snapping.ts

import {
  Bounds,
  getCommonBounds,
  getDraggedElementsBounds,
  getElementAbsoluteCoords,
} from "./element/bounds";
import { MaybeTransformHandleType } from "./element/transformHandles";
import { isBoundToContainer, isFrameElement } from "./element/typeChecks";
import {
  ExcalidrawElement,
  NonDeletedExcalidrawElement,
} from "./element/types";
import { getMaximumGroups } from "./groups";
import { KEYS } from "./keys";
import { rangeIntersection, rangesOverlap, rotatePoint } from "./math";
import { getVisibleAndNonSelectedElements } from "./scene/selection";
import { AppState, KeyboardModifiersObject, Point } from "./types";

const SNAP_DISTANCE = 8;

// do not comput more gaps per axis than this limit
// TODO increase or remove once we optimize
const VISIBLE_GAPS_LIMIT_PER_AXIS = 99999;

// snap distance with zoom value taken into consideration
export const getSnapDistance = (zoomValue: number) => {
  return SNAP_DISTANCE / zoomValue;
};

type Vector2D = {
  x: number;
  y: number;
};

type PointPair = [Point, Point];

export type PointSnap = {
  type: "point";
  points: PointPair;
  offset: number;
};

export type Gap = {
  //  start side ↓     length
  // ┌───────────┐◄───────────────►
  // │           │-----------------┌───────────┐
  // │  start    │       ↑         │           │
  // │  element  │    overlap      │  end      │
  // │           │       ↓         │  element  │
  // └───────────┘-----------------│           │
  //                               └───────────┘
  //                               ↑ end side
  startBounds: Bounds;
  endBounds: Bounds;
  startSide: [Point, Point];
  endSide: [Point, Point];
  overlap: [number, number];
  length: number;
};

export type GapSnap = {
  type: "gap";
  direction:
    | "center_horizontal"
    | "center_vertical"
    | "side_left"
    | "side_right"
    | "side_top"
    | "side_bottom";
  gap: Gap;
  offset: number;
};

export type GapSnaps = GapSnap[];

export type Snap = GapSnap | PointSnap;
export type Snaps = Snap[];

export type PointSnapLine = {
  type: "points";
  points: Point[];
};

export type PointerSnapLine = {
  type: "pointer";
  points: PointPair;
  direction: "horizontal" | "vertical";
};

export type GapSnapLine = {
  type: "gap";
  direction: "horizontal" | "vertical";
  points: PointPair;
};

export type SnapLine = PointSnapLine | GapSnapLine | PointerSnapLine;

// -----------------------------------------------------------------------------

export class SnapCache {
  private static referenceSnapPoints: Point[] | null = null;

  private static visibleGaps: {
    verticalGaps: Gap[];
    horizontalGaps: Gap[];
  } | null = null;

  public static setReferenceSnapPoints = (snapPoints: Point[] | null) => {
    SnapCache.referenceSnapPoints = snapPoints;
  };

  public static getReferenceSnapPoints = () => {
    return SnapCache.referenceSnapPoints;
  };

  public static setVisibleGaps = (
    gaps: {
      verticalGaps: Gap[];
      horizontalGaps: Gap[];
    } | null,
  ) => {
    SnapCache.visibleGaps = gaps;
  };

  public static getVisibleGaps = () => {
    return SnapCache.visibleGaps;
  };

  public static destroy = () => {
    SnapCache.referenceSnapPoints = null;
    SnapCache.visibleGaps = null;
  };
}

// -----------------------------------------------------------------------------

export const isSnappingEnabled = ({
  event,
  appState,
  selectedElements,
}: {
  appState: AppState;
  event: KeyboardModifiersObject;
  selectedElements: NonDeletedExcalidrawElement[];
}) => {
  if (event) {
    return (
      (appState.objectsSnapModeEnabled && !event[KEYS.CTRL_OR_CMD]) ||
      (!appState.objectsSnapModeEnabled &&
        event[KEYS.CTRL_OR_CMD] &&
        appState.gridSize === null)
    );
  }

