import { Arr, Fun, Optional } from '@ephox/katamari';
import { Compare, SugarElement, Traverse } from '@ephox/sugar';

import { getClientRects, NodeClientRect } from '../dom/Dimensions';
import * as NodeType from '../dom/NodeType';
import * as ClientRect from '../geom/ClientRect';
import * as CaretCandidate from './CaretCandidate';
import { isFakeCaretTarget } from './FakeCaret';

type GeomClientRect = ClientRect.ClientRect;

export enum FakeCaretPosition {
  Before = 'before',
  After = 'after'
}

export interface FakeCaretInfo {
  node: Node;
  position: FakeCaretPosition;
}

type DistanceFn = <T extends GeomClientRect>(rect: T, x: number, y: number) => number;

const distanceToRectLeft = (clientRect: GeomClientRect, clientX: number) => Math.abs(clientRect.left - clientX);
const distanceToRectRight = (clientRect: GeomClientRect, clientX: number) => Math.abs(clientRect.right - clientX);
const isInsideY = <T extends GeomClientRect>(clientY: number, clientRect: T): boolean => clientY >= clientRect.top && clientY <= clientRect.bottom;
const collidesY = <T extends GeomClientRect>(r1: T, r2: T): boolean => r1.top < r2.bottom && r1.bottom > r2.top;

const isOverlapping = <T extends GeomClientRect>(r1: T, r2: T) => {
  // Rectangles might overlap a bit so this checks if the overlap is more than 50% then we count that as on the same line
  const overlap = ClientRect.overlapY(r1, r2) / Math.min(r1.height, r2.height);
  return collidesY(r1, r2) && overlap > 0.5;
};

const splitRectsPerAxis = <T extends GeomClientRect>(rects: T[], y: number): [T[], T[]] => {
  const intersectingRects = Arr.filter(rects, (rect) => isInsideY(y, rect));

  return ClientRect.boundingClientRectFromRects(intersectingRects).fold(
    () => ([[], rects ]),
    (boundingRect) => {
      const { pass: horizontal, fail: vertical } = Arr.partition(rects, (rect) => isOverlapping(rect, boundingRect));
      return [ horizontal, vertical ];
    }
  );
};

const clientInfo = (rect: NodeClientRect, clientX: number): FakeCaretInfo => {
  return {
    node: rect.node,
    position: distanceToRectLeft(rect, clientX) < distanceToRectRight(rect, clientX) ? FakeCaretPosition.Before : FakeCaretPosition.After
  };
};

// Measure the distance between the x and the closest edge of the rect.
// If the x is inside the rect then always return 0.
const horizontalDistance: DistanceFn = (rect, x, _y) =>
  x > rect.left && x < rect.right ? 0 : Math.min(Math.abs(rect.left - x), Math.abs(rect.right - x));

const closestChildCaretCandidateNodeRect = (children: ChildNode[], clientX: number, clientY: number): Optional<NodeClientRect> => {
  const caretCandidateRect = (rect: NodeClientRect) => {
    if (CaretCandidate.isCaretCandidate(rect.node)) {
      return Optional.some(rect);
    } else if (NodeType.isElement(rect.node)) {
      return closestChildCaretCandidateNodeRect(Arr.from(rect.node.childNodes), clientX, clientY);
    } else {
      return Optional.none();
    }
  };

  // If an element and a text node has nearly equal distance then favor the text node over the element to make it easier to select text
  // since setting the selection range will cancel any text select operation.
  const getClosestTextNode = (rects: NodeClientRect[], distance: DistanceFn) => {
    if (rects.length >= 2) {
      const r1 = caretCandidateRect(rects[0]).getOr(rects[0]);
      const r2 = caretCandidateRect(rects[1]).getOr(rects[1]);
      const deltaDistance = Math.abs(distance(r1, clientX, clientY) - distance(r2, clientX, clientY));

      if (deltaDistance < 2) {
        if (NodeType.isText(r1.node)) {
          return Optional.some(r1);
        } else if (NodeType.isText(r2.node)) {
          return Optional.some(r2);
        }
      }
    }

