feat: add cache layer over api

internal/geodata/cache.go

@@ -0,0 +1,62 @@
+package geodata
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+const cacheDuration = 30 * 24 * time.Hour
+
+func getCachePath() string {
+	home, _ := os.UserHomeDir()
+	return filepath.Join(home, ".cache", "git-chronos", "geodata.json")
+}
+
+func loadFromCache() (TimezoneMap, error) {
+	path := getCachePath()
+
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	var cacheContainer cacheCountryData
+	if err := json.NewDecoder(file).Decode(&cacheContainer); err != nil {
+		return nil, err
+	}
+
+	if time.Since(cacheContainer.FetchedAt) > cacheDuration {
+		return nil, fmt.Errorf("cache expired")
+	}
+
+	return cacheContainer.Data, nil
+}
+
+func saveToCache(tzMap TimezoneMap) error {
+	path := getCachePath()
+	dir := filepath.Dir(path)
+
+	if err := os.MkdirAll(dir, 755); err != nil { // creates if not exists
+		return fmt.Errorf("failed to create cache dir")
+	}
+
+	file, err := os.Create(path) // create if not exists
+	if err != nil {
+		return err
+	}
+
+	defer file.Close()
+
+	container := cacheCountryData{
+		FetchedAt: time.Now(),
+		Data:      tzMap,
+	}
+
+	encoder := json.NewEncoder(file)
+	encoder.SetIndent("", " ") // so it looks better
+	return encoder.Encode(container)
+}

internal/geodata/fetcher.go

@@ -8,7 +8,7 @@ import (
 	"time"
 )
 
-func FetchLive() (TimezoneMap, error) {
+func fetchLive() (TimezoneMap, error) {
 	client := http.Client{Timeout: 10 * time.Second}
 
 	// from: https://restcountries.com
@@ -32,6 +32,26 @@ func FetchLive() (TimezoneMap, error) {
 	return buildTzMap(apidData), nil
 }
 
+func Fetch() (TimezoneMap, error) {
+	// try to get from cache
+	tzMap, err := loadFromCache()
+	if err == nil {
+		return tzMap, nil
+	}
+
+	// fetch live and save
+	tzMap, err = fetchLive()
+	if err != nil {
+		return nil, err
+	}
+
+	if err = saveToCache(tzMap); err != nil {
+		return nil, err
+	}
+
+	return tzMap, nil
+}
+
 func buildTzMap(data []countryApiReponse) TimezoneMap {
 	tzMap := make(TimezoneMap)
 

internal/geodata/fetcher_test.go

@@ -0,0 +1,43 @@
+package geodata
+
+import (
+	"os"
+	"testing"
+)
+
+func TestFetchLive(t *testing.T) {
+	tzMap, err := fetchLive()
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	testTzMap(tzMap, t)
+}
+
+func TestCache(t *testing.T) {
+	// delete cache
+	cachePath := getCachePath()
+	if err := os.Remove(cachePath); err != nil && !os.IsNotExist(err) {
+		t.Fatal(err)
+	}
+
+	_, err := Fetch() // this populates cache
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tzMap, err := loadFromCache()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	testTzMap(tzMap, t)
+}
+
+func testTzMap(tzMap TimezoneMap, t *testing.T) {
+	entry0100 := tzMap["+0100"]
+	if len(entry0100) == 0 {
+		t.Fatalf("no countries found to timezone")
+	}
+}

internal/geodata/models.go

@@ -1,5 +1,7 @@
 package geodata
 
+import "time"
+
 // Country info exposed to other packages
 type Country struct {
 	Name       string
@@ -17,3 +19,8 @@ type countryApiReponse struct {
 	Population int64    `json:"population"`
 	Timezones  []string `json:"timezones"` // example: [ "UTC+00:00" ]
 }
+
+type cacheCountryData struct {
+	FetchedAt time.Time   `json:"fetched_at"`
+	Data      TimezoneMap `json:"data"`
+}