1 files changed, 75 insertions, 0 deletions
diff --git a/packages/excalidraw/align.ts b/packages/excalidraw/align.ts
new file mode 100644
index 0000000..113ba27
--- /dev/null
+++ b/packages/excalidraw/align.ts
@@ -0,0 +1,75 @@
+import type { ElementsMap, ExcalidrawElement } from "./element/types";
+import { mutateElement } from "./element/mutateElement";
+import type { BoundingBox } from "./element/bounds";
+import { getCommonBoundingBox } from "./element/bounds";
+import { getMaximumGroups } from "./groups";
+import { updateBoundElements } from "./element/binding";
+import type Scene from "./scene/Scene";
+
+export interface Alignment {
+  position: "start" | "center" | "end";
+  axis: "x" | "y";
+}
+
+export const alignElements = (
+  selectedElements: ExcalidrawElement[],
+  elementsMap: ElementsMap,
+  alignment: Alignment,
+  scene: Scene,
+): ExcalidrawElement[] => {
+  const groups: ExcalidrawElement[][] = getMaximumGroups(
+    selectedElements,
+    elementsMap,
+  );
+  const selectionBoundingBox = getCommonBoundingBox(selectedElements);
+
+  return groups.flatMap((group) => {
+    const translation = calculateTranslation(
+      group,
+      selectionBoundingBox,
+      alignment,
+    );
+    return group.map((element) => {
+      // update element
+      const updatedEle = mutateElement(element, {
+        x: element.x + translation.x,
+        y: element.y + translation.y,
+      });
+      // update bound elements
+      updateBoundElements(element, scene.getNonDeletedElementsMap(), {
+        simultaneouslyUpdated: group,
+      });
+      return updatedEle;
+    });
+  });
+};
+
+const calculateTranslation = (
+  group: ExcalidrawElement[],
+  selectionBoundingBox: BoundingBox,
+  { axis, position }: Alignment,
+): { x: number; y: number } => {
+  const groupBoundingBox = getCommonBoundingBox(group);
+
+  const [min, max]: ["minX" | "minY", "maxX" | "maxY"] =
+    axis === "x" ? ["minX", "maxX"] : ["minY", "maxY"];
+
+  const noTranslation = { x: 0, y: 0 };
+  if (position === "start") {
+    return {
+      ...noTranslation,
+      [axis]: selectionBoundingBox[min] - groupBoundingBox[min],
+    };
+  } else if (position === "end") {
+    return {
+      ...noTranslation,
+      [axis]: selectionBoundingBox[max] - groupBoundingBox[max],
+    };
+  } // else if (position === "center") {
+  return {
+    ...noTranslation,
+    [axis]:
+      (selectionBoundingBox[min] + selectionBoundingBox[max]) / 2 -
+      (groupBoundingBox[min] + groupBoundingBox[max]) / 2,
+  };
+};