#include <stdint.h>
#include <stddef.h>
#include "compiler/attr.h"
#include "hal/hal.h"

#define GDT_SIZE 5

typedef struct {
  uint16_t limitlow;
  uint16_t baselow;
  uint8_t basemid;
  uint8_t access;
  uint8_t gran;
  uint8_t basehigh;
} PACKED GdtEntry;

typedef struct {
  uint16_t limit;
  uint64_t base;
} PACKED GdtPtr;

typedef struct {
  GdtEntry old[5];
  GdtEntry tsslow;
  GdtEntry tsshigh;
} PACKED ExtendedGdt;

typedef struct {
  uint32_t resv0;
  uint64_t rsp0;
  uint64_t rsp1;
  uint64_t rsp2;
  uint64_t resv1;
  uint64_t ist[7];
  uint64_t resv2;
  uint16_t resv3;
  uint16_t iopb_off;
} PACKED Tss;

static Tss tss = {0};
static ExtendedGdt *curgdt = NULL;

#define KCODE 0x08
#define KDATA 0x10
#define UCODE 0x18
#define UDATA 0x20
#define TSS   0x28

#define GDT_PRESENT 0x80
#define GDT_TSS     0x89

static uint64_t gdt_curretbase(void) {
  GdtPtr gdtr;
  asm volatile("sgdt %0" : "=m"(gdtr));
  return gdtr.base;
}

void gdt_setenty(GdtEntry *entry, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran) {
  entry->baselow = base & 0xffff;
  entry->basemid = (base >> 16) & 0xff;
  entry->basehigh = (base >> 24) & 0xff;
  entry->limitlow = limit & 0xffff;
  entry->gran = (limit >> 16) & 0x0f | (gran & 0xf0);
  entry->access = access;
}

void gdt_init(void) {
  uint64_t base = gdt_curretbase();
  curgdt = (ExtendedGdt *)base;

  HAL_MEMSET(&tss, 0, sizeof(tss));
  tss.iopb_off = sizeof(tss);

  uint64_t tss_base = (uint64_t)&tss;
  uint32_t tss_limit = sizeof(tss) - 1;

  gdt_setenty(&curgdt->tsslow, tss_base & 0xFFFFFFFF, tss_limit, GDT_PRESENT | GDT_TSS, 0x0);
  
  GdtEntry *tsshigh = &curgdt->tsshigh;
  tsshigh->baselow = (tss_base >> 32) & 0xffff;
  tsshigh->basemid = (tss_base >> 48) & 0xff;
  tsshigh->basehigh = (tss_base >> 56) & 0xff;
  tsshigh->access = 0;
  tsshigh->gran = 0;
  tsshigh->limitlow = 0;

  GdtPtr gdtr;
  asm volatile("sgdt %0" : "=m"(gdtr));
  gdtr.limit = sizeof(ExtendedGdt) - 1;
  asm volatile("lgdt %0" :: "m"(gdtr));

  asm volatile("ltr %0" :: "r"((uint16_t)0x28));
}