function modulus(i, n) {
	return ((i % n) + n) % n;
}

function definedProps(obj) {
	return Object.fromEntries(
		Object.entries(obj).filter(([k, v]) => v !== undefined)
	);
}

/**
 * Whether or not a string is in the format '<number>m'
 * @param {string} value
 * @returns Boolean
 */
function isInMeters(value) {
	return (
		value
			.toString()
			.trim()
			.slice(value.toString().length - 1, value.toString().length) === 'm'
	);
}

/**
 * Whether or not a string is in the format '<number>%'
 * @param {string} value
 * @returns Boolean
 */
function isInPercent(value) {
	return (
		value
			.toString()
			.trim()
			.slice(value.toString().length - 1, value.toString().length) === '%'
	);
}

/**
 * Whether or not a string is in the format '<number>px'
 * @param {string} value
 * @returns Boolean
 */
function isInPixels(value) {
	return (
		value
			.toString()
			.trim()
			.slice(value.toString().length - 2, value.toString().length) === 'px'
	);
}

function pixelsToMeters(pixels, map) {
	let refPoint1 = map.getCenter();
	let xy1 = map.latLngToLayerPoint(refPoint1);
	let xy2 = {
		x: xy1.x + Number(pixels),
		y: xy1.y,
	};
	let refPoint2 = map.layerPointToLatLng(xy2);
	let derivedMeters = map.distance(refPoint1, refPoint2);
	return derivedMeters;
}

L.Polyline.include({
	/**
	 * Adds arrowheads to an L.polyline
	 * @param {object} options The options for the arrowhead.  See documentation for details
	 * @returns The L.polyline instance that they arrowheads are attached to
	 */
	arrowheads: function (options = {}) {
		// Merge user input options with default options:
		const defaults = {
			yawn: 60,
			size: '15%',
			frequency: 'allvertices',
			proportionalToTotal: false,
		};

		this.options.noClip = true;

		let actualOptions = Object.assign({}, defaults, options);
		this._arrowheadOptions = actualOptions;

		this._hatsApplied = true;
		return this;
	},

	buildVectorHats: function (options) {
		// Reset variables from previous this._update()
		if (this._arrowheads) {
			this._arrowheads.remove();
		}

		if (this._ghosts) {
			this._ghosts.remove();
		}

		//  -------------------------------------------------------- //
		//  ------------  FILTER THE OPTIONS ----------------------- //
		/*
		 * The next 3 lines folds the options of the parent polyline into the default options for all polylines
		 * The options for the arrowhead are then folded in as well
		 * All options defined in parent polyline will be inherited by the arrowhead, unless otherwise specified in the arrowhead(options) call
		 */

		let defaultOptionsOfParent = Object.getPrototypeOf(
			Object.getPrototypeOf(this.options)
		);

		// merge default options of parent polyline (this.options's prototype's prototype) with options passed to parent polyline (this.options).
		let parentOptions = Object.assign({}, defaultOptionsOfParent, this.options);

		// now merge in the options the user has put in the arrowhead call
		let hatOptions = Object.assign({}, parentOptions, options);

		// ...with a few exceptions:
		hatOptions.smoothFactor = 1;
		hatOptions.fillOpacity = 1;
		hatOptions.fill = options.fill ? true : false;
		hatOptions.interactive = false;

		//  ------------  FILTER THE OPTIONS END -------------------- //
		//  --------------------------------------------------------- //

		//  --------------------------------------------------------- //
		//  ------ LOOP THROUGH EACH POLYLINE SEGMENT --------------- //
		//  ------ TO CALCULATE HAT SIZES AND CAPTURE IN ARRAY ------ //

		let size = options.size.toString(); // stringify if its a number
		let allhats = []; // empty array to receive hat polylines
		const { frequency, offsets } = options;

		if (offsets?.start || offsets?.end) {
			this._buildGhosts({ start: offsets.start, end: offsets.end });
		}

		const lineToTrace = this._ghosts || this;

		lineToTrace._parts.forEach((peice, index) => {
			// Immutable variables for each peice
			const latlngs = peice.map((point) => this._map.layerPointToLatLng(point));

			const totalLength = (() => {
				let total = 0;
				for (var i = 0; i < peice.length - 1; i++) {
					total += this._map.distance(latlngs[i], latlngs[i + 1]);
				}
				return total;
			})();

