feat: add chain writer

chain.go

@@ -0,0 +1,43 @@
+package script
+
+import "context"
+
+// Chain chains provided Processors.
+// When an error is returned by a Processor in chain, processing
+// stops and the error is retuned without running further stages.
+func ChainProcessor(processors ...Processor) Processor {
+	return func(ctx context.Context, in []string) ([]string, error) {
+		var err error
+		for _, p := range processors {
+			// not checking ctx expiry here,
+			// let the processor handle it
+
+			in, err = p(ctx, in)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		return in, nil
+	}
+}
+
+type chainWriter struct {
+	w []Writer
+}
+
+func (c *chainWriter) Write(in []string) error {
+	for _, w := range c.w {
+		if err := w.Write(in); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func ChainWriter(writers ...Writer) Writer {
+	return &chainWriter{
+		w: writers,
+	}
+}