#include <kernel/kernel.h>
#include <kernel/multiboot.h>
#include <kernel/mem.h>
#include <kernel/serial.h>
#include <kernel/idt.h>
#include <kernel/pic.h>
#include <kernel/pit.h>
#include <stdint.h>

kernel_ctx_t ctx = {0};
struct idt_entry idt[256] = {0};
struct idtr idtr = {0};
tss_t tss = {0};

extern uint32_t isr_stub_table[32];
extern void pit_isr(void);
extern void jmp_user_mode(uint32_t esp, uint32_t eip);
extern void flush_tss(uint32_t segment_selector);
extern gdt_t gdt[6];

void exception_handler(int_stack_frame_t r) {
    LOG("Exception 0x%X (0x%X) has occurred\nEAX: 0x%08X\nECX: 0x%08X\nEDX: 0x%08X\nEBX: 0x%08X\nESI: 0x%08X\nEDI: 0x%08X\nEBP: 0x%08X\nESP: 0x%08X\n",
            r.int_no, r.err_code, r.eax, r.ecx, r.edx, r.ebx, r.esi, r.edi, r.ebp, r.esp+24); 
    LOG("\nEIP:     0x%08X\nCS:      0x%08X\nEFLAGS:  0x%08X\n",
            r.eip, r.cs, r.eflags);
}

void sleep(int delay) {
    uint64_t end = ctx.ticks + delay;
    while (ctx.ticks < end)
	cpu_relax;
}

typedef struct {
    uint32_t eip;
    uint32_t esp;
    uint32_t cr3;
} task_t;

#define KERNEL_VMA 0xC0000000

void kernel(multiboot_info_t *info) {
    if (!CHECK_FLAG(info->flags, 3)) goto halt;  // Modules
    if (!CHECK_FLAG(info->flags, 6)) goto halt;  // Memory map
    if (!CHECK_FLAG(info->flags, 12)) goto halt; // VBE data 
    ctx.multi_mmap = (multi_mmap_t *)(info->memmapaddress + KERNEL_VMA);
    ctx.multi_mmap_size = info->memmaplength;

    if (serial_port_init(COM1)) ctx.log_method = LOG_COM1;
    LOG("Kernel log being sent to COM1\n");

    if (!mmap_init()) goto halt;
    LOG("%d bytes of RAM detected\nCreated a %d byte large physical memory map at 0x%08X\n", ctx.mmap_size*BLOCK_SIZE*8, ctx.mmap_size, (uint32_t)ctx.mmap);

    for (int i = 0; i < 32; i++) {
        idt_encode_entry(idt, i, isr_stub_table[i], GDT_SEGMENT_SELECTOR(1, 0), TRAP_GATE_32 | INT_RING0 | INT_PRESENT);
    }
    idt_encode_entry(idt, 32, (uint32_t)pit_isr, GDT_SEGMENT_SELECTOR(1, 0), INT_GATE_32 | INT_RING0 | INT_PRESENT);
    
    idtr.size = (sizeof(struct idt_entry) * 256) - 1;
    idtr.base = (uint32_t) idt;

    asm volatile ("lidt %0" :: "m"(idtr));
    pic_remap(PIC_1_START, PIC_2_START);
    asm volatile ("sti" ::);

    ctx.ticks = 0;
    pit_init();

    uint32_t base = (uint32_t)&tss;
    uint32_t limit = base + sizeof(tss_t);
    gdt[5].base_low = base & 0xFFFF;
    gdt[5].base_middle = (base >> 16) & 0xFF;
    gdt[5].base_high = (base >> 24) & 0xFF;
    gdt[5].limit_low = limit & 0xFFFF;
    gdt[5].granularity = (limit >> 16) & 0x0F;
    gdt[5].granularity |= 0x40;
    gdt[5].access = 0x89;
    tss.ss0 = GDT_SEGMENT_SELECTOR(2, RING0);
    uint32_t esp0 = 0;
    asm volatile ("mov %%esp, %0" : "=r" (esp0));
    tss.esp0 = esp0;
    tss.cs = GDT_SEGMENT_SELECTOR(3, RING3);
    tss.ss = tss.ds = tss.es = tss.fs = tss.gs = GDT_SEGMENT_SELECTOR(4, RING3);
    flush_tss(GDT_SEGMENT_SELECTOR(5, RING3));

#define PAGE_PRESENT (1<<0)
#define PAGE_RW (1<<1)
#define PAGE_USER (1<<2)

#define PAGE_DIR_INDEX(x) (((x) >> 22) & 0x3FF)
#define PAGE_TAB_INDEX(x) (((x) >> 12) & 0x3FF)
#define PAGE_OFFSET(x) ((x) & 0xFFF)

    uint32_t stack = (uint32_t)mmap_find_first_free_block();
    multi_mod_t *init = (multi_mod_t *)(info->moduleaddress + KERNEL_VMA);
    LOG("Switching to ring 3... EIP: 0x%08X ESP: 0x%08X\n", init->mod_start+KERNEL_VMA, stack+0x1000);

    jmp_user_mode(stack+0x1000, init->mod_start+KERNEL_VMA); 

halt:
    for (;;) {}
}