1 files changed, 105 insertions, 0 deletions
diff --git a/src/focus_ring.c b/src/focus_ring.c
new file mode 100644
index 0000000..45f64b2
--- /dev/null
+++ b/src/focus_ring.c
@@ -0,0 +1,105 @@
+/* Functions related to a ring of focusable items */
+
+#include "focus_ring.h"
+
+static gint find_by_value(gconstpointer data, gconstpointer user_data);
+
+
+/* Initialize the FocusRing with the given options, value getter, & label
+ *
+ * Returns NULL if the passed GList is NULL.
+ * Throws an error if cannot allocate memory for the FocusRing.
+ */
+FocusRing *initialize_focus_ring(const GList *options, gchar *(*getter_function)(gconstpointer), const gchar *const label)
+{
+    if (options == NULL) {
+        return NULL;
+    }
+
+    FocusRing *ring = malloc(sizeof(FocusRing));
+    if (ring == NULL) {
+        g_error("Could not allocate memory for FocusRing: %s", label);
+    }
+
+    ring->selected = options;
+    ring->beginning = options;
+    ring->end = g_list_last((GList *) options);
+
+    ring->getter_function = getter_function;
+
+    return ring;
+}
+
+/* Free only the FocusRing & not the underlying GList */
+void destroy_focus_ring(FocusRing *ring)
+{
+    free(ring);
+}
+
+/* Focus the next item in the ring, or loop back to the first item. */
+gchar *focus_ring_next(FocusRing *ring)
+{
+    if (ring->selected->next == NULL) {
+        ring->selected = ring->beginning;
+    } else {
+        ring->selected = ring->selected->next;
+    }
+    return focus_ring_get_value(ring);
+}
+
+/* Focus the previous item in the ring, or loop back to the last item. */
+gchar *focus_ring_prev(FocusRing *ring)
+{
+    if (ring->selected->prev == NULL) {
+        ring->selected = ring->end;
+    } else {
+        ring->selected = ring->selected->prev;
+    }
+    return focus_ring_get_value(ring);
+}
+
+/* Get the currently selected data. */
+gconstpointer focus_ring_get_selected(FocusRing *ring)
+{
+    return ring->selected->data;
+}
+
+/* Get the inner value of the currently selected item. */
+gchar *focus_ring_get_value(FocusRing *ring)
+{
+    return ring->getter_function(focus_ring_get_selected(ring));
+}
+
+
+/* Internal data used by the find_by_value & focus_ring_scroll_to_value
+ * functions.
+ */
+struct FindByValueData {
+    FocusRing *ring;
+    const gchar *target_value;
+};
+
+/* Attempt to scroll the ring to the item with the matching inner value.
+ *
+ * Does nothing if the item cannot be found.
+ */
+gchar *focus_ring_scroll_to_value(FocusRing *ring, const gchar *target_value)
+{
+    struct FindByValueData user_data = { .ring = ring, .target_value = target_value };
+    GList *find_result = g_list_find_custom((GList *) ring->beginning, (void *) &user_data, &find_by_value);
+    if (find_result != NULL) {
+        ring->selected = find_result;
+    }
+    return focus_ring_get_value(ring);
+}
+
+/* Determine if the given data's inner value matches what we're looking for.
+ *
+ * Used as callback to the g_list_find_custom function.
+ */
+static gint find_by_value(gconstpointer data, gconstpointer user_data)
+{
+    struct FindByValueData *local_user_data = (struct FindByValueData *) user_data;
+
+    return g_strcmp0(local_user_data->ring->getter_function(data), local_user_data->target_value);
+}