  // do not suggest snaps for an arrow to give way to binding
  if (selectedElements.length === 1 && selectedElements[0].type === "arrow") {
    return false;
  }
  return appState.objectsSnapModeEnabled;
};

export const areRoughlyEqual = (a: number, b: number, precision = 0.01) => {
  return Math.abs(a - b) <= precision;
};

export const getElementsCorners = (
  elements: ExcalidrawElement[],
  {
    omitCenter,
    boundingBoxCorners,
    dragOffset,
  }: {
    omitCenter?: boolean;
    boundingBoxCorners?: boolean;
    dragOffset?: Vector2D;
  } = {
    omitCenter: false,
    boundingBoxCorners: false,
  },
): Point[] => {
  let result: Point[] = [];

  if (elements.length === 1) {
    const element = elements[0];

    let [x1, y1, x2, y2, cx, cy] = getElementAbsoluteCoords(element);

    if (dragOffset) {
      x1 += dragOffset.x;
      x2 += dragOffset.x;
      cx += dragOffset.x;

      y1 += dragOffset.y;
      y2 += dragOffset.y;
      cy += dragOffset.y;
    }

    const halfWidth = (x2 - x1) / 2;
    const halfHeight = (y2 - y1) / 2;

    if (
      (element.type === "diamond" || element.type === "ellipse") &&
      !boundingBoxCorners
    ) {
      const leftMid = rotatePoint(
        [x1, y1 + halfHeight],
        [cx, cy],
        element.angle,
      );
      const topMid = rotatePoint([x1 + halfWidth, y1], [cx, cy], element.angle);
      const rightMid = rotatePoint(
        [x2, y1 + halfHeight],
        [cx, cy],
        element.angle,
      );
      const bottomMid = rotatePoint(
        [x1 + halfWidth, y2],
        [cx, cy],
        element.angle,
      );
      const center: Point = [cx, cy];

      result = omitCenter
        ? [leftMid, topMid, rightMid, bottomMid]
        : [leftMid, topMid, rightMid, bottomMid, center];
    } else {
      const topLeft = rotatePoint([x1, y1], [cx, cy], element.angle);
      const topRight = rotatePoint([x2, y1], [cx, cy], element.angle);
      const bottomLeft = rotatePoint([x1, y2], [cx, cy], element.angle);
      const bottomRight = rotatePoint([x2, y2], [cx, cy], element.angle);
      const center: Point = [cx, cy];

      result = omitCenter
        ? [topLeft, topRight, bottomLeft, bottomRight]
        : [topLeft, topRight, bottomLeft, bottomRight, center];
    }
  } else if (elements.length > 1) {
    const [minX, minY, maxX, maxY] = getDraggedElementsBounds(
      elements,
      dragOffset ?? { x: 0, y: 0 },
    );
    const width = maxX - minX;
    const height = maxY - minY;

    const topLeft: Point = [minX, minY];
    const topRight: Point = [maxX, minY];
    const bottomLeft: Point = [minX, maxY];
    const bottomRight: Point = [maxX, maxY];
    const center: Point = [minX + width / 2, minY + height / 2];

    result = omitCenter
      ? [topLeft, topRight, bottomLeft, bottomRight]
      : [topLeft, topRight, bottomLeft, bottomRight, center];
  }

  return result.map((point) => [round(point[0]), round(point[1])] as Point);
};

const getReferenceElements = (
  elements: readonly NonDeletedExcalidrawElement[],
  selectedElements: NonDeletedExcalidrawElement[],
  appState: AppState,
) => {
  const selectedFrames = selectedElements
    .filter((element) => isFrameElement(element))
    .map((frame) => frame.id);

  return getVisibleAndNonSelectedElements(
    elements,
    selectedElements,
    appState,
  ).filter(
    (element) => !(element.frameId && selectedFrames.includes(element.frameId)),
  );
};

export const getVisibleGaps = (
  elements: readonly NonDeletedExcalidrawElement[],
  selectedElements: ExcalidrawElement[],
  appState: AppState,
) => {
  const referenceElements: ExcalidrawElement[] = getReferenceElements(
    elements,
    selectedElements,
    appState,
  );

  const referenceBounds = getMaximumGroups(referenceElements)
    .filter(
      (elementsGroup) =>
        !(elementsGroup.length === 1 && isBoundToContainer(elementsGroup[0])),
    )
    .map(
      (group) =>
        getCommonBounds(group).map((bound) =>
          round(bound),
        ) as unknown as Bounds,
    );

  const horizontallySorted = referenceBounds.sort((a, b) => a[0] - b[0]);

  const horizontalGaps: Gap[] = [];

  let c = 0;

  horizontal: for (let i = 0; i < horizontallySorted.length; i++) {
    const startBounds = horizontallySorted[i];

    for (let j = i + 1; j < horizontallySorted.length; j++) {
      if (++c > VISIBLE_GAPS_LIMIT_PER_AXIS) {
        break horizontal;
      }

      const endBounds = horizontallySorted[j];

