Mid progress

main.go

@@ -1,38 +1,32 @@
 package main
 
 import (
+	"encoding/csv"
 	"encoding/json"
-	"fmt"
-	"io"
 	"log"
 	"net/http"
 	"os"
 	"path/filepath"
+	"strconv"
 	"time"
 )
 
-type VoltageBatch struct {
-	Voltages []float64 `json:"voltages"`
+type Summary struct {
+	StartMS float64   `json:"start_ms"`
+	EndMS   float64   `json:"end_ms"`
+	Values  []float64 `json:"values"` // [max, mean+std, mean, mean-std, min]
 }
 
-var dataFile *os.File
-var berlinTZ *time.Location
-
-func init() {
-	var err error
-	berlinTZ, err = time.LoadLocation("Europe/Berlin")
-	if err != nil {
-		log.Fatal(err)
-	}
-}
+var (
+	dataFile *os.File
+	writer   *csv.Writer
+)
 
 func initDataFile() {
 	_ = os.MkdirAll("data", 0755)
-
 	filename := filepath.Join(
 		"data",
-		fmt.Sprintf("voltages_%s.csv",
-			time.Now().In(berlinTZ).Format("20060102_150405")),
+		time.Now().Format("summary_20060102_150405.csv"),
 	)
 
 	f, err := os.OpenFile(filename,
@@ -42,7 +36,19 @@ func initDataFile() {
 	}
 
 	dataFile = f
-	dataFile.WriteString("timestamp,voltage\n")
+	writer = csv.NewWriter(dataFile)
+
+	// header for plotting
+	writer.Write([]string{
+		"start_ms",
+		"end_ms",
+		"max",
+		"mean_plus_std",
+		"mean",
+		"mean_minus_std",
+		"min",
+	})
+	writer.Flush()
 }
 
 func handler(w http.ResponseWriter, r *http.Request) {
@@ -51,41 +57,45 @@ func handler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	body, err := io.ReadAll(r.Body)
-	if err != nil {
-		http.Error(w, "read error", http.StatusBadRequest)
-		return
-	}
-	defer r.Body.Close()
-
-	var batch VoltageBatch
-	if err := json.Unmarshal(body, &batch); err != nil {
+	var s Summary
+	if err := json.NewDecoder(r.Body).Decode(&s); err != nil {
 		http.Error(w, "invalid JSON", http.StatusBadRequest)
 		return
 	}
 
-	start := time.Now().In(berlinTZ)
-
-	for i, v := range batch.Voltages {
-		ts := start.Add(time.Duration(i) * 33 * time.Millisecond)
-		dataFile.WriteString(
-			fmt.Sprintf("%s,%.6f\n",
-				ts.Format("2006-01-02 15:04:05.000"), v),
-		)
+	if len(s.Values) != 5 {
+		http.Error(w, "need 5 values", http.StatusBadRequest)
+		return
 	}
 
-	log.Println("Got batch!")
+	row := []string{
+		formatFloat(s.StartMS),
+		formatFloat(s.EndMS),
+		formatFloat(s.Values[0]),
+		formatFloat(s.Values[1]),
+		formatFloat(s.Values[2]),
+		formatFloat(s.Values[3]),
+		formatFloat(s.Values[4]),
+	}
+
+	writer.Write(row)
+	writer.Flush()
+
+	log.Println("Summary appended")
 
 	w.WriteHeader(http.StatusOK)
 	w.Write([]byte("ok"))
 }
 
+func formatFloat(v float64) string {
+	return strconv.FormatFloat(v, 'f', 6, 64)
+}
+
 func main() {
 	initDataFile()
 	defer dataFile.Close()
 
 	http.HandleFunc("/data", handler)
-
+	log.Println("Listening on :8080")
 	log.Fatal(http.ListenAndServe(":8080", nil))
 }
-