dom.js

/**
 * External dependencies
 */
import { includes } from 'lodash';

/**
 * Browser dependencies
 */

const { getComputedStyle } = window;
const {
	TEXT_NODE,
	ELEMENT_NODE,
	DOCUMENT_POSITION_PRECEDING,
	DOCUMENT_POSITION_FOLLOWING,
} = window.Node;

/**
 * Returns true if the given selection object is in the forward direction, or
 * false otherwise.
 *
 * @see https://developer.mozilla.org/en-US/docs/Web/API/Node/compareDocumentPosition
 *
 * @param {Selection} selection Selection object to check.
 *
 * @return {boolean} Whether the selection is forward.
 */
function isSelectionForward( selection ) {
	const {
		anchorNode,
		focusNode,
		anchorOffset,
		focusOffset,
	} = selection;

	const position = anchorNode.compareDocumentPosition( focusNode );

	// Disable reason: `Node#compareDocumentPosition` returns a bitmask value,
	// so bitwise operators are intended.
	/* eslint-disable no-bitwise */
	// Compare whether anchor node precedes focus node. If focus node (where
	// end of selection occurs) is after the anchor node, it is forward.
	if ( position & DOCUMENT_POSITION_PRECEDING ) {
		return false;
	}

	if ( position & DOCUMENT_POSITION_FOLLOWING ) {
		return true;
	}
	/* eslint-enable no-bitwise */

	// `compareDocumentPosition` returns 0 when passed the same node, in which
	// case compare offsets.
	if ( position === 0 ) {
		return anchorOffset <= focusOffset;
	}

	// This should never be reached, but return true as default case.
	return true;
}

/**
 * Check whether the selection is horizontally at the edge of the container.
 *
 * @param {Element} container Focusable element.
 * @param {boolean} isReverse Set to true to check left, false for right.
 *
 * @return {boolean} True if at the horizontal edge, false if not.
 */
export function isHorizontalEdge( container, isReverse ) {
	if ( includes( [ 'INPUT', 'TEXTAREA' ], container.tagName ) ) {
		if ( container.selectionStart !== container.selectionEnd ) {
			return false;
		}

		if ( isReverse ) {
			return container.selectionStart === 0;
		}

		return container.value.length === container.selectionStart;
	}

	if ( ! container.isContentEditable ) {
		return true;
	}

	const selection = window.getSelection();

	// Create copy of range for setting selection to find effective offset.
	const range = selection.getRangeAt( 0 ).cloneRange();

	// Collapse in direction of selection.
	if ( ! selection.isCollapsed ) {
		range.collapse( ! isSelectionForward( selection ) );
	}

	let node = range.startContainer;

	let extentOffset;
	if ( isReverse ) {
		// When in reverse, range node should be first.
		extentOffset = 0;
	} else if ( node.nodeValue ) {
		// Otherwise, vary by node type. A text node has no children. Its range
		// offset reflects its position in nodeValue.
		//
		// "If the startContainer is a Node of type Text, Comment, or
		// CDATASection, then the offset is the number of characters from the
		// start of the startContainer to the boundary point of the Range."
		//
		// See: https://developer.mozilla.org/en-US/docs/Web/API/Range/startOffset
		// See: https://developer.mozilla.org/en-US/docs/Web/API/Node/nodeValue
		extentOffset = node.nodeValue.length;
	} else {
		// "For other Node types, the startOffset is the number of child nodes
		// between the start of the startContainer and the boundary point of
		// the Range."
		//
		// See: https://developer.mozilla.org/en-US/docs/Web/API/Range/startOffset
		extentOffset = node.childNodes.length;
	}

	// Offset of range should be at expected extent.
	const position = isReverse ? 'start' : 'end';
	const offset = range[ `${ position }Offset` ];
	if ( offset !== extentOffset ) {
		return false;
	}

