Convert Resizer to Typescript and create a Percentage based sizer

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/resizer/sizer.ts

@@ -0,0 +1,106 @@
+/*
+Copyright 2018 New Vector Ltd
+
+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.
+*/
+
+/**
+implements DOM/CSS operations for resizing.
+The sizer determines what CSS mechanism is used for sizing items, like flexbox, ...
+*/
+export default class Sizer {
+    constructor(
+        protected readonly container: HTMLElement,
+        protected readonly vertical: boolean,
+        protected readonly reverse: boolean,
+    ) {}
+
+    /**
+        @param {Element} item the dom element being resized
+        @return {number} how far the edge of the item is from the edge of the container
+    */
+    public getItemOffset(item: HTMLElement): number {
+        const offset = (this.vertical ? item.offsetTop : item.offsetLeft) - this.getOffset();
+        if (this.reverse) {
+            return this.getTotalSize() - (offset + this.getItemSize(item));
+        } else {
+            return offset;
+        }
+    }
+
+    /**
+        @param {Element} item the dom element being resized
+        @return {number} the width/height of an item in the container
+    */
+    public getItemSize(item: HTMLElement): number {
+        return this.vertical ? item.offsetHeight : item.offsetWidth;
+    }
+
+    /** @return {number} the width/height of the container */
+    public getTotalSize(): number {
+        return this.vertical ? this.container.offsetHeight : this.container.offsetWidth;
+    }
+
+    /** @return {number} container offset to offsetParent */
+    private getOffset(): number {
+        return this.vertical ? this.container.offsetTop : this.container.offsetLeft;
+    }
+
+    /** @return {number} container offset to document */
+    private getPageOffset() {
+        let element = this.container;
+        let offset = 0;
+        while (element) {
+            const pos = this.vertical ? element.offsetTop : element.offsetLeft;
+            offset = offset + pos;
+            element = element.offsetParent as HTMLElement;
+        }
+        return offset;
+    }
+
+    public setItemSize(item: HTMLElement, size: number) {
+        if (this.vertical) {
+            item.style.height = `${Math.round(size)}px`;
+        } else {
+            item.style.width = `${Math.round(size)}px`;
+        }
+    }
+
+    public clearItemSize(item: HTMLElement) {
+        if (this.vertical) {
+            item.style.height = null;
+        } else {
+            item.style.width = null;
+        }
+    }
+
+    // TODO
+    public start(item: HTMLElement) {}
+
+    // TODO
+    public finish(item: HTMLElement) {}
+
+    /**
+        @param {MouseEvent} event the mouse event
+        @return {number} the distance between the cursor and the edge of the container,
+            along the applicable axis (vertical or horizontal)
+    */
+    public offsetFromEvent(event: MouseEvent) {
+        const pos = this.vertical ? event.pageY : event.pageX;
+        if (this.reverse) {
+            return (this.getPageOffset() + this.getTotalSize()) - pos;
+        } else {
+            return pos - this.getPageOffset();
+        }
+    }
+}