			// TBD by options if tree below
			let derivedLatLngs;
			let derivedBearings;
			let spacing;
			let noOfPoints;

			//  Determining latlng and bearing arrays based on frequency choice:
			if (!isNaN(frequency)) {
				spacing = 1 / frequency;
				noOfPoints = frequency;
			} else if (isInPercent(frequency)) {
				console.error(
					'Error: arrowhead frequency option cannot be given in percent.  Try another unit.'
				);
			} else if (isInMeters(frequency)) {
				spacing = frequency.slice(0, frequency.length - 1) / totalLength;
				noOfPoints = 1 / spacing;
				// round things out for more even spacing:
				noOfPoints = Math.floor(noOfPoints);
				spacing = 1 / noOfPoints;
			} else if (isInPixels(frequency)) {
				spacing = (() => {
					let chosenFrequency = frequency.slice(0, frequency.length - 2);
					let derivedMeters = pixelsToMeters(chosenFrequency, this._map);
					return derivedMeters / totalLength;
				})();

				noOfPoints = 1 / spacing;

				// round things out for more even spacing:
				noOfPoints = Math.floor(noOfPoints);
				spacing = 1 / noOfPoints;
			}

			if (options.frequency === 'allvertices') {
				derivedBearings = (() => {
					let bearings = [];
					for (var i = 1; i < latlngs.length; i++) {
						let bearing =
							L.GeometryUtil.angle(
								this._map,
								latlngs[modulus(i - 1, latlngs.length)],
								latlngs[i]
							) + 180;
						bearings.push(bearing);
					}
					return bearings;
				})();

				derivedLatLngs = latlngs;
				derivedLatLngs.shift();
			} else if (options.frequency === 'endonly' && latlngs.length >= 2) {
				derivedLatLngs = [latlngs[latlngs.length - 1]];

				derivedBearings = [
					L.GeometryUtil.angle(
						this._map,
						latlngs[latlngs.length - 2],
						latlngs[latlngs.length - 1]
					) + 180,
				];
			} else {
				derivedLatLngs = [];
				let interpolatedPoints = [];
				for (var i = 0; i < noOfPoints; i++) {
					let interpolatedPoint = L.GeometryUtil.interpolateOnLine(
						this._map,
						latlngs,
						spacing * (i + 1)
					);

					if (interpolatedPoint) {
						interpolatedPoints.push(interpolatedPoint);
						derivedLatLngs.push(interpolatedPoint.latLng);
					}
				}

				derivedBearings = (() => {
					let bearings = [];

					for (var i = 0; i < interpolatedPoints.length; i++) {
						let bearing = L.GeometryUtil.angle(
							this._map,
							latlngs[interpolatedPoints[i].predecessor + 1],
							latlngs[interpolatedPoints[i].predecessor]
						);
						bearings.push(bearing);
					}
					return bearings;
				})();
			}

			let hats = [];

			// Function to build hats based on index and a given hatsize in meters
			const pushHats = (size, localHatOptions = {}) => {
				let yawn = localHatOptions.yawn ?? options.yawn;

				let leftWingPoint = L.GeometryUtil.destination(
					derivedLatLngs[i],
					derivedBearings[i] - yawn / 2,
					size
				);

				let rightWingPoint = L.GeometryUtil.destination(
					derivedLatLngs[i],
					derivedBearings[i] + yawn / 2,
					size
				);

				let hatPoints = [
					[leftWingPoint.lat, leftWingPoint.lng],
					[derivedLatLngs[i].lat, derivedLatLngs[i].lng],
					[rightWingPoint.lat, rightWingPoint.lng],
				];

				let hat = options.fill
					? L.polygon(hatPoints, { ...hatOptions, ...localHatOptions })
					: L.polyline(hatPoints, { ...hatOptions, ...localHatOptions });

				hats.push(hat);
			}; // pushHats()

