From f8daa181706528a15ed32ee7a01408ed6fec026d Mon Sep 17 00:00:00 2001
From: Henning Dieterichs <henning.dieterichs@live.de>
Date: Sun, 29 Mar 2020 18:24:11 +0200
Subject: [PATCH] Adds cache helper function.

---
 data-extraction/src/js/helpers/cache.ts | 31 +++++++++++++++++++++++++
 data-extraction/src/js/helpers/index.ts |  1 +
 2 files changed, 32 insertions(+)
 create mode 100644 data-extraction/src/js/helpers/cache.ts

diff --git a/data-extraction/src/js/helpers/cache.ts b/data-extraction/src/js/helpers/cache.ts
new file mode 100644
index 0000000..d804554
--- /dev/null
+++ b/data-extraction/src/js/helpers/cache.ts
@@ -0,0 +1,31 @@
+import { DataExtractorApiImpl } from "../api";
+
+const cached = new Map<string, any>();
+
+/**
+ * Evaluates an expression
+ */
+export function cache<T>(
+	expression: string | (() => T),
+	id: string | number | undefined = undefined
+): T {
+	let resultFn: () => any;
+	let key: string;
+	if (typeof expression === "string") {
+		const evalFn = DataExtractorApiImpl.lastEvalFn!;
+		resultFn = () => evalFn(expression);
+		key = JSON.stringify({ expr: expression, id });
+	} else {
+		resultFn = () => expression();
+		key = JSON.stringify({ expr: expression.toString(), id });
+	}
+
+	if (cached.has(key)) {
+		return cached.get(key);
+	}
+
+	const result = resultFn();
+	cached.set(key, result);
+
+	return result;
+}
diff --git a/data-extraction/src/js/helpers/index.ts b/data-extraction/src/js/helpers/index.ts
index 23af5d4..43c5404 100644
--- a/data-extraction/src/js/helpers/index.ts
+++ b/data-extraction/src/js/helpers/index.ts
@@ -2,3 +2,4 @@ export * from "./createGraph";
 export * from "./createGraphFromPointers";
 export * from "./tryEval";
 export * from "./markedGrid";
+export * from "./cache";