    return Optional.none();
  };

  const findClosestCaretCandidateNodeRect = (rects: NodeClientRect[], distance: DistanceFn): Optional<NodeClientRect> => {
    const sortedRects = Arr.sort(rects, (r1, r2) => distance(r1, clientX, clientY) - distance(r2, clientX, clientY));
    return getClosestTextNode(sortedRects, distance).orThunk(() => Arr.findMap(sortedRects, caretCandidateRect));
  };

  const [ horizontalRects, verticalRects ] = splitRectsPerAxis(getClientRects(children), clientY);
  const { pass: above, fail: below } = Arr.partition(verticalRects, (rect) => rect.top < clientY);

  return findClosestCaretCandidateNodeRect(horizontalRects, horizontalDistance)
    .orThunk(() => findClosestCaretCandidateNodeRect(below, ClientRect.distanceToRectEdgeFromXY))
    .orThunk(() => findClosestCaretCandidateNodeRect(above, ClientRect.distanceToRectEdgeFromXY));
};

const traverseUp = (rootElm: SugarElement<Node>, scope: SugarElement<Element>, clientX: number, clientY: number): Optional<NodeClientRect> => {
  const helper = (scope: SugarElement<Element>, prevScope: Optional<SugarElement<Element>>): Optional<NodeClientRect> => {
    const isDragGhostContainer = (node: ChildNode) => NodeType.isElement(node) && node.classList.contains('mce-drag-container');
    const childNodesWithoutGhost = Arr.filter(scope.dom.childNodes, Fun.not(isDragGhostContainer));

    return prevScope.fold(
      () => closestChildCaretCandidateNodeRect(childNodesWithoutGhost, clientX, clientY),
      (prevScope) => {
        const uncheckedChildren = Arr.filter(childNodesWithoutGhost, (node) => node !== prevScope.dom);
        return closestChildCaretCandidateNodeRect(uncheckedChildren, clientX, clientY);
      }
    ).orThunk(() => {
      const parent = Compare.eq(scope, rootElm) ? Optional.none() : Traverse.parentElement(scope);
      return parent.bind((newScope) => helper(newScope, Optional.some(scope)));
    });
  };

  return helper(scope, Optional.none());
};

// Rough description of how this algorithm works:
// 1. It starts by finding the element at the specified X, Y coordinate.
// 2. Then it checks its children for the closest one and traverses down into those repeating step 2, 3 until it finds a caret candidate.
// 3. If no caret candidate is found in the closest child node then it checks the second closest and so on until all decendants have been checked.
// 4. If no caret candidate is found, it traverses up skips the element it already checked and checks its siblings using steps 2, 3.
// 5. If no caret candidate is found, it continues step 4 until it finds the root. Then we have checked all the nodes in the document.
//
// This is less accurate but more performant, since for the common case you are likely to find a caret candidate close to where you are clicking.
// The more accurate algorithm would be to read all caret candidates rects in the whole document in and in one big step to find the closest one, but that is just too slow for bigger documents.
const closestCaretCandidateNodeRect = (root: HTMLElement, clientX: number, clientY: number): Optional<NodeClientRect> => {
  const rootElm = SugarElement.fromDom(root);
  const ownerDoc = Traverse.documentOrOwner(rootElm);
  const elementAtPoint = SugarElement.fromPoint(ownerDoc, clientX, clientY).filter((elm) => Compare.contains(rootElm, elm));
  const element = elementAtPoint.getOr(rootElm);

  return traverseUp(rootElm, element, clientX, clientY);
};

const closestFakeCaretCandidate = (root: HTMLElement, clientX: number, clientY: number): Optional<FakeCaretInfo> =>
  closestCaretCandidateNodeRect(root, clientX, clientY)
    .filter((rect) => isFakeCaretTarget(rect.node))
    .map((rect) => clientInfo(rect, clientX));

export {
  closestCaretCandidateNodeRect,
  closestFakeCaretCandidate
};