	// If confirmed to be at extent, traverse up through DOM, verifying that
	// the node is at first or last child for reverse or forward respectively
	// (ignoring empty text nodes). Continue until container is reached.
	const order = isReverse ? 'previous' : 'next';

	while ( node !== container ) {
		let next = node[ `${ order }Sibling` ];

		// Skip over empty text nodes.
		while ( next && next.nodeType === TEXT_NODE && next.data === '' ) {
			next = next[ `${ order }Sibling` ];
		}

		if ( next ) {
			return false;
		}

		node = node.parentNode;
	}

	// If reached, range is assumed to be at edge.
	return true;
}

/**
 * Check whether the selection is vertically at the edge of the container.
 *
 * @param {Element} container Focusable element.
 * @param {boolean} isReverse Set to true to check top, false for bottom.
 *
 * @return {boolean} True if at the edge, false if not.
 */
export function isVerticalEdge( container, isReverse ) {
	if ( includes( [ 'INPUT', 'TEXTAREA' ], container.tagName ) ) {
		return isHorizontalEdge( container, isReverse );
	}

	if ( ! container.isContentEditable ) {
		return true;
	}

	const selection = window.getSelection();
	const range = selection.rangeCount ? selection.getRangeAt( 0 ) : null;
	if ( ! range ) {
		return false;
	}

	const rangeRect = getRectangleFromRange( range );

	if ( ! rangeRect ) {
		return false;
	}

	const buffer = rangeRect.height / 2;
	const editableRect = container.getBoundingClientRect();

	// Too low.
	if ( isReverse && rangeRect.top - buffer > editableRect.top ) {
		return false;
	}

	// Too high.
	if ( ! isReverse && rangeRect.bottom + buffer < editableRect.bottom ) {
		return false;
	}

	return true;
}

/**
 * Get the rectangle of a given Range.
 *
 * @param {Range} range The range.
 *
 * @return {DOMRect} The rectangle.
 */
export function getRectangleFromRange( range ) {
	// For uncollapsed ranges, get the rectangle that bounds the contents of the
	// range; this a rectangle enclosing the union of the bounding rectangles
	// for all the elements in the range.
	if ( ! range.collapsed ) {
		return range.getBoundingClientRect();
	}

	let rect = range.getClientRects()[ 0 ];

	// If the collapsed range starts (and therefore ends) at an element node,
	// `getClientRects` can be empty in some browsers. This can be resolved
	// by adding a temporary text node with zero-width space to the range.
	//
	// See: https://stackoverflow.com/a/6847328/995445
	if ( ! rect ) {
		const padNode = document.createTextNode( '\u200b' );
		range.insertNode( padNode );
		rect = range.getClientRects()[ 0 ];
		padNode.parentNode.removeChild( padNode );
	}

	return rect;
}

/**
 * Get the rectangle for the selection in a container.
 *
 * @param {Element} container Editable container.
 *
 * @return {?DOMRect} The rectangle.
 */
export function computeCaretRect( container ) {
	if ( ! container.isContentEditable ) {
		return;
	}

	const selection = window.getSelection();
	const range = selection.rangeCount ? selection.getRangeAt( 0 ) : null;

	if ( ! range ) {
		return;
	}

	return getRectangleFromRange( range );
}

/**
 * Places the caret at start or end of a given element.
 *
 * @param {Element} container Focusable element.
 * @param {boolean} isReverse True for end, false for start.
 */
export function placeCaretAtHorizontalEdge( container, isReverse ) {
	if ( ! container ) {
		return;
	}

	if ( includes( [ 'INPUT', 'TEXTAREA' ], container.tagName ) ) {
		container.focus();
		if ( isReverse ) {
			container.selectionStart = container.value.length;
			container.selectionEnd = container.value.length;
		} else {
			container.selectionStart = 0;
			container.selectionEnd = 0;
		}
		return;
	}

	container.focus();

	if ( ! container.isContentEditable ) {
		return;
	}

	// Select on extent child of the container, not the container itself. This
	// avoids the selection always being `endOffset` of 1 when placed at end,
	// where `startContainer`, `endContainer` would always be container itself.
	const rangeTarget = container[ isReverse ? 'lastChild' : 'firstChild' ];

