refactor(thumbnail): [PKG-TOOL-THUMB-04] type runtime modules and retain emitter attribution

packages/artplayer-tool-thumbnail/src/emitter.ts

@@ -0,0 +1,58 @@
+// Locally adapted from tiny-emitter; upstream reference 2.1.0. See THIRD_PARTY_NOTICES.
+type EventMap<Events> = { [Name in keyof Events]: readonly unknown[] }
+type Listener<Args extends unknown[]> = ((...args: Args) => unknown) & { _?: (...args: Args) => unknown }
+interface Registration<Args extends unknown[]> {
+  fn: Listener<Args>
+  ctx: unknown
+}
+type Registry<Events extends EventMap<Events>> = { [Name in keyof Events]?: Registration<[...Events[Name]]>[] }
+
+export default class Emitter<Events extends EventMap<Events> = Record<PropertyKey, unknown[]>> {
+  declare e?: Registry<Events>
+
+  on<Name extends keyof Events, Context>(name: Name, fn: (this: Context, ...args: [...Events[Name]]) => unknown, ctx?: Context): this {
+    const e: Registry<Events> = this.e || (this.e = {});
+    (e[name] || (e[name] = [])).push({ fn, ctx })
+    return this
+  }
+
+  once<Name extends keyof Events, Context>(name: Name, fn: (this: Context, ...args: [...Events[Name]]) => unknown, ctx?: Context): this {
+    // eslint-disable-next-line ts/no-this-alias -- Preserve the owning emitter independently of callback ctx.
+    const self = this
+    const callback: Listener<[...Events[Name]]> = fn
+    function listener(...args: [...Events[Name]]) {
+      self.off(name, listener)
+      callback.apply(ctx, args)
+    }
+    listener._ = fn
+    return this.on(name, listener, ctx)
+  }
+
+  emit<Name extends keyof Events>(name: Name, ...data: [...Events[Name]]): this {
+    const e: Registry<Events> = this.e || (this.e = {})
+    const evtArr = (e[name] || []).slice()
+    for (let i = 0; i < evtArr.length; i += 1) {
+      evtArr[i]!.fn.apply(evtArr[i]!.ctx, data)
+    }
+    return this
+  }
+
+  off<Name extends keyof Events>(name: Name, callback?: Listener<[...Events[Name]]>): this {
+    const e: Registry<Events> = this.e || (this.e = {})
+    const evts = e[name]
+    const liveEvents: Registration<[...Events[Name]]>[] = []
+    if (evts && callback) {
+      for (let i = 0, len = evts.length; i < len; i += 1) {
+        if (evts[i]!.fn !== callback && evts[i]!.fn._ !== callback)
+          liveEvents.push(evts[i]!)
+      }
+    }
+    if (liveEvents.length) {
+      e[name] = liveEvents
+    }
+    else {
+      delete e[name]
+    }
+    return this
+  }
+}