3 files changed, 35 insertions, 11 deletions

diff --git a/core/dive.h b/core/dive.h
index f80412a03..2d3edbc5c 100644
--- a/core/dive.h
+++ b/core/dive.h
@@ -418,6 +418,7 @@ extern void add_dive_to_trip(struct dive *, dive_trip_t *);
 
 struct dive *unregister_dive(int idx);
 extern void delete_single_dive(int idx);
+extern int dive_get_insertion_index(struct dive *dive);
 extern void add_single_dive(int idx, struct dive *dive);
 
 extern void insert_trip(dive_trip_t **trip);
diff --git a/core/divelist.c b/core/divelist.c
index 07c9ea87d..a25927e90 100644
--- a/core/divelist.c
+++ b/core/divelist.c
@@ -987,25 +987,29 @@ struct dive **grow_dive_table(struct dive_table *table)
 	return dives;
 }
 
+/* get the index where we want to insert the dive so that everything stays
+ * ordered reverse-chronologically */
+int dive_get_insertion_index(struct dive *dive)
+{
+	for (int i = 0; i < dive_table.nr; i++) {
+		if (dive->when <= dive_table.dives[i]->when)
+			return i;
+	}
+	return dive_table.nr;
+}
+
+/* add a dive at the given index. if the index is negative, the dive will
+ * be added according to reverse chronological order */
 void add_single_dive(int idx, struct dive *dive)
 {
 	int i;
+	if (idx < 0)
+		idx = dive_get_insertion_index(dive);
 	grow_dive_table(&dive_table);
 	dive_table.nr++;
 	if (dive->selected)
 		amount_selected++;
 
-	if (idx < 0) {
-		// convert an idx of -1 so we do insert-in-chronological-order
-		idx = dive_table.nr - 1;
-		for (int i = 0; i < dive_table.nr - 1; i++) {
-			if (dive->when <= dive_table.dives[i]->when) {
-				idx = i;
-				break;
-			}
-		}
-	}
-
 	for (i = idx; i < dive_table.nr; i++) {
 		struct dive *tmp = dive_table.dives[i];
 		dive_table.dives[i] = dive;
@@ -1453,6 +1457,24 @@ void process_imported_dives(struct dive_table *import_table, bool prefer_importe
 	mark_divelist_changed(true);
 }
 
+/* return the number a dive gets when inserted at the given index.
+ * this function is supposed to be called *before* a dive was added.
+ * this returns:
+ * 	- 1 for an empty log
+ * 	- last_nr+1 for addition at end of log (if last dive had a number)
+ * 	- 0 for all other cases
+ */
+int get_dive_nr_at_idx(int idx)
+{
+	if (dive_table.nr == 0)
+		return 1;
+	if (idx >= dive_table.nr) {
+		struct dive *last_dive = get_dive(dive_table.nr - 1);
+		return last_dive->number ? last_dive->number + 1 : 0;
+	}
+	return 0;
+}
+
 void set_dive_nr_for_current_dive()
 {
 	if (dive_table.nr == 1)
diff --git a/core/divelist.h b/core/divelist.h
index 3687b0881..2b2ee07a5 100644
--- a/core/divelist.h
+++ b/core/divelist.h
@@ -42,6 +42,7 @@ extern void find_new_trip_start_time(dive_trip_t *trip);
 extern struct dive *first_selected_dive();
 extern struct dive *last_selected_dive();
 extern bool is_trip_before_after(const struct dive *dive, bool before);
+extern int get_dive_nr_at_idx(int idx);
 extern void set_dive_nr_for_current_dive();
 extern timestamp_t get_surface_interval(timestamp_t when);
 extern void delete_dive_from_table(struct dive_table *table, int idx);