audio: Add InfiniteLoop (#291)

audio/infiniteloop.go

@@ -0,0 +1,74 @@
+// Copyright 2017 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package audio
+
+import (
+	"fmt"
+	"io"
+)
+
+// InfiniteLoop represents a loop which never ends.
+type InfiniteLoop struct {
+	stream ReadSeekCloser
+	size   int64
+}
+
+// NewInfiniteLoop creates a new infinite loop stream with a stream and size in bytes.
+func NewInfiniteLoop(stream ReadSeekCloser, size int64) *InfiniteLoop {
+	return &InfiniteLoop{
+		stream: stream,
+		size:   size,
+	}
+}
+
+// Read is implementation of ReadSeekCloser.
+func (i *InfiniteLoop) Read(b []byte) (int, error) {
+	n, err := i.stream.Read(b)
+	if err == io.EOF {
+		if _, err := i.Seek(0, 0); err != nil {
+			return 0, err
+		}
+		err = nil
+	}
+	return n, err
+}
+
+// Seek is implementation of ReadSeekCloser.
+func (i *InfiniteLoop) Seek(offset int64, whence int) (int64, error) {
+	next := int64(0)
+	switch whence {
+	case io.SeekStart:
+		next = offset
+	case io.SeekCurrent:
+		current, err := i.stream.Seek(0, io.SeekCurrent)
+		if err != nil {
+			return 0, err
+		}
+		next = current + offset
+	case io.SeekEnd:
+		return 0, fmt.Errorf("audio: whence must be 0 or 1 for InfiniteLoop")
+	}
+	next %= i.size
+	pos, err := i.stream.Seek(next, 0)
+	if err != nil {
+		return 0, err
+	}
+	return pos, nil
+}
+
+// Close is implementation of ReadSeekCloser.
+func (l *InfiniteLoop) Close() error {
+	return l.stream.Close()
+}