Extract scene functions to their respective modules (#208)

- Also, extract utilities into utils module -- capitalizeString, getDateTime, isInputLike

src/scene/selection.ts

@@ -0,0 +1,70 @@
+import { ExcalidrawElement } from "../element/types";
+import {
+  getElementAbsoluteX1,
+  getElementAbsoluteX2,
+  getElementAbsoluteY1,
+  getElementAbsoluteY2
+} from "../element";
+
+export function setSelection(
+  elements: ExcalidrawElement[],
+  selection: ExcalidrawElement
+) {
+  const selectionX1 = getElementAbsoluteX1(selection);
+  const selectionX2 = getElementAbsoluteX2(selection);
+  const selectionY1 = getElementAbsoluteY1(selection);
+  const selectionY2 = getElementAbsoluteY2(selection);
+  elements.forEach(element => {
+    const elementX1 = getElementAbsoluteX1(element);
+    const elementX2 = getElementAbsoluteX2(element);
+    const elementY1 = getElementAbsoluteY1(element);
+    const elementY2 = getElementAbsoluteY2(element);
+    element.isSelected =
+      element.type !== "selection" &&
+      selectionX1 <= elementX1 &&
+      selectionY1 <= elementY1 &&
+      selectionX2 >= elementX2 &&
+      selectionY2 >= elementY2;
+  });
+}
+
+export function clearSelection(elements: ExcalidrawElement[]) {
+  elements.forEach(element => {
+    element.isSelected = false;
+  });
+}
+
+export function deleteSelectedElements(elements: ExcalidrawElement[]) {
+  for (let i = elements.length - 1; i >= 0; --i) {
+    if (elements[i].isSelected) {
+      elements.splice(i, 1);
+    }
+  }
+}
+
+export function getSelectedIndices(elements: ExcalidrawElement[]) {
+  const selectedIndices: number[] = [];
+  elements.forEach((element, index) => {
+    if (element.isSelected) {
+      selectedIndices.push(index);
+    }
+  });
+  return selectedIndices;
+}
+
+export const someElementIsSelected = (elements: ExcalidrawElement[]) =>
+  elements.some(element => element.isSelected);
+
+export function getSelectedAttribute<T>(
+  elements: ExcalidrawElement[],
+  getAttribute: (element: ExcalidrawElement) => T
+): T | null {
+  const attributes = Array.from(
+    new Set(
+      elements
+        .filter(element => element.isSelected)
+        .map(element => getAttribute(element))
+    )
+  );
+  return attributes.length === 1 ? attributes[0] : null;
+}