1 files changed, 115 insertions, 0 deletions
diff --git a/internal/config/print.go b/internal/config/print.go
new file mode 100644
index 0000000..5c3d467
--- /dev/null
+++ b/internal/config/print.go
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package config
+
+import (
+	"strings"
+
+	"krino/internal/sexp"
+)
+
+// PrintRule renders a rule the way krino.conf(5) and the examples write
+// one: the name on the first line, then each item on its own line indented
+// two spaces, conditions inside (when ...) aligned under the first, and the
+// closing paren on the last line. A GUI that edits a rule through a form
+// writes the result back with this and Splice, leaving the rest of the file
+// untouched (GUI design §5.1).
+//
+// What it prints comes from the parsed rule, so anything the parser dropped
+// - comments inside the form, the writer's own line breaks - is not in the
+// output; Splice's caller warns about that before replacing a form that
+// holds comments.
+func PrintRule(r *Rule) string {
+	var b strings.Builder
+	b.WriteString("(rule " + sexp.Quote(r.Name) + "\n")
+	if r.HasWhen {
+		b.WriteString("  (when ")
+		for i, c := range r.When {
+			if i > 0 {
+				b.WriteString("\n        ")
+			}
+			b.WriteString(printNode(c))
+		}
+		b.WriteString(")\n")
+	}
+	for _, line := range printSettings(r.Settings) {
+		b.WriteString("  " + line + "\n")
+	}
+	for _, a := range r.Actions {
+		b.WriteString("  " + printAction(a) + "\n")
+	}
+	if r.Stop {
+		b.WriteString("  (stop)\n")
+	}
+	// The closing paren belongs to the last line written, whichever it was.
+	out := strings.TrimRight(b.String(), "\n")
+	return out + ")\n"
+}
+
+// PrintExclude renders an (exclude ...) form on one line.
+func PrintExclude(x *Exclude) string {
+	var b strings.Builder
+	b.WriteString("(exclude")
+	for _, c := range x.When {
+		b.WriteString(" " + printNode(c))
+	}
+	b.WriteString(")\n")
+	return b.String()
+}
+
+// Splice replaces the bytes of the form between start and end - a form's
+// Pos and End - with text, and returns the new file contents. Every other
+// byte of src, comments and layout included, is kept exactly.
+func Splice(src []byte, start, end sexp.Pos, text string) []byte {
+	out := make([]byte, 0, len(src)-(end.Offset-start.Offset)+len(text))
+	out = append(out, src[:start.Offset]...)
+	out = append(out, text...)
+	return append(out, src[end.Offset:]...)
+}
+
+// printAction renders one action form.
+func printAction(a Action) string {
+	switch a.Kind {
+	case Delete:
+		return "(delete)"
+	case DeletePermanent:
+		return "(delete permanent)"
+	}
+	return "(" + a.Kind.String() + " " + sexp.Quote(a.Arg) + ")"
+}
+
+// printSettings renders the settings a rule may carry (case, fold,
+// on-conflict), in that order, leaving out those it does not set.
+func printSettings(s Settings) []string {
+	var out []string
+	if s.Case != nil {
+		out = append(out, "(case "+s.Case.String()+")")
+	}
+	if s.Fold != nil {
+		word := "no"
+		if *s.Fold {
+			word = "yes"
+		}
+		out = append(out, "(fold "+word+")")
+	}
+	if s.OnConflict != nil {
+		out = append(out, "(on-conflict "+s.OnConflict.String()+")")
+	}
+	return out
+}
+
+// printNode renders one condition node: a symbol as written, a string
+// quoted, a list as its head and arguments separated by single spaces.
+func printNode(n *sexp.Node) string {
+	switch n.Kind {
+	case sexp.String:
+		return sexp.Quote(n.Text)
+	case sexp.Symbol:
+		return n.Text
+	}
+	parts := make([]string, 0, len(n.Children))
+	for _, c := range n.Children {
+		parts = append(parts, printNode(c))
+	}
+	return "(" + strings.Join(parts, " ") + ")"
+}