/**
 * A tree type data structure used to build scene and ...
 * @copyright MrKBear 2022
 * @typeParam T - Child type of `TreeNode`
 */
class TreeNode<T extends TreeNode = TreeNode<any>> implements Iterable<T> {

    /**
     * Record all child nodes when this node is the root node.
     * @remarks
     * Only maintained when the node is the root node. \
     * The array is arranged in depth first traversal order.
     */
    private _progenyNodes: Array<T> | undefined = [ ];

    /**
     * Whether the structure of the current tree has changed.
     * @remarks
     * Only maintained when the node is the root node.
     */
    private _isStructUpdated = false;

    /**
     * @remarks
     * When a node is just created, it defaults the root node. \
     * So this `rootNode` points to itself.
     */
    private _rootNode: T | this = this;

    private _parentNode: T | undefined = void 0;

    private _childNodes: Array<T> = [];

    /**
     * Pointer to the root node.
     */
    public get rootNode(): T | this { return this._rootNode; }

    /**
     * Pointer to the parent node.
     */
    public get parentNode(): T | undefined { return this._parentNode; }

    /**
     * Points to the children of the current node.
     */
    public get childNodes(): ReadonlyArray<T> { return this._childNodes; }

    /**
     * Is this a root node?
     */
    public get isRootNode(): boolean { return !this._parentNode && this._rootNode === this; }

    /**
     * Depth first traverses the current `TreeNode` and its children `TreeNode`.
     * @remarks
     * This will use {@link https://en.wikipedia.org/wiki/Tree_traversal#Pre-order,_NLR Pre-order (NLR) algorithm}. \
     * So... Do not call this getter frequently.
     * @example
     * ``` javascript
     * // ❌ Deprecated implementation !!!
     * for (let i = 0; i < treeNode.progenyNodes.length; i++) {
     *     doSomeThing(treeNode.progenyNodes[i]);
     * }
     * 
     * // ✔️ Best Practices
     * treeNode.progenyNodes.forEach((progenyNode)=> {
     *     doSomeThing(progenyNode);
     * });
     * 
     * // ✔️ Best Practices
     * for(const progenyNode of treeNode.progenyNodes) {
     *     doSomeThing(progenyNode);
     * }
     * ```
     * @return Progeny nodes list.
     */
    public get progenyNodes(): ReadonlyArray<T> {

        if (this.isRootNode && !this._isStructUpdated && this._progenyNodes) {
            return this._progenyNodes;
        }

        else {
            const cacheArray: Array<T> = [];
            const stack: Array<T> = this._childNodes.slice().reverse();

            while (stack.length > 0) {
                const currentNode: T | undefined = stack.pop();

                if (currentNode) {
                    cacheArray.push(currentNode);

                    // Push all child nodes in reverse order
                    for (let i = currentNode.childNodes.length - 1; i >= 0; i --) {
                        stack.push(<T>currentNode.childNodes[i]);
                    }
                }
            }

            if (this.isRootNode) {
                this._progenyNodes = cacheArray;
                this._isStructUpdated = false;
            }

            return cacheArray;
        }
    }

    /**
     * An iterator implementation for {@link TreeNode.progenyNodes}
     * @see {@link TreeNode.progenyNodes}
     */
    public *[Symbol.iterator](): Iterator<T> { yield * this.progenyNodes; }

    /**
     * Remove `nodes` from child nodes.
     * @param nodes - Nodes to be deleted.
     * @returns Success Times.
     */
    public removeChild(...nodes: ReadonlyArray<T>): number {

        let successCount = 0;
        for (const node of nodes) {

            let removeNodesIndex = -1;
            for (let i = 0; i < this._childNodes.length; i++) {
                
                if (this._childNodes[i] === node) {
                    removeNodesIndex = i;
                }
            }

            if (removeNodesIndex < 0) {
                continue;
            }

            // Perform the remove operation
            this._childNodes.splice(removeNodesIndex, 1);

            node._parentNode = void 0;
            node._rootNode = node;
            node.markStructUpdated();

            for (const progeny of node.progenyNodes) {
                progeny._rootNode = node;
            }

            successCount ++;
        }

        if (successCount) {
            this._rootNode.markStructUpdated();
        }

        return successCount;
    }

    /**
     * Remove this node from the parent node
     * @returns Success or not.
     */
    public removeFromParent(): number {

        if (this.isRootNode) {
            return 0;
        }

        else {
            return this._parentNode!.removeChild(this);
        }
    }

    /**
     * Append `nodes` into child nodes.
     * @param node - Nodes to be added.
     * @returns Success Times.
     */
    public appendChild(...nodes: ReadonlyArray<T>): number {

        let successCount = 0;
        for (const node of nodes) {

            if (!node.isRootNode) {
                node.removeFromParent();
            }

            for (const progeny of node.progenyNodes) {
                progeny._rootNode = this._rootNode;
            }
            
            node._rootNode = this._rootNode;
            node._parentNode = this;
            node._progenyNodes = void 0;

            this._childNodes.push(node);

            successCount ++;
        }

        if (successCount) {
            this._rootNode.markStructUpdated();
        }

        return successCount;
    }

    /**
     * Mark that the current tree structure has been updated
     * @returns true
     */
    public markStructUpdated(): boolean { 
        if (this.isRootNode) {
            return this._isStructUpdated = true;
        }
        else {
            return this.rootNode.markStructUpdated();
        }
    }
}

class B extends TreeNode<B> { b(){}; }
class A extends TreeNode<A> { a(){}; }
class C extends A { c(){}; }
const a = new A();
const b = new B();
const c = new C();
a.rootNode.rootNode.appendChild(c);
// a.rootNode.rootNode.appendChild(a);

console.log(a);

export { TreeNode };