Add ~emersion/go-scfg as a subdirectory

1 files changed, 107 insertions, 0 deletions

diff --git a/scfg/writer.go b/scfg/writer.go
new file mode 100644
index 0000000..97148a3
--- /dev/null
+++ b/scfg/writer.go
@@ -0,0 +1,107 @@
+package scfg
+
+import (
+	"errors"
+	"io"
+	"strings"
+)
+
+var (
+	errDirEmptyName = errors.New("scfg: directive with empty name")
+)
+
+// Write writes a parsed configuration to the provided io.Writer.
+func Write(w io.Writer, blk Block) error {
+	enc := newEncoder(w)
+	err := enc.encodeBlock(blk)
+	return err
+}
+
+// encoder write SCFG directives to an output stream.
+type encoder struct {
+	w   io.Writer
+	lvl int
+	err error
+}
+
+// newEncoder returns a new encoder that writes to w.
+func newEncoder(w io.Writer) *encoder {
+	return &encoder{w: w}
+}
+
+func (enc *encoder) push() {
+	enc.lvl++
+}
+
+func (enc *encoder) pop() {
+	enc.lvl--
+}
+
+func (enc *encoder) writeIndent() {
+	for i := 0; i < enc.lvl; i++ {
+		enc.write([]byte("\t"))
+	}
+}
+
+func (enc *encoder) write(p []byte) {
+	if enc.err != nil {
+		return
+	}
+	_, enc.err = enc.w.Write(p)
+}
+
+func (enc *encoder) encodeBlock(blk Block) error {
+	for _, dir := range blk {
+		enc.encodeDir(*dir)
+	}
+	return enc.err
+}
+
+func (enc *encoder) encodeDir(dir Directive) error {
+	if enc.err != nil {
+		return enc.err
+	}
+
+	if dir.Name == "" {
+		enc.err = errDirEmptyName
+		return enc.err
+	}
+
+	enc.writeIndent()
+	enc.write([]byte(maybeQuote(dir.Name)))
+	for _, p := range dir.Params {
+		enc.write([]byte(" "))
+		enc.write([]byte(maybeQuote(p)))
+	}
+
+	if len(dir.Children) > 0 {
+		enc.write([]byte(" {\n"))
+		enc.push()
+		enc.encodeBlock(dir.Children)
+		enc.pop()
+
+		enc.writeIndent()
+		enc.write([]byte("}"))
+	}
+	enc.write([]byte("\n"))
+
+	return enc.err
+}
+
+const specialChars = "\"\\\r\n'{} \t"
+
+func maybeQuote(s string) string {
+	if s == "" || strings.ContainsAny(s, specialChars) {
+		var sb strings.Builder
+		sb.WriteByte('"')
+		for _, ch := range s {
+			if strings.ContainsRune(`"\`, ch) {
+				sb.WriteByte('\\')
+			}
+			sb.WriteRune(ch)
+		}
+		sb.WriteByte('"')
+		return sb.String()
+	}
+	return s
+}