/*
 * Copyright (C) 2013 Freie Universität Berlin
 *
 * This file is subject to the terms and conditions of the GNU Lesser General
 * Public License. See the file LICENSE in the top level directory for more
 * details.
 */

/**
 * @ingroup     core_shed
 * @{
 *
 * @file        shed.c
 * @brief       Scheduler implementation
 *
 * @author      Freie Universität Berlin, Computer Systems & Telematics
 * @author      Kaspar Schleiser <kaspar.schleiser@fu-berlin.de>
 *
 * @}
 *
 * TODO: setup dependency from SCHEDSTATISTICS to MODULE_HWTIMER 
 */

#include <stdint.h>
#include <sched.h>
#include <kernel.h>
#include <kernel_internal.h>
#include <clist.h>
#include <bitarithm.h>
#include "thread.h"

#if SCHEDSTATISTICS
#include "hwtimer.h"
#endif

#define ENABLE_DEBUG (0)
#include <debug.h>

volatile int num_tasks = 0;

volatile unsigned int sched_context_switch_request;

volatile tcb_t *sched_threads[MAXTHREADS];
volatile tcb_t *active_thread;

volatile int thread_pid;
volatile int last_pid = -1;

clist_node_t *runqueues[SCHED_PRIO_LEVELS];
static uint32_t runqueue_bitcache = 0;

#if SCHEDSTATISTICS
static void (*sched_cb) (uint32_t timestamp, uint32_t value) = NULL;
schedstat pidlist[MAXTHREADS];
#endif

void sched_init()
{
    printf("Scheduler...");
    int i;

    for (i = 0; i < MAXTHREADS; i++) {
        sched_threads[i] = NULL;
#if SCHEDSTATISTICS
        pidlist[i].laststart = 0;
        pidlist[i].runtime_ticks = 0;
        pidlist[i].schedules = 0;
#endif
    }

    active_thread = NULL;
    thread_pid = -1;

    for (i = 0; i < SCHED_PRIO_LEVELS; i++) {
        runqueues[i] = NULL;
    }

    printf("[OK]\n");
}

void sched_run()
{
    sched_context_switch_request = 0;

    tcb_t *my_active_thread = (tcb_t *)active_thread;

    if (my_active_thread) {
        if (my_active_thread->status == STATUS_RUNNING) {
            my_active_thread->status = STATUS_PENDING;
        }

#ifdef SCHED_TEST_STACK

        if (*((unsigned int *)my_active_thread->stack_start) != (unsigned int) my_active_thread->stack_start) {
            printf("scheduler(): stack overflow detected, task=%s pid=%u\n", my_active_thread->name, my_active_thread->pid);
        }

#endif

    }

#ifdef SCHEDSTATISTICS
    unsigned long time = hwtimer_now();

    if (my_active_thread && (pidlist[my_active_thread->pid].laststart)) {
        pidlist[my_active_thread->pid].runtime_ticks += time - pidlist[my_active_thread->pid].laststart;
    }

#endif

    DEBUG("\nscheduler: previous task: %s\n", (my_active_thread == NULL) ? "none" : my_active_thread->name);

    if (num_tasks == 0) {
        DEBUG("scheduler: no tasks left.\n");

        while (!num_tasks) {
            /* loop until a new task arrives */
            ;
        }

        DEBUG("scheduler: new task created.\n");
    }

    my_active_thread = NULL;

    while (!my_active_thread) {
        int nextrq = number_of_lowest_bit(runqueue_bitcache);
        clist_node_t next = *(runqueues[nextrq]);
        DEBUG("scheduler: first in queue: %s\n", ((tcb_t *)next.data)->name);
        clist_advance(&(runqueues[nextrq]));
        my_active_thread = (tcb_t *)next.data;
        thread_pid = (volatile int) my_active_thread->pid;
#if SCHEDSTATISTICS
        pidlist[my_active_thread->pid].laststart = time;
        pidlist[my_active_thread->pid].schedules++;
        if ((sched_cb) && (my_active_thread->pid != last_pid)) {
            sched_cb(hwtimer_now(), my_active_thread->pid);
            last_pid = my_active_thread->pid;
        }
#endif
#ifdef MODULE_NSS

        if (active_thread && active_thread->pid != last_pid) {
            last_pid = active_thread->pid;
        }

#endif
    }

    DEBUG("scheduler: next task: %s\n", my_active_thread->name);

    if (my_active_thread != active_thread) {
        if (active_thread != NULL) {  /* TODO: necessary? */
            if (active_thread->status ==  STATUS_RUNNING) {
                active_thread->status =  STATUS_PENDING ;
            }
        }

        sched_set_status((tcb_t *)my_active_thread,  STATUS_RUNNING);
    }

    active_thread = (volatile tcb_t *) my_active_thread;

    DEBUG("scheduler: done.\n");
}

#if SCHEDSTATISTICS
void sched_register_cb(void (*callback)(uint32_t, uint32_t))
{
    sched_cb = callback;
}
#endif

void sched_set_status(tcb_t *process, unsigned int status)
{
    if (status &  STATUS_ON_RUNQUEUE) {
        if (!(process->status &  STATUS_ON_RUNQUEUE)) {
            DEBUG("adding process %s to runqueue %u.\n", process->name, process->priority);
            clist_add(&runqueues[process->priority], &(process->rq_entry));
            runqueue_bitcache |= 1 << process->priority;
        }
    }
    else {
        if (process->status & STATUS_ON_RUNQUEUE) {
            DEBUG("removing process %s from runqueue %u.\n", process->name, process->priority);
            clist_remove(&runqueues[process->priority], &(process->rq_entry));

            if (!runqueues[process->priority]) {
                runqueue_bitcache &= ~(1 << process->priority);
            }
        }
    }

    process->status = status;
}

void sched_switch(uint16_t current_prio, uint16_t other_prio, int in_isr)
{
    DEBUG("%s: %i %i %i\n", active_thread->name, (int)current_prio, (int)other_prio, in_isr);

    if (current_prio >= other_prio) {
        if (in_isr) {
            sched_context_switch_request = 1;
        }
        else {
            thread_yield();
        }
    }
}

void sched_task_exit(void)
{
    DEBUG("sched_task_exit(): ending task %s...\n", active_thread->name);

    dINT();
    sched_threads[active_thread->pid] = NULL;
    num_tasks--;

    sched_set_status((tcb_t *)active_thread,  STATUS_STOPPED);

    active_thread = NULL;
    cpu_switch_context_exit();
}