refactor: Decompose fetch func

internal/compression/decompress.go

@@ -0,0 +1,59 @@
+package compression
+
+import (
+	"compress/gzip"
+	"context"
+	"io"
+
+	"github.com/andybalholm/brotli"
+	"github.com/cosnicolaou/pbzip2"
+	"github.com/dsnet/compress/bzip2"
+	"github.com/klauspost/compress/zstd"
+	"github.com/klauspost/pgzip"
+	"github.com/pierrec/lz4/v4"
+	"github.com/pojntfx/stfs/pkg/config"
+)
+
+func Decompress(
+	src io.Reader,
+	compressionFormat string,
+) (io.ReadCloser, error) {
+	switch compressionFormat {
+	case config.CompressionFormatGZipKey:
+		fallthrough
+	case config.CompressionFormatParallelGZipKey:
+		if compressionFormat == config.CompressionFormatGZipKey {
+			return gzip.NewReader(src)
+		}
+
+		return pgzip.NewReader(src)
+	case config.CompressionFormatLZ4Key:
+		lz := lz4.NewReader(src)
+		if err := lz.Apply(lz4.ConcurrencyOption(-1)); err != nil {
+			return nil, err
+		}
+
+		return io.NopCloser(lz), nil
+	case config.CompressionFormatZStandardKey:
+		zz, err := zstd.NewReader(src)
+		if err != nil {
+			return nil, err
+		}
+
+		return io.NopCloser(zz), nil
+	case config.CompressionFormatBrotliKey:
+		br := brotli.NewReader(src)
+
+		return io.NopCloser(br), nil
+	case config.CompressionFormatBzip2Key:
+		return bzip2.NewReader(src, nil)
+	case config.CompressionFormatBzip2ParallelKey:
+		bz := pbzip2.NewReader(context.Background(), src)
+
+		return io.NopCloser(bz), nil
+	case config.NoneKey:
+		return io.NopCloser(src), nil
+	default:
+		return nil, config.ErrUnsupportedCompressionFormat
+	}
+}