add writer pattern object for later use

weed/filesys/page_writer/writer_pattern.go

@@ -0,0 +1,31 @@
+package page_writer
+
+type WriterPattern struct {
+	isStreaming     bool
+	lastWriteOffset int64
+}
+
+// For streaming write: only cache the first chunk
+// For random write: fall back to temp file approach
+
+func NewWriterPattern() *WriterPattern {
+	return &WriterPattern{
+		isStreaming:     true,
+		lastWriteOffset: 0,
+	}
+}
+
+func (rp *WriterPattern) MonitorWriteAt(offset int64, size int) {
+	if rp.lastWriteOffset > offset {
+		rp.isStreaming = false
+	}
+	rp.lastWriteOffset = offset
+}
+
+func (rp *WriterPattern) IsStreamingMode() bool {
+	return rp.isStreaming
+}
+
+func (rp *WriterPattern) IsRandomMode() bool {
+	return !rp.isStreaming
+}