Identify KML features

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// Copyright 2023 Esri
//
// 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
//
//   https://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 ArcGIS
import SwiftUI

struct IdentifyKMLFeaturesView: View {
    /// A map with a dark gray base basemap centered on the USA.
    @State private var map: Map = {
        let map = Map(basemapStyle: .arcGISDarkGrayBase)
        let center = Point(x: -48_885, y: 1_718_235, spatialReference: SpatialReference(wkid: WKID(5070)!))
        map.initialViewpoint = Viewpoint(center: center, scale: 5e7)
        return map
    }()

    /// The KML layer with forecast data that is on the map.
    @State private var forecastLayer: KMLLayer?

    /// The placement of the callout on the map.
    @State private var calloutPlacement: CalloutPlacement?

    /// The text of a KML placemark's balloon content that is shown in the callout.
    @State private var calloutText = AttributedString()

    /// The error shown in the error alert.
    @State private var error: Error?

    var body: some View {
        MapViewReader { mapViewProxy in
            GeometryReader { geometry in
                MapView(map: map)
                    .callout(placement: $calloutPlacement.animation(.default.speed(2))) { _ in
                        Text(calloutText)
                            .frame(maxWidth: geometry.size.width / 2)
                            .font(.callout)
                            .padding(8)
                    }
                    .onSingleTapGesture { screenPoint, _ in
                        Task {
                            do {
                                // Get the KML placemark for the screen point.
                                if let placemark = try await kmlPlacemark(for: screenPoint, using: mapViewProxy) {
                                    // Update the callout's text and placement.
                                    try updateCalloutText(using: placemark)
                                    if let location = mapViewProxy.location(fromScreenPoint: screenPoint) {
                                        calloutPlacement = .location(location)
                                    }
                                } else {
                                    // Dismiss the callout if a placemark was not found.
                                    calloutPlacement = nil
                                }
                            } catch {
                                self.error = error
                            }
                        }
                    }
                    .task {
                        do {
                            // Load a KML dataset from a URL.
                            let dataset = KMLDataset(url: .forecastKML)
                            try await dataset.load()

                            // Create a KML layer with the dataset.
                            forecastLayer = KMLLayer(dataset: dataset)

                            // Add the layer to the map.
                            map.addOperationalLayer(forecastLayer!)
                        } catch {
                            self.error = error
                        }
                    }
            }
        }
        .errorAlert(presentingError: $error)
    }
}

private extension IdentifyKMLFeaturesView {
    /// Identifies the placemark for a given point on the KML layer.
    /// - Parameters:
    ///   - screenPoint: The screen point corresponding to a placemark.
    ///   - proxy: The map view proxy used identify the screen point.
    /// - Precondition: `forecastLayer != nil`
    /// - Returns: The first KML placemark in the identify result.
    func kmlPlacemark(for screenPoint: CGPoint, using proxy: MapViewProxy) async throws -> KMLPlacemark? {
        guard let forecastLayer else { return nil }

        // Identify the screen point on the KML layer using the map view proxy.
        let identifyResult = try await proxy.identify(on: forecastLayer, screenPoint: screenPoint, tolerance: 2)

        // Get the first KML placemark from the result's geo elements.
        let placemark = identifyResult.geoElements.first(where: { $0 is KMLPlacemark })
        return placemark as? KMLPlacemark
    }

    /// Updates the callout text using the balloon content of a given placemark.
    /// - Parameter placemark: The KML placemark to get the data from.
    func updateCalloutText(using placemark: KMLPlacemark) throws {
        // Google Earth only displays the placemarks with description or extended data.
        // To match its behavior, add a description placeholder if it is empty.
        if placemark.description.isEmpty {
            placemark.description = "Weather condition"
        }

        // Convert the placemark's html balloon content to text.
        let data = Data(placemark.balloonContent.utf8)
        let text = try NSAttributedString(
            data: data,
            options: [.documentType: NSAttributedString.DocumentType.html],
            documentAttributes: nil
        )

        // Update the callout text.
        var attributedText = AttributedString(text)
        attributedText.foregroundColor = .label
        calloutText = attributedText
    }
}

private extension URL {
    /// A URL to an online KML file with forecast data.
    static var forecastKML: URL {
        URL(string: "https://www.wpc.ncep.noaa.gov/kml/noaa_chart/WPC_Day1_SigWx_latest.kml")!
    }
}

#Preview {
    IdentifyKMLFeaturesView()
}