import { diff, unmount } from './index';
import { coerceToVNode, Fragment } from '../create-element';
import { EMPTY_OBJ, EMPTY_ARR } from '../constants';
import { removeNode } from '../util';

/**
 * Diff the children of a virtual node
 * @param {import('../internal').PreactElement} parentDom The DOM element whose
 * children are being diffed
 * @param {import('../internal').VNode} newParentVNode The new virtual
 * node whose children should be diff'ed against oldParentVNode
 * @param {import('../internal').VNode} oldParentVNode The old virtual
 * node whose children should be diff'ed against newParentVNode
 * @param {object} context The current context object
 * @param {boolean} isSvg Whether or not this DOM node is an SVG node
 * @param {Array<import('../internal').PreactElement>} excessDomChildren
 * @param {Array<import('../internal').Component>} mounts The list of components
 * which have mounted
 * @param {import('../internal').Component} ancestorComponent The direct parent
 * component to the ones being diffed
 */
export function diffChildren(parentDom, newParentVNode, oldParentVNode, context, isSvg, excessDomChildren, mounts, ancestorComponent) {
	let childVNode, i, j, p, index, oldVNode, newDom,
		nextDom, sibDom, focus,
		childDom;

	let newChildren = newParentVNode._children || toChildArray(newParentVNode.props.children, newParentVNode._children=[], coerceToVNode);
	let oldChildren = oldParentVNode!=null && oldParentVNode!=EMPTY_OBJ && oldParentVNode._children || EMPTY_ARR;

	let oldChildrenLength = oldChildren.length;

	if (oldChildrenLength) {
		for (i = 0; i< oldChildrenLength; i++) {
			if (oldChildren[i] && oldChildren[i]._dom) {
				childDom = oldChildren[i]._dom;
				break;
			}
		}
	}

	if (excessDomChildren!=null) {
		for (i = 0; i < excessDomChildren.length; i++) {
			if (excessDomChildren[i]!=null) {
				childDom = excessDomChildren[i];
				break;
			}
		}
	}

	for (i=0; i<newChildren.length; i++) {
		childVNode = newChildren[i] = coerceToVNode(newChildren[i]);
		oldVNode = index = null;

		// Check if we find a corresponding element in oldChildren and store the
		// index where the element was found.
		p = oldChildren[i];
		if (p != null && (childVNode.key==null && p.key==null ? (childVNode.type === p.type) : (childVNode.key === p.key))) {
			index = i;
		}
		else {
			for (j=0; j<oldChildrenLength; j++) {
				p = oldChildren[j];
				if (p!=null) {
					if (childVNode.key==null && p.key==null ? (childVNode.type === p.type) : (childVNode.key === p.key)) {
						index = j;
						break;
					}
				}
			}
		}

		// If we have found a corresponding old element we store it in a variable
		// and delete it from the array. That way the next iteration can skip this
		// element.
		if (index!=null) {
			oldVNode = oldChildren[index];
			oldChildren[index] = null;
		}

		nextDom = childDom!=null && childDom.nextSibling;

		// Morph the old element into the new one, but don't append it to the dom yet
		newDom = diff(oldVNode==null ? null : oldVNode._dom, parentDom, childVNode, oldVNode, context, isSvg, excessDomChildren, mounts, ancestorComponent, null);

		// Only proceed if the vnode has not been unmounted by `diff()` above.
		if (childVNode!=null && newDom !=null) {
			// Store focus in case moving children around changes it. Note that we
			// can't just check once for every tree, because we have no way to
			// differentiate wether the focus was reset by the user in a lifecycle
			// hook or by reordering dom nodes.
			focus = document.activeElement;

			if (childVNode._lastDomChild != null) {
				// Only Fragments or components that return Fragment like VNodes will
				// have a non-null _lastDomChild. Continue the diff from the end of
				// this Fragment's DOM tree.
				newDom = childVNode._lastDomChild;
			}
			else if (excessDomChildren==oldVNode || newDom!=childDom || newDom.parentNode==null) {
				// NOTE: excessDomChildren==oldVNode above:
				// This is a compression of excessDomChildren==null && oldVNode==null!
				// The values only have the same type when `null`.

				outer: if (childDom==null || childDom.parentNode!==parentDom) {
					parentDom.appendChild(newDom);
				}
				else {
					sibDom = childDom;
					j = 0;
					while ((sibDom=sibDom.nextSibling) && j++<oldChildrenLength/2) {
						if (sibDom===newDom) {
							break outer;
						}
					}
					parentDom.insertBefore(newDom, childDom);
				}
			}

			// Restore focus if it was changed
			if (focus!==document.activeElement) {
				focus.focus();
			}

			childDom = newDom!=null ? newDom.nextSibling : nextDom;
		}
	}

	// Remove children that are not part of any vnode. Only used by `hydrate`
	if (excessDomChildren!=null && newParentVNode.type!==Fragment) for (i=excessDomChildren.length; i--; ) if (excessDomChildren[i]!=null) removeNode(excessDomChildren[i]);

	// Remove remaining oldChildren if there are any.
	for (i=oldChildrenLength; i--; ) if (oldChildren[i]!=null) unmount(oldChildren[i], ancestorComponent);
}

/**
 * Flatten a virtual nodes children to a single dimensional array
 * @param {import('../index').ComponentChildren} children The unflattened
 * children of a virtual node
 * @param {Array<import('../internal').VNode | null>} [flattened] An flat array of children to modify
 */
export function toChildArray(children, flattened, map) {
	if (flattened == null) flattened = [];
	if (children==null || typeof children === 'boolean') {}
	else if (Array.isArray(children)) {
		for (let i=0; i < children.length; i++) {
			toChildArray(children[i], flattened);
		}
	}
	else {
		flattened.push(map ? map(children) : children);
	}

	return flattened;
}

@@ -1555,35 +1555,8 @@
 h;%0A%0A
-%09if (oldChildrenLength) %7B%0A%09
 %09for
@@ -1565,16 +1565,17 @@
 i = 0; i
+ 
 %3C oldChi
@@ -1590,25 +1590,24 @@
 gth; i++) %7B%0A
-%09
 %09%09if (oldChi
@@ -1637,25 +1637,24 @@
 %5Bi%5D._dom) %7B%0A
-%09
 %09%09%09childDom 
@@ -1675,37 +1675,31 @@
 i%5D._dom;%0A%09%09%09
-%09
 break;%0A
-%09%09%09%7D%0A
 %09%09%7D%0A%09%7D%0A%0A%09if 

Remove if around for loop and add missing space