const requestp = require('request-promise-native');
const geolib = require('geolib');

const {makeCached} = require('../util');

const OVERPASS_ENDPOINT = 'https://lz4.overpass-api.de/api/interpreter';

const fetch = makeCached(async (lineRefs) =>
{
    // Retrieve routes, ways and stops from OpenStreetMap
    const rawData = await requestp.post(OVERPASS_ENDPOINT, {form: `\
data=[out:json];

// Find the public transport line bearing the requested reference
relation[network="TaM"][type="route_master"][ref~"^(${lineRefs.join('|')})$"];

// Recursively fetch routes, ways and stops inside the line
(._; >>;);

out body qt;
    `});

    // List of retrieved objects
    const elementsList = JSON.parse(rawData).elements;

    // List of retrieved lines
    const routeMasters = elementsList.filter(elt =>
        elt.tags && elt.tags.type === 'route_master'
    );

    // Retrieved objects indexed by ID
    const elements = elementsList.reduce((prev, elt) =>
    {
        prev[elt.id] = elt;
        return prev;
    }, {});

    // Result object containing all stops
    const stops = {};

    // Result object containing all segments between stops
    const segments = {};

    // Result object containing all lines
    const lines = {};

    for (let routeMaster of routeMasters)
    {
        const lineRef = routeMaster.tags.ref;
        const color = routeMaster.tags.colour || '#000000';

        // Extract all routes for the given line
        const rawRoutes = routeMaster.members.map(({ref}) => elements[ref]);

        // Add missing stops to the result object
        for (let route of rawRoutes)
        {
            for (let {ref, role} of route.members)
            {
                if (role === 'stop')
                {
                    const stop = elements[ref];

                    if (!('ref' in stop.tags))
                    {
                        console.warn(`Stop ${stop.id} is missing a “ref” tag`);
                        continue;
                    }

                    if (!(stop.tags.ref in stops))
                    {
                        stops[stop.tags.ref] = {
                            lat: stop.lat,
                            lon: stop.lon,
                            name: stop.tags.name,
                            lines: [lineRef],
                        };
                    }
                    else
                    {
                        stops[stop.tags.ref].lines.push(lineRef);
                    }
                }
            }
        }

        // Add missing segments between stops
        for (let route of rawRoutes)
        {
            const {from, to} = route.tags;

            const stops = route.members
                .filter(({role}) => role === 'stop')
                .map(({ref}) => elements[ref])
                .filter(stop => 'ref' in stop.tags)
                .map(stop => ({
                    id: stop.id,
                    lat: stop.lat,
                    lon: stop.lon,
                    ref: stop.tags.ref,
                    name: stop.tags.name,
                }));

            const ways = route.members
                .filter(({role}) => role === '')
                .map(({ref}) => ref);

            // Construct a graph with all connected nodes
            const nodeNeighbors = new Map();

            for (let id of ways)
            {
                const {type, nodes, tags} = elements[id];

                const isOneWay = (
                    tags.oneway === 'yes'
                    || tags.junction === 'roundabout'
                );

                const canGoBackward = (
                    !isOneWay
                    || parseInt(tags['lanes:psv:backward'], 10) > 0
                );

                if (type === 'way' && nodes.length >= 1)
                {
                    let previousNode = nodes[0];

                    if (!nodeNeighbors.has(previousNode))
                    {
                        nodeNeighbors.set(previousNode, new Set());
                    }

                    for (let node of nodes.slice(1))
                    {
                        if (!nodeNeighbors.has(node))
                        {
                            nodeNeighbors.set(node, new Set());
                        }

                        nodeNeighbors.get(previousNode).add(node);

                        if (canGoBackward)
                        {
                            nodeNeighbors.get(node).add(previousNode);
                        }

                        previousNode = node;
                    }
                }
            }

            // Find way from first stop through the end using DFS
            const numberOfStops = stops.length;
            let currentStopIndex = 0;

            while (currentStopIndex + 1 < numberOfStops)
            {
                const currentStop = stops[currentStopIndex];
                const nextStop = stops[currentStopIndex + 1];
                const segmentId = `${currentStop.ref}-${nextStop.ref}`;

                if (!(segmentId in segments))
                {
                    const visitedEdges = new Set();
                    const stack = [{
                        currentNode: currentStop.id,
                        segment: [currentStop.id],
                    }];

                    let found = false;

                    while (stack.length !== 0)
                    {
                        const {currentNode, segment} = stack.pop();

                        if (currentNode === nextStop.id)
                        {
                            // Arrived at next stop
                            segments[segmentId] = {
                                nodes: segment.map(id =>
                                {
                                    const {lat, lon} = elements[id];
                                    return {lat, lon};
                                }),
                                length: geolib.getPathLength(segment.map(id =>
                                {
                                    const {lat, lon} = elements[id];
                                    return {latitude: lat, longitude: lon};
                                })),
                                lines: [lineRef],
                            };

                            found = true;
                            break;
                        }

                        const neighbors = nodeNeighbors.get(currentNode) || [];

                        for (let nextNode of neighbors)
                        {
                            const edge = `${currentNode}-${nextNode}`;

                            if (!visitedEdges.has(edge))
                            {
                                visitedEdges.add(edge);
                                stack.push({
                                    currentNode: nextNode,
                                    segment: segment.concat([nextNode]),
                                });
                            }
                        }
                    }

                    if (!found)
                    {
                        throw new Error(`No way between stop \
“${currentStop.name}” (${currentStop.id}) and stop “${nextStop.name}” \
(${nextStop.id}) on line ${lineRef}’s route from “${from}” to “${to}”`);
                    }
                }
                else
                {
                    segments[segmentId].lines.push(lineRef);
                }

                ++currentStopIndex;
            }
        }

        // Construct line objects
        const routes = rawRoutes.map(route => ({
            from: route.tags.from,
            to: route.tags.to,

            // Retrieve each stop’s information (stop order in the relation is
            // assumed to reflect reality)
            stops: route.members
                .filter(({role}) => role === 'stop')
                .map(({ref}) => elements[ref])
                .filter(stop => 'ref' in stop.tags)
                .map(stop => stop.tags.ref)
        }));

        lines[lineRef] = {
            color,
            routes
        };
    }

    return {stops, segments, lines};
});

exports.fetch = fetch;