/**
 * Copyright 2018-present Facebook.
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 * @format
 */
import { Rect } from './geometry'

export const SNAP_SIZE = 16

export function snapGrid(val: number): number {
  return val - (val % SNAP_SIZE)
}

export function getPossibleSnappedPosition(
  windows: Rect[],
  {
    getGap,
    getNew,
  }: {
    getNew: (win: Rect) => number
    getGap: (win: Rect) => number
  },
): number | undefined {
  for (const win of windows) {
    const gap = Math.abs(getGap(win))
    if (gap >= 0 && gap < SNAP_SIZE) {
      return getNew(win)
    }
  }
}

export function getDistanceTo(props: Rect, win: Rect): number {
  const x1 = win.left
  const y1 = win.top
  const x1b = win.left + win.width
  const y1b = win.top + win.height

  const x2 = props.left
  const y2 = props.top
  const x2b = props.left + props.width
  const y2b = props.top + props.height

  const left = x2b < x1
  const right = x1b < x2
  const bottom = y2b < y1
  const top = y1b < y2

  if (top && left) {
    return distance(x1, y1b, x2b, y2)
  } else if (left && bottom) {
    return distance(x1, y1, x2b, y2b)
  } else if (bottom && right) {
    return distance(x1b, y1, x2, y2b)
  } else if (right && top) {
    return distance(x1b, y1b, x2, y2)
  } else if (left) {
    return x1 - x2b
  } else if (right) {
    return x2 - x1b
  } else if (bottom) {
    return y1 - y2b
  } else if (top) {
    return y2 - y1b
  } else {
    return 0
  }
}

export function distance(x1: number, y1: number, x2: number, y2: number): number {
  return Math.abs(x1 - x2) + Math.abs(y1 - y2)
}

export function maybeSnapLeft(props: Rect, windows: Rect[], left: number): number {
  // snap right side to left
  // ┌─┬─┐
  // │A│B│
  // └─┴─┘
  const snapRight = getPossibleSnappedPosition(windows, {
    getGap: win => win.left - (props.width + left),
    getNew: win => win.left - props.width,
  })
  if (snapRight != null) {
    return snapRight
  }

  // snap left side to right
  // ┌─┬─┐
  // │B│A│
  // └─┴─┘
  const snapLeft = getPossibleSnappedPosition(windows, {
    getGap: win => left - (win.left + win.width),
    getNew: win => win.left + win.width,
  })
  if (snapLeft != null) {
    return snapLeft
  }

  return snapGrid(left)
}

export function maybeSnapTop(_: Rect, windows: Rect[], top: number): number {
  // snap bottom to bottom
  // ┌─┐
  // │A├─┐
  // │ │B│
  // └─┴─┘
  const snapBottom2 = getPossibleSnappedPosition(windows, {
    getGap: win => top - win.top - win.height,
    getNew: win => win.top + win.height,
  })
  if (snapBottom2 != null) {
    return snapBottom2
  }

  // snap top to bottom
  // ┌─┐
  // │B│
  // ├─┤
  // │A│
  // └─┘
  const snapBottom = getPossibleSnappedPosition(windows, {
    getGap: win => top - win.top - win.height,
    getNew: win => win.top + win.height,
  })
  if (snapBottom != null) {
    return snapBottom
  }

  // snap top to top
  // ┌─┬─┐
  // │A│B│
  // │ ├─┘
  // └─┘
  const snapTop = getPossibleSnappedPosition(windows, {
    getGap: win => top - win.top,
    getNew: win => win.top,
  })
  if (snapTop != null) {
    return snapTop
  }

  return snapGrid(top)
}