      const [, startMinY, startMaxX, startMaxY] = startBounds;
      const [endMinX, endMinY, , endMaxY] = endBounds;

      if (
        startMaxX < endMinX &&
        rangesOverlap([startMinY, startMaxY], [endMinY, endMaxY])
      ) {
        horizontalGaps.push({
          startBounds,
          endBounds,
          startSide: [
            [startMaxX, startMinY],
            [startMaxX, startMaxY],
          ],
          endSide: [
            [endMinX, endMinY],
            [endMinX, endMaxY],
          ],
          length: endMinX - startMaxX,
          overlap: rangeIntersection(
            [startMinY, startMaxY],
            [endMinY, endMaxY],
          )!,
        });
      }
    }
  }

  const verticallySorted = referenceBounds.sort((a, b) => a[1] - b[1]);

  const verticalGaps: Gap[] = [];

  c = 0;

  vertical: for (let i = 0; i < verticallySorted.length; i++) {
    const startBounds = verticallySorted[i];

    for (let j = i + 1; j < verticallySorted.length; j++) {
      if (++c > VISIBLE_GAPS_LIMIT_PER_AXIS) {
        break vertical;
      }
      const endBounds = verticallySorted[j];

      const [startMinX, , startMaxX, startMaxY] = startBounds;
      const [endMinX, endMinY, endMaxX] = endBounds;

      if (
        startMaxY < endMinY &&
        rangesOverlap([startMinX, startMaxX], [endMinX, endMaxX])
      ) {
        verticalGaps.push({
          startBounds,
          endBounds,
          startSide: [
            [startMinX, startMaxY],
            [startMaxX, startMaxY],
          ],
          endSide: [
            [endMinX, endMinY],
            [endMaxX, endMinY],
          ],
          length: endMinY - startMaxY,
          overlap: rangeIntersection(
            [startMinX, startMaxX],
            [endMinX, endMaxX],
          )!,
        });
      }
    }
  }

  return {
    horizontalGaps,
    verticalGaps,
  };
};

const getGapSnaps = (
  selectedElements: ExcalidrawElement[],
  dragOffset: Vector2D,
  appState: AppState,
  event: KeyboardModifiersObject,
  nearestSnapsX: Snaps,
  nearestSnapsY: Snaps,
  minOffset: Vector2D,
) => {
  if (!isSnappingEnabled({ appState, event, selectedElements })) {
    return [];
  }

  if (selectedElements.length === 0) {
    return [];
  }

  const visibleGaps = SnapCache.getVisibleGaps();

  if (visibleGaps) {
    const { horizontalGaps, verticalGaps } = visibleGaps;

    const [minX, minY, maxX, maxY] = getDraggedElementsBounds(
      selectedElements,
      dragOffset,
    ).map((bound) => round(bound));
    const centerX = (minX + maxX) / 2;
    const centerY = (minY + maxY) / 2;

    for (const gap of horizontalGaps) {
      if (!rangesOverlap([minY, maxY], gap.overlap)) {
        continue;
      }

      // center gap
      const gapMidX = gap.startSide[0][0] + gap.length / 2;
      const centerOffset = round(gapMidX - centerX);
      const gapIsLargerThanSelection = gap.length > maxX - minX;

      if (gapIsLargerThanSelection && Math.abs(centerOffset) <= minOffset.x) {
        if (Math.abs(centerOffset) < minOffset.x) {
          nearestSnapsX.length = 0;
        }
        minOffset.x = Math.abs(centerOffset);

        const snap: GapSnap = {
          type: "gap",
          direction: "center_horizontal",
          gap,
          offset: centerOffset,
        };

        nearestSnapsX.push(snap);
        continue;
      }

      // side gap, from the right
      const [, , endMaxX] = gap.endBounds;
      const distanceToEndElementX = minX - endMaxX;
      const sideOffsetRight = round(gap.length - distanceToEndElementX);

      if (Math.abs(sideOffsetRight) <= minOffset.x) {
        if (Math.abs(sideOffsetRight) < minOffset.x) {
          nearestSnapsX.length = 0;
        }
        minOffset.x = Math.abs(sideOffsetRight);

        const snap: GapSnap = {
          type: "gap",
          direction: "side_right",
          gap,
          offset: sideOffsetRight,
        };
        nearestSnapsX.push(snap);
        continue;
      }

