'use strict';

/**
 * Licensed Materials - Property of IBM
 * IBM Cognos Products: BI Cloud (C) Copyright IBM Corp. 2015, 2017
 * US Government Users Restricted Rights - Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
 */
define(['../../../../lib/@waca/core-client/js/core-client/ui/core/Class', 'jquery', 'underscore'], function (Class, $, _) {

	//Constants representing whether a cursor is on the leading boundary of a node, inside it, or on the trailing boundary.
	var POSITIONS = { BEFORE: 0, INSIDE: 1, AFTER: 2 };

	//DOM NODE types used in this file.
	var NODE_TYPES = { ELEMENT: 1, TEXT: 3 };

	/*
  * A cursor position visually is where the text cursor (i.e. carot) appears.
  * This is represented in the document selection/range model in a somewhat ambiguous way: a (node, offset) pair. The ambiguity in this approach is that
  * when the cursor is on the boundary of nodes, which node is used in that (node, offset) pair? The answer changes based on which browser and platform you
  * are using. The NormalizedPosition class attempts to uniquely represent a cursor position by normalizing it.
  */
	var NormalizedPosition = Class.extend({
		/*
   * Create a NormalizedPosition.
   * @param {node} container - the DOM node of the position (usually corresponds to a range.startContainer or range.endContainer)
   * @param {number} offset - the offset into the DOM node (usually corresponds to a range.startOffset or range.endOffset). When offset is against a
   * 		text node, this number represents before which character in the text node the cursor appears; in an element node, it represents before which
   * 		child node the cursor appears
   */
		init: function init(container, offset) {
			this.container = container;
			this.offset = offset;
			this._normalize();
		},

		/*
   * Normalizes the (container, offset) pair set in the constructor.
   * In general: attempts to use the last leaf node which the position represents.
   * For example, consider this DOM snippet:
   *
   *  <div>
   * 	    <p>
   * 	        Hello, World!
   * 	    </p>
   * 	    <p>
   * 	    </p>
   * 	</div>
   *
   * This snippet will result in the following DOM structure:
   *
   * 	1	Element node: div
   *  2		Text node: \n\t
   *  3		Element node: p
   *  4	 		Text node: \n\t
   *  5	 		Text node: Hello, World!
   *  6	 		Text node \n
   *  7 		Text node: \n\t
   *  8	 	Element node: p
   *  9	 		Text node: \n
   *  10		Text node: \n
   *
   * If the text "Hello, World!" is selected, the start node could be any of: 1, 2, 3, 4 or 5 (offset 0) and the end node could be any of: 5 (offset 13),
   * 6, 7, 8 (offset 0). The "normalized" position will choose the last leaf which refers to a given position, so the normalized start is node 5, offset 0
   * and the normalized end is node 8, offset 0.
   *
   * Note that nodes 2, 4, 6, 7, 9 and 10 don't render anything. They are considered "trivial".
   */
		_normalize: function _normalize() {
			var container = null;

			//Populate the this.position value
			this._setCursorPosition();

			if (this.position === POSITIONS.BEFORE) {

				//Find most precise container (i.e. a leaf node)
				this.container = this._findDeepestDescendant(this.container);

				//Find closest non-trivial container (i.e. has content user can see)
				//(This may already be this.container)
				container = this._ensureNodeIsNontrivial(this.container);

				//Confirm a non-trivial container was found
				if (!container) {
					//At end of document, so need to revert to AFTER
					container = this._findNontrivialNode(this.container, true);
					this.position = POSITIONS.AFTER;
				}

				this.container = container;
			} else if (this.position === POSITIONS.INSIDE) {

				if (this.container.nodeType === NODE_TYPES.ELEMENT) {
					//Container is an element node, move selection to child node indicated by offset
					this.container = this._findDeepestDescendant(this.container.childNodes[this.offset]);
					this.position = POSITIONS.BEFORE;
				} //else: container is a text node and is already considered 'normal'
			} else {
				/*i.e. this.position === POSITIONS.AFTER*/

				//Find most precise container (i.e. a leaf node)
				this.container = this._findDeepestDescendant(this.container, true);

				//Find closest non-trivial container (i.e. has content user can see)
				//(This should be the next container, since we're trying to switch AFTER to BEFORE)
				container = this._findNontrivialNode(this.container);

				//Confirm a subsequent container was found and switch position
				if (container) {
					this.position = POSITIONS.BEFORE;
				} else {
					//At end of document, so need to keep AFTER
					container = this._ensureNodeIsNontrivial(this.container, true);
				}

				this.container = container;
			}

			//Update the this.offset value
			this._updateOffset();
		},

		/*
   * Initializes this.position from this.offset and this.container
   */
		_setCursorPosition: function _setCursorPosition() {
			if (this.container.nodeType === NODE_TYPES.TEXT) {
				if (this.offset === 0) {
					this.position = POSITIONS.BEFORE;
				} else if (this.offset === this.container.data.length) {
					this.position = POSITIONS.AFTER;
				} else {
					this.position = POSITIONS.INSIDE;
				}
			} else {
				//i.e. this.container.nodeType === NODE_TYPES.ELEMENT
				if (this.offset === 0) {
					this.position = POSITIONS.BEFORE;
				} else if (this.container.childNodes.length && this.offset === this.container.childNodes.length) {
					this.position = POSITIONS.AFTER;
				} else if (!this.container.childNodes.length && this.offset === 1) {
					this.position = POSITIONS.AFTER;
				} else {
					this.position = POSITIONS.INSIDE;
				}
			}
		},

