/*
 * Copyright (c) 2017-2019 Richard Braun.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <assert.h>
#include <errno.h>
#include <stdbool.h>
#include <stdint.h>

#include <kern/semaphore.h>
#include <kern/semaphore_i.h>
#include <kern/sleepq.h>

void
semaphore_init(struct semaphore *semaphore, uint16_t value, uint16_t max_value)
{
    assert(value <= max_value);

    semaphore->value = value;
    semaphore->max_value = max_value;
}

int
semaphore_trywait(struct semaphore *semaphore)
{
    struct sleepq *sleepq;
    unsigned long flags;
    int error;

    sleepq = sleepq_lend_intr_save(semaphore, false, &flags);

    if (semaphore->value == 0) {
        error = EAGAIN;
    } else {
        semaphore->value--;
        error = 0;
    }

    sleepq_return_intr_restore(sleepq, flags);

    return error;
}

void
semaphore_wait(struct semaphore *semaphore)
{
    struct sleepq *sleepq;
    unsigned long flags;

    sleepq = sleepq_lend_intr_save(semaphore, false, &flags);

    for (;;) {
        if (semaphore->value != 0) {
            semaphore->value--;
            break;
        }

        sleepq_wait(sleepq, "sem");
    }

    sleepq_return_intr_restore(sleepq, flags);
}

int
semaphore_timedwait(struct semaphore *semaphore, uint64_t ticks)
{
    struct sleepq *sleepq;
    unsigned long flags;
    int error;

    sleepq = sleepq_lend_intr_save(semaphore, false, &flags);

    for (;;) {
        if (semaphore->value != 0) {
            semaphore->value--;
            error = 0;
            break;
        }

        error = sleepq_timedwait(sleepq, "sem", ticks);

        if (error) {
            break;
        }
    }

    sleepq_return_intr_restore(sleepq, flags);

    return error;
}

int
semaphore_post(struct semaphore *semaphore)
{
    struct sleepq *sleepq;
    unsigned long flags;
    int error;

    sleepq = sleepq_lend_intr_save(semaphore, false, &flags);

    if (semaphore->value == semaphore->max_value) {
        error = EOVERFLOW;
    } else {
        assert(semaphore->value < semaphore->max_value);
        semaphore->value++;
        sleepq_signal(sleepq);
        error = 0;
    }

    sleepq_return_intr_restore(sleepq, flags);

    return error;
}