2 files changed, 155 insertions, 0 deletions
diff --git a/pkg/cache/interface.go b/pkg/cache/interface.go
new file mode 100644
index 0000000..606f50f
--- /dev/null
+++ b/pkg/cache/interface.go
@@ -0,0 +1,9 @@
+package cache
+
+type Cache interface {
+	Get(key string) ([]byte, error)
+	Set(key string, value []byte)
+	Expire(key string, exp int64)
+	GetAll() (resp map[string][]byte)
+	RemoveKey(key string)
+}
diff --git a/pkg/cache/main.go b/pkg/cache/main.go
new file mode 100644
index 0000000..d617f49
--- /dev/null
+++ b/pkg/cache/main.go
@@ -0,0 +1,146 @@
+package cache
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log/slog"
+	"os"
+	"sync"
+	"time"
+)
+
+const storeFileName = "store.json"
+
+// var MemCache Cache
+var (
+	MemCache *MemoryCache
+	log      = slog.New(slog.NewJSONHandler(os.Stdout, nil))
+)
+
+func readJSON(fileName string) (map[string][]byte, error) {
+	data := make(map[string][]byte)
+	file, err := os.Open(fileName)
+	if err != nil {
+		return data, err
+	}
+	defer file.Close()
+	decoder := json.NewDecoder(file)
+	if err := decoder.Decode(&data); err != nil {
+		return data, err
+	}
+	return data, nil
+}
+
+func init() {
+	data, err := readJSON(storeFileName)
+	if err != nil {
+		log.Warn("failed to load store from file", "error", err)
+	}
+	MemCache = &MemoryCache{
+		data:    data,
+		timeMap: make(map[string]time.Time),
+		lock:    &sync.RWMutex{},
+	}
+	MemCache.StartExpiryRoutine(time.Minute)
+	MemCache.StartBackupRoutine(time.Minute)
+}
+
+type MemoryCache struct {
+	data    map[string][]byte
+	timeMap map[string]time.Time
+	lock    *sync.RWMutex
+}
+
+// Get a value by key from the cache
+func (mc *MemoryCache) Get(key string) (value []byte, err error) {
+	var ok bool
+	mc.lock.RLock()
+	if value, ok = mc.data[key]; !ok {
+		err = fmt.Errorf("not found data in mc for the key: %v", key)
+	}
+	mc.lock.RUnlock()
+	return value, err
+}
+
+// Update a single value in the cache
+func (mc *MemoryCache) Set(key string, value []byte) {
+	// no async writing
+	mc.lock.Lock()
+	mc.data[key] = value
+	mc.lock.Unlock()
+}
+
+func (mc *MemoryCache) Expire(key string, exp int64) {
+	mc.lock.RLock()
+	mc.timeMap[key] = time.Now().Add(time.Duration(exp) * time.Second)
+	mc.lock.RUnlock()
+}
+
+func (mc *MemoryCache) GetAll() (resp map[string][]byte) {
+	resp = make(map[string][]byte)
+	mc.lock.RLock()
+	for k, v := range mc.data {
+		resp[k] = v
+	}
+	mc.lock.RUnlock()
+	return
+}
+
+func (mc *MemoryCache) GetAllTime() (resp map[string]time.Time) {
+	resp = make(map[string]time.Time)
+	mc.lock.RLock()
+	for k, v := range mc.timeMap {
+		resp[k] = v
+	}
+	mc.lock.RUnlock()
+	return
+}
+
+func (mc *MemoryCache) RemoveKey(key string) {
+	mc.lock.RLock()
+	delete(mc.data, key)
+	delete(mc.timeMap, key)
+	mc.lock.RUnlock()
+}
+
+func (mc *MemoryCache) StartExpiryRoutine(n time.Duration) {
+	ticker := time.NewTicker(n)
+	go func() {
+		for {
+			<-ticker.C
+			// get all
+			timeData := mc.GetAllTime()
+			// check time
+			currentTS := time.Now()
+			for k, ts := range timeData {
+				if ts.Before(currentTS) {
+					// delete exp keys
+					mc.RemoveKey(k)
+					log.Info("remove by expiry", "key", k)
+				}
+			}
+		}
+	}()
+}
+
+func (mc *MemoryCache) StartBackupRoutine(n time.Duration) {
+	ticker := time.NewTicker(n)
+	go func() {
+		for {
+			<-ticker.C
+			// get all
+			data := mc.GetAll()
+			jsonString, err := json.Marshal(data)
+			if err != nil {
+				log.Warn("failed to marshal kv store", "error", err)
+				continue
+			}
+			err = ioutil.WriteFile(storeFileName, jsonString, os.ModePerm)
+			if err != nil {
+				log.Warn("failed to write to json file", "error", err)
+				continue
+			}
+		}
+	}()
+}