prototyped svg reports

server/ui/svg/element_reader.go

@@ -0,0 +1,110 @@
+package svg
+
+import (
+	"bytes"
+	"errors"
+	"io"
+)
+
+type (
+	elementReader[T Tag, A Attribute, C MarshalerReader] struct {
+		element Element[T, A, C]
+		buf     *bytes.Buffer
+
+		openTagRead     bool
+		numChildrenRead int
+		childrenRead    bool
+		childReader     io.Reader
+		closeTagRead    bool
+	}
+)
+
+func newElementReader[T Tag, A Attribute, C MarshalerReader](e Element[T, A, C]) *elementReader[T, A, C] {
+	return &elementReader[T, A, C]{
+		element: e,
+	}
+}
+
+func (e *elementReader[T, A, C]) Read(p []byte) (totalRead int, err error) {
+	if e.buf == nil {
+		// just started reading.
+		// buffer the open tag
+
+		e.buf = new(bytes.Buffer)
+
+		// bytes.Buffer never returns an error on Write()
+		e.buf.WriteByte('<')
+		e.buf.WriteString(e.element.PrintTag())
+		for _, a := range e.element.Attributes {
+			e.buf.WriteByte(' ')
+			e.buf.WriteString(PrintAttribute(a))
+		}
+		e.buf.WriteByte('>')
+	}
+
+	if !e.openTagRead {
+		// read the open tag
+
+		n, err := e.buf.Read(p)
+		totalRead += n
+		if (err != nil && !errors.Is(err, io.EOF)) || n >= len(p) {
+			return totalRead, err
+		}
+
+		// done reading the open tag
+
+		e.openTagRead = true
+		e.buf.Reset()
+
+		p = p[n:]
+	}
+
+	// read the children
+
+	for ; e.numChildrenRead < len(e.element.Children); e.numChildrenRead += 1 {
+		if e.childReader == nil {
+			e.childReader = e.element.Children[e.numChildrenRead].GetMarkupReader()
+		}
+
+		// read the child
+
+		n, err := e.childReader.Read(p)
+		totalRead += n
+		if (err != nil && !errors.Is(err, io.EOF)) || n >= len(p) {
+			return totalRead, err
+		}
+
+		// done reading the child
+
+		e.childReader = nil
+
+		p = p[n:]
+	}
+
+	if !e.childrenRead {
+		// done reading the children
+
+		e.childrenRead = true
+
+		// buffer the close tag
+
+		e.buf.Write([]byte("</"))
+		e.buf.WriteString(e.element.PrintTag())
+		e.buf.WriteByte('>')
+	}
+
+	if !e.closeTagRead {
+		n, err := e.buf.Read(p)
+		totalRead += n
+		if (err != nil && !errors.Is(err, io.EOF)) || n >= len(p) {
+			return totalRead, err
+		}
+
+		// done writing the close tag
+
+		e.closeTagRead = true
+		return totalRead, err
+	}
+
+	return 0, io.EOF
+}