/**
 * Takes a {@link Point} and a {@link LineString} and calculates the closest Point on the (Multi)LineString.
 *
 * @name nearestPointOnLine
 * @param {Geometry|Feature<LineString|MultiLineString>} lines lines to snap to
 * @param {Geometry|Feature<Point>|number[]} pt point to snap from
 * @param {Object} [options={}] Optional parameters
 * @param {string} [options.units='kilometers'] can be degrees, radians, miles, or kilometers
 * @returns {Feature<Point>} closest point on the `line` to `point`. The properties object will contain three values: `index`: closest point was found on nth line part, `dist`: distance between pt and the closest point, `location`: distance along the line between start and the closest point.
 * @example
 * var line = turf.lineString([
 *     [-77.031669, 38.878605],
 *     [-77.029609, 38.881946],
 *     [-77.020339, 38.884084],
 *     [-77.025661, 38.885821],
 *     [-77.021884, 38.889563],
 *     [-77.019824, 38.892368]
 * ]);
 * var pt = turf.point([-77.037076, 38.884017]);
 *
 * var snapped = turf.nearestPointOnLine(line, pt, {units: 'miles'});
 *
 * //addToMap
 * var addToMap = [line, pt, snapped];
 * snapped.properties['marker-color'] = '#00f';
 */
function nearestPointOnLine<G extends LineString|MultiLineString>(
    lines: Feature<G> | G,
    pt: Coord,
    options: {units?: Units} = {}
): NearestPointOnLine {
    let closestPt: any = point([Infinity, Infinity], {
        dist: Infinity
    });

    let length = 0.0;
    flattenEach(lines, function (line: any) {
        const coords: any = getCoords(line);

        for (let i = 0; i < coords.length - 1; i++) {
            //start
            const start = point(coords[i]);
            start.properties.dist = distance(pt, start, options);
            //stop
            const stop = point(coords[i + 1]);
            stop.properties.dist = distance(pt, stop, options);
            // sectionLength
            const sectionLength = distance(start, stop, options);
            //perpendicular
            const heightDistance = Math.max(start.properties.dist, stop.properties.dist);
            const direction = bearing(start, stop);
            const perpendicularPt1 = destination(pt, heightDistance, direction + 90, options);
            const perpendicularPt2 = destination(pt, heightDistance, direction - 90, options);
            const intersect = lineIntersects(
                lineString([perpendicularPt1.geometry.coordinates, perpendicularPt2.geometry.coordinates]),
                lineString([start.geometry.coordinates, stop.geometry.coordinates])
            );
            let intersectPt = null;
            if (intersect.features.length > 0) {
                intersectPt = intersect.features[0];
                intersectPt.properties.dist = distance(pt, intersectPt, options);
                intersectPt.properties.location = length + distance(start, intersectPt, options);
            }

            if (start.properties.dist < closestPt.properties.dist) {
                closestPt = start;
                closestPt.properties.index = i;
                closestPt.properties.location = length;
            }
            if (stop.properties.dist < closestPt.properties.dist) {
                closestPt = stop;
                closestPt.properties.index = i + 1;
                closestPt.properties.location = length + sectionLength;
            }
            if (intersectPt && intersectPt.properties.dist < closestPt.properties.dist) {
                closestPt = intersectPt;
                closestPt.properties.index = i;
            }
            // update length
            length += sectionLength;
        }

    });

    return closestPt;
}

/**
 * Checks if GeoJSON is Homogenous
 *
 * @private
 * @param {GeoJSON} geojson GeoJSON
 * @returns {string|null} Homogenous type or null if multiple types
 */
function getHomogenousType(geojson: any) {
    const types: {[key: string]: boolean} = {};
    flattenEach(geojson, (feature) => {
        types[feature.geometry.type] = true;
    });
    const keys = Object.keys(types);
    if (keys.length === 1) { return keys[0]; }
    return null;
}

/**
 * Boolean-disjoint returns (TRUE) if the intersection of the two geometries is an empty set.
 *
 * @name booleanDisjoint
 * @param {Geometry|Feature<any>} feature1 GeoJSON Feature or Geometry
 * @param {Geometry|Feature<any>} feature2 GeoJSON Feature or Geometry
 * @returns {boolean} true/false
 * @example
 * var point = turf.point([2, 2]);
 * var line = turf.lineString([[1, 1], [1, 2], [1, 3], [1, 4]]);
 *
 * turf.booleanDisjoint(line, point);
 * //=true
 */
function booleanDisjoint(feature1: Feature<any> | Geometry, feature2: Feature<any> | Geometry): boolean {
    var boolean;
    flattenEach(feature1, function (flatten1) {
        flattenEach(feature2, function (flatten2) {
            if (boolean === false) return false;
            boolean = disjoint(flatten1.geometry, flatten2.geometry);
        });
    });
    return boolean;
}

/**
 * Boolean-disjoint returns (TRUE) if the intersection of the two geometries is an empty set.
 *
 * @name booleanDisjoint
 * @param {Geometry|Feature<any>} feature1 GeoJSON Feature or Geometry
 * @param {Geometry|Feature<any>} feature2 GeoJSON Feature or Geometry
 * @returns {boolean} true/false
 * @example
 * var point = turf.point([2, 2]);
 * var line = turf.lineString([[1, 1], [1, 2], [1, 3], [1, 4]]);
 *
 * turf.booleanDisjoint(line, point);
 * //=true
 */
function booleanDisjoint(feature1: Feature<any> | Geometry, feature2: Feature<any> | Geometry): boolean {
    let bool = true;
    flattenEach(feature1, (flatten1) => {
        flattenEach(feature2, (flatten2) => {
            if (bool === false) { return false; }
            bool = disjoint(flatten1.geometry, flatten2.geometry);
        });
    });
    return bool;
}

