/*
	Copyright (C) 2015 Szilard Biro
	Copyright (C) 2018 Harry Sintonen

	This software is provided 'as-is', without any express or implied
	warranty.	In no event will the authors be held liable for any damages
	arising from the use of this software.

	Permission is granted to anyone to use this software for any purpose,
	including commercial applications, and to alter it and redistribute it
	freely, subject to the following restrictions:

	1. The origin of this software must not be misrepresented; you must not
		 claim that you wrote the original software. If you use this software
		 in a product, an acknowledgment in the product documentation would be
		 appreciated but is not required.
	2. Altered source versions must be plainly marked as such, and must not be
		 misrepresented as being the original software.
	3. This notice may not be removed or altered from any source distribution.
*/

#include <proto/exec.h>

#include <string.h>
#include <stdlib.h>
#include <fcntl.h>

#include "semaphore.h"
#include "debug.h"

#if defined(__AMIGA__)
#include <exec/execbase.h>
#include <inline/alib.h>
#define NEWLIST(a) NewList(a)
#endif

#ifndef EOVERFLOW
#define EOVERFLOW EINVAL
#endif

static struct List semaphores;
static struct SignalSemaphore sema_sem;
static pthread_once_t once_control = PTHREAD_ONCE_INIT;

static void _Init_Semaphore(void)
{
	DB2(bug("%s()\n", __FUNCTION__));

	InitSemaphore(&sema_sem);
	NEWLIST(&semaphores);
}

sem_t *sem_open(const char *name, int oflag, mode_t mode, unsigned int value)
{
	sem_t *sem;

	D(bug("%s(%s, %d, %u, %u)\n", __FUNCTION__, name, oflag, mode, value));

	pthread_once(&once_control, _Init_Semaphore);

	if (name == NULL)
	{
		errno = EINVAL;
		return SEM_FAILED;
	}

	ObtainSemaphore(&sema_sem);
	sem = (sem_t *)FindName(&semaphores, (STRPTR)name);
	if (sem != NULL)
	{
		if ((oflag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL))
		{
			ReleaseSemaphore(&sema_sem);
			errno = EEXIST;
			return SEM_FAILED;
		}
	}
	else
	{
		if (!(oflag & O_CREAT))
		{
			ReleaseSemaphore(&sema_sem);
			errno = ENOENT;
			return SEM_FAILED;
		}

		sem = malloc(sizeof(sem_t) + strlen(name) + 1);
		if (sem == NULL)
		{
			ReleaseSemaphore(&sema_sem);
			errno = ENOMEM;
			return SEM_FAILED;
		}

		if (sem_init(sem, 0, value))
		{
			free(sem);
			ReleaseSemaphore(&sema_sem);
			return SEM_FAILED;
		}
		sem->node.ln_Name = (char *) (sem + 1);
		strcpy(sem->node.ln_Name, name);
		AddTail(&semaphores, (struct Node *)sem);
	}
	ReleaseSemaphore(&sema_sem);

	return sem;
}

int sem_close(sem_t *sem)
{
	D(bug("%s(%p)\n", __FUNCTION__, sem));

	return 0;
}

int sem_unlink(const char *name)
{
	sem_t *sem;

	D(bug("%s(%s)\n", __FUNCTION__, name));

	pthread_once(&once_control, _Init_Semaphore);

	if (name == NULL)
	{
		errno = EINVAL;
		return -1;
	}

	ObtainSemaphore(&sema_sem);
	sem = (sem_t *)FindName(&semaphores, (STRPTR)name);

	if (sem == NULL)
	{
		ReleaseSemaphore(&sema_sem);
		errno = ENOENT;
		return -1;
	}

	if (sem_destroy(sem) != 0)
	{
		ReleaseSemaphore(&sema_sem);
		return -1;
	}

	Remove((struct Node *)sem);
	free(sem);
	ReleaseSemaphore(&sema_sem);

	return 0;
}

int sem_init(sem_t *sem, int pshared, unsigned int value)
{
	D(bug("%s(%p, %d, %u)\n", __FUNCTION__, sem, pshared, value));

	if (sem == NULL || value > (unsigned int)SEM_VALUE_MAX)
	{
		errno = EINVAL;
		return -1;
	}

	sem->value = value;
	sem->waiters_count = 0;
	pthread_mutex_init(&sem->lock, NULL);
	pthread_cond_init(&sem->count_nonzero, NULL);

	return 0;
}

int sem_destroy(sem_t *sem)
{
	D(bug("%s(%p)\n", __FUNCTION__, sem));

	if (sem == NULL)
	{
		errno = EINVAL;
		return -1;
	}

	if (pthread_mutex_trylock(&sem->lock) != 0)
	{
		errno = EBUSY;
		return -1;
	}

	pthread_mutex_unlock(&sem->lock);
	pthread_mutex_destroy(&sem->lock);
	pthread_cond_destroy(&sem->count_nonzero);
	sem->value = sem->waiters_count = 0;

	return 0;
}

int sem_trywait(sem_t *sem)
{
	int result = 0;

	D(bug("%s(%p)\n", __FUNCTION__, sem));

	if (sem == NULL)
	{
		errno = EINVAL;
		return -1;
	}

	pthread_mutex_lock(&sem->lock);

	if (sem->value > 0)
		sem->value--;
	else
		result = EAGAIN;

	pthread_mutex_unlock(&sem->lock);

	if (result != 0)
	{
		errno = result;
		return -1;
	}

	return 0;
}

int sem_timedwait(sem_t *sem, const struct timespec *abstime)
{
	int result = 0;

	D(bug("%s(%p, %p)\n", __FUNCTION__, sem, abstime));

	if (sem == NULL)
	{
		errno = EINVAL;
		return -1;
	}

	pthread_mutex_lock(&sem->lock);

	sem->waiters_count++;

	while (sem->value == 0 && result == 0)
		result = pthread_cond_timedwait(&sem->count_nonzero, &sem->lock, abstime);

	sem->waiters_count--;

	if (result != 0)
	{
		pthread_mutex_unlock(&sem->lock);
		errno = result;
		return -1;
	}

	sem->value--;

	pthread_mutex_unlock(&sem->lock);

	return 0;
}

int sem_wait(sem_t *sem)
{
	D(bug("%s(%p)\n", __FUNCTION__, sem));

	return sem_timedwait(sem, NULL);
}

int sem_post(sem_t *sem)
{
	D(bug("%s(%p)\n", __FUNCTION__, sem));

	if (sem == NULL)
	{
		errno = EINVAL;
		return -1;
	}

	pthread_mutex_lock(&sem->lock);

	if (sem->value >= SEM_VALUE_MAX)
	{
		pthread_mutex_unlock(&sem->lock);
		errno = EOVERFLOW;
		return -1;
	}

	sem->value++;

	if (sem->waiters_count > 0)
		pthread_cond_signal(&sem->count_nonzero);

	pthread_mutex_unlock(&sem->lock);

	return 0;
}

int sem_getvalue(sem_t *sem, int *sval)
{
	D(bug("%s(%p)\n", __FUNCTION__, sem));

	if (sem == NULL || sval == NULL)
	{
		errno = EINVAL;
		return -1;
	}

	// if one or more threads are waiting to lock the semaphore,
	// then return the negative of the waiters
	if (pthread_mutex_trylock(&sem->lock) == 0)
	{
		if (sem->lock.incond)
			*sval = -sem->waiters_count;
		else
			*sval = sem->value;
		pthread_mutex_unlock(&sem->lock);
	}
	else
	{
		// TODO: should I lock the mutex here?
		*sval = -sem->waiters_count;
	}

	return 0;
}