feat: publish the queue and history atomically

Both files are written whole through a temporary file and a rename, so a
renderer never reads a half-written value. An empty queue is [] rather than
null, because the renderer parses it as an array.

1 files changed, 67 insertions, 0 deletions

diff --git a/internal/notify/files.go b/internal/notify/files.go
new file mode 100644
index 0000000..22e0ea9
--- /dev/null
+++ b/internal/notify/files.go
@@ -0,0 +1,67 @@
+// Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License version 2 as
+// published by the Free Software Foundation.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+package notify
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+)
+
+// RuntimeDir is where the daemon publishes. It is tmpfs, so a reboot clears
+// every file and there is no cleanup code.
+func RuntimeDir() string {
+	if d := os.Getenv("XDG_RUNTIME_DIR"); d != "" {
+		return filepath.Join(d, "notifyd")
+	}
+	return filepath.Join(os.TempDir(), "notifyd")
+}
+
+// Publish writes the live queue and the history ring, each whole, through a
+// temporary file and a rename. A reader never sees a half-written value, the
+// same atomic write the status registry relies on.
+func Publish(dir string, live, history []Popup) error {
+	if err := os.MkdirAll(dir, 0o700); err != nil {
+		return err
+	}
+	if live == nil {
+		live = []Popup{}
+	}
+	if history == nil {
+		history = []Popup{}
+	}
+	if err := writeJSON(filepath.Join(dir, "queue.json"), live); err != nil {
+		return err
+	}
+	return writeJSON(filepath.Join(dir, "history.json"), history)
+}
+
+func writeJSON(path string, v any) error {
+	data, err := json.Marshal(v)
+	if err != nil {
+		return err
+	}
+	tmp, err := os.CreateTemp(filepath.Dir(path), ".tmp-*")
+	if err != nil {
+		return err
+	}
+	if _, err := tmp.Write(data); err != nil {
+		tmp.Close()
+		os.Remove(tmp.Name())
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		os.Remove(tmp.Name())
+		return err
+	}
+	return os.Rename(tmp.Name(), path)
+}