/* See LICENSE file for copyright and license details. */
#include "types-ring.h"

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


/**
 * Initialise a ring buffer
 * 
 * @param  this  The ring buffer
 */
void
ring_initialise(struct ring *restrict this)
{
	this->start  = 0;
	this->end    = 0;
	this->size   = 0;
	this->buffer = NULL;
}


#if defined(__clang__)
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wcast-align"
#endif


/**
 * Marshal a ring buffer
 * 
 * @param   this  The ring buffer
 * @param   buf   Output buffer for the marshalled data,
 *                `NULL` to only measure how large buffer
 *                is needed
 * @return        The number of marshalled bytes
 */
size_t
ring_marshal(const struct ring *restrict this, void *restrict buf)
{
	size_t off = 0, n = this->end - this->start;
	char *bs = buf;

	if (bs)
		*(size_t *)&bs[off] = n;
	off += sizeof(size_t);

	if (bs)
		memcpy(&bs[off], this->buffer + this->start, n);
	off += n;

	return off;
}


/**
 * Unmarshal a ring buffer
 * 
 * @param   this  Output parameter for the ring buffer
 * @param   buf   Buffer with the marshalled data
 * @return        The number of unmarshalled bytes, 0 on error
 */
size_t
ring_unmarshal(struct ring *restrict this, const void *restrict buf)
{
	size_t off = 0;
	const char *bs = buf;

	ring_initialise(this);

	this->size = this->end = *(const size_t *)&bs[off];
	off += sizeof(size_t);

	if (this->end > 0) {
		this->buffer = malloc(this->end);
		if (!this->buffer)
			return 0;

		memcpy(this->buffer, bs + off, this->end);
		off += this->end;
	}

	return off;
}


#if defined(__clang__)
# pragma GCC diagnostic pop
#endif


/**
 * Append data to a ring buffer
 * 
 * @param   this  The ring buffer
 * @param   data  The new data
 * @param   n     The number of bytes in `data`
 * @return        Zero on success, -1 on error
 */
int
ring_push(struct ring *restrict this, void *restrict data, size_t n)
{
	size_t used = 0;
	char *restrict new;

	if (this->start == this->end) {
		if (this->buffer)
			used = this->size;
	} else if (this->start > this->end) {
		used = this->size - this->start + this->end;
	} else {
		used = this->start - this->end;
	}

	if (used + n > this->size) {
		new = malloc(used + n);
		if (!new)
			return -1;
		if (this->buffer) {
			if (this->start < this->end) {
				memcpy(new, this->buffer + this->start, this->end - this->start);
			} else {
				memcpy(new, this->buffer + this->start, this->size - this->start);
				memcpy(new + this->size - this->start, this->buffer, this->end);
			}
		}
		memcpy(new + used, data, n);
		this->buffer = new;
		this->start = 0;
		this->end = used + n;
		this->size = used + n;
	} else if (this->start >= this->end || this->end + n <= this->size) {
		memcpy(&this->buffer[this->end], data, n);
		this->end += n;
	} else {
		memcpy(&this->buffer[this->end], data, this->size - this->end);
		data = &((char *)data)[this->size - this->end];
		n -= this->size - this->end;
		memcpy(this->buffer, data, n);
		this->end = n;
	}

	return 0;
}


/**
 * Get queued data from a ring buffer
 * 
 * It can take up to two calls (with `ring_pop` between)
 * to get all queued data
 * 
 * @param   this  The ring buffer
 * @param   n     Output parameter for the length
 *                of the returned segment
 * @return        The beginning of the queued data,
 *                `NULL` if there is nothing more
 */
void *
ring_peek(struct ring *restrict this, size_t *restrict n)
{
	if (!this->buffer) {
		*n = 0;
		return NULL;
	}

	if (this->start < this->end)
		*n = this->end - this->start;
	else
		*n = this->size - this->start;
	return this->buffer + this->start;
}


/**
 * Dequeue data from a ring bubber
 * 
 * @param  this  The ring buffer
 * @param  n     The number of bytes to dequeue
 */
void
ring_pop(struct ring *restrict this, size_t n)
{
	this->start += n;
	this->start %= this->size;
	if (this->start == this->end) {
		free(this->buffer);
		this->start  = 0;
		this->end    = 0;
		this->size   = 0;
		this->buffer = NULL;
	}
}