cloud-services/pkg/timezone/timezone.go

package timezone

import (
	"encoding/json"
	"fmt"
	"io"
	"math"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"sync"

	"github.com/pkg/errors"

	"fiskerinc.com/modules/redis"
	"fiskerinc.com/modules/utils/envtool"
)

type Timezone struct {
	ID     string
	Name   string
	Offset int
	DST    bool
}

type TimezoneServiceInterface interface {
	GetTimezoneByCoordinate(latitude float32, longitude float32) (*Timezone, error)
	GetCachedTimezoneByQuadkey(conn redis.Client, quadkey string) (*Timezone, error)
	SetCachedTimezoneByQuadkey(conn redis.Client, quadkey string, timezone *Timezone) error
}

type HTTPClient interface {
	Do(req *http.Request) (*http.Response, error)
}

type TimezoneService struct {
	apiUrl string
	apiKey string
	Client HTTPClient
}

var (
	timezoneService TimezoneServiceInterface
	timezoneOnce    sync.Once
)

func GetTimezoneService() TimezoneServiceInterface {
	timezoneOnce.Do(func() {
		if timezoneService != nil {
			return
		}
		timezoneService = NewTimezoneService()
	})

	return timezoneService
}

func SetTimezoneService(timezoneInterface TimezoneServiceInterface) {
	timezoneService = timezoneInterface
}

func NewTimezoneService() TimezoneServiceInterface {
	return &TimezoneService{
		apiUrl: "https://atlas.microsoft.com/timezone/byCoordinates/json",
		apiKey: envtool.GetEnv("AZURE_TIMEZONE_API_KEY", "REPLACE_ME"),
		Client: http.DefaultClient,
	}
}

func (timezoneService *TimezoneService) GetTimezoneByCoordinate(latitude float32, longitude float32) (*Timezone, error) {
	timezone := &Timezone{}

	err := verifyCoordinate(latitude, longitude)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	request := timezoneService.createRequest(latitude, longitude)
	azureTimezone, err := getAzureTimezoneByCoordinate(timezoneService.Client, request)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	standardOffset, err := getOffsetInSeconds(azureTimezone.ReferenceTime.StandardOffset)
	if err != nil {
		return nil, errors.New("could not parse UTC")
	}

	dstOffset, _ := getOffsetInSeconds(azureTimezone.ReferenceTime.DaylightSavings)
	if err != nil {
		return nil, errors.New("could not parse DST")
	}

	timezone.ID = azureTimezone.ReferenceTime.Tag
	timezone.Name = azureTimezone.ID
	timezone.Offset = standardOffset + dstOffset
	timezone.DST = dstOffset != 0

	return timezone, nil
}

func getAzureTimezoneByCoordinate(client HTTPClient, url string) (*AzureTimezone, error) {
	request, err := http.NewRequest(http.MethodGet, url, nil)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	request.Header.Add("accept", "application/json")
	request.Header.Add("Content-Type", "application/json")

	resp, err := client.Do(request)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	respBody, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	timezoneResult := &AzureTimezoneResult{}
	err = json.Unmarshal(respBody, timezoneResult)
	if err != nil {
		return nil, err
	}

	if len(timezoneResult.Timezones) == 0 {
		return nil, errors.WithStack(errors.New("no timezone found"))
	}

	return &timezoneResult.Timezones[0], nil
}

func getOffsetInSeconds(offset string) (int, error) {
	var result int

	parts := strings.Split(offset, ":") // "-10:30:00" --> []string{"-10", "30", "00"}

	power := len(parts) - 1
	for _, part := range parts {
		digit, err := strconv.Atoi(part)
		if err != nil {
			return 0, errors.New("could not convert offset")
		}

		if power > 0 {
			// Seconds = Hours * 60^2
			// Seconds = Minutes * 60^1
			// Seconds = Seconds * 60^0 (there are no timezones off by seconds)
			digit = digit * int(math.Pow(60, float64(power)))
		}

		if result < 0 {
			// Honor existing negative value
			digit *= -1
		}

		result += digit
		power -= 1
	}

	return result, nil
}

func (timezoneService *TimezoneService) createRequest(latitude float32, longitude float32) string {
	queryParams := url.Values{
		"api-version":      {fmt.Sprintf("%f", 1.0)},
		"query":            {fmt.Sprintf("%f,%f", latitude, longitude)},
		"subscription-key": {timezoneService.apiKey},
	}
	return fmt.Sprintf("%s?%s", timezoneService.apiUrl, queryParams.Encode())
}

func verifyCoordinate(latitude, longitude float32) error {
	if latitude > 90 || latitude < -90 {
		return fmt.Errorf("latitude %f is out of bounds", latitude)
	}

	if longitude > 180 || longitude < -180 {
		return fmt.Errorf("longitude %f is out of bounds", longitude)
	}

	return nil
}

func (timezoneService *TimezoneService) GetCachedTimezoneByQuadkey(conn redis.Client, quadkey string) (*Timezone, error) {
	timezone := &Timezone{}
	key := redis.TimezoneQuadKey(quadkey, 13)
	err := conn.GetObject(key, timezone)
	if err != nil {
		return nil, err
	}

	return timezone, nil
}

func (timezoneService *TimezoneService) SetCachedTimezoneByQuadkey(conn redis.Client, quadkey string, timezone *Timezone) error {
	dayInSeconds := 86400
	key := redis.TimezoneQuadKey(quadkey, 13)
	return conn.SetObject(key, timezone, dayInSeconds*7)
}