			// Function to build hats based on pixel input
			const pushHatsFromPixels = (size, localHatOptions = {}) => {
				let sizePixels = size.slice(0, size.length - 2);
				let yawn = localHatOptions.yawn ?? options.yawn;

				let derivedXY = this._map.latLngToLayerPoint(derivedLatLngs[i]);

				let bearing = derivedBearings[i];

				let thetaLeft = (180 - bearing - yawn / 2) * (Math.PI / 180),
					thetaRight = (180 - bearing + yawn / 2) * (Math.PI / 180);

				let dxLeft = sizePixels * Math.sin(thetaLeft),
					dyLeft = sizePixels * Math.cos(thetaLeft),
					dxRight = sizePixels * Math.sin(thetaRight),
					dyRight = sizePixels * Math.cos(thetaRight);

				let leftWingXY = {
					x: derivedXY.x + dxLeft,
					y: derivedXY.y + dyLeft,
				};
				let rightWingXY = {
					x: derivedXY.x + dxRight,
					y: derivedXY.y + dyRight,
				};

				let leftWingPoint = this._map.layerPointToLatLng(leftWingXY),
					rightWingPoint = this._map.layerPointToLatLng(rightWingXY);

				let hatPoints = [
					[leftWingPoint.lat, leftWingPoint.lng],
					[derivedLatLngs[i].lat, derivedLatLngs[i].lng],
					[rightWingPoint.lat, rightWingPoint.lng],
				];

				let hat = options.fill
					? L.polygon(hatPoints, { ...hatOptions, ...localHatOptions })
					: L.polyline(hatPoints, { ...hatOptions, ...localHatOptions });

				hats.push(hat);
			}; // pushHatsFromPixels()

			//  -------  LOOP THROUGH POINTS IN EACH SEGMENT ---------- //
			for (var i = 0; i < derivedLatLngs.length; i++) {
				let { perArrowheadOptions, ...globalOptions } = options;

				perArrowheadOptions = perArrowheadOptions ? perArrowheadOptions(i) : {};
				perArrowheadOptions = Object.assign(
					globalOptions,
					definedProps(perArrowheadOptions)
				);

				size = perArrowheadOptions.size ?? size;

				// ---- If size is chosen in meters -------------------------
				if (isInMeters(size)) {
					let hatSize = size.slice(0, size.length - 1);
					pushHats(hatSize, perArrowheadOptions);

					// ---- If size is chosen in percent ------------------------
				} else if (isInPercent(size)) {
					let sizePercent = size.slice(0, size.length - 1);
					let hatSize = (() => {
						if (
							options.frequency === 'endonly' &&
							options.proportionalToTotal
						) {
							return (totalLength * sizePercent) / 100;
						} else {
							let averageDistance = totalLength / (peice.length - 1);
							return (averageDistance * sizePercent) / 100;
						}
					})(); // hatsize calculation

					pushHats(hatSize, perArrowheadOptions);

					// ---- If size is chosen in pixels --------------------------
				} else if (isInPixels(size)) {
					pushHatsFromPixels(options.size, perArrowheadOptions);

					// ---- If size unit is not given -----------------------------
				} else {
					console.error(
						'Error: Arrowhead size unit not defined.  Check your arrowhead options.'
					);
				} // if else block for Size
			} // for loop for each point witin a peice

			allhats.push(...hats);
		}); // forEach peice

		//  --------- LOOP THROUGH EACH POLYLINE END ---------------- //
		//  --------------------------------------------------------- //

		let arrowheads = L.layerGroup(allhats);
		this._arrowheads = arrowheads;

		return this;
	},

	getArrowheads: function () {
		if (this._arrowheads) {
			return this._arrowheads;
		} else {
			return console.error(
				`Error: You tried to call '.getArrowheads() on a shape that does not have a arrowhead.  Use '.arrowheads()' to add a arrowheads before trying to call '.getArrowheads()'`
			);
		}
	},

