/// This function is where the kernel sets up IRQ handlers
/// It is increcibly unsafe, and should be minimal in nature
/// It must create the IDT with the correct entries, those entries are
/// defined in other files inside of the `arch` module

use core::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, AtomicUsize, ATOMIC_USIZE_INIT, Ordering};
use x86::controlregs;

use acpi;
use allocator::{HEAP_START, HEAP_SIZE};
use externs::memset;
use gdt;
use idt;
use memory;
use paging::{self, entry, Page, VirtualAddress};

/// Test of zero values in BSS.
static BSS_TEST_ZERO: usize = 0;
/// Test of non-zero values in BSS.
static BSS_TEST_NONZERO: usize = 0xFFFFFFFFFFFFFFFF;

static AP_COUNT: AtomicUsize = ATOMIC_USIZE_INIT;
static BSP_READY: AtomicBool = ATOMIC_BOOL_INIT;
static BSP_PAGE_TABLE: AtomicUsize = ATOMIC_USIZE_INIT;

extern {
    /// Kernel main function
    fn kmain() -> !;
    /// Kernel main for APs
    fn kmain_ap(id: usize) -> !;
}

/// The entry to Rust, all things must be initialized
#[no_mangle]
pub unsafe extern fn kstart() -> ! {
    {
        extern {
            /// The starting byte of the _.bss_ (uninitialized data) segment.
            static mut __bss_start: u8;
            /// The ending byte of the _.bss_ (uninitialized data) segment.
            static mut __bss_end: u8;
        }

        // Zero BSS, this initializes statics that are set to 0
        {
            let start_ptr = &mut __bss_start as *mut u8;
            let end_ptr = & __bss_end as *const u8 as usize;

            if start_ptr as usize <= end_ptr {
                let size = end_ptr - start_ptr as usize;
                memset(start_ptr, 0, size);
            }

            debug_assert_eq!(BSS_TEST_ZERO, 0);
            debug_assert_eq!(BSS_TEST_NONZERO, 0xFFFFFFFFFFFFFFFF);
        }

        // Set up GDT
        gdt::init();

        // Set up IDT
        idt::init();

        // Initialize memory management
        memory::init(0, &__bss_end as *const u8 as usize);

        // TODO: allocate a stack
        let stack_start = 0x00080000;
        let stack_end = 0x0009F000;

        // Initialize paging
        let mut active_table = paging::init(stack_start, stack_end);

        // Reset AP variables
        AP_COUNT.store(0, Ordering::SeqCst);
        BSP_READY.store(false, Ordering::SeqCst);
        BSP_PAGE_TABLE.store(controlregs::cr3() as usize, Ordering::SeqCst);

        // Read ACPI tables, starts APs
        acpi::init(&mut active_table);

        // Map heap
        let heap_start_page = Page::containing_address(VirtualAddress::new(HEAP_START));
        let heap_end_page = Page::containing_address(VirtualAddress::new(HEAP_START + HEAP_SIZE-1));

        for page in Page::range_inclusive(heap_start_page, heap_end_page) {
            active_table.map(page, entry::WRITABLE | entry::NO_EXECUTE);
        }

        BSP_READY.store(true, Ordering::SeqCst);
    }

    kmain();
}

/// Entry to rust for an AP
pub unsafe extern fn kstart_ap(stack_start: usize, stack_end: usize) -> ! {
    {
        // Set up GDT for AP
        gdt::init_ap();

        // Set up IDT for aP
        idt::init_ap();

        // Initialize paging
        //let mut active_table =
        paging::init_ap(stack_start, stack_end, BSP_PAGE_TABLE.load(Ordering::SeqCst));
    }

    let ap_number = AP_COUNT.fetch_add(1, Ordering::SeqCst);

    while ! BSP_READY.load(Ordering::SeqCst) {
        asm!("pause" : : : : "intel", "volatile");
    }

    kmain_ap(ap_number);
}