feat: custom cache strategy (#42)

pkg/grib2/cache/boundary.go

@@ -1,53 +1,9 @@
 package cache
 
-import (
-	"context"
-	"strconv"
-
-	"golang.org/x/sync/singleflight"
-)
-
-type boundary struct {
-	minLat float32
-	maxLat float32
-	minLon float32
-	maxLon float32
-
-	cache      Store
-	datasource GridDataSource
-	sfg        singleflight.Group
-}
-
-func NewBoundary(minLat, maxLat, minLon, maxLon float32, datasource GridDataSource) GridCache {
-	return &boundary{
-		minLat:     minLat,
-		maxLat:     maxLat,
-		minLon:     minLon,
-		maxLon:     maxLon,
-		datasource: datasource,
-		cache:      NewMapStore(),
+func NewBoundary(minLat, maxLat, minLon, maxLon float32, datasource GridDataSource, cacheStore Store) GridCache {
+	inCache := func(lat, lon float32) bool {
+		return lat >= minLat && lat <= maxLat && lon >= minLon && lon <= maxLon
 	}
-}
-
-func (b *boundary) ReadGridAt(ctx context.Context, grid int, lat, lon float32) (float32, error) {
-	if lat < b.minLat || lat > b.maxLat || lon < b.minLon || lon > b.maxLon {
-		return b.datasource.ReadGridAt(ctx, grid)
-	}
-
-	v, err, _ := b.sfg.Do(strconv.Itoa(grid), func() (interface{}, error) {
-		vFromCache, ok := b.cache.Get(ctx, grid)
-		if !ok {
-			vFromSource, err := b.datasource.ReadGridAt(ctx, grid)
-			if err != nil {
-				return 0, err
-			}
-
-			b.cache.Set(ctx, grid, vFromSource)
-			vFromCache = vFromSource
-		}
-
-		return vFromCache, nil
-	})
 
-	return v.(float32), err
+	return NewCustom(inCache, datasource, cacheStore)
 }

pkg/grib2/cache/boundary_test.go

@@ -11,7 +11,7 @@ import (
 
 func TestBoundary(t *testing.T) {
 	ds := &mockGridDataSource{gridValue: 100}
-	bc := cache.NewBoundary(0, 10, 0, 10, ds)
+	bc := cache.NewBoundary(0, 10, 0, 10, ds, cache.NewMapStore())
 
 	// first read should be from source
 	v, err := bc.ReadGridAt(context.TODO(), 1, 1, 1)

pkg/grib2/cache/cache.go

@@ -8,6 +8,7 @@ type GridDataSource interface {
 
 type GridCache interface {
 	ReadGridAt(ctx context.Context, grid int, lat, lon float32) (float32, error)
+	InCache(lat, lon float32) bool
 }
 
 type noCache struct {
@@ -21,3 +22,7 @@ func NewNoCache(datasource GridDataSource) GridCache {
 func (n *noCache) ReadGridAt(ctx context.Context, grid int, lat, lon float32) (float32, error) {
 	return n.datasource.ReadGridAt(ctx, grid)
 }
+
+func (n *noCache) InCache(lat, lon float32) bool {
+	return false
+}

pkg/grib2/cache/custom.go

@@ -0,0 +1,47 @@
+package cache
+
+import (
+	"context"
+	"strconv"
+
+	"golang.org/x/sync/singleflight"
+)
+
+type custom struct {
+	inCache func(lat, lon float32) bool
+
+	cache      Store
+	datasource GridDataSource
+	sfg        singleflight.Group
+}
+
+func NewCustom(inCache func(lat, lon float32) bool, datasource GridDataSource, cacheStore Store) GridCache {
+	return &custom{inCache: inCache, datasource: datasource, cache: cacheStore}
+}
+
+func (c *custom) InCache(lat, lon float32) bool {
+	return c.inCache(lat, lon)
+}
+
+func (c *custom) ReadGridAt(ctx context.Context, grid int, lat, lon float32) (float32, error) {
+	if !c.InCache(lat, lon) {
+		return c.datasource.ReadGridAt(ctx, grid)
+	}
+
+	v, err, _ := c.sfg.Do(strconv.Itoa(grid), func() (interface{}, error) {
+		vFromCache, ok := c.cache.Get(ctx, grid)
+		if !ok {
+			vFromSource, err := c.datasource.ReadGridAt(ctx, grid)
+			if err != nil {
+				return 0, err
+			}
+
+			c.cache.Set(ctx, grid, vFromSource)
+			vFromCache = vFromSource
+		}
+
+		return vFromCache, nil
+	})
+
+	return v.(float32), err
+}

pkg/grib2/message.go

@@ -261,9 +261,15 @@ func NewSimplePackingMessageReaderFromMessage(r io.ReaderAt, m IndexedMessage, o
 
 type SimplePackingMessageReaderOptions func(r *simplePackingMessageReader)
 
-func WithBoundary(minLat, maxLat, minLon, maxLon float32) SimplePackingMessageReaderOptions {
+func WithBoundaryCache(minLat, maxLat, minLon, maxLon float32) SimplePackingMessageReaderOptions {
 	return func(r *simplePackingMessageReader) {
-		r.cache = cache.NewBoundary(minLat, maxLat, minLon, maxLon, r.spr)
+		r.cache = cache.NewBoundary(minLat, maxLat, minLon, maxLon, r.spr, cache.NewMapStore())
+	}
+}
+
+func WithCustomCacheStrategy(inCache func(lat, lon float32) bool) SimplePackingMessageReaderOptions {
+	return func(r *simplePackingMessageReader) {
+		r.cache = cache.NewCustom(inCache, r.spr, cache.NewMapStore())
 	}
 }