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plzfinder.go
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/
plzfinder.go
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package plzfinder
import (
"encoding/csv"
"errors"
"fmt"
"log"
"math"
"os"
"strconv"
)
type PlzLoc struct {
Plz string
Lat float64
Lon float64
LatR float64 // This will be calculated 1time to speed the code up
LonR float64
Dist float64 // This will be the distdance.
}
type ByDist []PlzLoc
// Implement sort.Interface for ByDist
func (a ByDist) Len() int {
return len(a)
}
func (a ByDist) Swap(i, j int) {
a[i], a[j] = a[j], a[i]
}
func (a ByDist) Less(i, j int) bool {
return a[i].Dist < a[j].Dist
}
// Global Variables
var Locations []PlzLoc // The Locations are stored in the RAM during runtime
const earthRadius = 6371.0
func ReturnNearestAvailablePLZ(requestPLZ string, maxIterations int) (string, error) { // Return the closest PLZ
convertPLZintToString := func(plz int) string {
if plz < 0 {
return fmt.Sprintf("%06d", plz)
}
return fmt.Sprintf("%05d", plz)
}
convertPLZstrToInt := func(plz string) (int, error) {
result, err := strconv.Atoi(plz)
return result, err
}
result := requestPLZ
number := 1
iteration := 0
match := false
check := func(tryPlz string) bool {
match := false
if len(tryPlz) > 5 {
return match
}
for _, loc := range Locations {
if loc.Plz == tryPlz {
match = true
break
}
}
return match
}
for {
if iteration > maxIterations {
return "99999", errors.New("no matching Plz found")
}
match = check(result)
if match {
return result, nil
}
plzAsInt, err := convertPLZstrToInt(result)
if err != nil {
return "99999", errors.New("no matching Plz found conversion error")
}
if iteration%2 == 0 {
plzAsInt = plzAsInt - number
} else {
plzAsInt = plzAsInt + number
}
result = convertPLZintToString(plzAsInt)
number++
iteration++
}
}
// In the init function the data is read from CSV. This will only run once so no need to speed up.
// Data can easily be udpated by changing the CSV content.
func LoadCSV(filename string) {
// Open the CSV file
file, err := os.Open(filename)
if err != nil {
fmt.Println("Error:", err)
return
}
defer file.Close()
// Create a CSV reader from the file
reader := csv.NewReader(file)
// Read the header (and ignore it as we assume the columns are always in the same order)
_, err = reader.Read()
if err != nil {
fmt.Println("Error:", err)
return
}
// Iterate through the rest of the records
for {
record, err := reader.Read()
if err != nil {
break
}
// Convert the fields to integers
plz := record[1]
lat, err1 := strconv.ParseFloat(record[9], 64)
lon, err2 := strconv.ParseFloat(record[10], 64)
// Do the radiant converstion once here, so we do not need it do to it later over again.
latR := lat * math.Pi / 180.0
lonR := lon * math.Pi / 180.0
// If any conversions fail, we'll skip this record
if err1 != nil || err2 != nil {
fmt.Printf("Error converting record: %+v\n", record)
continue
}
Locations = append(Locations, PlzLoc{Plz: plz, Lat: lat, Lon: lon, LatR: latR, LonR: lonR})
}
}
// Calculates a distance by assuming the earth is a perfect sphere
func haversine(lat1, lon1, lat2, lon2 float64) float64 {
// Convert degrees to radians
// Differences
deltaLat := lat2 - lat1
deltaLon := lon2 - lon1
// Haversine formula
// Complicated, probably slow
a := math.Pow(math.Sin(deltaLat/2), 2) + math.Cos(lat1)*math.Cos(lat2)*math.Pow(math.Sin(deltaLon/2), 2)
c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))
distance := earthRadius * c
return distance
}
// Finds the start location by the PLZ the user entered.
func findeStartPunkt(plz string) (PlzLoc, error) {
if plz == "99999" {
return PlzLoc{Plz: plz, Lat: 0, Lon: 0}, errors.New("no Fallback found")
}
for _, location := range Locations {
if location.Plz == plz {
return location, nil
}
}
// Uses the next PLZ from the database if there is a number missing. Hopefully it is close ;-)
intPlz, err := strconv.Atoi(plz)
if err != nil {
fmt.Println("Error converting string to int:", err)
return PlzLoc{Plz: plz, Lat: 0, Lon: 0}, errors.New("error parsing PLZ")
}
intPlz++
plz = strconv.Itoa(intPlz)
return findeStartPunkt(plz)
}
// Quick Check Function.
func isClose(lat1, lon1, lat2, lon2, distance float64) bool {
latDiff := math.Abs(lat1-lat2) * 111.32 // Average values for Germany
lonDiff := math.Abs(lon1-lon2) * 70.07
totalDiff := latDiff + lonDiff
return totalDiff < distance+10 // 10km Security added
}
func FindeOrte(plz string, radius int) ([]PlzLoc, error) {
startpunkt, err := findeStartPunkt(plz)
if err != nil {
log.Fatal("Startpunkt Err:", err)
}
var orte []PlzLoc
for _, location := range Locations {
if isClose(location.Lat, location.Lon, startpunkt.Lat, startpunkt.Lon, float64(radius)) { // quick check
dist := haversine(location.LatR, location.LonR, startpunkt.LatR, startpunkt.LonR)
if dist <= float64(radius) { // exact check
location.Dist = dist
orte = append(orte, location)
}
}
}
return orte, nil
}