#include <stdint.h>

#include "gdt.h"
#include "kprintf.h"

extern void set_gdt(uint32_t gdt_ptr);

struct tss TSS;
uint8_t gdt_entries[GDT_SIZE * 8];
struct gdt_descriptor *gdtr = (struct gdt_descriptor *)GDT_ADDRESS;

static void set_gdt_entry_value(uint8_t *target, uint32_t base, uint32_t limit,
                                uint8_t access, uint8_t granularity)
{
	if (limit > 0xFFFFF) {
		kprintf(KERN_ERR
		        "GDT cannot encode limits larger than 0xFFFFF");
	}

	// Encode the limit
	target[0] = limit & 0xFF;
	target[1] = (limit >> 8) & 0xFF;
	target[6] = (limit >> 16) & 0x0F;

	// Encode the base
	target[2] = base & 0xFF;
	target[3] = (base >> 8) & 0xFF;
	target[4] = (base >> 16) & 0xFF;
	target[7] = (base >> 24) & 0xFF;

	// Encode the access byte
	target[5] = access;

	// Encode the flags
	target[6] |= (granularity << 4);
}

void init_gdt(void)
{
	gdtr->size = 8 * GDT_SIZE - 1;
	gdtr->base = (uint32_t)&gdt_entries[0];

	set_gdt_entry_value(gdt_entries + 0x00, 0, 0, 0, 0); // Null segment

	set_gdt_entry_value(
	    gdt_entries + GDT_OFFSET_KERNEL_CODE, 0, 0xFFFFF,
	    GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_KERNEL_MODE |
		GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_EXECUTABLE |
		GDT_ACCESS_DC_NOT_CONFORM |
		GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
		GDT_ACCESS_A_ACCESSED,
	    GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // Kernel code
	set_gdt_entry_value(
	    gdt_entries + GDT_OFFSET_KERNEL_DATA, 0, 0xFFFFF,
	    GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_KERNEL_MODE |
		GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_NOT_EXECUTABLE |
		GDT_ACCESS_DC_NOT_CONFORM |
		GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
		GDT_ACCESS_A_ACCESSED,
	    GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // Kernel data
	set_gdt_entry_value(
	    gdt_entries + GDT_OFFSET_KERNEL_STACK, 0, 0xFFFFF,
	    GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_KERNEL_MODE |
		GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_NOT_EXECUTABLE |
		GDT_ACCESS_DC_CONFORM |
		GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
		GDT_ACCESS_A_ACCESSED,
	    GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // Kernel stack

	set_gdt_entry_value(
	    gdt_entries + GDT_OFFSET_USER_CODE, 0, 0xFFFFF,
	    GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_USER_MODE |
		GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_EXECUTABLE |
		GDT_ACCESS_DC_CONFORM |
		GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
		GDT_ACCESS_A_ACCESSED,
	    GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // User code
	set_gdt_entry_value(
	    gdt_entries + GDT_OFFSET_USER_DATA, 0, 0xFFFFF,
	    GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_USER_MODE |
		GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_NOT_EXECUTABLE |
		GDT_ACCESS_DC_NOT_CONFORM |
		GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
		GDT_ACCESS_A_ACCESSED,
	    GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // User data
	set_gdt_entry_value(
	    gdt_entries + GDT_OFFSET_USER_STACK, 0, 0xFFFFF,
	    GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_USER_MODE |
		GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_NOT_EXECUTABLE |
		GDT_ACCESS_DC_CONFORM |
		GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
		GDT_ACCESS_A_ACCESSED,
	    GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // User stack
	// TSS
	set_gdt_entry_value(gdt_entries + GDT_OFFSET_TSS, (uint32_t)&TSS,
	                    sizeof(struct tss) - 1, 0x89, 0);

	set_gdt(((uint32_t)gdtr));
}