1 files changed, 92 insertions, 0 deletions
diff --git a/web/api/queries/ses/ses.c b/web/api/queries/ses/ses.c
new file mode 100644
index 0000000..6ea40df
--- /dev/null
+++ b/web/api/queries/ses/ses.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "ses.h"
+
+
+// ----------------------------------------------------------------------------
+// single exponential smoothing
+
+struct grouping_ses {
+    calculated_number alpha;
+    calculated_number alpha_other;
+    calculated_number level;
+    size_t count;
+};
+
+static size_t max_window_size = 15;
+
+void grouping_init_ses(void) {
+    long long ret = config_get_number(CONFIG_SECTION_WEB, "ses max window", (long long)max_window_size);
+    if(ret <= 1) {
+        config_set_number(CONFIG_SECTION_WEB, "ses max window", (long long)max_window_size);
+    }
+    else {
+        max_window_size = (size_t) ret;
+    }
+}
+
+static inline calculated_number window(RRDR *r, struct grouping_ses *g) {
+    (void)g;
+
+    calculated_number points;
+    if(r->group == 1) {
+        // provide a running DES
+        points = r->internal.points_wanted;
+    }
+    else {
+        // provide a SES with flush points
+        points = r->group;
+    }
+
+    return (points > max_window_size) ? max_window_size : points;
+}
+
+static inline void set_alpha(RRDR *r, struct grouping_ses *g) {
+    // https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
+    // A commonly used value for alpha is 2 / (N + 1)
+    g->alpha = 2.0 / (window(r, g) + 1.0);
+    g->alpha_other = 1.0 - g->alpha;
+}
+
+void *grouping_create_ses(RRDR *r) {
+    struct grouping_ses *g = (struct grouping_ses *)callocz(1, sizeof(struct grouping_ses));
+    set_alpha(r, g);
+    g->level = 0.0;
+    return g;
+}
+
+// resets when switches dimensions
+// so, clear everything to restart
+void grouping_reset_ses(RRDR *r) {
+    struct grouping_ses *g = (struct grouping_ses *)r->internal.grouping_data;
+    g->level = 0.0;
+    g->count = 0;
+}
+
+void grouping_free_ses(RRDR *r) {
+    freez(r->internal.grouping_data);
+    r->internal.grouping_data = NULL;
+}
+
+void grouping_add_ses(RRDR *r, calculated_number value) {
+    struct grouping_ses *g = (struct grouping_ses *)r->internal.grouping_data;
+
+    if(isnormal(value)) {
+        if(unlikely(!g->count))
+            g->level = value;
+
+        g->level = g->alpha * value + g->alpha_other * g->level;
+        g->count++;
+    }
+}
+
+calculated_number grouping_flush_ses(RRDR *r, RRDR_VALUE_FLAGS *rrdr_value_options_ptr) {
+    struct grouping_ses *g = (struct grouping_ses *)r->internal.grouping_data;
+
+    if(unlikely(!g->count || !isnormal(g->level))) {
+        *rrdr_value_options_ptr |= RRDR_VALUE_EMPTY;
+        return 0.0;
+    }
+
+    return g->level;
+}