const isValidLocatorString = locatorString => locatorString.match(/^[A-Ra-r][A-Ra-r]\d\d[A-Xa-x][A-Xa-x]/) !== null;
const charToNumber = char => char.toUpperCase().charCodeAt(0) - CHAR_CODE_OFFSET;
const numberToChar = number => String.fromCharCode(number + CHAR_CODE_OFFSET);
const CHAR_CODE_OFFSET = 65;
const degToRad = deg => (deg % 360) * Math.PI / 180;
const radToDeg = rad => (rad / Math.PI *180) % 360;
const isValidPoint = (lat, lng) => (lat >= -90 && lat <= 90) && (lng >= -180 && lng <= 180);

function ConvertDDToDMS(lat, lng) {
	var LatLng = [];

	if (lng < -180) {
		lng = lng + 360;
	}
	if (lng > 180)  {
		lng = lng - 360;
	}
	
	LatLng['latDeg'] = (lat < 0 ? "S" : "N") + " " + (0 | (lat < 0 ? (lat = -lat) : lat)) + "° " + (0 | (((lat += 1e-9) % 1) * 60)) + "' " + ((0 | (((lat * 60) % 1) * 6000)) / 100) + "\"";

	LatLng['lngDeg'] = (lng < 0 ? "W" : "E") + " " + (0 | (lng < 0 ? (lng = -lng) : lng)) + "° " + (0 | (((lng += 1e-9) % 1) * 60)) + "' " + ((0 | (((lng * 60) % 1) * 6000)) / 100) + "\"";

	return LatLng;
}

const latLngToLocator = (lat, lng) => {
	if (lng < -180) {
		lng = lng + 360;
	}
	if (lng > 180)  {
		lng = lng - 360;
	}
	if (!isValidPoint(lat, lng)) {
		throw new Error('Input is not a valid coordinate');
	}

	const longitude = lng + 180;
	const latitude = lat + 90;

	const fieldLng = numberToChar(Math.floor(longitude / 20));
	const fieldLat = numberToChar(Math.floor(latitude / 10));

	const squareLng = Math.floor(longitude % 20 / 2);
	const squareLat = Math.floor(latitude % 10);

	const subsquareLng = numberToChar(Math.floor((longitude % 20 % 2) * 12)).toLowerCase();
	const subsquareLat = numberToChar((latitude % 10 - squareLat) * 24).toLowerCase();

	return fieldLng + fieldLat + squareLng + squareLat + subsquareLng + subsquareLat;
};

function onMapMove(event) {
	var LatLng = event.latlng;
	var lat = LatLng.lat; 
	var lng = LatLng.lng; 					
	var LatLng2 = ConvertDDToDMS(lat, lng);
	$('#latDeg').html(LatLng2.latDeg);
	$('#lngDeg').html(LatLng2.lngDeg);
	var locator = latLngToLocator(lat,lng);
	$('#locator').html(locator);
	var distance = bearingDistance(homegrid, locator);

	$('#bearing').html(distance.deg + ' deg');
	$('#distance').html(Math.round(distance.km * 10) / 10 + ' km');
};

const bearingDistance = (from, to) => {
	const fromCoords = locatorToLatLng(from);
	const toCoords = locatorToLatLng(to);
	const dLat = degToRad(toCoords[0] - fromCoords[0]);
	const dLon = degToRad(toCoords[1] - fromCoords[1]);
	const fromLat = degToRad(fromCoords[0]);
	const toLat = degToRad(toCoords[0]);
	const a = Math.pow(Math.sin(dLat / 2), 2) + Math.pow(Math.sin(dLon / 2), 2) * Math.cos(fromLat) * Math.cos(toLat);
	const b = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
	
	const y = (dLon) * Math.cos(fromLat) * Math.cos(toLat);
	const x = Math.sin(toLat) - Math.sin(fromLat) * Math.cos(b);
	
	let az = Math.atan2(y, x);
	
	if (az < 0) {
		az += 2 * Math.PI;
	}
	
	return {
		km: b * 6371,
		deg: calcAngle(fromCoords, toCoords)
	};
};

var calcAngle = function (p1, p2) {
	var lat1 = p1[0] / 180 * Math.PI;
	var lat2 = p2[0] / 180 * Math.PI;
	var lng1 = p1[1] / 180 * Math.PI;
	var lng2 = p2[1] / 180 * Math.PI;
	var y = Math.sin(lng2-lng1) * Math.cos(lat2);
	var x = Math.cos(lat1)*Math.sin(lat2) - Math.sin(lat1)*Math.cos(lat2)*Math.cos(lng2-lng1);
	var brng = (Math.atan2(y, x) * 180 / Math.PI + 360).toFixed(0);

	return (brng % 360);
}

const locatorToLatLng = (locatorString) => {
	locatorString += 'll'; // append subsquare in case is 4 chars long...  If not, is ignored.
	if (!isValidLocatorString(locatorString)) {
		throw new Error('Input is not valid locator string');
	}
	
	const fieldLng = charToNumber(locatorString[0]) * 20;
	const fieldLat = charToNumber(locatorString[1]) * 10;
	const squareLng = Number.parseInt(locatorString[2]) * 2;
	const squareLat = Number.parseInt(locatorString[3]);
	const subsquareLng = (charToNumber(locatorString[4]) + 0.5) / 12;
	const subsquareLat = (charToNumber(locatorString[5]) + 0.5) / 24;
	
	return [
		fieldLat + squareLat + subsquareLat - 90,
		fieldLng + squareLng + subsquareLng - 180
	];
};