type NODE_TYPE = 1 | 4 | 5;
const SHOW_ELEMENT = 1; // NodeFilter.SHOW_ELEMENT;
const SHOW_TEXT = 4; // NodeFilter.SHOW_TEXT;
const SHOW_ELEMENT_OR_TEXT = 5; // SHOW_ELEMENT|SHOW_TEXT;

const always = (): true => true;

class TreeIterator<T extends Node> {
    root: Node;
    currentNode: Node;
    nodeType: NODE_TYPE;
    filter: (n: T) => boolean;

    constructor(root: Node, nodeType: NODE_TYPE, filter?: (n: T) => boolean) {
        this.root = root;
        this.currentNode = root;
        this.nodeType = nodeType;
        this.filter = filter || always;
    }

    isAcceptableNode(node: Node): boolean {
        const nodeType = node.nodeType;
        const nodeFilterType =
            nodeType === Node.ELEMENT_NODE
                ? SHOW_ELEMENT
                : nodeType === Node.TEXT_NODE
                  ? SHOW_TEXT
                  : 0;
        return !!(nodeFilterType & this.nodeType) && this.filter(node as T);
    }

    nextNode(): T | null {
        const root = this.root;
        let current: Node | null = this.currentNode;
        let node: Node | null;
        while (true) {
            node = current.firstChild;
            while (!node && current) {
                if (current === root) {
                    break;
                }
                node = current.nextSibling;
                if (!node) {
                    current = current.parentNode;
                }
            }
            if (!node) {
                return null;
            }

            if (this.isAcceptableNode(node)) {
                this.currentNode = node;
                return node as T;
            }
            current = node;
        }
    }

    previousNode(): T | null {
        const root = this.root;
        let current: Node | null = this.currentNode;
        let node: Node | null;
        while (true) {
            if (current === root) {
                return null;
            }
            node = current.previousSibling;
            if (node) {
                while ((current = node.lastChild)) {
                    node = current;
                }
            } else {
                node = current.parentNode;
            }
            if (!node) {
                return null;
            }
            if (this.isAcceptableNode(node)) {
                this.currentNode = node;
                return node as T;
            }
            current = node;
        }
    }

    // Previous node in post-order.
    previousPONode(): T | null {
        const root = this.root;
        let current: Node | null = this.currentNode;
        let node: Node | null;
        while (true) {
            node = current.lastChild;
            while (!node && current) {
                if (current === root) {
                    break;
                }
                node = current.previousSibling;
                if (!node) {
                    current = current.parentNode;
                }
            }
            if (!node) {
                return null;
            }
            if (this.isAcceptableNode(node)) {
                this.currentNode = node;
                return node as T;
            }
            current = node;
        }
    }
}

// ---

export { TreeIterator, SHOW_ELEMENT, SHOW_TEXT, SHOW_ELEMENT_OR_TEXT };