      // side gap, from the left
      const [startMinX, , ,] = gap.startBounds;
      const distanceToStartElementX = startMinX - maxX;
      const sideOffsetLeft = round(distanceToStartElementX - gap.length);

      if (Math.abs(sideOffsetLeft) <= minOffset.x) {
        if (Math.abs(sideOffsetLeft) < minOffset.x) {
          nearestSnapsX.length = 0;
        }
        minOffset.x = Math.abs(sideOffsetLeft);

        const snap: GapSnap = {
          type: "gap",
          direction: "side_left",
          gap,
          offset: sideOffsetLeft,
        };
        nearestSnapsX.push(snap);
        continue;
      }
    }
    for (const gap of verticalGaps) {
      if (!rangesOverlap([minX, maxX], gap.overlap)) {
        continue;
      }

      // center gap
      const gapMidY = gap.startSide[0][1] + gap.length / 2;
      const centerOffset = round(gapMidY - centerY);
      const gapIsLargerThanSelection = gap.length > maxY - minY;

      if (gapIsLargerThanSelection && Math.abs(centerOffset) <= minOffset.y) {
        if (Math.abs(centerOffset) < minOffset.y) {
          nearestSnapsY.length = 0;
        }
        minOffset.y = Math.abs(centerOffset);

        const snap: GapSnap = {
          type: "gap",
          direction: "center_vertical",
          gap,
          offset: centerOffset,
        };

        nearestSnapsY.push(snap);
        continue;
      }

      // side gap, from the top
      const [, startMinY, ,] = gap.startBounds;
      const distanceToStartElementY = startMinY - maxY;
      const sideOffsetTop = round(distanceToStartElementY - gap.length);

      if (Math.abs(sideOffsetTop) <= minOffset.y) {
        if (Math.abs(sideOffsetTop) < minOffset.y) {
          nearestSnapsY.length = 0;
        }
        minOffset.y = Math.abs(sideOffsetTop);

        const snap: GapSnap = {
          type: "gap",
          direction: "side_top",
          gap,
          offset: sideOffsetTop,
        };
        nearestSnapsY.push(snap);
        continue;
      }

      // side gap, from the bottom
      const [, , , endMaxY] = gap.endBounds;
      const distanceToEndElementY = round(minY - endMaxY);
      const sideOffsetBottom = gap.length - distanceToEndElementY;

      if (Math.abs(sideOffsetBottom) <= minOffset.y) {
        if (Math.abs(sideOffsetBottom) < minOffset.y) {
          nearestSnapsY.length = 0;
        }
        minOffset.y = Math.abs(sideOffsetBottom);

        const snap: GapSnap = {
          type: "gap",
          direction: "side_bottom",
          gap,
          offset: sideOffsetBottom,
        };
        nearestSnapsY.push(snap);
        continue;
      }
    }
  }
};

export const getReferenceSnapPoints = (
  elements: readonly NonDeletedExcalidrawElement[],
  selectedElements: ExcalidrawElement[],
  appState: AppState,
) => {
  const referenceElements = getReferenceElements(
    elements,
    selectedElements,
    appState,
  );

  return getMaximumGroups(referenceElements)
    .filter(
      (elementsGroup) =>
        !(elementsGroup.length === 1 && isBoundToContainer(elementsGroup[0])),
    )
    .flatMap((elementGroup) => getElementsCorners(elementGroup));
};

const getPointSnaps = (
  selectedElements: ExcalidrawElement[],
  selectionSnapPoints: Point[],
  appState: AppState,
  event: KeyboardModifiersObject,
  nearestSnapsX: Snaps,
  nearestSnapsY: Snaps,
  minOffset: Vector2D,
) => {
  if (
    !isSnappingEnabled({ appState, event, selectedElements }) ||
    (selectedElements.length === 0 && selectionSnapPoints.length === 0)
  ) {
    return [];
  }

  const referenceSnapPoints = SnapCache.getReferenceSnapPoints();

  if (referenceSnapPoints) {
    for (const thisSnapPoint of selectionSnapPoints) {
      for (const otherSnapPoint of referenceSnapPoints) {
        const offsetX = otherSnapPoint[0] - thisSnapPoint[0];
        const offsetY = otherSnapPoint[1] - thisSnapPoint[1];

        if (Math.abs(offsetX) <= minOffset.x) {
          if (Math.abs(offsetX) < minOffset.x) {
            nearestSnapsX.length = 0;
          }

          nearestSnapsX.push({
            type: "point",
            points: [thisSnapPoint, otherSnapPoint],
            offset: offsetX,
          });

          minOffset.x = Math.abs(offsetX);
        }

        if (Math.abs(offsetY) <= minOffset.y) {
          if (Math.abs(offsetY) < minOffset.y) {
            nearestSnapsY.length = 0;
          }

