flecs_ecs 0.2.2

#![doc(hidden)]
// Implementation for lifecycle actions.
//
// Considerations on implementation for user experience vs performance.:
//
// 1. Unlike C++, Rust doesn't support compile-time checks for trivial types.
// 2. Current implementation prioritizes simplicity over performance optimizations.
//    - If trivial type registration incurs a significant performance penalty, reconsider this approach.
//
// Challenges:
// - Rust lacks several features for this scenario:
//   a) Trait specialization.
//   b) Compile-time trivial type checks.
//   c) A direct equivalent of `placement_new` from C++.
//      `ptr::write` still constructs the object on the stack and then moves it, barring optimizations.
//
// Potential Solutions:
// - Bypass the need for `placement_new` with a `placement_ctor` function.
//   - Drawback: Each field needs manual setting, which impacts user experience.
//      - example code:
//      ```
//           struct MyType {
//               vec: Vec<i32>,
//           }
//
//           trait PlacementNew {
//               unsafe fn placement_new(ptr: *mut Self);
//           }
//
//           impl PlacementNew for MyType {
//               unsafe fn placement_new(ptr: *mut Self) {
//                   (*ptr).vec = Vec::<i32>::default();
//               }
//           }
//      ```
// - For potential type optimizations, consider:
//   a) Utilizing the `Zeroable` trait and rely on user's proper implementation.
//   b) Implement pseudo-trait specialization, as detailed in:
//      - <http://lukaskalbertodt.github.io/2019/12/05/generalized-autoref-based-specialization.html/>
//      - <https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1e548abff8e35b97b25adcacdddaacda/>
//
// possible helpful crates for trait specialization / type specialization:
// - For type casting: <https://crates.io/crates/castaway/>
//
// Note: C does the same, where the user needs to opt in for non trivial types. We can do the same.
// Note2: zerobit pattern

use core::{ffi::c_void, mem::MaybeUninit, ptr};

use crate::core::*;
use crate::sys;

#[cfg(feature = "std")]
extern crate std;

extern crate alloc;
use alloc::boxed::Box;
use flecs_ecs_derive::extern_abi;

#[expect(dead_code, reason = "possibly used in the future")]
#[derive(Default)]
pub(crate) struct RegistersPanicHooks {
    pub(crate) ctor: bool,
    pub(crate) copy: bool,
}

#[expect(dead_code, reason = "possibly used in the future")]
#[extern_abi]
pub(crate) unsafe fn register_panic_hooks_free_ctx(ctx: *mut c_void) {
    let _box = unsafe { Box::from_raw(ctx as *mut RegistersPanicHooks) };
}

pub fn register_lifecycle_actions<T>(type_hooks: &mut sys::ecs_type_hooks_t) {
    //type_hooks.ctor = Some(ctor::<T>);
    type_hooks.dtor = Some(dtor::<T>);
    type_hooks.move_dtor = Some(move_dtor::<T>); //same implementation as ctor_move_dtor

    //type_hooks.move_ctor = Some(move_ctor::<T>);
    type_hooks.ctor_move_dtor = Some(ctor_move_dtor::<T>);

    //TODO we could potentially add an autoamtic check if the type is unmoveable to add
    //a sparse component tag
}

pub fn register_ctor_lifecycle_actions<T: Default>(type_hooks: &mut sys::ecs_type_hooks_t) {
    type_hooks.ctor = Some(ctor::<T>);
    // if let Some(_) = type_hooks.move_dtor {
    //     type_hooks.move_dtor = Some(move_dtor_impls_default::<T>); //same implementation as move_dtor
    // }
}

pub fn register_ctor_panic_lifecycle_actions<T>(type_hooks: &mut sys::ecs_type_hooks_t) {
    type_hooks.ctor = Some(panic_ctor::<T>);
}

pub fn register_copy_lifecycle_action<T: Clone>(type_hooks: &mut sys::ecs_type_hooks_t) {
    type_hooks.copy = Some(copy::<T>);
    type_hooks.copy_ctor = Some(copy_ctor::<T>); //same implementation as copy
}

pub fn register_copy_panic_lifecycle_action<T>(type_hooks: &mut sys::ecs_type_hooks_t) {
    type_hooks.copy = Some(panic_copy::<T>);
    type_hooks.copy_ctor = Some(panic_copy::<T>); //same implementation as copy
}

pub fn register_partial_ord_lifecycle_action<T: core::cmp::PartialOrd>(
    type_hooks: &mut sys::ecs_type_hooks_t,
) {
    type_hooks.cmp = Some(compare::<T>);
}

pub fn register_partial_ord_panic_lifecycle_action<T>(type_hooks: &mut sys::ecs_type_hooks_t) {
    type_hooks.cmp = Some(panic_compare::<T>);
}

pub fn register_partial_eq_lifecycle_action<T: core::cmp::PartialEq>(
    type_hooks: &mut sys::ecs_type_hooks_t,
) {
    type_hooks.equals = Some(equals::<T>);
}

pub fn register_partial_eq_panic_lifecycle_action<T>(type_hooks: &mut sys::ecs_type_hooks_t) {
    type_hooks.equals = Some(panic_equals::<T>);
}

