import * as d3 from 'd3';
import { geoEuclideanDistance } from '../geo/index';


export function svgOneWaySegments(projection, graph, dt) {
    return function(entity) {
        var a,
            b,
            i = 0,
            offset = dt,
            segments = [],
            clip = d3.geoIdentity().clipExtent(projection.clipExtent()).stream,
            coordinates = graph.childNodes(entity).map(function(n) {
                return n.loc;
            });

        if (entity.tags.oneway === '-1') coordinates.reverse();

        d3.geoStream({
            type: 'LineString',
            coordinates: coordinates
        }, projection.stream(clip({
            lineStart: function() {},
            lineEnd: function() {
                a = null;
            },
            point: function(x, y) {
                b = [x, y];

                if (a) {
                    var span = geoEuclideanDistance(a, b) - offset;

                    if (span >= 0) {
                        var angle = Math.atan2(b[1] - a[1], b[0] - a[0]),
                            dx = dt * Math.cos(angle),
                            dy = dt * Math.sin(angle),
                            p = [a[0] + offset * Math.cos(angle),
                                 a[1] + offset * Math.sin(angle)];

                        var segment = 'M' + a[0] + ',' + a[1] +
                                      'L' + p[0] + ',' + p[1];

                        for (span -= dt; span >= 0; span -= dt) {
                            p[0] += dx;
                            p[1] += dy;
                            segment += 'L' + p[0] + ',' + p[1];
                        }

                        segment += 'L' + b[0] + ',' + b[1];
                        segments.push({id: entity.id, index: i, d: segment});
                    }

                    offset = -span;
                    i++;
                }

                a = b;
            }
        })));

        return segments;
    };
}