          nearestSnapsY.push({
            type: "point",
            points: [thisSnapPoint, otherSnapPoint],
            offset: offsetY,
          });

          minOffset.y = Math.abs(offsetY);
        }
      }
    }
  }
};

export const snapDraggedElements = (
  selectedElements: ExcalidrawElement[],
  dragOffset: Vector2D,
  appState: AppState,
  event: KeyboardModifiersObject,
) => {
  if (
    !isSnappingEnabled({ appState, event, selectedElements }) ||
    selectedElements.length === 0
  ) {
    return {
      snapOffset: {
        x: 0,
        y: 0,
      },
      snapLines: [],
    };
  }

  dragOffset.x = round(dragOffset.x);
  dragOffset.y = round(dragOffset.y);
  const nearestSnapsX: Snaps = [];
  const nearestSnapsY: Snaps = [];
  const snapDistance = getSnapDistance(appState.zoom.value);
  const minOffset = {
    x: snapDistance,
    y: snapDistance,
  };

  const selectionPoints = getElementsCorners(selectedElements, {
    dragOffset,
  });

  // get the nearest horizontal and vertical point and gap snaps
  getPointSnaps(
    selectedElements,
    selectionPoints,
    appState,
    event,
    nearestSnapsX,
    nearestSnapsY,
    minOffset,
  );

  getGapSnaps(
    selectedElements,
    dragOffset,
    appState,
    event,
    nearestSnapsX,
    nearestSnapsY,
    minOffset,
  );

  // using the nearest snaps to figure out how
  // much the elements need to be offset to be snapped
  // to some reference elements
  const snapOffset = {
    x: nearestSnapsX[0]?.offset ?? 0,
    y: nearestSnapsY[0]?.offset ?? 0,
  };

  // once the elements are snapped
  // and moved to the snapped position
  // we want to use the element's snapped position
  // to update nearest snaps so that we can create
  // point and gap snap lines correctly without any shifting

  minOffset.x = 0;
  minOffset.y = 0;
  nearestSnapsX.length = 0;
  nearestSnapsY.length = 0;
  const newDragOffset = {
    x: round(dragOffset.x + snapOffset.x),
    y: round(dragOffset.y + snapOffset.y),
  };

  getPointSnaps(
    selectedElements,
    getElementsCorners(selectedElements, {
      dragOffset: newDragOffset,
    }),
    appState,
    event,
    nearestSnapsX,
    nearestSnapsY,
    minOffset,
  );

  getGapSnaps(
    selectedElements,
    newDragOffset,
    appState,
    event,
    nearestSnapsX,
    nearestSnapsY,
    minOffset,
  );

  const pointSnapLines = createPointSnapLines(nearestSnapsX, nearestSnapsY);

  const gapSnapLines = createGapSnapLines(
    selectedElements,
    newDragOffset,
    [...nearestSnapsX, ...nearestSnapsY].filter(
      (snap) => snap.type === "gap",
    ) as GapSnap[],
  );

  return {
    snapOffset,
    snapLines: [...pointSnapLines, ...gapSnapLines],
  };
};

const round = (x: number) => {
  const decimalPlaces = 6;
  return Math.round(x * 10 ** decimalPlaces) / 10 ** decimalPlaces;
};

const dedupePoints = (points: Point[]): Point[] => {
  const map = new Map<string, Point>();

  for (const point of points) {
    const key = point.join(",");

    if (!map.has(key)) {
      map.set(key, point);
    }
  }

  return Array.from(map.values());
};

const createPointSnapLines = (
  nearestSnapsX: Snaps,
  nearestSnapsY: Snaps,
): PointSnapLine[] => {
  const snapsX = {} as { [key: string]: Point[] };
  const snapsY = {} as { [key: string]: Point[] };

  if (nearestSnapsX.length > 0) {
    for (const snap of nearestSnapsX) {
      if (snap.type === "point") {
        // key = thisPoint.x
        const key = round(snap.points[0][0]);
        if (!snapsX[key]) {
          snapsX[key] = [];
        }
        snapsX[key].push(
          ...snap.points.map(
            (point) => [round(point[0]), round(point[1])] as Point,
          ),
        );
      }
    }
  }

  if (nearestSnapsY.length > 0) {
    for (const snap of nearestSnapsY) {
      if (snap.type === "point") {
        // key = thisPoint.y
        const key = round(snap.points[0][1]);
        if (!snapsY[key]) {
          snapsY[key] = [];
        }
        snapsY[key].push(
          ...snap.points.map(
            (point) => [round(point[0]), round(point[1])] as Point,
          ),
        );
      }
    }
  }

