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, 57 insertions, 0 deletions

diff --git a/internal/notify/files_test.go b/internal/notify/files_test.go
new file mode 100644
index 0000000..b17a4f6
--- /dev/null
+++ b/internal/notify/files_test.go
@@ -0,0 +1,57 @@
+// 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"
+	"testing"
+)
+
+func TestPublishWritesBothFiles(t *testing.T) {
+	dir := t.TempDir()
+	live := []Popup{{ID: 1, App: "a", Urgency: Normal, Created: 1, Expires: 2}}
+	history := []Popup{{ID: 2, App: "b", Urgency: Low, Created: 3}}
+	if err := Publish(dir, live, history); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	var gotLive []Popup
+	data, err := os.ReadFile(filepath.Join(dir, "queue.json"))
+	if err != nil {
+		t.Fatalf("read queue: %v", err)
+	}
+	if err := json.Unmarshal(data, &gotLive); err != nil {
+		t.Fatalf("queue not JSON: %v", err)
+	}
+	if len(gotLive) != 1 || gotLive[0].ID != 1 {
+		t.Errorf("queue = %+v, want one id 1", gotLive)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "history.json")); err != nil {
+		t.Errorf("history.json missing: %v", err)
+	}
+}
+
+func TestPublishEmptyIsAnEmptyArray(t *testing.T) {
+	dir := t.TempDir()
+	if err := Publish(dir, nil, nil); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	data, _ := os.ReadFile(filepath.Join(dir, "queue.json"))
+	var got []Popup
+	if err := json.Unmarshal(data, &got); err != nil {
+		t.Fatalf("empty queue not JSON array: %v (%s)", err, data)
+	}
+	if string(data) != "[]" {
+		t.Errorf("empty queue encoded as %q, want []", data)
+	}
+}