package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"time"
)

func getTime(location string) (time.Time, error) {
	loc, err := time.LoadLocation(location)
	if err != nil {
		return time.Now(), err
	}
	return time.Now().In(loc), err
}

var zoneDir string

func loadZoneLocations(path string) []string {
	var locations []string
	zoneFiles, _ := os.ReadDir("/usr/share/zoneinfo/" + path)
	for _, file := range zoneFiles {
		if file.IsDir() {
			locations = append(locations, loadZoneLocations(path+"/"+file.Name())...)
		} else {
			if _, err := time.LoadLocation((path + "/" + file.Name())[1:]); err != nil {
				continue
			}
			locations = append(locations, (path + "/" + file.Name())[1:])
		}
	}
	return locations
}

var runtimeLocations = loadZoneLocations(zoneDir)

func mainHandler(w http.ResponseWriter, r *http.Request) {
	now, err := getTime("UTC")
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		fmt.Fprint(w, "Could not get current time")
		return
	}

	fmt.Fprintf(w, now.Format("2006-01-02 15:04:05"))
}

func dayInYearHandler(w http.ResponseWriter, r *http.Request) {
	now, err := getTime("UTC")
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		fmt.Fprint(w, "Could not get current time")
		return
	}
	fmt.Fprintf(w, "%s%d", string(now.Format("06")[1]), now.YearDay())
}

func timeAtZoneHandler(w http.ResponseWriter, r *http.Request) {
	timezone := r.PathValue("timezone")
	now, err := getTime(timezone)
	if err != nil {
		w.WriteHeader(http.StatusNotFound)
		fmt.Fprint(w, "Timezone not found")
		return
	}
	fmt.Fprintf(w, now.Format("2006-01-02 15:04:05"))
}

func ZoneListHandler(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	err := json.NewEncoder(w).Encode(runtimeLocations)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		fmt.Fprint(w, "Could not encode zones")
	}
}

func main() {
	http.HandleFunc("GET /", mainHandler)
	http.HandleFunc("GET /diy", dayInYearHandler)
	http.HandleFunc("GET /at/{timezone...}", timeAtZoneHandler)
	http.HandleFunc("GET /timezones", ZoneListHandler)

	listen := ":8000"
	fmt.Println("Listening on " + listen)
	http.ListenAndServe(listen, nil)
}