basic: introduce Document.WriteTo() and Document.String()

producing an INI-style representation of the Document

Signed-off-by: Alejandro Mery <amery@jpi.io>

basic/write.go

@@ -0,0 +1,88 @@
+package basic
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+
+	"asciigoat.org/ini/parser"
+)
+
+// WriteNewLine is the new line representation used by [doc.WriteTo]
+const WriteNewLine = "\n"
+
+// AsBuffer returns a INI representation of the document on
+// a memory buffer
+func (doc *Document) AsBuffer(nl string) *bytes.Buffer {
+	var buf bytes.Buffer
+
+	if len(doc.Global) > 0 {
+		_, _ = writeFieldsTo(&buf, doc.Global, nl)
+	}
+
+	for _, sec := range doc.Sections {
+		if buf.Len() > 0 {
+			_, _ = buf.WriteString(nl)
+		}
+
+		_ = writeSectionToBuffer(&buf, &sec, nl)
+	}
+
+	return &buf
+}
+
+func writeFieldsTo(w io.Writer, fields []Field, nl string) (int64, error) {
+	var written int
+	for _, field := range fields {
+		n, err := fmt.Fprintf(w, "%s = %q%s", field.Key, field.Value, nl)
+		switch {
+		case err != nil:
+			return int64(written), err
+		case n > 0:
+			written += n
+		}
+	}
+	return int64(written), nil
+}
+
+func writeSectionToBuffer(w *bytes.Buffer, sec *Section, nl string) int {
+	var written, n int
+
+	_, _ = w.WriteRune(parser.RuneSectionStart)
+	written++
+
+	n, _ = w.WriteString(sec.Key)
+	written += n
+
+	switch {
+	case sec.EmptyID:
+		n, _ = w.WriteString(" \"\"")
+		written += n
+	case sec.ID != "":
+		_, _ = w.WriteRune(' ')
+		n, _ = fmt.Fprintf(w, "%q", sec.ID)
+		written += n + 1
+	}
+
+	_, _ = w.WriteRune(parser.RuneSectionEnd)
+	written++
+
+	n, _ = w.WriteString(nl)
+	written += n
+
+	n64, _ := writeFieldsTo(w, sec.Fields, nl)
+	return written + int(n64)
+}
+
+// WriteTo writes a INI representation of the document
+// onto the provided writer.
+func (doc *Document) WriteTo(w io.Writer) (int64, error) {
+	buf := doc.AsBuffer(WriteNewLine)
+	return buf.WriteTo(w)
+}
+
+// GoString generates a string output for "%s"
+func (doc *Document) String() string {
+	buf := doc.AsBuffer(WriteNewLine)
+	return buf.String()
+}