/// Initialize the memory with the default constructor.
///
/// # Arguments
///
/// * `ptr` - pointer to the memory to be initialized
/// * `count` - number of elements to be initialized
/// * `_type_info` - type info for the type to be initialized
#[extern_abi]
fn ctor<T: Default>(ptr: *mut c_void, count: i32, _type_info: *const sys::ecs_type_info_t) {
    // tags and types with size 0 don't need to be initialized
    let size = const { core::mem::size_of::<T>() };
    if size == 0 {
        return;
    }

    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );

    let arr = ptr as *mut MaybeUninit<T>;
    for i in 0..count as usize {
        unsafe {
            // Default construct the value in place
            MaybeUninit::write(&mut *arr.add(i), T::default());
        }
    }
}

/// Runs the destructor for the type.
///
/// # Arguments
///
/// * `ptr` - pointer to the memory to be destructed
/// * `count` - number of elements to be destructed
/// * `_type_info` - type info for the type to be destructed
#[extern_abi]
fn dtor<T>(ptr: *mut c_void, count: i32, _type_info: *const sys::ecs_type_info_t) {
    let size = const { core::mem::size_of::<T>() };
    if size == 0 {
        let arr = ptr as *mut u8; // tags with drop are (usually) modules with size 1 and alignment 1 
        for i in 0..count as isize {
            unsafe {
                let item = arr.offset(i);
                ptr::drop_in_place(item as *mut T);
            }
        }
    } else {
        ecs_assert!(
            check_type_info::<T>(_type_info),
            FlecsErrorCode::InternalError
        );

        let arr = ptr as *mut T;
        for i in 0..count as isize {
            unsafe {
                let item = arr.offset(i);
                ptr::drop_in_place(item);
            }
        }
    }
}

/// This is the generic copy for trivial types
/// It will copy the memory
#[extern_abi]
fn copy<T: Clone>(
    dst_ptr: *mut c_void,
    src_ptr: *const c_void,
    count: i32,
    _type_info: *const sys::ecs_type_info_t,
) {
    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );
    let dst_arr = dst_ptr as *mut T;
    let src_arr = src_ptr as *const T;
    for i in 0..count as isize {
        //this is safe because C manages the memory and we're cloning the internal data
        unsafe {
            let src_value = &*(src_arr.offset(i)); //get value of src
            let dst_value = dst_arr.offset(i); // get ptr to dest
            core::ptr::drop_in_place(dst_value); //calls destructor
            core::ptr::write(dst_value, src_value.clone()); //overwrite the memory of dest with new value
        }
    }
}

/// This is the generic copy for trivial types
/// It will copy the memory
#[extern_abi]
fn copy_ctor<T: Clone>(
    dst_ptr: *mut c_void,
    src_ptr: *const c_void,
    count: i32,
    _type_info: *const sys::ecs_type_info_t,
) {
    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );
    let dst_arr = dst_ptr as *mut T;
    let src_arr = src_ptr as *const T;
    for i in 0..count as isize {
        //this is safe because C manages the memory and we're cloning the internal data
        unsafe {
            let src_value = &*(src_arr.offset(i)); //get value of src
            let dst_value = dst_arr.offset(i); // get ptr to dest
            core::ptr::write(dst_value, src_value.clone()); //overwrite the memory of dest with new value
        }
    }
}

#[extern_abi]
fn panic_ctor<T>(_dst_ptr: *mut c_void, _count: i32, _type_info: *const sys::ecs_type_info_t) {
    panic!(
        "Default is not implemented for type {} which requires drop and it's being used in an operation which calls the constructor",
        core::any::type_name::<T>()
    );
}

#[extern_abi]
fn panic_copy<T>(
    _dst_ptr: *mut c_void,
    _src_ptr: *const c_void,
    _count: i32,
    _type_info: *const sys::ecs_type_info_t,
) {
    panic!(
        "Clone is not implemented for type {} and it's being used in a copy / duplicate operation such as component overriding or duplicating entities / components or prefab copying",
        core::any::type_name::<T>()
    );
}

