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// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

use crate::alloc::{vec, vec::Vec};
use core::any::{type_name, TypeId};
use core::ptr::NonNull;
use core::{fmt, mem};

use crate::archetype::TypeInfo;
use crate::Component;

/// A dynamically typed collection of components
pub unsafe trait DynamicBundle {
    /// Returns a `TypeId` uniquely identifying the set of components, if known
    #[doc(hidden)]
    fn key(&self) -> Option<TypeId> {
        None
    }

    /// Invoke a callback on the fields' type IDs, sorted by descending alignment then id
    #[doc(hidden)]
    fn with_ids<T>(&self, f: impl FnOnce(&[TypeId]) -> T) -> T;

    /// Obtain the fields' TypeInfos, sorted by descending alignment then id
    #[doc(hidden)]
    fn type_info(&self) -> Vec<TypeInfo>;
    /// Allow a callback to move all components out of the bundle
    ///
    /// Must invoke `f` only with a valid pointer and the pointee's type and size. `put` may only be
    /// called at most once on any given value.
    #[doc(hidden)]
    unsafe fn put(self, f: impl FnMut(*mut u8, TypeInfo));
}

/// A statically typed collection of components
pub unsafe trait Bundle: DynamicBundle {
    #[doc(hidden)]
    fn with_static_ids<T>(f: impl FnOnce(&[TypeId]) -> T) -> T;

    /// Obtain the fields' TypeInfos, sorted by descending alignment then id
    #[doc(hidden)]
    fn static_type_info() -> Vec<TypeInfo>;

    /// Construct `Self` by moving components out of pointers fetched by `f`
    ///
    /// # Safety
    ///
    /// `f` must produce pointers to the expected fields. The implementation must not read from any
    /// pointers if any call to `f` returns `None`.
    #[doc(hidden)]
    unsafe fn get(f: impl FnMut(TypeInfo) -> Option<NonNull<u8>>) -> Result<Self, MissingComponent>
    where
        Self: Sized;
}

/// Error indicating that an entity did not have a required component
#[derive(Debug, Clone, Eq, PartialEq, Hash)]
pub struct MissingComponent(&'static str);

impl MissingComponent {
    /// Construct an error representing a missing `T`
    pub fn new<T: Component>() -> Self {
        Self(type_name::<T>())
    }
}

impl fmt::Display for MissingComponent {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "missing {} component", self.0)
    }
}

#[cfg(feature = "std")]
impl std::error::Error for MissingComponent {}

macro_rules! tuple_impl {
    ($($name: ident),*) => {
        unsafe impl<$($name: Component),*> DynamicBundle for ($($name,)*) {
            fn key(&self) -> Option<TypeId> {
                Some(TypeId::of::<Self>())
            }

            fn with_ids<T>(&self, f: impl FnOnce(&[TypeId]) -> T) -> T {
                Self::with_static_ids(f)
            }

            fn type_info(&self) -> Vec<TypeInfo> {
                Self::static_type_info()
            }

            #[allow(unused_variables, unused_mut)]
            unsafe fn put(self, mut f: impl FnMut(*mut u8, TypeInfo)) {
                #[allow(non_snake_case)]
                let ($(mut $name,)*) = self;
                $(
                    f(
                        (&mut $name as *mut $name).cast::<u8>(),
                        TypeInfo::of::<$name>()
                    );
                    mem::forget($name);
                )*
            }
        }

        unsafe impl<$($name: Component),*> Bundle for ($($name,)*) {
            fn with_static_ids<T>(f: impl FnOnce(&[TypeId]) -> T) -> T {
                const N: usize = count!($($name),*);
                let mut xs: [(usize, TypeId); N] = [$((mem::align_of::<$name>(), TypeId::of::<$name>())),*];
                xs.sort_unstable_by(|x, y| x.0.cmp(&y.0).reverse().then(x.1.cmp(&y.1)));
                let mut ids = [TypeId::of::<()>(); N];
                for (slot, &(_, id)) in ids.iter_mut().zip(xs.iter()) {
                    *slot = id;
                }
                f(&ids)
            }

            fn static_type_info() -> Vec<TypeInfo> {
                let mut xs = vec![$(TypeInfo::of::<$name>()),*];
                xs.sort_unstable();
                xs
            }

            #[allow(unused_variables, unused_mut)]
            unsafe fn get(mut f: impl FnMut(TypeInfo) -> Option<NonNull<u8>>) -> Result<Self, MissingComponent> {
                #[allow(non_snake_case)]
                let ($(mut $name,)*) = ($(
                    f(TypeInfo::of::<$name>()).ok_or_else(MissingComponent::new::<$name>)?
                        .as_ptr()
                        .cast::<$name>(),)*
                );
                Ok(($($name.read(),)*))
            }
        }
    }
}

macro_rules! count {
    () => { 0 };
    ($x: ident $(, $rest: ident)*) => { 1 + count!($($rest),*) };
}

smaller_tuples_too!(tuple_impl, O, N, M, L, K, J, I, H, G, F, E, D, C, B, A);