queue: implement song "priorities"

Sorts remaining songs by priority.  This can be used for the
much-demanded "queue feature".

test/test_queue_priority.c

@@ -0,0 +1,174 @@
+#include "queue.h"
+#include "song.h"
+
+void
+song_free(G_GNUC_UNUSED struct song *song)
+{
+}
+
+G_GNUC_UNUSED
+static void
+dump_order(const struct queue *queue)
+{
+	g_printerr("queue length=%u, order:\n", queue_length(queue));
+	for (unsigned i = 0; i < queue_length(queue); ++i)
+		g_printerr("  [%u] -> %u (prio=%u)\n", i, queue->order[i],
+			   queue->items[queue->order[i]].priority);
+}
+
+static void
+check_descending_priority(G_GNUC_UNUSED const struct queue *queue,
+			 unsigned start_order)
+{
+	assert(start_order < queue_length(queue));
+
+	uint8_t last_priority = 0xff;
+	for (unsigned order = start_order; order < queue_length(queue); ++order) {
+		unsigned position = queue_order_to_position(queue, order);
+		uint8_t priority = queue->items[position].priority;
+		assert(priority <= last_priority);
+		last_priority = priority;
+	}
+}
+
+int
+main(G_GNUC_UNUSED int argc, G_GNUC_UNUSED char **argv)
+{
+	struct song songs[16];
+
+	struct queue queue;
+	queue_init(&queue, 32);
+
+	for (unsigned i = 0; i < G_N_ELEMENTS(songs); ++i)
+		queue_append(&queue, &songs[i]);
+
+	assert(queue_length(&queue) == G_N_ELEMENTS(songs));
+
+	/* priority=10 for 4 items */
+
+	queue_set_priority_range(&queue, 4, 8, 10, -1);
+
+	queue.random = true;
+	queue_shuffle_order(&queue);
+	check_descending_priority(&queue, 0);
+
+	for (unsigned i = 0; i < 4; ++i) {
+		assert(queue_position_to_order(&queue, i) >= 4);
+	}
+
+	for (unsigned i = 4; i < 8; ++i) {
+		assert(queue_position_to_order(&queue, i) < 4);
+	}
+
+	for (unsigned i = 8; i < G_N_ELEMENTS(songs); ++i) {
+		assert(queue_position_to_order(&queue, i) >= 4);
+	}
+
+	/* priority=50 one more item */
+
+	queue_set_priority_range(&queue, 15, 16, 50, -1);
+	check_descending_priority(&queue, 0);
+
+	assert(queue_position_to_order(&queue, 15) == 0);
+
+	for (unsigned i = 0; i < 4; ++i) {
+		assert(queue_position_to_order(&queue, i) >= 4);
+	}
+
+	for (unsigned i = 4; i < 8; ++i) {
+		assert(queue_position_to_order(&queue, i) >= 1 &&
+		       queue_position_to_order(&queue, i) < 5);
+	}
+
+	for (unsigned i = 8; i < 15; ++i) {
+		assert(queue_position_to_order(&queue, i) >= 5);
+	}
+
+	/* priority=20 for one of the 4 priority=10 items */
+
+	queue_set_priority_range(&queue, 3, 4, 20, -1);
+	check_descending_priority(&queue, 0);
+
+	assert(queue_position_to_order(&queue, 3) == 1);
+	assert(queue_position_to_order(&queue, 15) == 0);
+
+	for (unsigned i = 0; i < 3; ++i) {
+		assert(queue_position_to_order(&queue, i) >= 5);
+	}
+
+	for (unsigned i = 4; i < 8; ++i) {
+		assert(queue_position_to_order(&queue, i) >= 2 &&
+		       queue_position_to_order(&queue, i) < 6);
+	}
+
+	for (unsigned i = 8; i < 15; ++i) {
+		assert(queue_position_to_order(&queue, i) >= 6);
+	}
+
+	/* priority=20 for another one of the 4 priority=10 items;
+	   pass "after_order" (with priority=10) and see if it's moved
+	   after that one */
+
+	unsigned current_order = 4;
+	unsigned current_position =
+		queue_order_to_position(&queue, current_order);
+
+	unsigned a_order = 3;
+	unsigned a_position = queue_order_to_position(&queue, a_order);
+	assert(queue.items[a_position].priority == 10);
+	queue_set_priority(&queue, a_position, 20, current_order);
+
+	current_order = queue_position_to_order(&queue, current_position);
+	assert(current_order == 3);
+
+	a_order = queue_position_to_order(&queue, a_position);
+	assert(a_order == 4);
+
+	check_descending_priority(&queue, current_order + 1);
+
+	/* priority=70 for one of the last items; must be inserted
+	   right after the current song, before the priority=20 one we
+	   just created */
+
+	unsigned b_order = 10;
+	unsigned b_position = queue_order_to_position(&queue, b_order);
+	assert(queue.items[b_position].priority == 0);
+	queue_set_priority(&queue, b_position, 70, current_order);
+
+	current_order = queue_position_to_order(&queue, current_position);
+	assert(current_order == 3);
+
+	b_order = queue_position_to_order(&queue, b_position);
+	assert(b_order == 4);
+
+	check_descending_priority(&queue, current_order + 1);
+
+	/* priority=60 for the old prio50 item; must not be moved,
+	   because it's before the current song, and it's status
+	   hasn't changed (it was already higher before) */
+
+	unsigned c_order = 0;
+	unsigned c_position = queue_order_to_position(&queue, c_order);
+	assert(queue.items[c_position].priority == 50);
+	queue_set_priority(&queue, c_position, 60, current_order);
+
+	current_order = queue_position_to_order(&queue, current_position);
+	assert(current_order == 3);
+
+	c_order = queue_position_to_order(&queue, c_position);
+	assert(c_order == 0);
+
+	/* move the prio=20 item back */
+
+	a_order = queue_position_to_order(&queue, a_position);
+	assert(a_order == 5);
+	assert(queue.items[a_position].priority == 20);
+	queue_set_priority(&queue, a_position, 5, current_order);
+
+
+	current_order = queue_position_to_order(&queue, current_position);
+	assert(current_order == 3);
+
+	a_order = queue_position_to_order(&queue, a_position);
+	assert(a_order == 6);
+}