#include <stdlib.h>
#include "channel.h"
#include "util.h"

struct channel {
	Ptr* ringbuf;
	size_t reader;
	size_t writer;
	size_t size;
	size_t count;	
};

channel* channel_open(size_t bufsize) {
	channel* ch = xmalloc(sizeof(*ch));
	ch->ringbuf = xmalloc(bufsize * sizeof(Ptr));
	ch->reader = ch->writer = 0;
	ch->size = bufsize;
	ch->count = 0;
	return ch;
}

void channel_close(channel* ch) {
	if (!ch) return;
	free(ch->ringbuf);
	free(ch);
}

/* A channel is full if it is not empty and the reader
 * and writer are at the same cell. */
static inline bool channel_full(channel* ch)
{
	return (ch->count && ch->reader == ch->writer); 
}

/* A channel is empty if count==0. */
static inline bool channel_empty(channel* ch)
{
	return ch->count == 0;
}

short channel_send(channel* ch, Ptr data)
{
	if (channel_full(ch))
		return -1;
	
	ch->ringbuf[ch->writer++] = data;
	ch->count++;
	
	ch->writer %= ch->size;
	
	return 0;
}

short channel_recv(channel* ch, Ptr* data)
{
	if (channel_empty(ch))
		return -1;
		
	if (!data)
		die("channel_recv: data == NULL");
	
	*data = ch->ringbuf[ch->reader++];
	ch->count--;
	ch->reader %= ch->size;
	
	return 0;
}