  return Object.entries(snapsX)
    .map(([key, points]) => {
      return {
        type: "points",
        points: dedupePoints(
          points
            .map((point) => {
              return [Number(key), point[1]] as Point;
            })
            .sort((a, b) => a[1] - b[1]),
        ),
      } as PointSnapLine;
    })
    .concat(
      Object.entries(snapsY).map(([key, points]) => {
        return {
          type: "points",
          points: dedupePoints(
            points
              .map((point) => {
                return [point[0], Number(key)] as Point;
              })
              .sort((a, b) => a[0] - b[0]),
          ),
        } as PointSnapLine;
      }),
    );
};

const dedupeGapSnapLines = (gapSnapLines: GapSnapLine[]) => {
  const map = new Map<string, GapSnapLine>();

  for (const gapSnapLine of gapSnapLines) {
    const key = gapSnapLine.points
      .flat()
      .map((point) => [round(point)])
      .join(",");

    if (!map.has(key)) {
      map.set(key, gapSnapLine);
    }
  }

  return Array.from(map.values());
};

const createGapSnapLines = (
  selectedElements: ExcalidrawElement[],
  dragOffset: Vector2D,
  gapSnaps: GapSnap[],
): GapSnapLine[] => {
  const [minX, minY, maxX, maxY] = getDraggedElementsBounds(
    selectedElements,
    dragOffset,
  );

  const gapSnapLines: GapSnapLine[] = [];

  for (const gapSnap of gapSnaps) {
    const [startMinX, startMinY, startMaxX, startMaxY] =
      gapSnap.gap.startBounds;
    const [endMinX, endMinY, endMaxX, endMaxY] = gapSnap.gap.endBounds;

    const verticalIntersection = rangeIntersection(
      [minY, maxY],
      gapSnap.gap.overlap,
    );

    const horizontalGapIntersection = rangeIntersection(
      [minX, maxX],
      gapSnap.gap.overlap,
    );

    switch (gapSnap.direction) {
      case "center_horizontal": {
        if (verticalIntersection) {
          const gapLineY =
            (verticalIntersection[0] + verticalIntersection[1]) / 2;

          gapSnapLines.push(
            {
              type: "gap",
              direction: "horizontal",
              points: [
                [gapSnap.gap.startSide[0][0], gapLineY],
                [minX, gapLineY],
              ],
            },
            {
              type: "gap",
              direction: "horizontal",
              points: [
                [maxX, gapLineY],
                [gapSnap.gap.endSide[0][0], gapLineY],
              ],
            },
          );
        }
        break;
      }
      case "center_vertical": {
        if (horizontalGapIntersection) {
          const gapLineX =
            (horizontalGapIntersection[0] + horizontalGapIntersection[1]) / 2;

          gapSnapLines.push(
            {
              type: "gap",
              direction: "vertical",
              points: [
                [gapLineX, gapSnap.gap.startSide[0][1]],
                [gapLineX, minY],
              ],
            },
            {
              type: "gap",
              direction: "vertical",
              points: [
                [gapLineX, maxY],
                [gapLineX, gapSnap.gap.endSide[0][1]],
              ],
            },
          );
        }
        break;
      }
      case "side_right": {
        if (verticalIntersection) {
          const gapLineY =
            (verticalIntersection[0] + verticalIntersection[1]) / 2;

          gapSnapLines.push(
            {
              type: "gap",
              direction: "horizontal",
              points: [
                [startMaxX, gapLineY],
                [endMinX, gapLineY],
              ],
            },
            {
              type: "gap",
              direction: "horizontal",
              points: [
                [endMaxX, gapLineY],
                [minX, gapLineY],
              ],
            },
          );
        }
        break;
      }
      case "side_left": {
        if (verticalIntersection) {
          const gapLineY =
            (verticalIntersection[0] + verticalIntersection[1]) / 2;

          gapSnapLines.push(
            {
              type: "gap",
              direction: "horizontal",
              points: [
                [maxX, gapLineY],
                [startMinX, gapLineY],
              ],
            },
            {
              type: "gap",
              direction: "horizontal",
              points: [
                [startMaxX, gapLineY],
                [endMinX, gapLineY],
              ],
            },
          );
        }
        break;
      }
      case "side_top": {
        if (horizontalGapIntersection) {
          const gapLineX =
            (horizontalGapIntersection[0] + horizontalGapIntersection[1]) / 2;

