// http://hosted.cjmovie.net/TutMultitask.htm
//
//
#define FOOLOS_MODULE_NAME "task"

#include "kernel.h"
#include "lib/logger/log.h"	// logger facilities
#include "mem.h"
#include "timer.h"
#include "asm/x86.h"

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

#define MAX_TASKS 10

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 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=esp;
	    task_list[i].active=true;
	    task_list[i].waiting=false;
	    task_list[i].skipwait=false;
	    task_list[i].brk=task_list[current_task].brk;
	    return i;
	}
    }

    panic(FOOLOS_MODULE_NAME,"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)
{

    // allows skipping scheduling from gdb 
    volatile int skippy=0;
    if(skippy)return 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)
//		    log(FOOLOS_MODULE_NAME,FOOLOS_LOG_INFO,"switch from %d to %d", current_task, pid);

	    current_task=pid;

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

    }

    panic(FOOLOS_MODULE_NAME,"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;

    log(FOOLOS_MODULE_NAME,FOOLOS_LOG_INFO,"[%d] exit ", current_task);

    if(task_list[parent_pid].active)
    {
	if(task_list[parent_pid].waiting)
	{
    
	   log(FOOLOS_MODULE_NAME,FOOLOS_LOG_INFO,"[%d] wake up", parent_pid);
	   task_list[parent_pid].waiting=false;
	}
	else
	{
	   log(FOOLOS_MODULE_NAME,FOOLOS_LOG_INFO,"[%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)
{ 
    log(FOOLOS_MODULE_NAME,FOOLOS_LOG_INFO,"[%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));
   log(FOOLOS_MODULE_NAME,FOOLOS_LOG_INFO,"[%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 task_init(pdirectory *dir)
{
    current_task=0;
    
    // this is our main 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); //  0; // will be set by next task_switch_next() call.

    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); // fresh 16kb stack from here.

    log(FOOLOS_MODULE_NAME,FOOLOS_LOG_INFO,"fresh esp on: 0x%08X",1,task_list[1].esp);
    log(FOOLOS_MODULE_NAME,FOOLOS_LOG_INFO,"fresh esp on: 0x%08X",0,task_list[0].esp);

    task_pusha(task_list[1].esp); // pusha but to alternative location
    task_pusha(task_list[0].esp); // pusha but to alternative location

    /*
    current_task=0;
    unsigned esp, ebp, eax, ebx, ecx, edx;

    asm(
        "movl %%esp, %0;"
        "movl %%ebp, %1;"
        "movl %%eax, %2;"
        "movl %%ebx, %3;"
        "movl %%ecx, %4;"
        "movl %%edx, %5;"
        :"=r"(esp), "=r"(ebp), "=r"(eax), "=r"(ebx), "=r"(ecx), "=r"(edx)
        );

    // TODO: prepare stack so popa get's what it wants!
    int i=task_fork(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;
}