/**
 * @file
 * @author Steve Karg
 * @date 2009
 * @brief Millisecond timer library header file.
 *
 * @section DESCRIPTION
 *
 * The mstimer library provides functions for setting, resetting and
 * restarting timers, and for checking if a timer has expired. An
 * application must "manually" check if its timers have expired; this
 * is not done automatically.
 *
 * A timer is declared as a \c struct \c mstimer and all access to the
 * timer is made by a pointer to the declared timer.
 *
 * Adapted from the Contiki operating system.
 * Original Authors: Adam Dunkels <adam@sics.se>, Nicolas Tsiftes <nvt@sics.se>
 */
#include <stdio.h>
#include <stdbool.h>
#include <stdint.h>
#include "bacnet/basic/sys/mstimer.h"

/**
 * @brief Set a timer for a time sometime in the future
 *
 * This function is used to set a timer for a time sometime in the
 * future. The function mstimer_expired() will evaluate to true after
 * the timer has expired.
 *
 * @param t A pointer to the timer
 * @param interval The interval before the timer expires.
 */
void mstimer_set(struct mstimer *t, unsigned long interval)
{
    t->interval = interval;
    t->start = mstimer_now();
}

/**
 * @brief Reset the timer with the same interval.
 *
 * This function resets the timer with the same interval that was
 * given to the mstimer_set() function. The start point of the interval
 * is the exact time that the timer last expired. Therefore, this
 * function will cause the timer to be stable over time, unlike the
 * mstimer_restart() function.
 *
 * @param t A pointer to the timer.
 * @sa mstimer_restart()
 */
void mstimer_reset(struct mstimer *t)
{
    t->start += t->interval;
}

/**
 * @brief Restart the timer from the current point in time
 *
 * This function restarts a timer with the same interval that was
 * given to the mstimer_set() function. The timer will start at the
 * current time.
 *
 * @note A periodic timer will drift if this function is used to reset
 * it. For preioric timers, use the mstimer_reset() function instead.
 * @param t A pointer to the timer.
 * @sa mstimer_reset()
 */
void mstimer_restart(struct mstimer *t)
{
    t->start = mstimer_now();
}

/**
 * @brief Check if a timer has expired.
 *
 * This function tests if a timer has expired and returns true or
 * false depending on its status.
 *
 * @param t A pointer to the timer
 * @return Non-zero if the timer has expired, zero otherwise.
 */
int mstimer_expired(struct mstimer *t)
{
    if (t->interval) {
        return ((unsigned long)((mstimer_now()) - (t->start + t->interval)) <
            ((unsigned long)(~((unsigned long)0)) >> 1));
    }

    return 0;
}
/*---------------------------------------------------------------------------*/
/**
 * The time until the timer expires
 *
 * This function returns the time until the timer expires.
 *
 * @param t A pointer to the timer
 *
 * @return The time until the timer expires
 *
 */
unsigned long mstimer_remaining(struct mstimer *t)
{
    return t->start + t->interval - mstimer_now();
}

/**
 * The time elapsed since the timer started
 *
 * This function returns the time elapsed.
 *
 * @param t A pointer to the timer
 *
 * @return The time elapsed since the last start of the timer
 *
 */
unsigned long mstimer_elapsed(struct mstimer *t)
{
    return mstimer_now() - t->start;
}

/**
 * The value of the interval
 *
 * This function returns the interval value
 *
 * @param t A pointer to the timer
 *
 * @return The interval value
 *
 */
unsigned long mstimer_interval(struct mstimer *t)
{
    return t->interval;
}
