CLLocation+H3.swift

//
//  CLLocation+H3.swift
//
//  The MIT License (MIT)
//
//  Copyright (c) 2020-present patrick piemonte (http://patrickpiemonte.com/)
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

import Foundation
import CoreLocation
import H3kit

/// CLLocation additions for Swift wrapper https://github.com/ehmjaysee/H3kit and C interface https://github.com/long1eu/h3-ios
extension CLLocation {

    public static func h3_resolution(for areaInMeters: Double) -> Int32 {
        var resolution: Int32 = 0
        while resolution <= 15 {
            let hexAreaInMeters = hexAreaM2(resolution)
            if areaInMeters > hexAreaInMeters {
                break
            } else {
                resolution += 1
            }
        }
        return resolution
    }

    public func h3_cellIndex( resolution: Int32 ) -> UInt64 {
        let lat = degsToRads(coordinate.latitude)
        let lon = degsToRads(coordinate.longitude)
        var location = GeoCoord(lat: lat, lon: lon)
        let index = geoToH3(&location, resolution)
        return index
    }

    public func h3_neighbors( resolution: Int32, ringLevel: Int32 ) -> [H3Index] {
        let index = h3_cellIndex(resolution: resolution)
        let count = Int(maxKringSize(ringLevel))
        var neighbors = Array(repeating: H3Index(), count: count)
        kRing(index, ringLevel, &neighbors)
        return neighbors
    }

}

usage:

var area: Double = 0
if let areaInMeters = areaInMeters {
        area = areaInMeters
} else {
        area = Double.pi * pow(Double(radiusInMeters), 2.0)
}

let resolution: Int32 = CLLocation.h3_resolution(for: area)
let centerIndex = location.h3_cellIndex(resolution: resolution)
let neighborIndexes = location.h3_neighbors(resolution: resolution, ringLevel: 1)

var h3Indexes = [String(centerIndex, radix: 16, uppercase: true)]
h3Indexes.append(contentsOf: neighborIndexes.map { String($0, radix: 16, uppercase: true) })

// perform query