	// If no range target, it implies that the container is empty. Focusing is
	// sufficient for caret to be placed correctly.
	if ( ! rangeTarget ) {
		return;
	}

	const selection = window.getSelection();
	const range = document.createRange();

	range.selectNodeContents( rangeTarget );
	range.collapse( ! isReverse );

	selection.removeAllRanges();
	selection.addRange( range );
}

/**
 * Polyfill.
 * Get a collapsed range for a given point.
 *
 * @see https://developer.mozilla.org/en-US/docs/Web/API/Document/caretRangeFromPoint
 *
 * @param {Document} doc The document of the range.
 * @param {number}    x   Horizontal position within the current viewport.
 * @param {number}    y   Vertical position within the current viewport.
 *
 * @return {?Range} The best range for the given point.
 */
function caretRangeFromPoint( doc, x, y ) {
	if ( doc.caretRangeFromPoint ) {
		return doc.caretRangeFromPoint( x, y );
	}

	if ( ! doc.caretPositionFromPoint ) {
		return null;
	}

	const point = doc.caretPositionFromPoint( x, y );

	// If x or y are negative, outside viewport, or there is no text entry node.
	// https://developer.mozilla.org/en-US/docs/Web/API/Document/caretRangeFromPoint
	if ( ! point ) {
		return null;
	}

	const range = doc.createRange();

	range.setStart( point.offsetNode, point.offset );
	range.collapse( true );

	return range;
}

/**
 * Get a collapsed range for a given point.
 * Gives the container a temporary high z-index (above any UI).
 * This is preferred over getting the UI nodes and set styles there.
 *
 * @param {Document} doc       The document of the range.
 * @param {number}    x         Horizontal position within the current viewport.
 * @param {number}    y         Vertical position within the current viewport.
 * @param {Element}  container Container in which the range is expected to be found.
 *
 * @return {?Range} The best range for the given point.
 */
function hiddenCaretRangeFromPoint( doc, x, y, container ) {
	container.style.zIndex = '10000';

	const range = caretRangeFromPoint( doc, x, y );

	container.style.zIndex = null;

	return range;
}

/**
 * Places the caret at the top or bottom of a given element.
 *
 * @param {Element} container           Focusable element.
 * @param {boolean} isReverse           True for bottom, false for top.
 * @param {DOMRect} [rect]              The rectangle to position the caret with.
 * @param {boolean} [mayUseScroll=true] True to allow scrolling, false to disallow.
 */
export function placeCaretAtVerticalEdge( container, isReverse, rect, mayUseScroll = true ) {
	if ( ! container ) {
		return;
	}

	if ( ! rect || ! container.isContentEditable ) {
		placeCaretAtHorizontalEdge( container, isReverse );
		return;
	}

	// Offset by a buffer half the height of the caret rect. This is needed
	// because caretRangeFromPoint may default to the end of the selection if
	// offset is too close to the edge. It's unclear how to precisely calculate
	// this threshold; it may be the padded area of some combination of line
	// height, caret height, and font size. The buffer offset is effectively
	// equivalent to a point at half the height of a line of text.
	const buffer = rect.height / 2;
	const editableRect = container.getBoundingClientRect();
	const x = rect.left;
	const y = isReverse ? ( editableRect.bottom - buffer ) : ( editableRect.top + buffer );

	let range = hiddenCaretRangeFromPoint( document, x, y, container );

	if ( ! range || ! container.contains( range.startContainer ) ) {
		if ( mayUseScroll && (
			( ! range || ! range.startContainer ) ||
				! range.startContainer.contains( container ) ) ) {
			// Might be out of view.
			// Easier than attempting to calculate manually.
			container.scrollIntoView( isReverse );
			placeCaretAtVerticalEdge( container, isReverse, rect, false );
			return;
		}

