FnMut(&T, &T) + 'static) -> Self {
        Self {
            val: T::default(),
            cb: Box::new(f),
        }
    }
    pub fn cb(&mut self, f: impl FnMut(&T, &T) + 'static) {
        self.cb = Box::new(f);
    }
    pub fn set(&mut self, new_val: T) -> () {
        (self.cb)(&self.val, &new_val);
        self.val = new_val;
    }
    pub fn get(&self) -> T {
        self.val.clone()
    }
}

impl<T> Default for Setting<T>
where
    T: Default + Debug + Clone,
{
    fn default() -> Self {
        Self::new(|_, _| {})
    }
}

#[cfg(test)]
mod tests {
    use crate::Setting;
    use std::cell::{Cell, RefCell};

    #[derive(Default, Debug)]
    struct Settings {
        num: Setting<u16>,
        str: Setting<String>,
        cell: Setting<Cell<u16>>,
        refcell: Setting<RefCell<u8>>,
        vec: Setting<Vec<u8>>,
    }

    #[test]
    fn default_settings() {
        let settings = Settings::default();
        assert_eq!("", settings.str.get());
        assert_eq!(0, settings.num.get());
    }

    #[test]
    fn set_get_value_type() {
        let mut settings = Settings::default();
        settings.str.set("abc".to_string());
        assert_eq!("abc", settings.str.get());
        settings.num.set(8080);
        assert_eq!(8080, settings.num.get());
    }

    #[test]
    fn set_get_cell_type() {
        let mut settings = Settings::default();
        settings.cell.set(10.into());
        assert_eq!(settings.cell.get(), 10.into());
    }

    #[test]
    fn set_get_refcell_type() {
        let mut settings = Settings::default();
        settings.refcell.set(11.into());
        assert_eq!(settings.refcell.get(), 11.into());
    }

    #[test]
    fn set_get_vec_type() {
        let mut settings = Settings::default();
        let mut vec: Vec<u8> = settings.vec.get();
        vec.push(10);
        vec.push(20);
        settings.vec.set(vec); // Actual Vec modification happens here
        assert_eq!(settings.vec.get().get(0).unwrap().to_owned(), 10);
        assert_eq!(settings.vec.get().get(1).unwrap().to_owned(), 20);
    }
}