package main

import (
	"encoding/csv"
	"encoding/json"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
	"time"
)

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
	writer   *csv.Writer
)

func initDataFile() {
	_ = os.MkdirAll("data", 0755)
	filename := filepath.Join(
		"data",
		time.Now().Format("summary_20060102_150405.csv"),
	)

	f, err := os.OpenFile(filename,
		os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
	if err != nil {
		log.Fatal(err)
	}

	dataFile = f
	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) {
	if r.Method != http.MethodPost {
		http.Error(w, "POST only", http.StatusMethodNotAllowed)
		return
	}

	var s Summary
	if err := json.NewDecoder(r.Body).Decode(&s); err != nil {
		http.Error(w, "invalid JSON", http.StatusBadRequest)
		return
	}

	if len(s.Values) != 5 {
		http.Error(w, "need 5 values", http.StatusBadRequest)
		return
	}

	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))
}