	/**
	 * Builds ghost polylines that are clipped versions of the polylines based on the offsets
	 * If offsets are used, arrowheads are drawn from 'this._ghosts' rather than 'this'
	 */
	_buildGhosts: function ({ start, end }) {
		if (start || end) {
			let latlngs = this.getLatLngs();

			latlngs = Array.isArray(latlngs[0]) ? latlngs : [latlngs];

			const newLatLngs = latlngs.map((segment) => {
				// Get total distance of original latlngs
				const totalLength = (() => {
					let total = 0;
					for (var i = 0; i < segment.length - 1; i++) {
						total += this._map.distance(segment[i], segment[i + 1]);
					}
					return total;
				})();

				// Modify latlngs to end at interpolated point
				if (start) {
					let endOffsetInMeters = (() => {
						if (isInMeters(start)) {
							return Number(start.slice(0, start.length - 1));
						} else if (isInPixels(start)) {
							let pixels = Number(start.slice(0, start.length - 2));
							return pixelsToMeters(pixels, this._map);
						}
					})();

					let newStart = L.GeometryUtil.interpolateOnLine(
						this._map,
						segment,
						endOffsetInMeters / totalLength
					);

					segment = segment.slice(
						newStart.predecessor === -1 ? 1 : newStart.predecessor + 1,
						segment.length
					);
					segment.unshift(newStart.latLng);
				}

				if (end) {
					let endOffsetInMeters = (() => {
						if (isInMeters(end)) {
							return Number(end.slice(0, end.length - 1));
						} else if (isInPixels(end)) {
							let pixels = Number(end.slice(0, end.length - 2));
							return pixelsToMeters(pixels, this._map);
						}
					})();

					let newEnd = L.GeometryUtil.interpolateOnLine(
						this._map,
						segment,
						(totalLength - endOffsetInMeters) / totalLength
					);

					segment = segment.slice(0, newEnd.predecessor + 1);
					segment.push(newEnd.latLng);
				}

				return segment;
			});

			this._ghosts = L.polyline(newLatLngs, {
				...this.options,
				color: 'rgba(0,0,0,0)',
				stroke: 0,
				smoothFactor: 0,
				interactive: false,
			});
			this._ghosts.addTo(this._map);
		}
	},

	deleteArrowheads: function () {
		if (this._arrowheads) {
			this._arrowheads.remove();
			delete this._arrowheads;
			delete this._arrowheadOptions;
			this._hatsApplied = false;
		}
		if (this._ghosts) {
			this._ghosts.remove();
		}
	},

	_update: function () {
		if (!this._map) {
			return;
		}

		this._clipPoints();
		this._simplifyPoints();
		this._updatePath();

		if (this._hatsApplied) {
			this.buildVectorHats(this._arrowheadOptions);
			this._map.addLayer(this._arrowheads);
		}
	},

	remove: function () {
		if (this._arrowheads) {
			this._arrowheads.remove();
		}
		if (this._ghosts) {
			this._ghosts.remove();
		}
		return this.removeFrom(this._map || this._mapToAdd);
	},
});

L.LayerGroup.include({
	removeLayer: function (layer) {
		var id = layer in this._layers ? layer : this.getLayerId(layer);

		if (this._map && this._layers[id]) {
			if (this._layers[id]._arrowheads) {
				this._layers[id]._arrowheads.remove();
			}
			this._map.removeLayer(this._layers[id]);
		}

		delete this._layers[id];

		return this;
	},

	onRemove: function (map, layer) {
		for (var layer in this._layers) {
			if (this._layers[layer]) {
				this._layers[layer].remove();
			}
		}

		this.eachLayer(map.removeLayer, map);
	},
});

