initial code (#6)

* initial code commit

cache/cache.go

@@ -0,0 +1,86 @@
+package cache
+
+import (
+	"context"
+	"fmt"
+	"github.com/l3uddz/nabarr/logger"
+	"github.com/lefelys/state"
+	"github.com/rs/zerolog"
+	"github.com/xujiajun/nutsdb"
+	"time"
+)
+
+type Client struct {
+	log zerolog.Logger
+
+	st state.State
+	db *nutsdb.DB
+}
+
+func New(path string) (*Client, error) {
+	db, err := nutsdb.Open(nutsdb.Options{
+		Dir:                  path,
+		EntryIdxMode:         nutsdb.HintKeyValAndRAMIdxMode,
+		SegmentSize:          8 * 1024 * 1024,
+		NodeNum:              1,
+		RWMode:               nutsdb.FileIO,
+		SyncEnable:           true,
+		StartFileLoadingMode: nutsdb.MMap,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("open: %w", err)
+	}
+
+	log := logger.New("trace").With().Logger()
+
+	// start cleaner
+	st, tail := state.WithShutdown()
+	ticker := time.NewTicker(24 * time.Hour)
+	go func() {
+		for {
+			select {
+			case <-tail.End():
+				ticker.Stop()
+				tail.Done()
+				return
+			case <-ticker.C:
+				// clean cache
+				err := db.Update(func(tx *nutsdb.Tx) error {
+					return db.Merge()
+				})
+
+				switch {
+				case err == nil:
+					log.Info().Msg("Cleaned cache")
+				case err.Error() == "the number of files waiting to be merged is at least 2":
+				// there were no data files to be merged
+				default:
+					// unexpected error
+					log.Error().
+						Err(err).
+						Msg("Failed cleaning cache")
+				}
+			}
+		}
+	}()
+
+	return &Client{
+		log: log,
+		st:  st,
+		db:  db,
+	}, nil
+}
+
+func (c *Client) Close() error {
+	// shutdown cleaner
+	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
+	defer cancel()
+	if err := c.st.Shutdown(ctx); err != nil {
+		c.log.Error().
+			Err(err).
+			Msg("Failed shutting down cache cleaner gracefully")
+	}
+
+	// close cache
+	return c.db.Close()
+}