/**
 * Boolean-intersects returns (TRUE) two geometries intersect.
 *
 * @name booleanIntersects
 * @param {Geometry|Feature<any>} feature1 GeoJSON Feature or Geometry
 * @param {Geometry|Feature<any>} feature2 GeoJSON Feature or Geometry
 * @returns {boolean} true/false
 * @example
 * var point = turf.point([2, 2]);
 * var line = turf.lineString([[1, 1], [1, 2], [1, 3], [1, 4]]);
 *
 * turf.booleanIntersects(line, point);
 * //=true
 */
function booleanIntersects(feature1: Feature<any> | Geometry, feature2: Feature<any> | Geometry) {
    var boolean;
    flattenEach(feature1, function (flatten1) {
        flattenEach(feature2, function (flatten2) {
            if (boolean === true) return true;
            boolean = !booleanDisjoint(flatten1.geometry, flatten2.geometry);
        });
    });
    return boolean;
}

/**
 * Boolean-intersects returns (TRUE) two geometries intersect.
 *
 * @name booleanIntersects
 * @param {Geometry|Feature<any>} feature1 GeoJSON Feature or Geometry
 * @param {Geometry|Feature<any>} feature2 GeoJSON Feature or Geometry
 * @returns {boolean} true/false
 * @example
 * var point = turf.point([2, 2]);
 * var line = turf.lineString([[1, 1], [1, 2], [1, 3], [1, 4]]);
 *
 * turf.booleanIntersects(line, point);
 * //=true
 */
export default function booleanIntersects(feature1: Feature<any> | Geometry, feature2: Feature<any> | Geometry) {
    let bool = false;
    flattenEach(feature1, (flatten1) => {
        flattenEach(feature2, (flatten2) => {
            if (bool === true) { return true; }
            bool = !booleanDisjoint(flatten1.geometry, flatten2.geometry);
        });
    });
    return bool;
}

/**
 * Creates a {@link FeatureCollection} of 2-vertex {@link LineString} segments from a {@link LineString|(Multi)LineString} or {@link Polygon|(Multi)Polygon}.
 *
 * @name lineSegment
 * @param {Geometry|FeatureCollection|Feature<LineString|MultiLineString|MultiPolygon|Polygon>} geojson GeoJSON Polygon or LineString
 * @returns {FeatureCollection<LineString>} 2-vertex line segments
 * @example
 * var polygon = turf.polygon([[[-50, 5], [-40, -10], [-50, -10], [-40, 5], [-50, 5]]]);
 * var segments = turf.lineSegment(polygon);
 *
 * //addToMap
 * var addToMap = [polygon, segments]
 */
function lineSegment<G extends LineString | MultiLineString | Polygon | MultiPolygon>(
    geojson: Feature<G> | FeatureCollection<G> | G
): FeatureCollection<LineString> {
    if (!geojson) throw new Error('geojson is required');

    var results: Feature<LineString>[] = [];
    flattenEach(geojson, function (feature) {
        lineSegmentFeature(feature, results);
    });
    return featureCollection(results);
}

/**
 * Creates a {@link FeatureCollection} of 2-vertex {@link LineString} segments from a
 * {@link LineString|(Multi)LineString} or {@link Polygon|(Multi)Polygon}.
 *
 * @name lineSegment
 * @param {GeoJSON} geojson GeoJSON Polygon or LineString
 * @returns {FeatureCollection<LineString>} 2-vertex line segments
 * @example
 * var polygon = turf.polygon([[[-50, 5], [-40, -10], [-50, -10], [-40, 5], [-50, 5]]]);
 * var segments = turf.lineSegment(polygon);
 *
 * //addToMap
 * var addToMap = [polygon, segments]
 */
function lineSegment<G extends LineString | MultiLineString | Polygon | MultiPolygon>(
    geojson: Feature<G> | FeatureCollection<G> | G,
): FeatureCollection<LineString> {
    if (!geojson) { throw new Error("geojson is required"); }

    const results: Array<Feature<LineString>> = [];
    flattenEach(geojson, (feature: Feature<any>) => {
        lineSegmentFeature(feature, results);
    });
    return featureCollection(results);
}

/**
 * Dissolves all overlapping (Multi)Polygon
 *
 * @param {FeatureCollection<Polygon|MultiPolygon>} geojson Polygons to dissolve
 * @param {Object} [options={}] Optional parameters
 * @param {boolean} [options.mutate=false] Prevent input mutation
 * @returns {Feature<Polygon|MultiPolygon>} Dissolved Polygons
 */
export default function polygonDissolve(
    geojson: FeatureCollection<Polygon|MultiPolygon>,
    options: {mutate?: boolean} = {},
): Feature<Polygon|MultiPolygon> | null {
    // Validation
    if (getType(geojson) !== "FeatureCollection") { throw new Error("geojson must be a FeatureCollection"); }
    if (!geojson.features.length) { throw new Error("geojson is empty"); }

    // Clone geojson to avoid side effects
    // Topojson modifies in place, so we need to deep clone first
    if (options.mutate === false || options.mutate === undefined) { geojson = clone(geojson); }

    const geoms: any[] = [];
    flattenEach(geojson, (feature) => {
        geoms.push(feature.geometry);
    });
    const topo: any = topology({geoms: geometryCollection(geoms).geometry});
    const merged: any = merge(topo, topo.objects.geoms.geometries);
    return merged;
}