From 3f163309add7d1939a50762e80e7ee4cb53cf81a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20Z=C3=ADpek?= <jan@zipek.cz>
Date: Sun, 4 Sep 2022 09:22:38 +0200
Subject: [PATCH] Experiment with value batching

---
 server/services/sensor_values_service.go | 78 ++++++++++++++++++------
 1 file changed, 59 insertions(+), 19 deletions(-)

diff --git a/server/services/sensor_values_service.go b/server/services/sensor_values_service.go
index 4165270..8a79b07 100644
--- a/server/services/sensor_values_service.go
+++ b/server/services/sensor_values_service.go
@@ -14,6 +14,13 @@ type sensorValue struct {
 	Value     float64 `json:"value"`
 }
 
+func min(a, b int64) int64 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
 func (s *SensorValuesService) Push(sensorId int64, value float64) (int64, error) {
 	res, err := s.ctx.DB.Exec("INSERT INTO sensor_values (timestamp, sensor_id, value) VALUES (?, ?, ?)", time.Now().Unix(), sensorId, value)
 
@@ -25,34 +32,33 @@ func (s *SensorValuesService) Push(sensorId int64, value float64) (int64, error)
 }
 
 func (s *SensorValuesService) GetList(sensorId int64, from int64, to int64) ([]sensorValue, error) {
-	var value float64
-	var timestamp int64
-	values := make([]sensorValue, 0)
+	intervalSize := to - from
+	batchSize := intervalSize
 
-	rows, err := s.ctx.DB.Query("SELECT timestamp, value FROM sensor_values WHERE sensor_id = ? AND timestamp > ? AND timestamp < ? ORDER BY timestamp ASC", sensorId, from, to)
-
-	if err != nil {
-		if err == sql.ErrNoRows {
-			return values, nil
-		}
-
-		return nil, err
+	if intervalSize > 100*24*60 {
+		batchSize = 24 * 60
 	}
 
-	defer rows.Close()
+	values := make([]sensorValue, 0)
+	current := from
+
+	for current < to {
+		nextValue := min(to, current+batchSize)
+
+		batchValues, err := s.getValueItems(sensorId, current, nextValue)
 
-	for rows.Next() {
-		err := rows.Scan(&timestamp, &value)
 		if err != nil {
 			return nil, err
 		}
 
-		values = append(values, sensorValue{Timestamp: timestamp, Value: value})
-	}
+		sum := 0.0
 
-	err = rows.Err()
-	if err != nil {
-		return nil, err
+		for _, item := range batchValues {
+			sum += item.Value
+		}
+
+		values = append(values, sensorValue{Timestamp: int64((nextValue + current) / 2.0), Value: sum / float64(len(batchValues))})
+		current += batchSize
 	}
 
 	return values, nil
@@ -70,3 +76,37 @@ func (s *SensorValuesService) GetLatest(sensorId int64, to int64) (*sensorValue,
 
 	return &value, nil
 }
+
+func (s *SensorValuesService) getValueItems(sensorId int64, from int64, to int64) ([]sensorValue, error) {
+	values := make([]sensorValue, 0)
+
+	rows, err := s.ctx.DB.Query("SELECT timestamp, value FROM sensor_values WHERE sensor_id = ? AND timestamp > ? AND timestamp < ? ORDER BY timestamp ASC", sensorId, from, to)
+
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return values, nil
+		}
+
+		return nil, err
+	}
+
+	defer rows.Close()
+
+	for rows.Next() {
+		item := sensorValue{}
+
+		err := rows.Scan(&item.Timestamp, &item.Value)
+		if err != nil {
+			return nil, err
+		}
+
+		values = append(values, item)
+	}
+
+	err = rows.Err()
+	if err != nil {
+		return nil, err
+	}
+
+	return values, nil
+}