/*
 * Copyright 2018-present Open Networking Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the 'License');
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an 'AS IS' BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import { EventEmitter } from '@angular/core';
import { Link } from './link';
import { Node } from './node';
import * as d3 from 'd3';

const FORCES = {
    LINKS: 1 / 50,
    COLLISION: 1,
    CHARGE: -10
};

export interface Options {
    width: number;
    height: number;
}

export class ForceDirectedGraph {
    public ticker: EventEmitter<d3.Simulation<Node, Link>> = new EventEmitter();
    public simulation: d3.Simulation<any, any>;

    public nodes: Node[] = [];
    public links: Link[] = [];

    constructor(options: Options) {
        this.initSimulation(options);
    }

    initNodes() {
        if (!this.simulation) {
            throw new Error('simulation was not initialized yet');
        }

        this.simulation.nodes(this.nodes);
    }

    initLinks() {
        if (!this.simulation) {
            throw new Error('simulation was not initialized yet');
        }

        // Initializing the links force simulation
        this.simulation.force('links',
            d3.forceLink(this.links)
                .strength(FORCES.LINKS)
        );
    }

    initSimulation(options: Options) {
        if (!options || !options.width || !options.height) {
            throw new Error('missing options when initializing simulation');
        }

        /** Creating the simulation */
        if (!this.simulation) {
            const ticker = this.ticker;

            // Creating the force simulation and defining the charges
            this.simulation = d3.forceSimulation()
                .force('charge',
                    d3.forceManyBody()
                        .strength(FORCES.CHARGE)
                );

            // Connecting the d3 ticker to an angular event emitter
            this.simulation.on('tick', function () {
                ticker.emit(this);
            });

            this.initNodes();
            this.initLinks();
        }

        /** Updating the central force of the simulation */
        this.simulation.force('centers', d3.forceCenter(options.width / 2, options.height / 2));

        /** Restarting the simulation internal timer */
        this.simulation.restart();
    }

    stopSimulation() {
        this.simulation.stop();
    }
}