use core::alloc::{Allocator, Layout};
use core::ops::{Deref, DerefMut};
use core::ptr::NonNull;

pub(crate) mod block_allocator;
pub(crate) mod bump_allocator;

use block_allocator::BlockAllocator;

use self::bump_allocator::StartEnd;

struct SendNonNull<T>(NonNull<T>);
unsafe impl<T> Send for SendNonNull<T> {}

impl<T> Clone for SendNonNull<T> {
    fn clone(&self) -> Self {
        SendNonNull(self.0)
    }
}
impl<T> Copy for SendNonNull<T> {}

impl<T> Deref for SendNonNull<T> {
    type Target = NonNull<T>;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl<T> DerefMut for SendNonNull<T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

const EWRAM_END: usize = 0x0204_0000;
const IWRAM_END: usize = 0x0300_8000;

#[global_allocator]
static GLOBAL_ALLOC: BlockAllocator = unsafe {
    BlockAllocator::new(StartEnd {
        start: data_end,
        end: || EWRAM_END,
    })
};

macro_rules! impl_zst_allocator {
    ($name_of_struct: ty, $name_of_static: ident) => {
        unsafe impl Allocator for $name_of_struct {
            fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, core::alloc::AllocError> {
                $name_of_static.allocate(layout)
            }

            unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
                $name_of_static.deallocate(ptr, layout)
            }
        }
    };
}

/// This is the allocator for the External Working Ram. This is currently
/// equivalent to the Global Allocator (where things are allocated if no allocator is provided). This implements the allocator trait, so
/// is meant to be used in specifying where certain structures should be
/// allocated.
///
/// ```rust,no_run
/// #![feature(allocator_api)]
/// # #![no_std]
/// # #![no_main]
/// # use agb::ExternalAllocator;
/// # extern crate alloc;
/// # use alloc::vec::Vec;
/// # fn foo(gba: &mut agb::Gba) {
/// let mut v = Vec::new_in(ExternalAllocator);
/// v.push("hello, world");
/// assert!(
///     (0x0200_0000..0x0204_0000).contains(&(v.as_ptr() as usize)),
///     "the address of the vector is inside ewram"
/// );
/// # }
/// ```
#[derive(Clone)]
pub struct ExternalAllocator;

impl_zst_allocator!(ExternalAllocator, GLOBAL_ALLOC);

/// This is the allocator for the Internal Working Ram. This implements the
/// allocator trait, so is meant to be used in specifying where certain
/// structures should be allocated.
///
/// ```rust,no_run
/// #![feature(allocator_api)]
/// # #![no_std]
/// # #![no_main]
/// # use agb::InternalAllocator;
/// # extern crate alloc;
/// # use alloc::vec::Vec;
/// # fn foo(gba: &mut agb::Gba) {
/// let mut v = Vec::new_in(InternalAllocator);
/// v.push("hello, world");
/// assert!(
///     (0x0300_0000..0x0300_8000).contains(&(v.as_ptr() as usize)),
///     "the address of the vector is inside iwram"
/// );
/// # }
/// ```
#[derive(Clone)]
pub struct InternalAllocator;

impl_zst_allocator!(InternalAllocator, __IWRAM_ALLOC);

static __IWRAM_ALLOC: BlockAllocator = unsafe {
    BlockAllocator::new(StartEnd {
        start: iwram_data_end,
        end: || IWRAM_END,
    })
};

#[cfg(any(test, feature = "testing"))]
pub(crate) unsafe fn number_of_blocks() -> u32 {
    GLOBAL_ALLOC.number_of_blocks()
}

fn iwram_data_end() -> usize {
    extern "C" {
        static __iwram_end: usize;
    }

    // TODO: This seems completely wrong, but without the &, rust generates
    // a double dereference :/. Maybe a bug in nightly?
    (unsafe { &__iwram_end }) as *const _ as usize
}

fn data_end() -> usize {
    extern "C" {
        static __ewram_data_end: usize;
    }

    // TODO: This seems completely wrong, but without the &, rust generates
    // a double dereference :/. Maybe a bug in nightly?
    (unsafe { &__ewram_data_end }) as *const _ as usize
}

#[cfg(test)]
mod test {
    const EWRAM_START: usize = 0x0200_0000;

    use super::*;
    use alloc::boxed::Box;
    use alloc::vec;
    use alloc::vec::Vec;

