import { Injectable } from '@angular/core';

import { Displayable } from 'app/site/base/displayable';
import { Identifiable } from 'app/shared/models/base/identifiable';

/**
 * A basic representation of a tree node. This node does not stores any data.
 */
export interface OSTreeNodeWithoutItem {
    name: string;
    id: number;
    children?: OSTreeNodeWithoutItem[];
}

/**
 * A representation of nodes with the item atached.
 */
export interface OSTreeNode<T> extends OSTreeNodeWithoutItem {
    item: T;
    children?: OSTreeNode<T>[];
}

/**
 * This services handles all operations belonging to trees. It can build trees of plain lists (giving the weight
 * and parentId property) and traverse the trees in pre-order.
 */
@Injectable({
    providedIn: 'root'
})
export class TreeService {
    /**
     * Returns the weight casted to a number from a given model.
     *
     * @param item The model to get the weight from.
     * @param key
     * @returns the weight of the model
     */
    private getAttributeAsNumber<T extends Identifiable & Displayable>(item: T, key: keyof T): number {
        return (<any>item[key]) as number;
    }

    /**
     * Build our representation of a tree node given the model and optional children
     * to append to this node.
     *
     * @param item The model to create a node of.
     * @param children Optional children to append to this node.
     * @returns The created node.
     */
    private buildTreeNode<T extends Identifiable & Displayable>(item: T, children?: OSTreeNode<T>[]): OSTreeNode<T> {
        return {
            name: item.getTitle(),
            id: item.id,
            item: item,
            children: children
        };
    }

    /**
     * Builds a tree from the given items on the relations between items with weight and parentId
     *
     * @param items All items to traverse
     * @param weightKey The key giving access to the weight property
     * @param parentIdKey The key giving access to the parentId property
     * @returns An iterator for all items in the right order.
     */
    public makeTree<T extends Identifiable & Displayable>(
        items: T[],
        weightKey: keyof T,
        parentIdKey: keyof T
    ): OSTreeNode<T>[] {
        // Sort items after their weight
        items.sort((a, b) => this.getAttributeAsNumber(a, weightKey) - this.getAttributeAsNumber(b, weightKey));
        // Build a dict with all children (dict-value) to a specific
        // item id (dict-key).
        const children: { [parendId: number]: T[] } = {};
        items.forEach(model => {
            if (model[parentIdKey]) {
                const parentId = this.getAttributeAsNumber(model, parentIdKey);
                if (children[parentId]) {
                    children[parentId].push(model);
                } else {
                    children[parentId] = [model];
                }
            }
        });
        // Recursive function that generates a nested list with all
        // items with there children
        const getChildren: (_models?: T[]) => OSTreeNode<T>[] = _models => {
            if (!_models) {
                return;
            }
            const nodes: OSTreeNode<T>[] = [];
            _models.forEach(_model => {
                nodes.push(this.buildTreeNode(_model, getChildren(children[_model.id])));
            });
            return nodes;
        };
        // Generates the list of root items (with no parents)
        const parentItems = items.filter(model => !this.getAttributeAsNumber(model, parentIdKey));
        return getChildren(parentItems);
    }

    /**
     * Traverses the given tree in pre order.
     *
     * @param tree The tree to traverse
     * @returns An iterator for all items in the right order.
     */
    public *traverseTree<T>(tree: OSTreeNode<T>[]): Iterator<T> {
        const nodesToVisit = tree.reverse();
        while (nodesToVisit.length > 0) {
            const node = nodesToVisit.pop();
            if (node.children) {
                node.children.reverse().forEach(n => {
                    nodesToVisit.push(n);
                });
            }
            yield node.item;
        }
    }

    /**
     * Removes `item` from the tree.
     *
     * @param tree The tree with items
     * @returns The tree without items
     */
    public stripTree<T>(tree: OSTreeNode<T>[]): OSTreeNodeWithoutItem[] {
        return tree.map(node => {
            const nodeWithoutItem: OSTreeNodeWithoutItem = {
                name: node.name,
                id: node.id
            };
            if (node.children) {
                nodeWithoutItem.children = this.stripTree(node.children);
            }
            return nodeWithoutItem;
        });
    }

    /**
     * Traverses items in pre-order givem (implicit) by the weight and parentId.
     *
     * Just builds the tree with `makeTree` and get the iterator from `traverseTree`.
     *
     * @param items All items to traverse
     * @param weightKey The key giving access to the weight property
     * @param parentIdKey The key giving access to the parentId property
     * @returns An iterator for all items in the right order.
     */
    public traverseItems<T extends Identifiable & Displayable>(
        items: T[],
        weightKey: keyof T,
        parentIdKey: keyof T
    ): Iterator<T> {
        const tree = this.makeTree(items, weightKey, parentIdKey);
        return this.traverseTree(tree);
    }

    /**
     * Reduce a list of items to nodes independent from each other in a given
     * branch of a tree
     *
     * @param branch the tree to traverse
     * @param items the items to check
     * @returns the selection of items that belong to different branches
     */
    private getTopItemsFromBranch<T extends Identifiable & Displayable>(branch: OSTreeNode<T>, items: T[]): T[] {
        const item = items.find(i => branch.item.id === i.id);
        if (item) {
            return [item];
        } else if (!branch.children) {
            return [];
        } else {
            return [].concat(...branch.children.map(child => this.getTopItemsFromBranch(child, items)));
        }
    }

    /**
     * Reduce a list of items to nodes independent from each other in a given tree
     *
     * @param tree the tree to traverse
     * @param items the items to check
     * @returns the selection of items that belong to different branches
     */
    public getTopItemsFromTree<T extends Identifiable & Displayable>(tree: OSTreeNode<T>[], items: T[]): T[] {
        let results: T[] = [];
        tree.forEach(branch => {
            const i = this.getTopItemsFromBranch(branch, items);
            if (i.length) {
                results = results.concat(i);
            }
        });
        return results;
    }

    /**
     * Return all items not being hierarchically dependant on the items in the input arrray
     *
     * @param tree
     * @param items
     * @returns all items that are neither in the input nor dependants of  items in the input
     */
    public getTreeWithoutSelection<T extends Identifiable & Displayable>(tree: OSTreeNode<T>[], items: T[]): T[] {
        let result: T[] = [];
        tree.forEach(branch => {
            if (!items.find(i => i.id === branch.item.id)) {
                result.push(branch.item);
                if (branch.children) {
                    result = result.concat(this.getTreeWithoutSelection(branch.children, items));
                }
            }
        });
        return result;
    }
}