// http://hosted.cjmovie.net/TutMultitask.htm
//
//


#include "kernel.h"
#include "mem.h"
#include "asm/x86.h"

#include "vmem.h"
#include "syscalls.h"
#include "fs/fs.h"
#include "fs/ext2.h"

static volatile int volatile current_task=-1;

static volatile struct task_list_struct
{
    volatile int parent;
    volatile bool active;
    volatile uint32_t esp; // stack pointer of the task;
    volatile pdirectory *vmem; // number of virtual memory table to switch to
    volatile bool waiting;
    volatile bool skipwait;
    volatile uint32_t brk;
    volatile uint32_t esp0;
    
}volatile task_list[MAX_TASKS];

volatile int add_task(uint32_t esp, uint32_t vmem)
{
    for(int i=0;i<MAX_TASKS;i++)
    {
	if(task_list[i].active!=true)
	{
	    task_list[i].parent=current_task;
	    task_list[i].vmem=vmem;
	    task_list[i].esp  = kballoc(4)+4*4096;
            task_list[i].esp0 = kballoc(4)+4*4096;
	    task_list[i].active=true;
	    task_list[i].waiting=false;
	    task_list[i].skipwait=false;
	    task_list[i].brk=task_list[current_task].brk;

            uint32_t *addi2=(uint32_t *)esp;
	    addi2+=14;

	    for(int x=0;x<15;x++)
	    {
		task_list[i].esp-=4;
		uint32_t *addi1=(uint32_t *)task_list[i].esp;
		*addi1=*addi2;
		addi2--;
	    }
	    return i;
	}
    }

    kpanic("out of task slots!");
}

//
// REMEMBER WE ARE INSIDE AN INTERRUPT HERE - DON'T WASTE TIME!
//
// oldesp - is the adress of the stack pointer when pit_interrupt_handler was entered.
// registers have been pushed with pusha to this old stack.
//
// stack pointer was moved to the 16kb stack we have from multiboot.s
//
// we need to return a NEW stack pointer where popa will get the registers the new task requires
//
static int first=1;
volatile uint32_t my_scheduler(uint32_t oldesp)
{

    if(!first)
    {
	task_list[current_task].esp=oldesp;
    }
	first=0;

    for(int i=0;i<MAX_TASKS;i++)
    {
	int pid=(current_task+1+i)%MAX_TASKS; // schedule round robin style

	if(task_list[pid].active && !task_list[pid].waiting)
	{
//	    if(current_task!=pid)
//		    klog("switch from %d to %d", current_task, pid);

	    current_task=pid;
	    install_tss(task_list[pid].esp0);

	    x86_set_page_directory(task_list[pid].vmem);
	    return task_list[pid].esp;
	}

    }

    kpanic("nothing to schedule!");
}

// this gets called by our clock interrupt regularly!
volatile uint32_t task_switch_next(uint32_t oldesp)
{
    // check if multitasking has been started
    if(current_task<0)return oldesp; 
    return my_scheduler(oldesp);
}

//TODO: free vmem too!
//TODO: notify waiting parent when child finished;
volatile uint32_t task_exit(uint32_t oldesp)
{ 

    task_list[current_task].active=false;
    int parent_pid=task_list[current_task].parent;

    klog("[%d] exit ", current_task);

    if(task_list[parent_pid].active)
    {
	if(task_list[parent_pid].waiting)
	{
    
	   klog("[%d] wake up", parent_pid);
	   task_list[parent_pid].waiting=false;
	}
	else
	{
	   klog("[%d] skipwait", parent_pid);
	   task_list[parent_pid].skipwait=true;
	}
	
    }

    vmem_free_dir(task_list[current_task].vmem);

    return my_scheduler(oldesp);

}

volatile uint32_t task_wait(uint32_t oldesp)
{ 
    klog("[%d] wait", current_task);
    if(task_list[current_task].skipwait)
    {
	task_list[current_task].skipwait=false;
    }
    else
    {
	task_list[current_task].waiting=true;
    }
    return my_scheduler(oldesp);
}

volatile uint32_t task_fork(uint32_t oldesp)
{ 
   int pid=add_task(oldesp,vmem_new_space_dir(task_list[current_task].vmem));
   klog("[%d] forked -> [%d] (free blocks remaining: %d )", current_task, pid,mem_get_free_blocks_count());
   return pid;
}

// init task (root of all other tasks / processes) //
volatile void scheduler_init(pdirectory *dir)
{
    current_task=0;
    
    // this is our main user task on slot 0 
    task_list[0].parent=0;
    task_list[0].active=true;
    task_list[0].waiting=false;
    task_list[0].vmem=dir;
    task_list[0].esp = kballoc(4)+4*4096;
    task_list[0].esp0 = kballoc(4)+4*4096;

    task_list[1].parent=0;
    task_list[1].active=true;
    task_list[1].waiting=false;
    task_list[1].vmem=dir;
    task_list[1].esp = kballoc(4)+4*4096; 
    task_list[1].esp0 = 0; // not needed by kernel space tasks

    task_pusha(task_list[1].esp);
    task_pusha(task_list[0].esp);

    // finally enable interrrupts so the scheduler is called (by timer)
    x86_sti(); 

    // loop until scheduler kicks in and reschedules us...
    while(1);
}

volatile int task_get_current_pid()
{
    return current_task;
}

volatile uint32_t task_get_brk()
{
    return task_list[current_task].brk;
}

volatile void task_set_brk(uint32_t brk)
{
    task_list[current_task].brk=brk;
}