Identify layer 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 IdentifyLayerFeaturesView: View {
    /// A map with a topographic basemap centered on the United States.
    @State private var map: Map = {
        let map = Map(basemapStyle: .arcGISTopographic)
        map.initialViewpoint = Viewpoint(
            center: Point(x: -10977012.785807, y: 4514257.550369, spatialReference: .webMercator),
            scale: 68015210
        )
        return map
    }()

    /// The tapped screen point.
    @State private var tapScreenPoint: CGPoint?

    /// The string text for the identify layer results overlay.
    @State private var overlayText = "Tap on the map to identify feature layers."

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

    var body: some View {
        ZStack {
            MapViewReader { proxy in
                MapView(map: map)
                    .onSingleTapGesture { screenPoint, _ in
                        tapScreenPoint = screenPoint
                    }
                    .task {
                        do {
                            // Add map image layer to the map.
                            let mapImageLayer = ArcGISMapImageLayer(url: .worldCities)
                            try await mapImageLayer.load()

                            // Hide continent and world layers.
                            mapImageLayer.subLayerContents[1].isVisible = false
                            mapImageLayer.subLayerContents[2].isVisible = false
                            map.addOperationalLayer(mapImageLayer)

                            // Add feature layer to the map.
                            let featureTable = ServiceFeatureTable(url: .damageAssessment)
                            try await featureTable.load()
                            let featureLayer = FeatureLayer(featureTable: featureTable)
                            map.addOperationalLayer(featureLayer)
                        } catch {
                            // Present error load the layers if any.
                            self.error = error
                        }
                    }
                    .task(id: tapScreenPoint) {
                        // Identify layers using the screen point.
                        if let screenPoint = tapScreenPoint,
                           let results = try? await proxy.identifyLayers(
                            screenPoint: screenPoint,
                            tolerance: 12,
                            returnPopupsOnly: false,
                            maximumResultsPerLayer: 10
                           ) {
                            handleIdentifyResults(results)
                        }
                    }
                    .overlay(alignment: .top) {
                        Text(overlayText)
                            .frame(maxWidth: .infinity, alignment: .center)
                            .padding(8)
                            .background(.thinMaterial, ignoresSafeAreaEdges: .horizontal)
                    }
                    .errorAlert(presentingError: $error)
            }
        }
    }
}

private extension IdentifyLayerFeaturesView {
    /// Updates the overlay text based on the identify layer results.
    /// - Parameter results: An `IdentifyLayerResult` array to handle.
    func handleIdentifyResults(_ results: [IdentifyLayerResult]) {
        // Get layer names and geoelement counts from the results.
        let identifyLayerResultInfo: [(layerName: String, geoElementsCount: Int)] = results.map { identifyLayerResult in
            let layerName = identifyLayerResult.layerContent.name
            let geoElementsCount = geoElementsCountFromResult(identifyLayerResult)
            return (layerName, geoElementsCount)
        }

        let message = identifyLayerResultInfo
            .map { "\($0.layerName): \($0.geoElementsCount)" }
            .joined(separator: "\n")

        let totalGeoElementsCount = identifyLayerResultInfo.map(\.geoElementsCount).reduce(0, +)

        // Update overlay text with the geo-elements found if any.
        overlayText = totalGeoElementsCount > 0 ? message : "No element found."
    }

    /// Counts the geo-elements from an identify layer result using recursion.
    /// - Parameter result: The `IdentifyLayerResult` to count.
    /// - Returns: The count of the geo-elements.
    private func geoElementsCountFromResult(_ identifyResult: IdentifyLayerResult) -> Int {
        // Get geoElements count from the result.
        var count = identifyResult.geoElements.count

        // Get the count using recursion from the result's sublayer results if any.
        for result in identifyResult.sublayerResults {
            count += geoElementsCountFromResult(result)
        }
        return count
    }
}

private extension URL {
    /// A world cities image layer URL.
    static var worldCities: URL {
        URL(string: "https://sampleserver6.arcgisonline.com/arcgis/rest/services/SampleWorldCities/MapServer")!
    }

    /// A damage assessment feature layer URL.
    static var damageAssessment: URL {
        URL(string: "https://sampleserver6.arcgisonline.com/arcgis/rest/services/DamageAssessment/FeatureServer/0")!
    }
}

#Preview {
    IdentifyLayerFeaturesView()
}