Adjust recording waveform behaviour for voice messages

Fixes https://github.com/vector-im/element-web/issues/17683

src/utils/FixedRollingArray.ts

@@ -0,0 +1,54 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { arrayFastClone, arraySeed } from "./arrays";
+
+/**
+ * An array which is of fixed length and accepts rolling values. Values will
+ * be inserted on the left, falling off the right.
+ */
+export class FixedRollingArray<T> {
+    private samples: T[] = [];
+
+    /**
+     * Creates a new fixed rolling array.
+     * @param width The width of the array.
+     * @param padValue The value to seed the array with.
+     */
+    constructor(private width: number, padValue: T) {
+        this.samples = arraySeed(padValue, this.width);
+    }
+
+    /**
+     * The array, as a fixed length.
+     */
+    public get value(): T[] {
+        return this.samples;
+    }
+
+    /**
+     * Pushes a value to the array.
+     * @param value The value to push.
+     */
+    public pushValue(value: T) {
+        let swap = arrayFastClone(this.samples);
+        swap.splice(0, 0, value);
+        if (swap.length > this.width) {
+            swap = swap.slice(0, this.width);
+        }
+        this.samples = swap;
+    }
+}