use std::{
    fmt::{self, Debug},
    hash::Hash,
    marker::PhantomData,
};

pub trait IdKind: Debug + Copy + Clone + Hash + PartialEq + Eq + Default {
    fn tag() -> &'static str;
}

/// A generalized abstract identifier type of up to 2^32-1 entries.
#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, Default)]
pub struct Id<T>
where T: IdKind
{
    idx: u32,
    t: PhantomData<T>,
}

impl<T> Id<T>
where T: IdKind
{
    fn new(n: u32) -> Self {
        Self { idx: n, t: PhantomData }
    }

    #[allow(dead_code)]
    pub fn as_u32(&self) -> u32 {
        self.idx
    }
}

impl<T> fmt::Display for Id<T>
where T: IdKind
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}:{}", self.idx, T::tag())
    }
}

pub struct IdStore<T>
where T: IdKind
{
    last_idx: u32,
    t: PhantomData<T>,
}

impl<T> IdStore<T>
where T: IdKind
{
    pub fn new() -> Self {
        Self { last_idx: 0, t: PhantomData }
    }

    pub fn fresh(&mut self) -> Id<T> {
        let idx = self.last_idx;
        self.last_idx += 1;
        Id::new(idx)
    }
}

macro_rules! define_id_kind {
    ($name:ident) => {
        #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, Default)]
        pub struct $name;
        impl crate::identifier::IdKind for $name {
            fn tag() -> &'static str {
                stringify!($name)
            }
        }
    };
}

pub(crate) use define_id_kind;