cache.go

package main

import (
	"encoding/gob"
	"fmt"
	"os"
	"path/filepath"
)

const cacheDir = "cache"

func init() {
	if _, err := os.Stat(cacheDir); os.IsNotExist(err) {
		os.Mkdir(cacheDir, 0755)
	}
}

func getCacheKey(lat, lon, dist float64) string {
	return fmt.Sprintf("osm_%f_%f_%f.gob", lat, lon, dist)
}

func getCachedOSM(lat, lon, dist float64) (*OverpassResponse, error) {
	key := getCacheKey(lat, lon, dist)
	path := filepath.Join(cacheDir, key)
	if _, err := os.Stat(path); os.IsNotExist(err) {
		return nil, nil
	}

	file, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	var resp OverpassResponse
	if err := gob.NewDecoder(file).Decode(&resp); err != nil {
		return nil, err
	}

	return &resp, nil
}

func cacheOSM(lat, lon, dist float64, resp *OverpassResponse) error {
	key := getCacheKey(lat, lon, dist)
	path := filepath.Join(cacheDir, key)

	file, err := os.Create(path)
	if err != nil {
		return err
	}
	defer file.Close()

	if err := gob.NewEncoder(file).Encode(resp); err != nil {
		return err
	}

	return nil
}