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//! Traits implementing raw function calls for cloning, dropping, and creating default values for
//! Rust types.

use std::{
    ffi::c_void,
    hash::{Hash, Hasher},
};

use bones_utils::fxhash::FxHasher;

use crate::Unsafe;

#[cfg(doc)]
use crate::SchemaData;

/// Trait implemented automatically for types that implement [`Clone`] and can be used to clone the
/// type through raw pointers.
pub trait RawClone {
    /// Write the default value of the type to the pointer.
    ///
    /// # Safety
    ///
    /// The `dst` pointer must be aligned, writable, and have the same layout that this function is
    /// assocated to, and the `src` pointer must be readable and point to a valid instance of the
    /// type that this function is associated with.
    unsafe fn raw_clone(src: *const c_void, dst: *mut c_void);

    /// Get a callback suitable for [`SchemaData`].
    fn raw_clone_cb(
    ) -> Unsafe<&'static (dyn Fn(*const c_void, *mut c_void) + Sync + Send + 'static)> {
        unsafe { Unsafe::new(Box::leak(Box::new(|a, b| Self::raw_clone(a, b)))) }
    }
}
impl<T: Clone> RawClone for T {
    unsafe fn raw_clone(src: *const c_void, dst: *mut c_void) {
        let t = &*(src as *const T);
        let t = t.clone();
        (dst as *mut T).write(t)
    }
}

/// Trait implemented automatically for types that implement [`Drop`] and can be used to drop the
/// type through a raw pointer.
pub trait RawDrop {
    /// Write the default value of the type to the pointer.
    ///
    /// # Safety
    ///
    /// The pointer must be aligned, writable, and have the same layout that this function is
    /// assocated to.
    unsafe fn raw_drop(ptr: *mut c_void);

    /// Get a callback suitable for [`SchemaData`].
    fn raw_drop_cb() -> Unsafe<&'static (dyn Fn(*mut c_void) + Sync + Send + 'static)> {
        unsafe { Unsafe::new(Box::leak(Box::new(|a| Self::raw_drop(a)))) }
    }
}
impl<T> RawDrop for T {
    unsafe fn raw_drop(ptr: *mut c_void) {
        if std::mem::needs_drop::<T>() {
            (ptr as *mut T).drop_in_place()
        }
    }
}

/// Trait implemented automatically for types that implement [`Hash`] and can be used compute a
/// [`u64`] hash for a type using a pointer to it.
pub trait RawHash {
    /// Get the hash of the type.
    ///
    /// # Safety
    ///
    /// The pointer must be aligned, readable, and be a pointer to the type that this Hash function
    /// was created for.
    unsafe fn raw_hash(ptr: *const c_void) -> u64;

    /// Get a callback suitable for [`SchemaData`].
    fn raw_hash_cb() -> Unsafe<&'static (dyn Fn(*const c_void) -> u64 + Sync + Send + 'static)> {
        unsafe { Unsafe::new(Box::leak(Box::new(|a| Self::raw_hash(a)))) }
    }
}
impl<T: Hash> RawHash for T {
    unsafe fn raw_hash(ptr: *const c_void) -> u64 {
        let this = unsafe { &*(ptr as *const Self) };
        let mut hasher = FxHasher::default();
        this.hash(&mut hasher);
        hasher.finish()
    }
}

/// Trait implemented automatically for types that implement [`Eq`] that can compare two values
/// through their pointers.
pub trait RawEq {
    /// Get the hash of the type.
    ///
    /// # Safety
    ///
    /// The pointer must be aligned, readable, and be a pointer to the type that this Hash function
    /// was created for.
    unsafe fn raw_eq(a: *const c_void, b: *const c_void) -> bool;

    /// Get a callback suitable for [`SchemaData`].
    fn raw_eq_cb(
    ) -> Unsafe<&'static (dyn Fn(*const c_void, *const c_void) -> bool + Sync + Send + 'static)>
    {
        unsafe { Unsafe::new(Box::leak(Box::new(|a, b| Self::raw_eq(a, b)))) }
    }
}
impl<T: Eq> RawEq for T {
    unsafe fn raw_eq(a: *const c_void, b: *const c_void) -> bool {
        let a = unsafe { &*(a as *const Self) };
        let b = unsafe { &*(b as *const Self) };
        a.eq(b)
    }
}

/// Trait implemented automatically for types that implement [`Default`] and can be used to write
/// the default value of the type to a pointer.
pub trait RawDefault {
    /// Write the default value of the type to the pointer.
    ///
    /// # Safety
    ///
    /// The pointer must be aligned, writable, and have the same layout that this function is
    /// assocated to.
    unsafe fn raw_default(dst: *mut c_void);

    /// Get a callback suitable for [`SchemaData`].
    fn raw_default_cb() -> Unsafe<&'static (dyn Fn(*mut c_void) + Sync + Send + 'static)> {
        unsafe { Unsafe::new(Box::leak(Box::new(|a| Self::raw_default(a)))) }
    }
}
impl<T: Default> RawDefault for T {
    unsafe fn raw_default(dst: *mut c_void) {
        let d = T::default();
        (dst as *mut T).write(d)
    }
}