    #[test_case]
    fn test_box(_gba: &mut crate::Gba) {
        let first_box = Box::new(1);
        let second_box = Box::new(2);

        assert!(&*first_box as *const _ < &*second_box as *const _);
        assert_eq!(*first_box, 1);
        assert_eq!(*second_box, 2);

        let address = &*first_box as *const _ as usize;
        assert!(
            (EWRAM_START..EWRAM_END).contains(&address),
            "ewram is located between 0x0200_0000 and 0x0204_0000, address was actually found to be {address:#010X}"
        );
    }

    #[test_case]
    fn test_vec(_gba: &mut crate::Gba) {
        let mut v = Vec::with_capacity(5);

        for i in 0..100 {
            v.push(i);
        }

        for (i, &e) in v.iter().enumerate() {
            assert_eq!(e, i);
        }
    }

    #[test_case]
    fn test_creating_and_removing_things(_gba: &mut crate::Gba) {
        let item = Box::new(1);
        for i in 0..1_000 {
            let x = Box::new(i);
            assert_eq!(*x, i);
            let address = &*x as *const _ as usize;
            assert!(
                (EWRAM_START..EWRAM_END).contains(&address),
                "ewram is located between 0x0200_0000 and 0x0204_0000, address was actually found to be {address:#010X}"
            );
        }

        assert_eq!(*item, 1);
    }

    #[test_case]
    fn test_adding_to_2_different_vectors(_gba: &mut crate::Gba) {
        let mut v1 = vec![1, 2, 3];
        let mut v2 = vec![4, 5, 6];

        for i in 0..100 {
            v1.push(i + 100);
            v2.push(i + 1000);
        }

        assert_eq!(v1[40], 137);
        assert_eq!(v2[78], 1075);
    }

    #[test_case]
    fn should_return_data_end_somewhere_in_ewram(_gba: &mut crate::Gba) {
        let data_end = data_end();

        assert!(
            0x0200_0000 <= data_end,
            "data end should be bigger than 0x0200_0000, got {data_end}"
        );
        assert!(
            0x0204_0000 > data_end,
            "data end should be smaller than 0x0203_0000"
        );
    }

    #[test_case]
    fn should_return_data_end_somewhere_in_iwram(_gba: &mut crate::Gba) {
        let data_end = iwram_data_end();

        assert!(
            (0x0300_0000..0x0300_8000).contains(&data_end),
            "iwram data end should be in iwram, instead was {data_end}"
        );
    }

    #[test_case]
    fn allocate_to_iwram_works(_gba: &mut crate::Gba) {
        let a = Box::new_in(1, InternalAllocator);
        let p = &*a as *const i32;
        let addr = p as usize;
        assert!(
            (0x0300_0000..0x0300_8000).contains(&addr),
            "address of allocation should be within iwram, instead at {p:?}"
        );
    }

    #[test_case]
    fn benchmark_allocation(_gba: &mut crate::Gba) {
        let mut stored: Vec<Vec<u8>> = Vec::new();

        let mut rng = crate::rng::RandomNumberGenerator::new();

        const MAX_VEC_LENGTH: usize = 100;

        enum Action {
            Add { size: usize },
            Remove { index: usize },
        }

        let next_action = |rng: &mut crate::rng::RandomNumberGenerator, stored: &[Vec<u8>]| {
            if stored.len() >= MAX_VEC_LENGTH {
                Action::Remove {
                    index: (rng.gen() as usize) % stored.len(),
                }
            } else if stored.is_empty() || rng.gen() as usize % 4 != 0 {
                Action::Add {
                    size: rng.gen() as usize % 32,
                }
            } else {
                Action::Remove {
                    index: (rng.gen() as usize) % stored.len(),
                }
            }
        };

        for _ in 0..10000 {
            match next_action(&mut rng, &stored) {
                Action::Add { size } => {
                    stored.push(Vec::with_capacity(size));
                }
                Action::Remove { index } => {
                    stored.swap_remove(index);
                }
            }
        }
    }

    #[test_case]
    fn growth_works(_gba: &mut crate::Gba) {
        let mut growing_vector = Vec::with_capacity(1);

        for i in 0..1000 {
            growing_vector.push(i);
            growing_vector.reserve_exact(i + 2);

            for (idx, elem) in growing_vector.iter().enumerate() {
                assert_eq!(idx, *elem);
            }
        }
    }
}