const proj4 = require('proj4'),
	turf = require('@turf/turf'),
	jsts = require('jsts'),
	utils = require('./utils');

/**
 * Convert a line buffer to a polygon coordinates
 * @param {*} lineGeoCoors buffer line coordinates
 * @param {*} width in meters
 */
function lineBuffer(lineGeoCoors, width) {
	let dBufCoors = [];
	if (!utils.isEmptyArray(lineGeoCoors)) {

		const _width = width || 10;   // default is 10 meter 
		try {
			// 1. Transform to Earth Azimuthal Equidistant projection centered by the centeroid of the geometry's bounds
			const line = turf.lineString(lineGeoCoors);
			const bbox = turf.bbox(line);
			const bboxPolygon = turf.bboxPolygon(bbox);
			const centroid = turf.centroid(bboxPolygon);
			proj4.defs([
				[
					'EPSG:4326',
					'+title=WGS 84 (long/lat) +proj=longlat +ellps=WGS84 +datum=WGS84 +units=degrees'],
			]);
			const aeqdProjection = `+proj=aeqd +lat_0=${centroid.geometry.coordinates[1]} +lon_0=${centroid.geometry.coordinates[0]} +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs`;

			const projectedCoors = lineGeoCoors.map(co => {
				return proj4(aeqdProjection, co);
			});

			// 2. Do the buffer using JSTS geolib
			const pathCoords = projectedCoors.map(coor => {
				return new jsts.geom.Coordinate(coor[0], coor[1]);
			});
			const geometryFactory = new jsts.geom.GeometryFactory();
			const shell = geometryFactory.createLineString(pathCoords);
			const meters = _width * .5;
			const polygon = shell.buffer(meters, 16, 2);  // 16: quadrants point for arc, 2: flat endStyle
			const polygonCoords = polygon.getCoordinates();

			// 3. Transform back to WGS84 latlon
			dBufCoors = polygonCoords.map(co => {
				const proj = proj4(aeqdProjection, proj4('EPSG:4326'), co);
				return [proj.x, proj.y];
			});

		} catch (error) {
			// debug(error);
			return [];
		}
	}
	return dBufCoors;
};

module.exports = {
	lineBuffer
};