1 files changed, 127 insertions, 6 deletions
diff --git a/web/api/queries/des/des.h b/web/api/queries/des/des.h
index 05fa01b3..3153d497 100644
--- a/web/api/queries/des/des.h
+++ b/web/api/queries/des/des.h
@@ -6,12 +6,133 @@
 #include "../query.h"
 #include "../rrdr.h"
 
-void grouping_init_des(void);
+struct tg_des {
+    NETDATA_DOUBLE alpha;
+    NETDATA_DOUBLE alpha_other;
+    NETDATA_DOUBLE beta;
+    NETDATA_DOUBLE beta_other;
 
-void grouping_create_des(RRDR *r, const char *options __maybe_unused);
-void grouping_reset_des(RRDR *r);
-void grouping_free_des(RRDR *r);
-void grouping_add_des(RRDR *r, NETDATA_DOUBLE value);
-NETDATA_DOUBLE grouping_flush_des(RRDR *r, RRDR_VALUE_FLAGS *rrdr_value_options_ptr);
+    NETDATA_DOUBLE level;
+    NETDATA_DOUBLE trend;
+
+    size_t count;
+};
+
+static size_t tg_des_max_window_size = 15;
+
+static inline void tg_des_init(void) {
+    long long ret = config_get_number(CONFIG_SECTION_WEB, "des max tg_des_window", (long long)tg_des_max_window_size);
+    if(ret <= 1) {
+        config_set_number(CONFIG_SECTION_WEB, "des max tg_des_window", (long long)tg_des_max_window_size);
+    }
+    else {
+        tg_des_max_window_size = (size_t) ret;
+    }
+}
+
+static inline NETDATA_DOUBLE tg_des_window(RRDR *r, struct tg_des *g) {
+    (void)g;
+
+    NETDATA_DOUBLE points;
+    if(r->view.group == 1) {
+        // provide a running DES
+        points = (NETDATA_DOUBLE)r->time_grouping.points_wanted;
+    }
+    else {
+        // provide a SES with flush points
+        points = (NETDATA_DOUBLE)r->view.group;
+    }
+
+    // https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
+    // A commonly used value for alpha is 2 / (N + 1)
+    return (points > (NETDATA_DOUBLE)tg_des_max_window_size) ? (NETDATA_DOUBLE)tg_des_max_window_size : points;
+}
+
+static inline void tg_des_set_alpha(RRDR *r, struct tg_des *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 / (tg_des_window(r, g) + 1.0);
+    g->alpha_other = 1.0 - g->alpha;
+
+    //info("alpha for chart '%s' is " CALCULATED_NUMBER_FORMAT, r->st->name, g->alpha);
+}
+
+static inline void tg_des_set_beta(RRDR *r, struct tg_des *g) {
+    // https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
+    // A commonly used value for alpha is 2 / (N + 1)
+
+    g->beta = 2.0 / (tg_des_window(r, g) + 1.0);
+    g->beta_other = 1.0 - g->beta;
+
+    //info("beta for chart '%s' is " CALCULATED_NUMBER_FORMAT, r->st->name, g->beta);
+}
+
+static inline void tg_des_create(RRDR *r, const char *options __maybe_unused) {
+    struct tg_des *g = (struct tg_des *)onewayalloc_mallocz(r->internal.owa, sizeof(struct tg_des));
+    tg_des_set_alpha(r, g);
+    tg_des_set_beta(r, g);
+    g->level = 0.0;
+    g->trend = 0.0;
+    g->count = 0;
+    r->time_grouping.data = g;
+}
+
+// resets when switches dimensions
+// so, clear everything to restart
+static inline void tg_des_reset(RRDR *r) {
+    struct tg_des *g = (struct tg_des *)r->time_grouping.data;
+    g->level = 0.0;
+    g->trend = 0.0;
+    g->count = 0;
+
+    // fprintf(stderr, "\nDES: ");
+
+}
+
+static inline void tg_des_free(RRDR *r) {
+    onewayalloc_freez(r->internal.owa, r->time_grouping.data);
+    r->time_grouping.data = NULL;
+}
+
+static inline void tg_des_add(RRDR *r, NETDATA_DOUBLE value) {
+    struct tg_des *g = (struct tg_des *)r->time_grouping.data;
+
+    if(likely(g->count > 0)) {
+        // we have at least a number so far
+
+        if(unlikely(g->count == 1)) {
+            // the second value we got
+            g->trend = value - g->trend;
+            g->level = value;
+        }
+
+        // for the values, except the first
+        NETDATA_DOUBLE last_level = g->level;
+        g->level = (g->alpha * value) + (g->alpha_other * (g->level + g->trend));
+        g->trend = (g->beta * (g->level - last_level)) + (g->beta_other * g->trend);
+    }
+    else {
+        // the first value we got
+        g->level = g->trend = value;
+    }
+
+    g->count++;
+
+    //fprintf(stderr, "value: " CALCULATED_NUMBER_FORMAT ", level: " CALCULATED_NUMBER_FORMAT ", trend: " CALCULATED_NUMBER_FORMAT "\n", value, g->level, g->trend);
+}
+
+static inline NETDATA_DOUBLE tg_des_flush(RRDR *r, RRDR_VALUE_FLAGS *rrdr_value_options_ptr) {
+    struct tg_des *g = (struct tg_des *)r->time_grouping.data;
+
+    if(unlikely(!g->count || !netdata_double_isnumber(g->level))) {
+        *rrdr_value_options_ptr |= RRDR_VALUE_EMPTY;
+        return 0.0;
+    }
+
+    //fprintf(stderr, " RESULT for %zu values = " CALCULATED_NUMBER_FORMAT " \n", g->count, g->level);
+
+    return g->level;
+}
 
 #endif //NETDATA_API_QUERIES_DES_H