1 files changed, 38 insertions, 0 deletions
diff --git a/shortid.go b/shortid.go
new file mode 100644
index 0000000..9cfd076
--- /dev/null
+++ b/shortid.go
@@ -0,0 +1,38 @@
+package main
+
+import (
+	"encoding/base32"
+	"encoding/binary"
+	"fmt"
+	"strings"
+)
+
+var b32 = base32.StdEncoding.WithPadding(base32.NoPadding)
+
+func encodeID(id int64) (string, error) {
+	if id < 0 {
+		return "", fmt.Errorf("id out of range: %d", id)
+	}
+	buf := make([]byte, 8)
+	binary.BigEndian.PutUint64(buf, uint64(id))
+	// Trim leading zero bytes, keep at least 2 bytes (4 chars).
+	i := 0
+	for i < 6 && buf[i] == 0 {
+		i++
+	}
+	return b32.EncodeToString(buf[i:]), nil
+}
+
+func decodeID(s string) (int64, error) {
+	s = strings.ToUpper(s)
+	buf, err := b32.DecodeString(s)
+	if err != nil {
+		return 0, fmt.Errorf("invalid short id: %w", err)
+	}
+	if len(buf) == 0 || len(buf) > 8 {
+		return 0, fmt.Errorf("invalid short id")
+	}
+	padded := make([]byte, 8)
+	copy(padded[8-len(buf):], buf)
+	return int64(binary.BigEndian.Uint64(padded)), nil
+}