Rework logger, improve plaintext caching

packages/app/src/plugins/logger.ts

@@ -0,0 +1,29 @@
+import {writable} from "svelte/store"
+import {randomId} from "@welshman/lib"
+import {projection} from "./base.js"
+import type {IApp} from "../app.js"
+
+export type LogMessage = {
+  source: string
+  id: string
+  at: number
+  [key: string]: unknown
+}
+
+/**
+ * A logger which stores messages durably for inspection. Subscribe to `messages`
+ * (a projection) to read the log; append with `log(source, {...})`.
+ */
+export class Logger {
+  protected store = writable<LogMessage[]>([])
+  messages = projection(this.store)
+
+  constructor(protected readonly app: IApp) {}
+
+  log(
+    source: string,
+    {id = randomId(), at = Date.now(), ...message}: {id?: string; at?: number; [key: string]: unknown},
+  ) {
+    this.store.update($messages => $messages.concat({source, id, at, ...message}).slice(-1000))
+  }
+}