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use crate::sv::{SvCall, SvService};
use core::mem::size_of;

/// A service to switch to a process stack.
///
/// See [`Switch::switch_context`] for details.
pub struct SwitchContextService {
    stack_ptr: *mut *const u8,
    data_ptr: *mut u8,
}

/// A service to switch back from a process stack.
///
/// See [`Switch::switch_back`] for details.
pub struct SwitchBackService {
    data_ptr: *mut *mut u8,
    data_size: usize,
}

/// Extends [`Supervisor`](crate::sv::Supervisor) types with
/// [`switch_context`](Switch::switch_context) and
/// [`switch_back`](Switch::switch_back) methods.
pub trait Switch<T>
where
    Self: SvCall<SwitchContextService>,
    Self: SvCall<SwitchBackService>,
{
    /// Switches to the given process stack.
    ///
    /// # Safety
    ///
    /// * `data` must be word-aligned.
    /// * `*stack_ptr` must be word-aligned.
    unsafe fn switch_context(data: *mut T, stack_ptr: *mut *const u8);

    /// Switches to the previous stack.
    ///
    /// # Safety
    ///
    /// * Must be called only from Process Stack.
    /// * `T` must match the previous [`switch_context`](Switch::switch_context).
    /// * `*data` must be word-aligned.
    unsafe fn switch_back(data: *mut *mut T);
}

unsafe impl Send for SwitchContextService {}
unsafe impl Send for SwitchBackService {}

impl SvService for SwitchContextService {
    #[allow(clippy::too_many_lines)]
    unsafe extern "C" fn handler(&mut self) {
        #[cfg(feature = "std")]
        return unimplemented!();
        let Self { stack_ptr, data_ptr } = *self;
        #[cfg(all(not(feature = "std"), feature = "floating-point-unit"))]
        unsafe {
            asm!(
                "    mrs      r3, control",
                "    tst      lr, #0x4",
                "    bne      3f",
                "    tst      lr, #0x10",
                "    it       eq",
                "    vstmdbeq sp!, {{s16-s31}}",
                "    stmdb    sp!, {{r3, r4-r11}}",
                "0:  ldr      r2, [r0]",
                "    ldmia    r2!, {{r3}}",
                "    push     {{r0, r1, r3, lr}}",
                "    cmp      r3, #0",
                "    bne      2f",
                "1:  ldmia    r2!, {{r3, r4-r11, lr}}",
                "    tst      lr, #0x10",
                "    it       eq",
                "    vldmiaeq r2!, {{s16-s31}}",
                "    msr      psp, r2",
                "    msr      control, r3",
                "    bx       lr",
                "2:  movw     r0, #0xED9C",
                "    movt     r0, #0xE000",
                "    ldmia    r3!, {{r4-r11}}",
                "    stmia    r0, {{r4-r11}}",
                "    ldmia    r3!, {{r4-r11}}",
                "    stmia    r0, {{r4-r11}}",
                "    mov      r3, #5",
                "    str      r3, [r0, #-8]",
                "    b        1b",
                "3:  mrs      r2, psp",
                "    tst      lr, #0x10",
                "    it       eq",
                "    vstmdbeq r2!, {{s16-s31}}",
                "    stmdb    r2!, {{r3, r4-r11}}",
                "    ldr      r3, [sp]",
                "    str      r2, [r3]",
                "    b        0b",
                in("r0") stack_ptr,
                in("r1") data_ptr,
                options(noreturn),
            );
        }
        #[cfg(all(not(feature = "std"), not(feature = "floating-point-unit")))]
        unsafe {
            asm!(
                "    mrs      r3, control",
                "    tst      lr, #0x4",
                "    bne      3f",
                "    stmdb    sp!, {{r3, r4-r11}}",
                "0:  ldr      r2, [r0]",
                "    ldmia    r2!, {{r3}}",
                "    push     {{r0, r1, r3, lr}}",
                "    cmp      r3, #0",
                "    bne      2f",
                "1:  ldmia    r2!, {{r3, r4-r11, lr}}",
                "    msr      psp, r2",
                "    msr      control, r3",
                "    bx       lr",
                "2:  movw     r0, #0xED9C",
                "    movt     r0, #0xE000",
                "    ldmia    r3!, {{r4-r11}}",
                "    stmia    r0, {{r4-r11}}",
                "    ldmia    r3!, {{r4-r11}}",
                "    stmia    r0, {{r4-r11}}",
                "    mov      r3, #5",
                "    str      r3, [r0, #-8]",
                "    b        1b",
                "3:  mrs      r2, psp",
                "    stmdb    r2!, {{r3, r4-r11}}",
                "    ldr      r3, [sp]",
                "    str      r2, [r3]",
                "    b        0b",
                in("r0") stack_ptr,
                in("r1") data_ptr,
                options(noreturn),
            );
        }
    }
}

