use std::any::TypeId;
use std::fmt::Debug;
use std::hash::Hash;

use seq_macro::seq;

pub trait Event: Debug + 'static {}

/// The ID of a [`Event`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Id
{
    inner: TypeId,
}

impl Id
{
    /// Returns the id of a [`Event`];
    #[must_use]
    pub fn of<EventT: Event>() -> Self
    {
        Self { inner: TypeId::of::<EventT>() }
    }
}

pub trait Ids
{
    type Iter<'a>: Iterator<Item = &'a Id>
    where
        Self: 'a;

    fn iter(&self) -> Self::Iter<'_>;
}

/// A sequence of events.
pub trait Sequence
{
    type Ids: Ids;

    fn ids() -> Self::Ids;
}

macro_rules! impl_sequence {
    ($c: tt) => {
        seq!(I in 0..=$c {
            impl Ids for [Id; $c + 1]
            {
                type Iter<'a> = std::slice::Iter<'a, Id>;

                fn iter(&self) -> Self::Iter<'_> {
                    self.into_iter()
                }
            }

            impl<#(Event~I: Event,)*> Sequence for (#(Event~I,)*) {
                type Ids = [Id; $c + 1];

                fn ids() -> Self::Ids {
                    [#(
                        Id::of::<Event~I>(),
                    )*]
                }
            }
        });
    };
}

seq!(C in 0..=64 {
    impl_sequence!(C);
});