From 05ccb4d8f1bbe3fb64e117136b4a89bcfb0b0b33 Mon Sep 17 00:00:00 2001
From: crupest <crupest@outlook.com>
Date: Tue, 27 Oct 2020 19:21:35 +0800
Subject: Split front and back end.

---
 FrontEnd/src/app/common.ts | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 FrontEnd/src/app/common.ts

(limited to 'FrontEnd/src/app/common.ts')

diff --git a/FrontEnd/src/app/common.ts b/FrontEnd/src/app/common.ts
new file mode 100644
index 00000000..0a2d345f
--- /dev/null
+++ b/FrontEnd/src/app/common.ts
@@ -0,0 +1,44 @@
+import React from "react";
+import { Observable, Subject } from "rxjs";
+
+// This error is thrown when ui goes wrong with bad logic.
+// Such as a variable should not be null, but it does.
+// This error should never occur. If it does, it indicates there is some logic bug in codes.
+export class UiLogicError extends Error {}
+
+export function useEventEmiiter(): [() => Observable<null>, () => void] {
+  const ref = React.useRef<Subject<null> | null>(null);
+
+  return React.useMemo(() => {
+    const getter = (): Subject<null> => {
+      if (ref.current == null) {
+        ref.current = new Subject<null>();
+      }
+      return ref.current;
+    };
+    const trigger = (): void => {
+      getter().next(null);
+    };
+    return [getter, trigger];
+  }, []);
+}
+
+export function useValueEventEmiiter<T>(): [
+  () => Observable<T>,
+  (value: T) => void
+] {
+  const ref = React.useRef<Subject<T> | null>(null);
+
+  return React.useMemo(() => {
+    const getter = (): Subject<T> => {
+      if (ref.current == null) {
+        ref.current = new Subject<T>();
+      }
+      return ref.current;
+    };
+    const trigger = (value: T): void => {
+      getter().next(value);
+    };
+    return [getter, trigger];
+  }, []);
+}
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