/// This is the generic move for non-trivial types
/// It will move the memory
#[extern_abi]
fn move_dtor<T>(
    dst_ptr: *mut c_void,
    src_ptr: *mut c_void,
    count: i32,
    _type_info: *const sys::ecs_type_info_t,
) {
    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );
    let dst_arr = dst_ptr as *mut T;
    let src_arr = src_ptr as *mut T;
    for i in 0..count as isize {
        //this is safe because C manages the memory and we are just moving the internal data around
        unsafe {
            let src_value = src_arr.offset(i); //get value of src
            let dst_value = dst_arr.offset(i); // get ptr to dest

            //memcpy the bytes of src to dest
            //src value and dest value point to the same thing
            core::ptr::copy_nonoverlapping(src_value, dst_value, 1);
        }
    }
}

/// This is the generic move for non-trivial types
/// It will move the memory
#[extern_abi]
fn move_dtor_impls_default<T: Default>(
    dst_ptr: *mut c_void,
    src_ptr: *mut c_void,
    count: i32,
    _type_info: *const sys::ecs_type_info_t,
) {
    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );
    let dst_arr = dst_ptr as *mut T;
    let src_arr = src_ptr as *mut T;
    for i in 0..count as isize {
        //this is safe because C manages the memory and we are just moving the internal data around
        unsafe {
            let src_value = src_arr.offset(i); //get value of src
            let dst_value = dst_arr.offset(i); // get ptr to dest

            core::ptr::drop_in_place(dst_value); //calls destructor on dest

            //memcpy the bytes of src to dest
            //src value and dest value point to the same thing
            core::ptr::copy_nonoverlapping(src_value, dst_value, 1);
        }
    }
}

/// a move to from src to dest where src will not be used anymore and dest is in control of the drop.
#[extern_abi]
fn move_ctor<T>(
    dst_ptr: *mut c_void,
    src_ptr: *mut c_void,
    count: i32,
    _type_info: *const sys::ecs_type_info_t,
) {
    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );
    let dst_arr = dst_ptr as *mut T;
    let src_arr = src_ptr as *mut T;
    for i in 0..count as isize {
        //this is safe because src will not get dropped and dst will get dropped
        unsafe {
            // memcpy the bytes from src to dst
            core::ptr::copy_nonoverlapping(src_arr.offset(i), dst_arr.offset(i), 1);
        }
    }
}

#[extern_abi]
fn ctor_move_dtor<T>(
    dst_ptr: *mut c_void,
    src_ptr: *mut c_void,
    count: i32,
    _type_info: *const sys::ecs_type_info_t,
) {
    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );
    let dst_arr = dst_ptr as *mut T;
    let src_arr = src_ptr as *mut T;
    for i in 0..count as isize {
        //this is safe because src will not get dropped and dst will get dropped
        unsafe {
            // memcpy the bytes from src to dst
            core::ptr::copy_nonoverlapping(src_arr.offset(i), dst_arr.offset(i), 1);
        }
    }
}

#[extern_abi]
fn compare<T: core::cmp::PartialOrd>(
    a: *const c_void,
    b: *const c_void,
    _type_info: *const sys::ecs_type_info_t,
) -> i32 {
    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );
    let lhs = unsafe { &*(a as *const T) };
    let rhs = unsafe { &*(b as *const T) };

    if lhs == rhs {
        0
    } else if lhs < rhs {
        -1 //less
    } else {
        1 //greater
    }
}

#[extern_abi]
fn panic_compare<T>(
    _a: *const c_void,
    _b: *const c_void,
    _type_info: *const sys::ecs_type_info_t,
) -> i32 {
    panic!(
        "PartialOrd is not implemented for type {} and it's being used in a comparison operation",
        core::any::type_name::<T>()
    );
}

#[extern_abi]
fn equals<T: core::cmp::PartialEq>(
    a: *const c_void,
    b: *const c_void,
    _type_info: *const sys::ecs_type_info_t,
) -> bool {
    ecs_assert!(
        check_type_info::<T>(_type_info),
        FlecsErrorCode::InternalError
    );
    let lhs = unsafe { &*(a as *const T) };
    let rhs = unsafe { &*(b as *const T) };

    lhs == rhs
}

#[extern_abi]
fn panic_equals<T>(
    _a: *const c_void,
    _b: *const c_void,
    _type_info: *const sys::ecs_type_info_t,
) -> bool {
    panic!(
        "PartialEq is not implemented for type {} and it's being used in an equality operation",
        core::any::type_name::<T>()
    );
}

fn check_type_info<T>(_type_info: *const sys::ecs_type_info_t) -> bool {
    if !_type_info.is_null() {
        unsafe { (*_type_info).size == core::mem::size_of::<T>() as i32 }
    } else {
        true
    }
}