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

/// Test of zero values in BSS.
static BSS_TEST_ZERO: usize = 0;
/// Test of non-zero values in data.
static DATA_TEST_NONZERO: usize = 0xFFFFFFFFFFFFFFFF;
/// Test of zero values in thread BSS
#[thread_local]
static mut TBSS_TEST_ZERO: usize = 0;
/// Test of non-zero values in thread data.
#[thread_local]
static mut TDATA_TEST_NONZERO: usize = 0xFFFFFFFFFFFFFFFF;

static AP_COUNT: AtomicUsize = ATOMIC_USIZE_INIT;
pub static AP_READY: AtomicBool = ATOMIC_BOOL_INIT;
static BSP_READY: AtomicBool = ATOMIC_BOOL_INIT;
static HEAP_FRAME: 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;
            /// The end of the tbss.
            static mut __tbss_end: u8;
            /// The end of the kernel
            static mut __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);
            }

            assert_eq!(BSS_TEST_ZERO, 0);
            assert_eq!(DATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFF);
        }

        // Initialize memory management
        memory::init(0, &__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);

        // Set up GDT
        gdt::init((&__tbss_end as *const u8 as *const usize).offset(-1) as usize, stack_end);

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

        // Test tdata and tbss
        {
            assert_eq!(TBSS_TEST_ZERO, 0);
            TBSS_TEST_ZERO += 1;
            assert_eq!(TBSS_TEST_ZERO, 1);
            assert_eq!(TDATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFF);
            TDATA_TEST_NONZERO -= 1;
            assert_eq!(TDATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFE);
        }

        // Reset AP variables
        AP_COUNT.store(0, Ordering::SeqCst);
        AP_READY.store(false, Ordering::SeqCst);
        BSP_READY.store(false, Ordering::SeqCst);
        HEAP_FRAME.store(0, Ordering::SeqCst);

        // 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));

            {
                let index = heap_start_page.p4_index();
                assert_eq!(index, heap_end_page.p4_index());

                let frame = memory::allocate_frame().expect("no frames available");
                HEAP_FRAME.store(frame.start_address().get(), Ordering::SeqCst);

                let p4 = active_table.p4_mut();
                {
                    let entry = &mut p4[index];
                    assert!(entry.is_unused());
                    entry.set(frame, entry::PRESENT | entry::WRITABLE);
                }
                p4.next_table_mut(index).unwrap().zero();
            }

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

        // Initialize devices
        device::init(&mut active_table);

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

        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) -> ! {
    {
        extern {
            /// The end of the tbss.
            static mut __tbss_end: u8;
        }

        assert_eq!(BSS_TEST_ZERO, 0);
        assert_eq!(DATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFF);

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

        // Set up GDT for AP
        gdt::init_ap((&__tbss_end as *const u8 as *const usize).offset(-1) as usize, stack_end);

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

        // Test tdata and tbss
        {
            assert_eq!(TBSS_TEST_ZERO, 0);
            TBSS_TEST_ZERO += 1;
            assert_eq!(TBSS_TEST_ZERO, 1);
            assert_eq!(TDATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFF);
            TDATA_TEST_NONZERO -= 1;
            assert_eq!(TDATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFE);
        }

        // 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));

            {
                assert_eq!(heap_start_page.p4_index(), heap_end_page.p4_index());

                while HEAP_FRAME.load(Ordering::SeqCst) == 0 {
                    interrupt::pause();
                }
                let frame = Frame::containing_address(PhysicalAddress::new(HEAP_FRAME.load(Ordering::SeqCst)));

                let p4 = active_table.p4_mut();
                let entry = &mut p4[heap_start_page.p4_index()];
                assert!(entry.is_unused());
                entry.set(frame, entry::PRESENT | entry::WRITABLE);
            }
        }

        // Init devices for AP
        device::init_ap(&mut active_table);

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

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

    while ! BSP_READY.load(Ordering::SeqCst) {
        interrupt::pause();
    }

    kmain_ap(ap_number);
}

pub unsafe fn usermode(ip: usize, sp: usize) {
    // Test usermode
    asm!("xchg bx, bx
        mov rax, 0x2B
        mov ds, ax
        mov es, ax
        mov fs, ax
        mov gs, ax

        push rax
        push rbx
        pushfq
        mov rax, 0x23
        push rax
        push rcx
        iretq"
        :
        : "{rbx}"(sp), "{rcx}"(ip)
        : "rax", "rbx", "rcx", "sp"
        : "intel", "volatile");
}