Add some code refactoring from the blackboard branch

pkg/obiformats/seqfile_chunk_write.go

@@ -0,0 +1,51 @@
+package obiformats
+
+import (
+	"io"
+
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiiter"
+
+	log "github.com/sirupsen/logrus"
+)
+
+func WriteSeqFileChunk(
+	writer io.WriteCloser,
+	toBeClosed bool) ChannelSeqFileChunk {
+
+	obiiter.RegisterAPipe()
+
+	chunk_channel := make(ChannelSeqFileChunk)
+
+	go func() {
+		nextToPrint := 0
+		toBePrinted := make(map[int]SeqFileChunk)
+		for chunk := range chunk_channel {
+			if chunk.Order == nextToPrint {
+				_, _ = writer.Write(chunk.Raw.Bytes())
+				nextToPrint++
+
+				chunk, ok := toBePrinted[nextToPrint]
+				for ok {
+					_, _ = writer.Write(chunk.Raw.Bytes())
+					delete(toBePrinted, nextToPrint)
+					nextToPrint++
+					chunk, ok = toBePrinted[nextToPrint]
+				}
+			} else {
+				toBePrinted[chunk.Order] = chunk
+			}
+		}
+
+		if toBeClosed {
+			err := writer.Close()
+			if err != nil {
+				log.Fatalf("Cannot close the writer : %v", err)
+			}
+		}
+
+		obiiter.UnregisterPipe()
+		log.Warnf("The writer has been closed")
+	}()
+
+	return chunk_channel
+}