impl SvService for SwitchBackService {
    #[allow(clippy::too_many_lines)]
    unsafe extern "C" fn handler(&mut self) {
        #[cfg(feature = "std")]
        return unimplemented!();
        let Self { data_ptr, data_size } = *self;
        #[cfg(all(not(feature = "std"), feature = "floating-point-unit"))]
        unsafe {
            asm!(
                "    movw     r2, #0xED94",
                "    movt     r2, #0xE000",
                "    mov      r3, #0",
                "    str      r3, [r2]",
                "    mrs      r3, control",
                "    mrs      r12, psp",
                "    tst      lr, #0x10",
                "    it       eq",
                "    vstmdbeq r12!, {{s16-s31}}",
                "    stmdb    r12!, {{r3, r4-r11, lr}}",
                "    pop      {{r2, r3, r4, lr}}",
                "    stmdb    r12!, {{r4}}",
                "    str      r12, [r2]",
                "    ldr      r2, [r0]",
                "    cmp      r2, r3",
                "    beq      2f",
                "    str      r3, [r0]",
                "    and      r12, r1, #3",
                "    subs     r1, r1, r12",
                "    beq      1f",
                "0:  ldr      r0, [r2], #4",
                "    str      r0, [r3], #4",
                "    subs     r1, r1, #4",
                "    bne      0b",
                "1:  lsrs     r12, r12, #1",
                "    itt      ne",
                "    ldrhne   r0, [r2], #2",
                "    strhne   r0, [r3], #2",
                "    itt      cs",
                "    ldrbcs   r0, [r2], #1",
                "    strbcs   r0, [r3], #1",
                "2:  tst      lr, #0x4",
                "    bne      3f",
                "    ldmia    sp!, {{r3, r4-r11}}",
                "    tst      lr, #0x10",
                "    it       eq",
                "    vldmiaeq sp!, {{s16-s31}}",
                "    msr      control, r3",
                "    bx       lr",
                "3:  ldr      r0, [sp]",
                "    ldr      r0, [r0]",
                "    ldmia    r0!, {{r3, r4-r11}}",
                "    tst      lr, #0x10",
                "    it       eq",
                "    vldmiaeq r0!, {{s16-s31}}",
                "    msr      psp, r0",
                "    msr      control, r3",
                "    bx       lr",
                in("r0") data_ptr,
                in("r1") data_size,
                options(noreturn),
            );
        }
        #[cfg(all(not(feature = "std"), not(feature = "floating-point-unit")))]
        unsafe {
            asm!(
                "    movw     r2, #0xED94",
                "    movt     r2, #0xE000",
                "    mov      r3, #0",
                "    str      r3, [r2]",
                "    mrs      r3, control",
                "    mrs      r12, psp",
                "    stmdb    r12!, {{r3, r4-r11, lr}}",
                "    pop      {{r2, r3, r4, lr}}",
                "    stmdb    r12!, {{r4}}",
                "    str      r12, [r2]",
                "    ldr      r2, [r0]",
                "    cmp      r2, r3",
                "    beq      2f",
                "    str      r3, [r0]",
                "    and      r12, r1, #3",
                "    subs     r1, r1, r12",
                "    beq      1f",
                "0:  ldr      r0, [r2], #4",
                "    str      r0, [r3], #4",
                "    subs     r1, r1, #4",
                "    bne      0b",
                "1:  lsrs     r12, r12, #1",
                "    itt      ne",
                "    ldrhne   r0, [r2], #2",
                "    strhne   r0, [r3], #2",
                "    itt      cs",
                "    ldrbcs   r0, [r2], #1",
                "    strbcs   r0, [r3], #1",
                "2:  tst      lr, #0x4",
                "    ittt     eq",
                "    ldmiaeq  sp!, {{r3, r4-r11}}",
                "    msreq    control, r3",
                "    bxeq     lr",
                "    ldr      r0, [sp]",
                "    ldr      r0, [r0]",
                "    ldmia    r0!, {{r3, r4-r11}}",
                "    msr      psp, r0",
                "    msr      control, r3",
                "    bx       lr",
                in("r0") data_ptr,
                in("r1") data_size,
                options(noreturn),
            );
        }
    }
}

impl<Sv, T> Switch<T> for Sv
where
    Sv: SvCall<SwitchContextService>,
    Sv: SvCall<SwitchBackService>,
{
    unsafe fn switch_context(data: *mut T, stack_ptr: *mut *const u8) {
        unsafe { Self::call(&mut SwitchContextService { stack_ptr, data_ptr: data.cast::<u8>() }) };
    }

    unsafe fn switch_back(data: *mut *mut T) {
        unsafe {
            Self::call(&mut SwitchBackService {
                data_ptr: data.cast::<*mut u8>(),
                data_size: size_of::<T>(),
            });
        }
    }
}