// Copyright 2020 Google LLC. All rights reserved.
//
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this
// file except in compliance with the License. You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software distributed under
// the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
// ANY KIND, either express or implied. See the License for the specific language governing
// permissions and limitations under the License.

import GoogleMaps
import UIKit

struct Coordinate: Decodable {
  let latitude: Double
  let longitude: Double
  let elevation: Double

  enum CodingKeys: String, CodingKey {
    case elevation
    case latitude = "lat"
    case longitude = "lng"
  }

  init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    latitude = try container.decode(Double.self, forKey: .latitude)
    longitude = try container.decode(Double.self, forKey: .longitude)
    elevation = try container.decode(Double.self, forKey: .elevation)
  }
}

final class GradientPolylinesViewController: UIViewController {

  private lazy var mapView: GMSMapView = {
    let camera = GMSCameraPosition(
      latitude: 44.1314, longitude: 9.6921, zoom: 14.059, bearing: 328, viewingAngle: 40)
    return GMSMapView(frame: .zero, camera: camera)
  }()

  override func loadView() {
    view = mapView
  }

  override func viewDidLoad() {
    super.viewDidLoad()
    addTrackToMap()
  }

  private func addTrackToMap() {
    guard let filePath = Bundle.main.path(forResource: "track", ofType: "json") else { return }
    guard let data = try? Data(contentsOf: URL(fileURLWithPath: filePath)) else { return }
    guard let track = try? JSONDecoder().decode([Coordinate].self, from: data)
    else {
      return
    }
    let path = GMSMutablePath()
    var colorSpans: [GMSStyleSpan] = []
    var previousColor: UIColor?

    for coordinate in track {
      path.addLatitude(coordinate.latitude, longitude: coordinate.longitude)

      let elevation = CGFloat(coordinate.elevation)
      let toColor = UIColor(hue: elevation / 700.0, saturation: 1, brightness: 0.9, alpha: 1)
      let fromColor = previousColor ?? toColor
      let style = GMSStrokeStyle.gradient(from: fromColor, to: toColor)
      colorSpans.append(GMSStyleSpan(style: style))
      previousColor = toColor
    }
    let polyline = GMSPolyline(path: path)
    polyline.strokeWidth = 6
    polyline.map = mapView
    polyline.spans = colorSpans
  }
}