		placeCaretAtHorizontalEdge( container, isReverse );
		return;
	}

	// Check if the closest text node is actually further away.
	// If so, attempt to get the range again with the y position adjusted to get the right offset.
	if ( range.startContainer.nodeType === TEXT_NODE ) {
		const parentNode = range.startContainer.parentNode;
		const parentRect = parentNode.getBoundingClientRect();
		const side = isReverse ? 'bottom' : 'top';
		const padding = parseInt( getComputedStyle( parentNode ).getPropertyValue( `padding-${ side }` ), 10 ) || 0;
		const actualY = isReverse ? ( parentRect.bottom - padding - buffer ) : ( parentRect.top + padding + buffer );

		if ( y !== actualY ) {
			range = hiddenCaretRangeFromPoint( document, x, actualY, container );
		}
	}

	const selection = window.getSelection();
	selection.removeAllRanges();
	selection.addRange( range );
	container.focus();
	// Editable was already focussed, it goes back to old range...
	// This fixes it.
	selection.removeAllRanges();
	selection.addRange( range );
}

/**
 * Check whether the given element is a text field, where text field is defined
 * by the ability to select within the input, or that it is contenteditable.
 *
 * See: https://html.spec.whatwg.org/#textFieldSelection
 *
 * @param {HTMLElement} element The HTML element.
 *
 * @return {boolean} True if the element is an text field, false if not.
 */
export function isTextField( element ) {
	try {
		const { nodeName, selectionStart, contentEditable } = element;

		return (
			( nodeName === 'INPUT' && selectionStart !== null ) ||
			( nodeName === 'TEXTAREA' ) ||
			contentEditable === 'true'
		);
	} catch ( error ) {
		// Safari throws an exception when trying to get `selectionStart`
		// on non-text <input> elements (which, understandably, don't
		// have the text selection API). We catch this via a try/catch
		// block, as opposed to a more explicit check of the element's
		// input types, because of Safari's non-standard behavior. This
		// also means we don't have to worry about the list of input
		// types that support `selectionStart` changing as the HTML spec
		// evolves over time.
		return false;
	}
}

/**
 * Check wether the current document has a selection.
 * This checks both for focus in an input field and general text selection.
 *
 * @return {boolean} True if there is selection, false if not.
 */
export function documentHasSelection() {
	if ( isTextField( document.activeElement ) ) {
		return true;
	}

	const selection = window.getSelection();
	const range = selection.rangeCount ? selection.getRangeAt( 0 ) : null;

	return range && ! range.collapsed;
}

/**
 * Check whether the contents of the element have been entirely selected.
 * Returns true if there is no possibility of selection.
 *
 * @param {Element} element The element to check.
 *
 * @return {boolean} True if entirely selected, false if not.
 */
export function isEntirelySelected( element ) {
	if ( includes( [ 'INPUT', 'TEXTAREA' ], element.nodeName ) ) {
		return element.selectionStart === 0 && element.value.length === element.selectionEnd;
	}

	if ( ! element.isContentEditable ) {
		return true;
	}

	const selection = window.getSelection();
	const range = selection.rangeCount ? selection.getRangeAt( 0 ) : null;

	if ( ! range ) {
		return true;
	}

	const { startContainer, endContainer, startOffset, endOffset } = range;

	if (
		startContainer === element &&
		endContainer === element &&
		startOffset === 0 &&
		endOffset === element.childNodes.length
	) {
		return true;
	}

	const lastChild = element.lastChild;
	const lastChildContentLength = lastChild.nodeType === TEXT_NODE ?
		lastChild.data.length :
		lastChild.childNodes.length;

	return (
		startContainer === element.firstChild &&
		endContainer === element.lastChild &&
		startOffset === 0 &&
		endOffset === lastChildContentLength
	);
}

