use std::sync::atomic::{AtomicU64, Ordering};

static NEXT_UID: AtomicU64 = AtomicU64::new(0);

/// Unique entity ID.
#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
pub struct Uid
{
    inner: u64,
}

impl Uid
{
    pub fn new(uid: u64) -> Self
    {
        debug_assert!(
            uid < NEXT_UID.load(Ordering::Relaxed),
            "Invalid entity UID {uid}"
        );

        Self { inner: uid }
    }

    pub fn new_unique() -> Self
    {
        Self {
            inner: NEXT_UID.fetch_add(1, Ordering::Relaxed),
        }
    }
}