#include <stdlib.h>
#include <string.h>

#include <drivers/irq.h>

#include <scheduler.h>


#define STACK_SIZE (8192)

task_t* current_task = NULL;
task_t* task_list = NULL;
uint32_t next_pid = 1;


void init_scheduler(void)
{
  set_irq_handler(0, (irq_func_t) schedule);
}

void scheduler(registers_t* boot_regs)
{
  task_t* task = malloc(sizeof(task_t));

  task->id = next_pid++;
  task->regs = boot_regs;
  task->next = task;

  task_list = task;
  current_task = task;
}

registers_t* schedule(registers_t* regs)
{
  if (!current_task)
  {
    return regs;
  }

  current_task->regs = regs;

  current_task = current_task->next;

  return current_task->regs;
}

task_t* create_task(void (*entry)())
{
  task_t* task = malloc(sizeof(task_t));
  uint32_t* stack = malloc(STACK_SIZE);

  uint32_t stack_top = (uint32_t)stack + 4096;

  stack_top -= sizeof(registers_t);
  registers_t* regs = (registers_t*)stack_top;

  memset(regs, 0, sizeof(registers_t));

  regs->eip = (uint32_t) entry;
  regs->cs  = 0x08; /* kernel code */
  regs->ds  = 0x10;
  regs->es  = 0x10;
  regs->fs  = 0x10;
  regs->gs  = 0x10;
  regs->eflags = 0x202; /* IF = 1 */

  task->id = next_pid++;
  task->regs = regs;

  /* insert into circular list */
  task->next = task_list->next;
  task_list->next = task;

  return task;
}