feat: read and write from cache

Signed-off-by: Matt Gleich <[email protected]>

main.go

@@ -65,7 +65,7 @@ func main() {
 	stravaActivities := strava.FetchActivities(*minioClient, stravaTokens)
 	stravaCache := cache.New("strava", stravaActivities)
 	r.Get("/strava/cache", stravaCache.Route())
-	r.Post("/strava/event", strava.EventRoute(&stravaCache, *minioClient, stravaTokens))
+	r.Post("/strava/event", strava.EventRoute(stravaCache, *minioClient, stravaTokens))
 	r.Get("/strava/event", strava.ChallengeRoute)
 	lumber.Success("init strava cache")
 

pkg/cache/cache.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"path/filepath"
 	"reflect"
 	"sync"
 	"time"
@@ -22,13 +23,12 @@ type Cache[T any] struct {
 	updated        time.Time
 	updateCounter  prometheus.Counter
 	requestCounter prometheus.Counter
+	filePath       string
 }
 
-func New[T any](name string, data T) Cache[T] {
-	return Cache[T]{
-		Name:    name,
-		data:    data,
-		updated: time.Now(),
+func New[T any](name string, data T) *Cache[T] {
+	cache := Cache[T]{
+		Name: name,
 		updateCounter: promauto.NewCounter(prometheus.CounterOpts{
 			Name: fmt.Sprintf("cache_%s_updates", name),
 			Help: fmt.Sprintf(`The total number of times the cache "%s" has been updated`, name),
@@ -37,10 +37,15 @@ func New[T any](name string, data T) Cache[T] {
 			Name: fmt.Sprintf("cache_%s_requests", name),
 			Help: fmt.Sprintf(`The total number of times the cache "%s" has been requested`, name),
 		}),
+		filePath: filepath.Join(cacheFolder, fmt.Sprintf("%s.json", name)),
 	}
+	cache.seedFromFile()
+	cache.Update(data)
+	cache.writeToFile()
+	return &cache
 }
 
-type response[T any] struct {
+type cacheData[T any] struct {
 	Data    T         `json:"data"`
 	Updated time.Time `json:"updated"`
 }
@@ -54,7 +59,7 @@ func (c *Cache[T]) Route() http.HandlerFunc {
 		}
 		c.mutex.RLock()
 		w.Header().Set("Content-Type", "application/json")
-		err := json.NewEncoder(w).Encode(response[T]{Data: c.data, Updated: c.updated})
+		err := json.NewEncoder(w).Encode(cacheData[T]{Data: c.data, Updated: c.updated})
 		c.mutex.RUnlock()
 		c.requestCounter.Inc()
 		if err != nil {
@@ -75,6 +80,7 @@ func (c *Cache[T]) Update(data T) {
 	c.mutex.Unlock()
 	c.updateCounter.Inc()
 	metrics.CacheUpdates.Inc()
+	c.writeToFile()
 	if updated {
 		lumber.Success(c.Name, "updated")
 	}

pkg/cache/file.go

@@ -0,0 +1,67 @@
+package cache
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+
+	"github.com/gleich/lumber/v2"
+)
+
+const cacheFolder = "/caches/"
+
+func (c *Cache[T]) writeToFile() {
+	var file *os.File
+	if _, err := os.Stat(c.filePath); os.IsNotExist(err) {
+		folder := filepath.Dir(c.filePath)
+		err := os.MkdirAll(folder, 0700)
+		if err != nil {
+			lumber.Error(err, "failed to create folder at path:", folder)
+			return
+		}
+		file, err = os.Create(c.filePath)
+		if err != nil {
+			lumber.Error(err, "failed to create file at path:", c.filePath)
+			return
+		}
+	} else {
+		file, err = os.OpenFile(c.filePath, os.O_WRONLY|os.O_TRUNC, 0600)
+		if err != nil {
+			lumber.Error(err, "failed to read file at path:", c.filePath)
+			return
+		}
+	}
+	defer file.Close()
+
+	b, err := json.Marshal(c.data)
+	if err != nil {
+		lumber.Error(err, "encoding data to json failed")
+		return
+	}
+	_, err = file.Write(b)
+	if err != nil {
+		lumber.Error(err, "writing data to json failed")
+	}
+}
+
+// Seed the cache from the persistent cache file
+// returns if the cache was able to be seeded or not
+func (c *Cache[T]) seedFromFile() {
+	if _, err := os.Stat(c.filePath); !os.IsNotExist(err) {
+		b, err := os.ReadFile(c.filePath)
+		if err != nil {
+			lumber.Error(err, "reading from cache file from", c.filePath, "failed")
+			return
+		}
+
+		var data cacheData[T]
+		err = json.Unmarshal(b, &data)
+		if err != nil {
+			lumber.Error(err, "unmarshal json data failed from:", string(b))
+			return
+		}
+
+		c.data = data.Data
+		c.updated = data.Updated
+	}
+}