/**
 * Kernel thread functionality.
 */
module hulk.thread;

import hulk.hurl.a1;
import hulk.him;
import hulk.gdt;
import hulk.memory;
import hulk.list;
import hulk.cpu;
import hulk.hurl;
import ldc.llvmasm;

struct Thread
{
    /* TODO: currently kernel thread stack size is fixed. */
    enum STACK_SIZE = 16 * 1024;

    enum ulong INT_TCTRL_YIELD = 0;

    /** Interrupt stack template. */
    static immutable __gshared ulong[ISF_COUNT] interrupt_stack_template = [
        0x16161616_16161616u, /* RBP */
        0x15151515_15151515u, /* R15 */
        0x14141414_14141414u, /* R14 */
        0x13131313_13131313u, /* R13 */
        0x12121212_12121212u, /* R12 */
        0x11111111_11111111u, /* R11 */
        0x10101010_10101010u, /* R10 */
        0x09090909_09090909u, /* R9 */
        0x08080808_08080808u, /* R8 */
        0x06060606_06060606u, /* RDI */
        0x05050505_05050505u, /* RSI */
        0x04040404_04040404u, /* RDX */
        0x03030303_03030303u, /* RCX */
        0x02020202_02020202u, /* RBX */
        0x01010101_01010101u, /* RAX */
        0u, /* Error Code */
        0u, /* RIP */
        Gdt.SELECTOR_KERNEL_CODE, /* CS */
        0u, /* RFLAGS */
        0u, /* RSP */
        Gdt.SELECTOR_KERNEL_DATA, /* SS */
    ];

    /** List of all runnable kernel threads. */
    private static __gshared Thread * runnable_threads;

    /** Currently executing kernel thread. */
    static __gshared Thread * current_thread;

    /** Current kernel thread stack pointer. */
    ulong * stack_pointer;
    static assert(stack_pointer.offsetof == 0);

    /** Base address of kernel thread stack. */
    void * stack_addr;

    mixin List!Thread;

    /**
     * Initialize a kernel thread.
     */
    public void initialize(void function() fn)
    {
        list_init();
        suspend_interrupts();
        list_insert_after(current_thread);
        resume_interrupts();
        stack_addr = A1.allocate(STACK_SIZE);
        ulong * stack_top = cast(ulong *)(stack_addr + STACK_SIZE);
        stack_pointer = stack_top - ISF_COUNT;
        memcpy64(stack_pointer, &interrupt_stack_template[0], ISF_COUNT);
        stack_pointer[ISF_RIP] = cast(ulong)fn;
        stack_pointer[ISF_RFLAGS] = read_rflags();
        stack_pointer[ISF_RSP] = cast(ulong)stack_top;
    }

    /**
     * Initialize first kernel thread.
     */
    public void initialize_first_thread()
    {
        list_init();
        runnable_threads = &this;
        stack_addr = cast(void *)(Hurl.HULK_STACK_TOP - STACK_SIZE);
    }

    /**
     * Initialize kernel threading.
     */
    public static void initialize()
    {
        Thread * thread = A1.allocate!Thread();
        thread.initialize_first_thread();
        current_thread = thread;
    }

    /**
     * Create and start a kernel thread.
     *
     * TODO: fn must not return.
     * TODO: threads are always runnable.
     * TODO: threads cannot be destroyed.
     */
    public static Thread * start(void function() fn)
    {
        Thread * thread = A1.allocate!Thread();
        thread.initialize(fn);
        swint(INT_TCTRL_YIELD);
        return thread;
    }

    /**
     * Trigger a thread management software interrupt.
     */
    public static void swint(T1)(T1 v1)
    {
        mixin(`__asm("int $$`, cast(int)INT_KERNEL_SWINT, `", "{rax}", v1);`);
    }

    /**
     * Handle a thread management software interrupt.
     *
     * This function is called in interrupt context.
     *
     * @param stack_frame
     *   Pointer to the stack frame.
     */
    public static void handle_swint(ulong * stack_frame)
    {
        switch (stack_frame[ISF_RAX])
        {
        case INT_TCTRL_YIELD:
            Thread.current_thread = Thread.current_thread.list_next;
            break;

        default:
            break;
        }
    }
}