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#![forbid(unsafe_code)]

use core::fmt::{Debug, Display, Formatter};

pub enum OptionAB<A, B> {
    A(A),
    B(B),
}

impl<T> OptionAB<T, T> {
    pub fn take(self) -> T {
        match self {
            OptionAB::A(value) => value,
            OptionAB::B(value) => value,
        }
    }
}

impl<A, B> OptionAB<A, B> {
    pub fn as_ref(&self) -> OptionAB<&A, &B> {
        match self {
            OptionAB::A(value) => OptionAB::A(&value),
            OptionAB::B(value) => OptionAB::B(&value),
        }
    }
    pub fn a(&self) -> Option<&A> {
        match self {
            OptionAB::A(value) => Some(value),
            _ => None,
        }
    }
    pub fn b(&self) -> Option<&B> {
        match self {
            OptionAB::B(value) => Some(value),
            _ => None,
        }
    }
}

impl<A: Debug, B: Debug> OptionAB<A, B> {
    pub fn unwrap_a(self) -> A {
        match self {
            OptionAB::A(value) => value,
            _ => panic!("expected OptionAB::A(_) but found {:?}", self),
        }
    }
    pub fn unwrap_b(self) -> B {
        match self {
            OptionAB::B(value) => value,
            _ => panic!("expected OptionAB::B(_) but found {:?}", self),
        }
    }
}

impl<A: Clone, B: Clone> Clone for OptionAB<A, B> {
    fn clone(&self) -> Self {
        match self {
            OptionAB::A(value) => OptionAB::A(value.clone()),
            OptionAB::B(value) => OptionAB::B(value.clone()),
        }
    }
}

impl<A: Debug, B: Debug> Debug for OptionAB<A, B> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), std::fmt::Error> {
        match self {
            OptionAB::A(value) => write!(f, "OptionAB::A({:?})", value),
            OptionAB::B(value) => write!(f, "OptionAB::B({:?})", value),
        }
    }
}

impl<A: Display, B: Display> Display for OptionAB<A, B> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), std::fmt::Error> {
        match self {
            OptionAB::A(value) => write!(f, "{}", value),
            OptionAB::B(value) => write!(f, "{}", value),
        }
    }
}

impl<A: PartialEq, B: PartialEq> PartialEq for OptionAB<A, B> {
    fn eq(&self, other: &Self) -> bool {
        match (self, other) {
            (OptionAB::A(value), OptionAB::A(other)) if value == other => true,
            (OptionAB::B(value), OptionAB::B(other)) if value == other => true,
            _ => false,
        }
    }
}
impl<A: PartialEq, B: PartialEq> Eq for OptionAB<A, B> {}

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

    #[test]
    fn test() {
        let a: OptionAB<bool, u8> = OptionAB::A(true);
        let b: OptionAB<bool, u8> = OptionAB::B(42);
        // Test as_ref()
        let _: OptionAB<&bool, &u8> = a.as_ref();
        let _: &u8 = b.as_ref().unwrap_b();
        assert_eq!(true, *(a.as_ref().unwrap_a()));
        assert_eq!(42u8, *(b.as_ref().unwrap_b()));
        // Test accessors
        assert_eq!(true, *(a.a().unwrap()));
        assert_eq!(None, a.b());
        assert_eq!(None, b.a());
        assert_eq!(42u8, *(b.b().unwrap()));
        // Test Debug
        assert_eq!("OptionAB::A(true)", format!("{:?}", a));
        assert_eq!("OptionAB::B(42)", format!("{:?}", b));
        // Test Display
        assert_eq!("true", format!("{}", a));
        assert_eq!("42", format!("{}", b));
        // Test Eq
        assert_eq!(OptionAB::A(true), a);
        assert_ne!(OptionAB::A(false), a);
        assert_eq!(OptionAB::B(42u8), b);
        assert_ne!(OptionAB::B(2u8), b);
        assert_ne!(a, b);
        // Test unwrappers
        let a_clone = a.clone();
        assert_eq!(true, a_clone.unwrap_a());
        let a_clone = a.clone();
        assert_eq!(
            "expected OptionAB::B(_) but found OptionAB::A(true)",
            std::panic::catch_unwind(|| a_clone.unwrap_b())
                .unwrap_err()
                .downcast::<String>()
                .unwrap()
                .as_str()
        );

        let b_clone = b.clone();
        assert_eq!(
            "expected OptionAB::A(_) but found OptionAB::B(42)",
            std::panic::catch_unwind(|| b_clone.unwrap_a())
                .unwrap_err()
                .downcast::<String>()
                .unwrap()
                .as_str()
        );
        let b_clone = b.clone();
        assert_eq!(42u8, b_clone.unwrap_b());

        // Test take()
        let same_a: OptionAB<u8, u8> = OptionAB::A(42u8);
        let same_b: OptionAB<u8, u8> = OptionAB::B(42u8);
        assert_eq!(42u8, same_a.take());
        assert_eq!(42u8, same_b.take());
    }
}