encoding.go

package uule

import (
	"encoding/base64"
	"fmt"
	"time"
)

type uuleVersion int

const (
	// uuleVersion1 represents a UULE which is a location string.
	uuleVersion1 uuleVersion = 1

	// uuleVersion2 represents a UULE which is a latitude and longitude string.
	uuleVersion2 uuleVersion = 2
)

var lengthPrefixKey = "EFGHIjKLMN0PQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789- ABCDEFGHIJKLMNOPQRSTUVWXYZL"

func getLengthPrefix(length int) (string, bool) {
	if length < 4 || length > 89 {
		return "", false
	}
	return string(lengthPrefixKey[length-4]), true
}

func encodeUULELatLong(latitude, longitude float64, radius int) (string, error) {
	timestamp := time.Now().UnixMicro()
	latitudeE7 := int(latitude * 1e7)
	longitudeE7 := int(longitude * 1e7)

	payload := fmt.Sprintf(`role:1
producer:12
provenance:6
timestamp:%d
latlng{
latitude_e7:%d
longitude_e7:%d
}
radius:%d`, timestamp, latitudeE7, longitudeE7, radius*620)

	return encodeUULEString(payload, uuleVersion2)
}

func encodeUULEString(uuleString string, version uuleVersion) (string, error) {
	encodedLocation := base64.StdEncoding.EncodeToString([]byte(uuleString))

	if version == uuleVersion1 {
		lengthPrefix, exists := getLengthPrefix(len(uuleString))
		if !exists {
			return "", fmt.Errorf("no length prefix found for length %d", len(uuleString))
		}

		// "w+CAIQICI" is the standard prefix for all UULEs
		return "w+CAIQICI" + lengthPrefix + encodedLocation, nil
	}

	return "a+" + encodedLocation, nil
}