#include <kernel/x86/gdt.h>
#include <stdint.h>
#include <stdio.h>

#ifdef __TESTING__
#include <kernel/_kernel.h>
#endif

/**
 * What is this file?
 *
 * Well, to properly set up a lot of the system, we need something called a GDT
 * or, a Global Descriptor Table.
 *
 * This table, establishes a few things.
 *
 * Mainly it sets 4 segments,
 * 	A kernel code segment, with RING 0 permissions
 * 	A kernel data segment, with RING 0 permissions
 * 	A user code segment, with RING 3 permissions
 * 	A user data segment, with RING 3 permissions
 *
 * This allows for future userspace to properly segment code and data,
 * anything in userspace shouldn't have access to hardware like the kernel does
 * So by passing through this GDT, we can dish out authority to access certain data, functions,
 * etc, by going through the CPU permission system (RING 0 - 3)
 */

uint64_t gdt[GDT_SIZE];

uint64_t create_descriptor(uint32_t base, uint32_t limit, uint16_t flag)
{
	uint64_t descriptor;

	descriptor = limit & 0x000F0000;
	descriptor |= (flag << 8) & 0x00F0FF00;
	descriptor |= (base >> 16) & 0x000000FF;
	descriptor |= base & 0xFF000000;

	descriptor <<= 32;

	descriptor |= base << 16;
	descriptor |= limit & 0x0000FFFF;

	return descriptor;
}

#ifdef __TESTING__
void dump_gdt(void)
{
	for (int i = 0; i < GDT_SIZE; i++) {
		printf("GDT_ENTRY %d: %4 | %2\n", i, gdt[i], gdt[i]);
	}
}
#endif


void gdt_init(void)
{ 
#ifdef __TESTING__
	kinfo("Initializing the GDT");
#endif
	gdt[0] = create_descriptor(0, 0, 0); // null
	gdt[1] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL0)); // kernel code
	gdt[2] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL0)); // kernel data
	//gdt[3] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3)); // user code
	//gdt[4] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3)); // user data

	setGdt((sizeof(uint64_t) * GDT_SIZE) - 1, &(gdt[0])); // limit, base
	//reloadSegments();
#ifdef __TESTING__
	kinfo("Initialized the GDT");
	dump_gdt();
#endif
}