/*
 * This React component is a long way from perfect, but it's a start for
 * handling custom layouts.
 *
 * There are a few reasons that (at least in my opinion) implementing this is non-trivial:
 *
 * 1) React re-render vs DOM updates
 *
 *    For performance reasons, we can't re-render with React when the user drags a
 *    pattern part (or rotates it). It would kill performance.
 *    So, we don't re-render with React upon dragging/rotating, but instead manipulate
 *    the DOM directly.
 *
 *    So far so good, but of course we don't want a pattern that's only correctly laid
 *    out in the DOM. We want to update the pattern gist so that the new layout is stored.
 *    For this, we re-render with React on the end of the drag (or rotate).
 *
 *    Handling this balance between DOM updates and React re-renders is a first contributing
 *    factor to why this component is non-trivial
 *
 * 2) SVG vs DOM coordinates
 *
 *    When we drag or rotate with the mouse, all the events are giving us coordinates of
 *    where the mouse is in the DOM.
 *
 *    The layout uses coordinates from the embedded SVG which are completely different.
 *
 *    We run `getScreenCTM().inverse()` on the svg element to pass to `matrixTransform` on a `DOMPointReadOnly` for dom to svg space conversions.
 *
 * 3) Part-level transforms
 *
 *    All parts use their center as the transform-origin to simplify transforms, especially flipping and rotating.
 *
 * 4) Bounding box
 *
 *    We use `getBoundingClientRect` rather than `getBBox` because it provides more data and factors in the transforms.
 * We then use our `domToSvg` function to move the points back into the SVG space.
 *
 *
 *  Known issues
 *  - currently none
 *
 *  I've sort of left it at this because I'm starting to wonder if we should perhaps re-think
 *  how custom layouts are supported in the core. And I would like to discuss this with the core team.
 */
import {PartInner} from '../../draft/part'
import { generatePartTransform } from '@freesewing/core'
import { getProps, angle } from '../../draft/utils'
import { drag } from 'd3-drag'
import { select } from 'd3-selection'
import { useRef, useState, useEffect} from 'react'
import Buttons from './buttons'


const Part = props => {
  const { layout, part, partName} = props

  const partLayout = layout.parts?.[partName]

  // Don't just assume this makes sense
  if (typeof partLayout?.move?.x === 'undefined') return null

  // Use a ref for direct DOM manipulation
  const partRef = useRef(null)
  const centerRef = useRef(null)
  const innerRef = useRef(null)

  // State variable to switch between moving or rotating the part
  const [rotate, setRotate] = useState(false)

  // update the layout on mount
  useEffect(() => {
    // only update if there's a rendered part and it's not the pages or fabric part
    if (partRef.current && !props.isLayoutPart) {
      updateLayout(false)
    }
  }, [partRef, partLayout])

  // Initialize drag handler
  useEffect(() => {
    // don't drag the pages
    if (props.isLayoutPart) return
    handleDrag(select(partRef.current))
  }, [rotate, partRef, partLayout])

  // These are kept as vars because re-rendering on drag would kill performance
  // Managing the difference between re-render and direct DOM updates makes this
  // whole thing a bit tricky to wrap your head around
  let translateX = partLayout.move.x
  let translateY = partLayout.move.y
  let partRotation = partLayout.rotate || 0;
  let rotation = partRotation;
  let flipX = !!partLayout.flipX
  let flipY = !!partLayout.flipY

  const center = {
    x: part.topLeft.x + (part.bottomRight.x - part.topLeft.x)/2,
    y: part.topLeft.y + (part.bottomRight.y - part.topLeft.y)/2,
  }

