payloadcms/packages/richtext-lexical/src/lexical/plugins/handles/DraggableBlockPlugin/setTargetLine.ts

'use client'
import { getCollapsedMargins } from '../utils/getCollapsedMargins.js'
const TARGET_LINE_HALF_HEIGHT = 0
const TEXT_BOX_HORIZONTAL_PADDING = -24
const DEBUG = false

let animationTimer = 0

export function setTargetLine(
  offsetWidth: string,
  offsetLeft: number,
  targetLineElem: HTMLElement,
  targetBlockElem: HTMLElement,
  lastTargetBlock: {
    boundingBox?: DOMRect
    elem: HTMLElement | null
    isBelow: boolean
  },
  mouseY: number,
  anchorElem: HTMLElement,
  event: DragEvent,
  debugHighlightRef: React.RefObject<HTMLDivElement | null>,
  isFoundNodeEmptyParagraph: boolean = false,
) {
  const { height: targetBlockElemHeight, top: targetBlockElemTop } =
    targetBlockElem.getBoundingClientRect() // used to be getBoundingClientRectWithoutTransform. Not sure what's better, but the normal getBoundingClientRect seems to work fine
  const { top: anchorTop, width: anchorWidth } = anchorElem.getBoundingClientRect()

  const { marginBottom, marginTop } = getCollapsedMargins(targetBlockElem)
  let lineTop = targetBlockElemTop

  const isBelow = mouseY >= targetBlockElemTop + targetBlockElemHeight / 2 + window.scrollY

  let willStayInSamePosition = false

  /**
   * Do not run any transform or changes if the actual new line position would be the same (even if it's now inserted BEFORE rather than AFTER - position would still be the same)
   * This prevents unnecessary flickering.
   *
   * We still need to let it run even if the position (IGNORING the transform) would not change, as the transform animation is not finished yet. This is what animationTimer does. Otherwise, the positioning will be inaccurate
   */
  if (lastTargetBlock?.elem) {
    if (targetBlockElem !== lastTargetBlock?.elem) {
      if (
        isBelow &&
        lastTargetBlock?.elem &&
        lastTargetBlock?.elem === targetBlockElem.nextElementSibling
      ) {
        animationTimer++

        if (animationTimer < 200) {
          willStayInSamePosition = true
        }
      } else if (
        !isBelow &&
        lastTargetBlock?.elem &&
        lastTargetBlock?.elem === targetBlockElem.previousElementSibling
      ) {
        animationTimer++
        if (animationTimer < 200) {
          willStayInSamePosition = true
        }
      }
    } else {
      animationTimer++

      const lastBoundingBoxPosition = lastTargetBlock?.boundingBox?.y
      const currentBoundingBoxPosition = targetBlockElem.getBoundingClientRect().y

      if (
        (isBelow === lastTargetBlock?.isBelow &&
          lastBoundingBoxPosition === currentBoundingBoxPosition) ||
        animationTimer < 200
      ) {
        willStayInSamePosition = false
      }
    }
  }
  if (willStayInSamePosition) {
    return {
      isBelow,
      willStayInSamePosition,
    }
  }

  /**
   * Paragraphs need no isBelow/above handling,
   */
  if (!isFoundNodeEmptyParagraph) {
    //if (!isFoundNodeEmptyParagraph) {
    if (isBelow) {
      // below targetBlockElem
      lineTop += targetBlockElemHeight + marginBottom / 2
    } else {
      // above targetBlockElem
      lineTop -= marginTop / 2
    }
  } else {
    lineTop += targetBlockElemHeight / 2
  }

  let targetElemTranslate2 = 0

  if (!isFoundNodeEmptyParagraph) {
    if (isBelow) {
      targetElemTranslate2 = -TARGET_LINE_HALF_HEIGHT
    } else {
      targetElemTranslate2 = TARGET_LINE_HALF_HEIGHT
    }
  }

  const top = lineTop - anchorTop + targetElemTranslate2

  const left = TEXT_BOX_HORIZONTAL_PADDING - offsetLeft

  targetLineElem.style.width = `calc(${anchorWidth}px - ${offsetWidth})`
  targetLineElem.style.opacity = '.8'

  // if (DEBUG) {
  //   //targetBlockElem.style.border = '3px solid red'
  //   highlightElemOriginalPosition(debugHighlightRef, targetBlockElem, anchorElem)
  // }

  targetLineElem.style.transform = `translate(${left}px, calc(${top}px - ${'2px'}))`

  /**
   * Properly reset previous targetBlockElem styles
   */
  if (lastTargetBlock?.elem) {
    lastTargetBlock.elem.style.opacity = ''

    if (lastTargetBlock?.elem === targetBlockElem) {
      if (isBelow) {
        lastTargetBlock.elem.style.marginTop = ''
      } else {
        lastTargetBlock.elem.style.marginBottom = ''
      }
    } else {
      lastTargetBlock.elem.style.marginBottom = ''
      lastTargetBlock.elem.style.marginTop = ''
    }
  }

  animationTimer = 0
  return {
    isBelow,
    willStayInSamePosition,
  }
}