L.Map.include({
	removeLayer: function (layer) {
		var id = L.Util.stamp(layer);

		if (layer._arrowheads) {
			layer._arrowheads.remove();
		}
		if (layer._ghosts) {
			layer._ghosts.remove();
		}

		if (!this._layers[id]) {
			return this;
		}

		if (this._loaded) {
			layer.onRemove(this);
		}

		if (layer.getAttribution && this.attributionControl) {
			this.attributionControl.removeAttribution(layer.getAttribution());
		}

		delete this._layers[id];

		if (this._loaded) {
			this.fire('layerremove', { layer: layer });
			layer.fire('remove');
		}

		layer._map = layer._mapToAdd = null;

		return this;
	},
});

L.GeoJSON.include({
	geometryToLayer: function (geojson, options) {
		var geometry = geojson.type === 'Feature' ? geojson.geometry : geojson,
			coords = geometry ? geometry.coordinates : null,
			layers = [],
			pointToLayer = options && options.pointToLayer,
			_coordsToLatLng =
				(options && options.coordsToLatLng) || L.GeoJSON.coordsToLatLng,
			latlng,
			latlngs,
			i,
			len;

		if (!coords && !geometry) {
			return null;
		}

		switch (geometry.type) {
			case 'Point':
				latlng = _coordsToLatLng(coords);
				return this._pointToLayer(pointToLayer, geojson, latlng, options);

			case 'MultiPoint':
				for (i = 0, len = coords.length; i < len; i++) {
					latlng = _coordsToLatLng(coords[i]);
					layers.push(
						this._pointToLayer(pointToLayer, geojson, latlng, options)
					);
				}
				return new L.FeatureGroup(layers);

			case 'LineString':
			case 'MultiLineString':
				latlngs = L.GeoJSON.coordsToLatLngs(
					coords,
					geometry.type === 'LineString' ? 0 : 1,
					_coordsToLatLng
				);
				var polyline = new L.Polyline(latlngs, options);
				if (options.arrowheads) {
					polyline.arrowheads(options.arrowheads);
				}
				return polyline;

			case 'Polygon':
			case 'MultiPolygon':
				latlngs = L.GeoJSON.coordsToLatLngs(
					coords,
					geometry.type === 'Polygon' ? 1 : 2,
					_coordsToLatLng
				);
				return new L.Polygon(latlngs, options);

			case 'GeometryCollection':
				for (i = 0, len = geometry.geometries.length; i < len; i++) {
					var layer = this.geometryToLayer(
						{
							geometry: geometry.geometries[i],
							type: 'Feature',
							properties: geojson.properties,
						},
						options
					);

					if (layer) {
						layers.push(layer);
					}
				}
				return new L.FeatureGroup(layers);

			default:
				throw new Error('Invalid GeoJSON object.');
		}
	},

	addData: function (geojson) {
		var features = L.Util.isArray(geojson) ? geojson : geojson.features,
			i,
			len,
			feature;

		if (features) {
			for (i = 0, len = features.length; i < len; i++) {
				// only add this if geometry or geometries are set and not null
				feature = features[i];
				if (
					feature.geometries ||
					feature.geometry ||
					feature.features ||
					feature.coordinates
				) {
					this.addData(feature);
				}
			}
			return this;
		}

		var options = this.options;

		if (options.filter && !options.filter(geojson)) {
			return this;
		}

		var layer = this.geometryToLayer(geojson, options);
		if (!layer) {
			return this;
		}
		layer.feature = L.GeoJSON.asFeature(geojson);

		layer.defaultOptions = layer.options;
		this.resetStyle(layer);

		if (options.onEachFeature) {
			options.onEachFeature(geojson, layer);
		}

		return this.addLayer(layer);
	},

	_pointToLayer: function (pointToLayerFn, geojson, latlng, options) {
		return pointToLayerFn
			? pointToLayerFn(geojson, latlng)
			: new L.Marker(
					latlng,
					options && options.markersInheritOptions && options
			  );
	},
});