/*
 * Copyright (c) 2011 Jan Vesely
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * @addtogroup kbd
 * @{
 */

/** @file
 * @brief Cyclic buffer structure.
 */

#ifndef BUFFER_H_
#define BUFFER_H_

#include <assert.h>
#include <fibril_synch.h>

/** Cyclic buffer that blocks on full/empty.
 *
 * read_head == write_head means that the buffer is empty.
 * write_head + 1 == read_head means that the buffer is full.
 * Attempt to insert byte into the full buffer will block until it can succeed.
 * Attempt to read from empty buffer will block until it can succeed.
 *
 */
typedef struct {
	uint8_t *buffer;          /**< Storage space. */
	uint8_t *buffer_end;      /**< End of storage place. */
	fibril_mutex_t guard;     /**< Protects buffer structures. */
	fibril_condvar_t change;  /**< Indicates change (empty/full). */
	uint8_t *read_head;       /**< Place of the next readable element. */
	uint8_t *write_head;      /**< Pointer to the next writable place. */
} buffer_t;

/** Initialize cyclic buffer using provided memory space.
 *
 * @param buffer Cyclic buffer structure to initialize.
 * @param data   Memory space to use.
 * @param size   Size of the memory place.
 *
 */
static inline void buffer_init(buffer_t *buffer, uint8_t *data, size_t size)
{
	assert(buffer);
	
	fibril_mutex_initialize(&buffer->guard);
	fibril_condvar_initialize(&buffer->change);
	buffer->buffer = data;
	buffer->buffer_end = data + size;
	buffer->read_head = buffer->buffer;
	buffer->write_head = buffer->buffer;
	memset(buffer->buffer, 0, size);
}

/** Write byte to cyclic buffer.
 *
 * @param buffer Cyclic buffer to write to.
 * @param data   Data to write.
 *
 */
static inline void buffer_write(buffer_t *buffer, uint8_t data)
{
	fibril_mutex_lock(&buffer->guard);
	
	/* Next position. */
	uint8_t *new_head = buffer->write_head + 1;
	if (new_head == buffer->buffer_end)
		new_head = buffer->buffer;
	
	/* Buffer full. */
	while (new_head == buffer->read_head)
		fibril_condvar_wait(&buffer->change, &buffer->guard);
	
	/* Write data. */
	*buffer->write_head = data;
	
	/* Buffer was empty. */
	if (buffer->write_head == buffer->read_head)
		fibril_condvar_broadcast(&buffer->change);
	
	/* Move head */
	buffer->write_head = new_head;
	fibril_mutex_unlock(&buffer->guard);
}

/** Read byte from cyclic buffer.
 *
 * @param buffer Cyclic buffer to read from.
 *
 * @return Byte read.
 *
 */
static inline uint8_t buffer_read(buffer_t *buffer)
{
	fibril_mutex_lock(&buffer->guard);
	
	/* Buffer is empty. */
	while (buffer->write_head == buffer->read_head)
		fibril_condvar_wait(&buffer->change, &buffer->guard);
	
	/* Next position. */
	uint8_t *new_head = buffer->read_head + 1;
	if (new_head == buffer->buffer_end)
		new_head = buffer->buffer;
	
	/* Read data. */
	const uint8_t data = *buffer->read_head;
	
	/* Buffer was full. */
	uint8_t *new_write_head = buffer->write_head + 1;
	if (new_write_head == buffer->buffer_end)
		new_write_head = buffer->buffer;
	if (new_write_head == buffer->read_head)
		fibril_condvar_broadcast(&buffer->change);
	
	/* Move head */
	buffer->read_head = new_head;
	
	fibril_mutex_unlock(&buffer->guard);
	return data;
}

#endif

/**
 * @}
 */