          gapSnapLines.push(
            {
              type: "gap",
              direction: "vertical",
              points: [
                [gapLineX, maxY],
                [gapLineX, startMinY],
              ],
            },
            {
              type: "gap",
              direction: "vertical",
              points: [
                [gapLineX, startMaxY],
                [gapLineX, endMinY],
              ],
            },
          );
        }
        break;
      }
      case "side_bottom": {
        if (horizontalGapIntersection) {
          const gapLineX =
            (horizontalGapIntersection[0] + horizontalGapIntersection[1]) / 2;

          gapSnapLines.push(
            {
              type: "gap",
              direction: "vertical",
              points: [
                [gapLineX, startMaxY],
                [gapLineX, endMinY],
              ],
            },
            {
              type: "gap",
              direction: "vertical",
              points: [
                [gapLineX, endMaxY],
                [gapLineX, minY],
              ],
            },
          );
        }
        break;
      }
    }
  }

  return dedupeGapSnapLines(
    gapSnapLines.map((gapSnapLine) => {
      return {
        ...gapSnapLine,
        points: gapSnapLine.points.map(
          (point) => [round(point[0]), round(point[1])] as Point,
        ) as PointPair,
      };
    }),
  );
};

export const snapResizingElements = (
  // use the latest elements to create snap lines
  selectedElements: ExcalidrawElement[],
  // while using the original elements to appy dragOffset to calculate snaps
  selectedOriginalElements: ExcalidrawElement[],
  appState: AppState,
  event: KeyboardModifiersObject,
  dragOffset: Vector2D,
  transformHandle: MaybeTransformHandleType,
) => {
  if (
    !isSnappingEnabled({ event, selectedElements, appState }) ||
    selectedElements.length === 0 ||
    (selectedElements.length === 1 &&
      !areRoughlyEqual(selectedElements[0].angle, 0))
  ) {
    return {
      snapOffset: { x: 0, y: 0 },
      snapLines: [],
    };
  }

  let [minX, minY, maxX, maxY] = getCommonBounds(selectedOriginalElements);

  if (transformHandle) {
    if (transformHandle.includes("e")) {
      maxX += dragOffset.x;
    } else if (transformHandle.includes("w")) {
      minX += dragOffset.x;
    }

    if (transformHandle.includes("n")) {
      minY += dragOffset.y;
    } else if (transformHandle.includes("s")) {
      maxY += dragOffset.y;
    }
  }

  const selectionSnapPoints: Point[] = [];

  if (transformHandle) {
    switch (transformHandle) {
      case "e": {
        selectionSnapPoints.push([maxX, minY], [maxX, maxY]);
        break;
      }
      case "w": {
        selectionSnapPoints.push([minX, minY], [minX, maxY]);
        break;
      }
      case "n": {
        selectionSnapPoints.push([minX, minY], [maxX, minY]);
        break;
      }
      case "s": {
        selectionSnapPoints.push([minX, maxY], [maxX, maxY]);
        break;
      }
      case "ne": {
        selectionSnapPoints.push([maxX, minY]);
        break;
      }
      case "nw": {
        selectionSnapPoints.push([minX, minY]);
        break;
      }
      case "se": {
        selectionSnapPoints.push([maxX, maxY]);
        break;
      }
      case "sw": {
        selectionSnapPoints.push([minX, maxY]);
        break;
      }
    }
  }

  const snapDistance = getSnapDistance(appState.zoom.value);

  const minOffset = {
    x: snapDistance,
    y: snapDistance,
  };

  const nearestSnapsX: Snaps = [];
  const nearestSnapsY: Snaps = [];

  getPointSnaps(
    selectedOriginalElements,
    selectionSnapPoints,
    appState,
    event,
    nearestSnapsX,
    nearestSnapsY,
    minOffset,
  );

  const snapOffset = {
    x: nearestSnapsX[0]?.offset ?? 0,
    y: nearestSnapsY[0]?.offset ?? 0,
  };