/**
 * Given a DOM node, finds the closest scrollable container node.
 *
 * @param {Element} node Node from which to start.
 *
 * @return {?Element} Scrollable container node, if found.
 */
export function getScrollContainer( node ) {
	if ( ! node ) {
		return;
	}

	// Scrollable if scrollable height exceeds displayed...
	if ( node.scrollHeight > node.clientHeight ) {
		// ...except when overflow is defined to be hidden or visible
		const { overflowY } = window.getComputedStyle( node );
		if ( /(auto|scroll)/.test( overflowY ) ) {
			return node;
		}
	}

	// Continue traversing
	return getScrollContainer( node.parentNode );
}

/**
 * Returns the closest positioned element, or null under any of the conditions
 * of the offsetParent specification. Unlike offsetParent, this function is not
 * limited to HTMLElement and accepts any Node (e.g. Node.TEXT_NODE).
 *
 * @see https://drafts.csswg.org/cssom-view/#dom-htmlelement-offsetparent
 *
 * @param {Node} node Node from which to find offset parent.
 *
 * @return {?Node} Offset parent.
 */
export function getOffsetParent( node ) {
	// Cannot retrieve computed style or offset parent only anything other than
	// an element node, so find the closest element node.
	let closestElement;
	while ( ( closestElement = node.parentNode ) ) {
		if ( closestElement.nodeType === ELEMENT_NODE ) {
			break;
		}
	}

	if ( ! closestElement ) {
		return null;
	}

	// If the closest element is already positioned, return it, as offsetParent
	// does not otherwise consider the node itself.
	if ( getComputedStyle( closestElement ).position !== 'static' ) {
		return closestElement;
	}

	return closestElement.offsetParent;
}

/**
 * Given two DOM nodes, replaces the former with the latter in the DOM.
 *
 * @param {Element} processedNode Node to be removed.
 * @param {Element} newNode       Node to be inserted in its place.
 * @return {void}
 */
export function replace( processedNode, newNode ) {
	insertAfter( newNode, processedNode.parentNode );
	remove( processedNode );
}

/**
 * Given a DOM node, removes it from the DOM.
 *
 * @param {Element} node Node to be removed.
 * @return {void}
 */
export function remove( node ) {
	node.parentNode.removeChild( node );
}

/**
 * Given two DOM nodes, inserts the former in the DOM as the next sibling of
 * the latter.
 *
 * @param {Element} newNode       Node to be inserted.
 * @param {Element} referenceNode Node after which to perform the insertion.
 * @return {void}
 */
export function insertAfter( newNode, referenceNode ) {
	referenceNode.parentNode.insertBefore( newNode, referenceNode.nextSibling );
}

/**
 * Unwrap the given node. This means any child nodes are moved to the parent.
 *
 * @param {Node} node The node to unwrap.
 *
 * @return {void}
 */
export function unwrap( node ) {
	const parent = node.parentNode;

	while ( node.firstChild ) {
		parent.insertBefore( node.firstChild, node );
	}

	parent.removeChild( node );
}

/**
 * Replaces the given node with a new node with the given tag name.
 *
 * @param {Element}  node    The node to replace
 * @param {string}   tagName The new tag name.
 *
 * @return {Element} The new node.
 */
export function replaceTag( node, tagName ) {
	const newNode = node.ownerDocument.createElement( tagName );

	while ( node.firstChild ) {
		newNode.appendChild( node.firstChild );
	}

	node.parentNode.replaceChild( newNode, node );

	return newNode;
}

/**
 * Wraps the given node with a new node with the given tag name.
 *
 * @param {Element} newNode       The node to insert.
 * @param {Element} referenceNode The node to wrap.
 */
export function wrap( newNode, referenceNode ) {
	referenceNode.parentNode.insertBefore( newNode, referenceNode );
	newNode.appendChild( referenceNode );
}