#include <stdlib.h>
#include "list.h"
#include "shuffle.h"
#define RAND_REAL() ((double) rand() / (double)RAND_MAX)
int shuffle_init(struct shuffle_chain * s, unsigned window_size) {
list_init(&s->pool);
list_init(&s->window);
s->max_window = window_size;
return 0;
}
/* get then number of songs in the shuffle chain */
int shuffle_length(struct shuffle_chain *s) {
return s->pool.length + s->window.length;
}
/* add an item to the chain by simply pushing it into the pool */
int shuffle_add(struct shuffle_chain * s, const void * data, size_t size) {
list_push(&s->pool, node_from(data, size));
return 0;
}
/* ensure that our window is as full as it can possibly be. */
static int fill_window(struct shuffle_chain *s) {
/* while our window isn't full and there's songs in the pool */
while (s->window.length <= s->max_window && s->pool.length > 0) {
/* push a random song from the pool onto the end of the window */
list_pop_push(&s->pool, &s->window, rand() % s->pool.length);
}
return 0;
}
/* Randomly pick an element added via 'shuffle_add' and return
* a pointer to it. */
const void * shuffle_pick(struct shuffle_chain * s) {
const void * data = NULL;
fill_window(s);
/* get the first element off the window */
data = list_at(&s->window, 0);
/* push the retrived element back into the pool */
list_pop_push(&s->window, &s->pool, 0);
return data;
}
/* Free memory associated with the shuffle chain. */
int shuffle_free(struct shuffle_chain * s) {
list_free(&s->pool);
list_free(&s->window);
return 0;
}