		/*
   * Updates this.offset from this.position and this.container
   */
		_updateOffset: function _updateOffset() {
			if (this.position === POSITIONS.BEFORE) {
				this.offset = 0;
			} else if (this.position === POSITIONS.AFTER) {
				this.offset = this.container.nodeType === NODE_TYPES.TEXT ? this.container.data.length : this.container.childNodes.length;
			} //else: this.position === POSITIONS.INSIDE, don't need to update offset
		},

		/*
   * @param {node} n
   * @param {boolean} [isLast=false] - indicates whether to find the first-child ancestor of 'n' (false) or the last-child ancestor of 'n' (true)
   * @return {node} which is a leaf and either the very first descendant of 'n' ('isLast'=false) or the very last descendant of 'n' ('isLast'=true)
   */
		_findDeepestDescendant: function _findDeepestDescendant(n, isLast) {
			while (n.firstChild) {
				n = isLast ? n.lastChild : n.firstChild;
			}
			return n;
		},

		/*
   * @param {node} n
   * @return {boolean} true iff 'n' is a blank text node, i.e. the browser will collapse it into the visible text so it doesn't participate in cursor
   * 		positioning
   */
		_isTrivialNode: function _isTrivialNode(n) {
			return n && n.nodeType === NODE_TYPES.TEXT /*text node*/ && n.data.trim() === '' /*no text*/;
		},

		/*
   * This utility function's purpose is to gather all the nodes which will be collapsed into a single cursor-point by the browser.
   * @param {node} n - the node to start at; will be included in the returned list
   * @param {boolean} [isPrev=false] - a flag to control the direction of the search: forward (false) or backward (true)
   * @return {object[]} a list of objects, with members 'container' and 'offset', which all represent equivalent points when selecting. Note that these
   * 		are only nodes in a specific direction (forward or backward) so there may be more equivalent ones in the other directions if 'n' is trivial.
   */
		_collectEquivalentNodes: function _collectEquivalentNodes(n, isPrev) {
			var nodeList = [];
			function list(container, beginningOrEnd) {
				nodeList.push({
					container: container,
					offset: beginningOrEnd ? container.nodeType === NODE_TYPES.TEXT ? container.data.length : container.childNodes.length : 0
				});
			}

			//Include parameter n as first entry in list
			list(n, !isPrev);

			var m = null;

			while (!m && n) {
				//Step to next sibling
				m = isPrev ? n.previousSibling : n.nextSibling;

				if (m) {
					//There is a sibling:
					//If there are children, drill down to a leaf
					if (m.childNodes.length) {
						m = this._findDeepestDescendant(m, isPrev);
					}
					//If this node is trivial, continue looping
					if (this._isTrivialNode(m)) {
						n = m;
						m = null;
						//Include this as one of the trivial leaf nodes in the list
						list(n, false);
					} //else: will exit loop
				} else {
					//There is no sibling: walk the parent chain (so as to then look at their siblings)
					n = n.parentNode;
				}
			}

			//Include non-trivial element which ends the list; or null if end of document reached
			list(n ? m : null, isPrev);

			return nodeList;
		},

		/*
   * @param {node} n
   * @param {boolean} [isPrev=false] - indicate whether to look forward (false) or backward (true) in the document
   * @return {node} the next (or, if 'isPrev'=true, previous) non-trivial node after (or before) 'n'
   */
		_findNontrivialNode: function _findNontrivialNode(n, isPrev) {
			return this._collectEquivalentNodes(n, isPrev).pop().container;
		},

		/*
   * @param {node} n
   * @param {boolean} [isPrev=false]
   * @return {node} 'n' if it is non-trivial, otherwise same behaviour as '_findNontrivialNode'
   */
		_ensureNodeIsNontrivial: function _ensureNodeIsNontrivial(n, isPrev) {
			return this._isTrivialNode(n) ? this._findNontrivialNode(n, isPrev) : n;
		},

		/**
   * @param {NormalizedPosition} position
   * @return {boolean} true iff 'position' refers to the same position as this
   */
		equals: function equals(position) {
			return this.container === position.container && this.offset === position.offset;
		},

		/**
   * Finds an object representing a valid (not necessarily normalized) range position reference which is equivalent to this, which satisfies the provided
   * parameters.
   * @param {boolean} favourEarlier - whether to return a position reference which is earlier in the document (true) or later (false)
   * @param {string} [selector] - a jQuery selector, describing the desired node
   * @return {object} an object with 'container' and 'offset' members, or null if no position was found matching the given selector
   */
		chooseDocumentPosition: function chooseDocumentPosition(favourEarlier, selector) {
			selector = selector || '*';

			var nodes = [];

			if (this.position === POSITIONS.INSIDE) {
				//When the normalized position is inside, there is only ever one node with the equivalent position
				nodes.push(this);
			} else if (this.position === POSITIONS.BEFORE) {
				//Get the nodes starting with the normalized one, then work backward
				nodes = this._collectEquivalentNodes(this.container, true);
				if (favourEarlier) {
					nodes.reverse();
				}
			} else {
				//(This case only occurs when there is no non-trivial node after this one in the document)
				//Get the nodes starting with the normalized one, then work forward
				nodes = this._collectEquivalentNodes(this.container, false);
				nodes.splice(nodes.length - 1, 1); //The last is expected to be null; remove it
				if (!favourEarlier) {
					nodes.reverse();
				}
			}

			//Find the first node matching the provided selector
			return _.find(nodes, function (n) {
				var node = n.container;
				if (node.nodeType === NODE_TYPES.TEXT) {
					node = node.parentNode; //Text nodes never match jQuery expressions, so get the parent
				}
				return $(node).is(selector);
			});
		}
	});

	return NormalizedPosition;
});
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