feat(store): keep an in-memory newest-first message store

Provide a concurrency-safe, per-topic message store with id-based deduplication, delete, clear, and a search predicate.

internal/store/store_test.go

@@ -0,0 +1,32 @@
+package store
+
+import "testing"
+
+func TestPutDedupeOrderDeleteClear(t *testing.T) {
+	s := New()
+	s.Put(Message{ID: "a", Time: 1, Topic: "alerts", Body: "old"})
+	s.Put(Message{ID: "b", Time: 2, Topic: "alerts", Body: "new"})
+	s.Put(Message{ID: "b", Time: 3, Topic: "alerts", Body: "dup"})
+	s.Put(Message{ID: "c", Time: 2, Topic: "backups", Body: "bak"})
+	list := s.List("alerts")
+	if len(list) != 2 || list[0].ID != "b" || list[1].ID != "a" {
+		t.Fatalf("%+v", list)
+	}
+	if got := s.Topics(); len(got) != 2 || got[0] != "alerts" || got[1] != "backups" {
+		t.Fatalf("topics %v", got)
+	}
+	s.Delete("a")
+	if len(s.List("alerts")) != 1 {
+		t.Fatal(s.List("alerts"))
+	}
+	s.Clear("alerts")
+	if len(s.List("alerts")) != 0 || len(s.List("backups")) != 1 {
+		t.Fatal("clear")
+	}
+	if !Match(Message{Body: "Hello Disk"}, "DiskFull", "disk") {
+		t.Fatal("match")
+	}
+	if Match(Message{Body: "Hello"}, "x", "nope") {
+		t.Fatal("unexpected match")
+	}
+}