krino: planning — chains, placeholders, conflicts, JSON

1 files changed, 44 insertions, 0 deletions

diff --git a/internal/plan/index.go b/internal/plan/index.go
new file mode 100644
index 0000000..abe073f
--- /dev/null
+++ b/internal/plan/index.go
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package plan
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// MaxIndex returns the highest {N} used in s, 0 when none. It reports the
+// same errors Expand does for a malformed placeholder: an unclosed
+// placeholder, or {0} (capture groups are numbered from 1). It shares
+// Expand's scanner shape: "{{" and "}}" each emit one literal brace, and any
+// other "{" opens a placeholder that runs to the next "}".
+func MaxIndex(s string) (int, error) {
+	max := 0
+	for i := 0; i < len(s); {
+		switch {
+		case s[i] == '{' && i+1 < len(s) && s[i+1] == '{':
+			i += 2
+		case s[i] == '}' && i+1 < len(s) && s[i+1] == '}':
+			i += 2
+		case s[i] == '{':
+			end := strings.IndexByte(s[i+1:], '}')
+			if end < 0 {
+				return 0, fmt.Errorf("unclosed placeholder")
+			}
+			body := s[i+1 : i+1+end]
+			if n, err := strconv.Atoi(body); err == nil {
+				if n == 0 {
+					return 0, fmt.Errorf("capture groups are numbered from 1")
+				}
+				if n >= 1 && n <= 9 && n > max {
+					max = n
+				}
+			}
+			i += end + 2
+		default:
+			i++
+		}
+	}
+	return max, nil
+}