  // again, once snap offset is calculated
  // reset to recompute for creating snap lines to be rendered
  minOffset.x = 0;
  minOffset.y = 0;
  nearestSnapsX.length = 0;
  nearestSnapsY.length = 0;

  const [x1, y1, x2, y2] = getCommonBounds(selectedElements).map((bound) =>
    round(bound),
  );

  const corners: Point[] = [
    [x1, y1],
    [x1, y2],
    [x2, y1],
    [x2, y2],
  ];

  getPointSnaps(
    selectedElements,
    corners,
    appState,
    event,
    nearestSnapsX,
    nearestSnapsY,
    minOffset,
  );

  const pointSnapLines = createPointSnapLines(nearestSnapsX, nearestSnapsY);

  return {
    snapOffset,
    snapLines: pointSnapLines,
  };
};

export const snapNewElement = (
  draggingElement: ExcalidrawElement,
  appState: AppState,
  event: KeyboardModifiersObject,
  origin: Vector2D,
  dragOffset: Vector2D,
) => {
  if (
    !isSnappingEnabled({ event, selectedElements: [draggingElement], appState })
  ) {
    return {
      snapOffset: { x: 0, y: 0 },
      snapLines: [],
    };
  }

  const selectionSnapPoints: Point[] = [
    [origin.x + dragOffset.x, origin.y + dragOffset.y],
  ];

  const snapDistance = getSnapDistance(appState.zoom.value);

  const minOffset = {
    x: snapDistance,
    y: snapDistance,
  };

  const nearestSnapsX: Snaps = [];
  const nearestSnapsY: Snaps = [];

  getPointSnaps(
    [draggingElement],
    selectionSnapPoints,
    appState,
    event,
    nearestSnapsX,
    nearestSnapsY,
    minOffset,
  );

  const snapOffset = {
    x: nearestSnapsX[0]?.offset ?? 0,
    y: nearestSnapsY[0]?.offset ?? 0,
  };

  minOffset.x = 0;
  minOffset.y = 0;
  nearestSnapsX.length = 0;
  nearestSnapsY.length = 0;

  const corners = getElementsCorners([draggingElement], {
    boundingBoxCorners: true,
    omitCenter: true,
  });

  getPointSnaps(
    [draggingElement],
    corners,
    appState,
    event,
    nearestSnapsX,
    nearestSnapsY,
    minOffset,
  );

  const pointSnapLines = createPointSnapLines(nearestSnapsX, nearestSnapsY);

  return {
    snapOffset,
    snapLines: pointSnapLines,
  };
};

export const getSnapLinesAtPointer = (
  elements: readonly ExcalidrawElement[],
  appState: AppState,
  pointer: Vector2D,
  event: KeyboardModifiersObject,
) => {
  if (!isSnappingEnabled({ event, selectedElements: [], appState })) {
    return {
      originOffset: { x: 0, y: 0 },
      snapLines: [],
    };
  }

  const referenceElements = getVisibleAndNonSelectedElements(
    elements,
    [],
    appState,
  );

  const snapDistance = getSnapDistance(appState.zoom.value);

  const minOffset = {
    x: snapDistance,
    y: snapDistance,
  };

  const horizontalSnapLines: PointerSnapLine[] = [];
  const verticalSnapLines: PointerSnapLine[] = [];

  for (const referenceElement of referenceElements) {
    const corners = getElementsCorners([referenceElement]);

    for (const corner of corners) {
      const offsetX = corner[0] - pointer.x;

      if (Math.abs(offsetX) <= Math.abs(minOffset.x)) {
        if (Math.abs(offsetX) < Math.abs(minOffset.x)) {
          verticalSnapLines.length = 0;
        }

        verticalSnapLines.push({
          type: "pointer",
          points: [corner, [corner[0], pointer.y]],
          direction: "vertical",
        });

        minOffset.x = offsetX;
      }

      const offsetY = corner[1] - pointer.y;

      if (Math.abs(offsetY) <= Math.abs(minOffset.y)) {
        if (Math.abs(offsetY) < Math.abs(minOffset.y)) {
          horizontalSnapLines.length = 0;
        }

        horizontalSnapLines.push({
          type: "pointer",
          points: [corner, [pointer.x, corner[1]]],
          direction: "horizontal",
        });

        minOffset.y = offsetY;
      }
    }
  }

  return {
    originOffset: {
      x:
        verticalSnapLines.length > 0
          ? verticalSnapLines[0].points[0][0] - pointer.x
          : 0,
      y:
        horizontalSnapLines.length > 0
          ? horizontalSnapLines[0].points[0][1] - pointer.y
          : 0,
    },
    snapLines: [...verticalSnapLines, ...horizontalSnapLines],
  };
};

export const isActiveToolNonLinearSnappable = (
  activeToolType: AppState["activeTool"]["type"],
) => {
  return (
    activeToolType === "rectangle" ||
    activeToolType === "ellipse" ||
    activeToolType === "diamond" ||
    activeToolType === "frame" ||
    activeToolType === "image"
  );
};