  /** get the delta rotation from the start of the drag event to now */
  const getRotation = (event) => angle(center, event.subject) - angle(center, { x:event.x, y: event.y });

  const setTransforms = () => {
    // get the transform attributes
    const transforms = generatePartTransform(translateX, translateY, rotation, flipX, flipY, part);

    const me = select(partRef.current);
    for (var t in transforms) {
      me.attr(t, transforms[t])
    }
  }

  let didDrag = false;
  const handleDrag = drag()
    // subject allows us to save data from the start of the event to use throughout event handing
    .subject(function(event) {
      return rotate ?
      // if we're rotating, the subject is the mouse position
      { x: event.x, y: event.y } :
      // if we're moving, the subject is the part's x,y coordinates
      {x: translateX, y: translateY}
    })
    .on('drag', function(event) {
      if (!event.dx && !event.dy) return

      if (rotate) {
        let newRotation = getRotation(event);
        // shift key to snap the rotation
        if (event.sourceEvent.shiftKey) {
          newRotation = Math.ceil(newRotation/15) * 15
        }
        // reverse the rotation direction one time per flip. if we're flipped both directions, rotation will be positive again
        if (flipX) newRotation *= -1
        if (flipY) newRotation *= -1

        rotation = partRotation + newRotation
      }
      else {
        translateX = event.x
        translateY = event.y
      }

      // a drag happened, so we should update the layout when we're done
      didDrag = true;
      setTransforms()
    })
    .on('end', function(event) {
      // save to gist if anything actually changed
      if (didDrag) updateLayout()

      didDrag = false
    })

  /** reset the part's transforms */
  const resetPart = (event) => {
    rotation = 0
    flipX = 0
    flipY = 0
    updateLayout()
  }

  /** toggle between dragging and rotating */
  const toggleDragRotate = () => {
    // only respond if the part should be able to drag/rotate
    if (!partRef.current || props.isLayoutPart) {return}

    setRotate(!rotate)
  }

  /** update the layout either locally or in the gist */
  const updateLayout = (history=true) => {
    /** don't mess with what we don't lay out */
    if (!partRef.current || props.isLayoutPart) return

    // set the transforms on the part in order to calculate from the latest position
    setTransforms()

    // get the bounding box and the svg's current transform matrix
    const partRect = innerRef.current.getBoundingClientRect();
    const matrix = innerRef.current.ownerSVGElement.getScreenCTM().inverse();

    // a function to convert dom space to svg space
    const domToSvg = (point) => DOMPointReadOnly.fromPoint(point).matrixTransform(matrix)

    // include the new top left and bottom right to ease calculating the pattern width and height
    const tl = domToSvg({x: partRect.left, y: partRect.top});
    const br = domToSvg({x: partRect.right, y: props.isLayoutPart ? 0 : partRect.bottom});

    // update it on the draft component
    props.updateLayout(partName, {
      move: {
        x: translateX,
        y: translateY,
      },
      rotate: rotation % 360,
      flipX,
      flipY,
      tl,
      br
    }, history)
  }

  /** Method to flip (mirror) the part along the X or Y axis */
  const flip = axis => {
    if (axis === 'x') flipX = !flipX
    else flipY = !flipY
    updateLayout()
  }

  /** method to rotate 90 degrees */
  const rotate90 = (direction = 1) => {
    if (flipX) direction *= -1
    if (flipY) direction *= -1

    rotation += 90 * direction

    updateLayout()
  }

  // don't render if the part is empty
  if (Object.keys(part.snippets).length === 0 && Object.keys(part.paths).length === 0) return null;

  return (
    <g
      id={`part-${partName}`}
      ref={partRef}
      {...getProps(part)}
    >
      <PartInner {...props} ref={innerRef}/>
      {!props.isLayoutPart && <>
      <text x={center.x} y={center.y} ref={centerRef} />
      <rect
        ref={partRef}
        x={part.topLeft.x}
        y={part.topLeft.y}
        width={part.width}
        height={part.height}
        className={`layout-rect ${rotate ? 'rotate' : 'move'}`}
        id={`${partName}-layout-rect`}
        onClick={toggleDragRotate}
      />
      <Buttons
        transform={`translate(${center.x}, ${center.y}) rotate(${-rotation}) scale(${flipX ? -1 : 1},${flipY ? -1 : 1})`}
        flip={flip}
        rotate={rotate}
        setRotate={setRotate}
        resetPart={resetPart}
        rotate90={rotate90}
        partName={partName}
       />
      </>}
    </g>
  )
}

export default Part