#ifdef __CSCAN_TEST__
#include <tools.h>

struct buf {
	int id;
	int b_pblkno;
	int b_flags;
	TAILQ_ENTRY(buf) b_act;
};
#endif

struct cscan_queue {
	TAILQ_HEAD(cscanq, buf) queue;
	daddr_t	lastpos;
};

static __inline void
cscan_init(struct cscan_queue *head)
{
	TAILQ_INIT(&head->queue);
	head->lastpos = 0;
}

/* not required to remove the cscan_select()ed buffer */
static __inline void
cscan_dequeue(struct cscan_queue *head, struct buf *bp)
{
	if (bp == NULL) return;
	TAILQ_REMOVE(&head->queue, bp, b_act);
	head->lastpos = bp->b_pblkno;
}

static __inline struct buf *
cscan_select(struct cscan_queue *head)
{
	struct buf *bp = 0, *bp1 = 0, *bp2 = 0;
	daddr_t d1 = INT_MAX, d2 = 0;
	TAILQ_FOREACH(bp, &head->queue, b_act) {
		daddr_t d = bp->b_pblkno - head->lastpos;
		if (d >= 0) {  if (d <= d1) d1 = d, bp1 = bp; }
		else { d = -d; if (d >= d2) d2 = d, bp2 = bp; }
	}

	return bp1 ? bp1 : bp2;
}

static __inline void
cscan_enqueue(head, bp)
	struct cscan_queue *head;
	struct buf *bp;
{
	TAILQ_INSERT_TAIL(&head->queue, bp, b_act);
}

#ifdef __CSCAN_TEST__
int main(int argc, char *argv[])
{
#define N 10
	struct buf buf[N], *b;
	int i;
	struct cscan_queue q; cscan_init(&q);
	for (i = 0; i < N; i++) {
		bzero(&buf[i], sizeof(struct buf));
		buf[i].b_pblkno = i;
		buf[i].id = i;
	}

	for (i = N-1; i >= 1; i--)
		cscan_enqueue(&q, &buf[i]);

#define P b = cscan_select(&q); printf("xx %d\n", b ? b->id : -1);

	P
	/* cscan_dequeue(&q, &buf[0]); */
	cscan_dequeue(&q, &buf[1]);
	cscan_dequeue(&q, &buf[2]);
	cscan_dequeue(&q, &buf[4]);
	/* cscan_enqueue(&q, &buf[2]); */
	/* cscan_enqueue(&q, &buf[0]); */
	cscan_enqueue(&q, &buf[1]);
	P
	cscan_dequeue(&q, &buf[1]);
	P

	for (i = 0; i < N; i++) {
		b = cscan_select(&q);
		printf("%d\n", b ? b->id : -1);
		if (b) cscan_dequeue(&q, b);
	}
	return 0;
}
#endif

#define cscan_foreach(q,bp) TAILQ_FOREACH(bp, &(q)->queue, b_act)