source: imaps-frontend/node_modules/@popperjs/core/lib/utils/computeAutoPlacement.js.flow

// @flow
import type { State, Padding } from '../types';
import type {
  Placement,
  ComputedPlacement,
  Boundary,
  RootBoundary,
} from '../enums';
import getVariation from './getVariation';
import {
  variationPlacements,
  basePlacements,
  placements as allPlacements,
} from '../enums';
import detectOverflow from './detectOverflow';
import getBasePlacement from './getBasePlacement';

type Options = {
  placement: Placement,
  padding: Padding,
  boundary: Boundary,
  rootBoundary: RootBoundary,
  flipVariations: boolean,
  allowedAutoPlacements?: Array<Placement>,
};

type OverflowsMap = { [ComputedPlacement]: number };

export default function computeAutoPlacement(
  state: $Shape<State>,
  options: Options = {}
): Array<ComputedPlacement> {
  const {
    placement,
    boundary,
    rootBoundary,
    padding,
    flipVariations,
    allowedAutoPlacements = allPlacements,
  } = options;

  const variation = getVariation(placement);

  const placements = variation
    ? flipVariations
      ? variationPlacements
      : variationPlacements.filter(
          (placement) => getVariation(placement) === variation
        )
    : basePlacements;

  let allowedPlacements = placements.filter(
    (placement) => allowedAutoPlacements.indexOf(placement) >= 0
  );

  if (allowedPlacements.length === 0) {
    allowedPlacements = placements;
  }

  // $FlowFixMe[incompatible-type]: Flow seems to have problems with two array unions...
  const overflows: OverflowsMap = allowedPlacements.reduce((acc, placement) => {
    acc[placement] = detectOverflow(state, {
      placement,
      boundary,
      rootBoundary,
      padding,
    })[getBasePlacement(placement)];

    return acc;
  }, {});

  return Object.keys(overflows).sort((a, b) => overflows[a] - overflows[b]);
}