const Queue = require('./queue');
const Graph = require('./graph');

function findPathWithDijkstra(cities, roads, startNode, endNode) {
    const graph = new Graph();
    
    // Add cities and roads to graph
    for (let city of cities) {
        graph.addNode(city.id)
    }

    for (let { start_city_id, end_city_id, distance } of roads) {
        graph.addEdge(start_city_id, end_city_id, distance)
    }
    
    // Dijkstra path search algo
    let times = {};
    let backtrace = {};
    let queue = new Queue();

    times[startNode] = 0;

    graph.nodes.forEach(node => {
        if (node !== startNode) {
            times[node] = Infinity
        }
    });

    queue.enqueue([startNode, 0]);

    while (queue.size()) {
        let shortestStep = queue.dequeue();
        let currentNode = shortestStep[0];   
        graph.adjacencyList[currentNode].forEach(neighbor => {
            let time = times[currentNode] + neighbor.distance;
        
            if (time < times[neighbor.node]) {
                times[neighbor.node] = time;
                backtrace[neighbor.node] = currentNode;
                queue.enqueue([neighbor.node, time]);
            }
        });
    }

    let path = [endNode];
    let lastStep = endNode;  while(lastStep !== startNode) {
        path.unshift(backtrace[lastStep])
        lastStep = backtrace[lastStep]
    } 
    
    // return `Path is ${path} and time is ${times[endNode]}`
    return {path, distance: times[endNode]}
}

module.exports = findPathWithDijkstra;