/** @file
 *  @brief Buffer management.
 */

/*
 * Copyright (c) 2015 Intel Corporation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#ifndef __NET_BUF_H
#define __NET_BUF_H

#include <stddef.h>
#include <stdint.h>
#include <toolchain.h>
#include <misc/util.h>
#include <nanokernel.h>

/* Alignment needed for various parts of the buffer definition */
#define __net_buf_align __aligned(sizeof(int))

struct net_buf {
	/** FIFO uses first 4 bytes itself, reserve space */
	int __unused;

	/** Size of the user data associated with this buffer. */
	const uint16_t user_data_size;

	/** Reference count. */
	uint8_t ref;

	/** Pointer to the start of data in the buffer. */
	uint8_t *data;

	/** Length of the data behind the data pointer. */
	uint16_t len;

	/** Amount of data that this buffer can store. */
	const uint16_t size;

	/** Where the buffer should go when freed up. */
	struct nano_fifo * const free;

	/** Function to be called when the buffer is freed. */
	void (*const destroy)(struct net_buf *buf);

	/** Start of the data storage. Not to be accessed directly
	 *  (the data pointer should be used instead).
	 */
	uint8_t __buf[0] __net_buf_align;
};

/** @brief Define a pool of buffers of a certain amount and size.
 *
 *  Defines the necessary memory space (array of structs) for the needed
 *  amount of buffers. After this the net_buf_pool_init() API still
 *  needs to be used (at runtime), after which the buffers can be
 *  accessed using the fifo given as one of the parameters.
 *
 *  If provided with a custom destroy callback this callback is
 *  responsible for eventually returning the buffer back to the free
 *  buffers FIFO through nano_fifo_put(buf->free, buf).
 *
 *  @param _name     Name of buffer pool.
 *  @param _count    Number of buffers in the pool.
 *  @param _size     Maximum data size for each buffer.
 *  @param _fifo     FIFO for the buffers when they are unused.
 *  @param _destroy  Optional destroy callback when buffer is freed.
 *  @param _ud_size  Amount of user data space to reserve.
 */
#define NET_BUF_POOL(_name, _count, _size, _fifo, _destroy, _ud_size)	\
	struct {							\
		struct net_buf buf;					\
		uint8_t data[ROUND_UP(_size, 4)] __net_buf_align;	\
		uint8_t ud[ROUND_UP(_ud_size, 4)] __net_buf_align;	\
	} _name[_count] = {						\
		[0 ... (_count - 1)] = { .buf = {			\
			.user_data_size = ROUND_UP(_ud_size, 4),	\
			.free = _fifo,					\
			.destroy = _destroy,				\
			.size = ROUND_UP(_size, 4) } },			\
	}

/** @brief Initialize an available buffers FIFO based on a pool.
 *
 *  Initializes a buffer pool created using NET_BUF_POOL(). After
 *  calling this API the buffers can ge accessed through the FIFO that
 *  was given to NET_BUF_POOL(), i.e. after this call there should be no
 *  need to access the buffer pool (struct array) directly anymore.
 *
 *  @param pool  Buffer pool to initialize.
 */
#define net_buf_pool_init(pool)						\
	do {								\
		int i;							\
									\
		nano_fifo_init(pool[0].buf.free);			\
									\
		for (i = 0; i < ARRAY_SIZE(pool); i++) {		\
			nano_fifo_put(pool[i].buf.free, &pool[i]);	\
		}							\
	} while (0)

/** @brief Get a new buffer from the pool.
 *
 *  Get buffer from the available buffers pool with specified type and
 *  reserved headroom.
 *
 *  @param fifo Which FIFO to take the buffer from.
 *  @param reserve_head How much headroom to reserve.
 *
 *  @return New buffer or NULL if out of buffers.
 *
 *  @warning If there are no available buffers and the function is
 *  called from a task or fiber the call will block until a buffer
 *  becomes available in the pool.
 */
struct net_buf *net_buf_get(struct nano_fifo *fifo, size_t reserve_head);

/** @brief Decrements the reference count of a buffer.
 *
 *  Decrements the reference count of a buffer and puts it back into the
 *  pool if the count reaches zero.
 *
 *  @param buf Buffer.
 */
void net_buf_unref(struct net_buf *buf);

/** Increment the reference count of a buffer.
 *
 *  Increment the reference count of a buffer.
 *
 *  @param buf Buffer.
 */
struct net_buf *net_buf_ref(struct net_buf *buf);

/** @brief Duplicate buffer
 *
 *  Duplicate given buffer including any data and headers currently stored.
 *
 *  @param buf Buffer.
 *
 *  @return Duplicated buffer or NULL if out of buffers.
 */
struct net_buf *net_buf_clone(struct net_buf *buf);

/** Get a pointer to the user data of a buffer.
 *
 *  @param buf  The buffer in question.
 *
 *  @return Pointer to the user data of the buffer.
 */
#define net_buf_user_data(buf) \
	((void *)(ROUND_UP(((buf)->__buf + (buf)->size), sizeof(int))))

/** @brief Prepare data to be added at the end of the buffer
 *
 *  Increments the data length of a buffer to account for more data
 *  at the end.
 *
 *  @param buf Buffer to update.
 *  @param len Number of bytes to increment the length with.
 *
 *  @return The original tail of the buffer.
 */
void *net_buf_add(struct net_buf *buf, size_t len);

/** @brief Add 16-bit value at the end of the buffer
 *
 *  Adds 16-bit value in little endian format at the end of buffer.
 *  Increments the data length of a buffer to account for more data
 *  at the end.
 *
 *  @param buf Buffer to update.
 *  @param value 16-bit value to be added.
 *
 *  @return void
 */
void net_buf_add_le16(struct net_buf *buf, uint16_t value);

/** @brief Push data to the beginning of the buffer.
 *
 *  Modifies the data pointer and buffer length to account for more data
 *  in the beginning of the buffer.
 *
 *  @param buf Buffer to update.
 *  @param len Number of bytes to add to the beginning.
 *
 *  @return The new beginning of the buffer data.
 */
void *net_buf_push(struct net_buf *buf, size_t len);

/** @brief Remove data from the beginning of the buffer.
 *
 *  Removes data from the beginnig of the buffer by modifying the data
 *  pointer and buffer length.
 *
 *  @param buf Buffer to update.
 *  @param len Number of bytes to remove.
 *
 *  @return New beginning of the buffer data.
 */
void *net_buf_pull(struct net_buf *buf, size_t len);

/** @brief Remove and convert 16 bits from the beginning of the buffer.
 *
 *  Same idea as with bt_buf_pull(), but a helper for operating on
 *  16-bit little endian data.
 *
 *  @param buf Buffer.
 *
 *  @return 16-bit value converted from little endian to host endian.
 */
uint16_t net_buf_pull_le16(struct net_buf *buf);

/** @brief Check buffer tailroom.
 *
 *  Check how much free space there is at the end of the buffer.
 *
 *  @return Number of bytes available at the end of the buffer.
 */
size_t net_buf_tailroom(struct net_buf *buf);

/** @brief Check buffer headroom.
 *
 *  Check how much free space there is in the beginning of the buffer.
 *
 *  @return Number of bytes available in the beginning of the buffer.
 */
size_t net_buf_headroom(struct net_buf *buf);

/** @def net_buf_tail
 *  @brief Get the tail pointer for a buffer.
 *
 *  Get a pointer to the end of the data in a buffer.
 *
 *  @param buf Buffer.
 *
 *  @return Tail pointer for the buffer.
 */
#define net_buf_tail(buf) ((buf)->data + (buf)->len)

#endif /* __NET_BUF_H */