package main

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"time"
)

var dataFile *os.File
var berlinTZ *time.Location

type VoltageData struct {
	Voltage float64 `json:"voltage"`
}

func init() {
	var err error
	berlinTZ, err = time.LoadLocation("Europe/Berlin")
	if err != nil {
		log.Fatalf("Failed to load Berlin timezone: %v", err)
	}
}

func initDataFile() {
	// Ensure the data/ directory exists
	if err := os.MkdirAll("data", os.ModePerm); err != nil {
		log.Fatalf("Failed to create data directory: %v", err)
	}

	// Generate a filename with timestamp in Berlin local time
	filename := filepath.Join("data", fmt.Sprintf("voltages_%s.csv", time.Now().In(berlinTZ).Format("20060102_150405")))
	file, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
	if err != nil {
		log.Fatalf("Failed to open data file: %v", err)
	}

	dataFile = file
	log.Printf("Logging voltage data to %s\n", filename)

	// Write CSV header
	_, _ = dataFile.WriteString("timestamp,voltage\n")
}

func handler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "POST only", http.StatusMethodNotAllowed)
		return
	}

	body, err := io.ReadAll(r.Body)
	if err != nil {
		http.Error(w, "read error", http.StatusBadRequest)
		return
	}
	defer r.Body.Close()

	// Parse JSON
	var v VoltageData
	if err := json.Unmarshal(body, &v); err != nil {
		http.Error(w, "invalid JSON", http.StatusBadRequest)
		return
	}

	// Get current timestamp in Berlin
	timestamp := time.Now().In(berlinTZ).Format("2006-01-02 15:04:05.000")

	// Print voltage to console
	fmt.Printf("Received voltage: %f at %s\n", v.Voltage, timestamp)

	// Append CSV line to file
	if dataFile != nil {
		if _, err := dataFile.WriteString(fmt.Sprintf("%s,%.6f\n", timestamp, v.Voltage)); err != nil {
			log.Printf("Failed to write to file: %v", err)
		}
	}

	w.WriteHeader(http.StatusOK)
	w.Write([]byte("ok"))
}

func main() {
	initDataFile()
	defer dataFile.Close()

	http.HandleFunc("/data", handler)

	addr := ":8080"
	log.Println("Listening on", addr)
	log.Fatal(http.ListenAndServe(addr, nil))
}