Query feature count and extent

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// Copyright 2024 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 QueryFeatureCountAndExtentView: View {
    /// The view model for the sample.
    @StateObject private var model = Model()

    /// The currently selected state abbreviation.
    @State private var selectedState: String?

    /// A Boolean value indicating whether the feature count bar is showing.
    @State private var showFeatureCountBar = false

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

    /// The current viewpoint of the map.
    @State private var viewpoint: Viewpoint?

    /// The count of features within the current viewpoint.
    @State private var featureCountResult: Int?

    var body: some View {
        MapViewReader { proxy in
            MapView(map: model.map)
                .onViewpointChanged(kind: .boundingGeometry) { newViewpoint in
                    // Update viewpoint when it changes.
                    viewpoint = newViewpoint
                }
                .task(id: selectedState) {
                    // Perform query and update the viewpoint when the selected state changes.
                    guard let state = selectedState else { return }
                    do {
                        if let combinedExtent = try await model.queryExtent(stateAbbreviation: state) {
                            await proxy.setViewpointGeometry(combinedExtent)
                            showFeatureCountBar = false
                        }
                    } catch {
                        self.error = error
                    }
                    selectedState = nil
                }
        }
        .overlay(alignment: .top) {
            if showFeatureCountBar {
                Text("\(featureCountResult ?? 0) feature(s) in extent")
                    .frame(maxWidth: .infinity)
                    .padding(.vertical, 6)
                    .background(.thinMaterial, ignoresSafeAreaEdges: .horizontal)
                    .transition(.move(edge: .top))
            }
        }
        .toolbar {
            ToolbarItemGroup(placement: .bottomBar) {
                // Menu to select a state.
                Menu("Select State") {
                    ForEach(model.stateAbbreviations, id: \.self) { abbreviation in
                        Button {
                            selectedState = abbreviation
                        } label: {
                            Text(abbreviation)
                        }
                    }
                }

                // Button to count features within the visible extent.
                Button("Count Features") {
                    Task {
                        do {
                            if let viewpoint = viewpoint {
                                featureCountResult = try await model.countFeaturesWithinExtent(extent: viewpoint.targetGeometry)
                                showFeatureCountBar = true
                            }
                        } catch {
                            self.error = error
                        }
                    }
                }
            }
        }
        .errorAlert(presentingError: $error)
    }
}

private extension QueryFeatureCountAndExtentView {
    /// The view model for the sample.
    @MainActor
    class Model: ObservableObject {
        /// The map with a basemap and initial viewpoint.
        let map: Map = {
            let map = Map(basemapStyle: .arcGISDarkGray)
            map.initialViewpoint = Viewpoint(
                center: Point(x: -11e6, y: 5e6, spatialReference: .webMercator),
                scale: 9e7
            )
            return map
        }()

        /// The layer that displays features on the map.
        private let featureLayer: FeatureLayer

        /// The table for querying features from a server.
        private let featureTable: ServiceFeatureTable

        /// The list of state abbreviations for selection.
        let stateAbbreviations = [
            "AL", "AK", "AZ", "AR", "CA", "CO", "CT", "DE", "DC", "FL", "GA", "HI",
            "ID", "IL", "IN", "IA", "KS", "KY", "LA", "ME", "MD", "MA", "MI", "MN",
            "MS", "MO", "MT", "NE", "NV", "NH", "NJ", "NM", "NY", "NC", "ND", "OH",
            "OK", "OR", "PA", "RI", "SC", "SD", "TN", "TX", "UT", "VT", "VA", "WA",
            "WV", "WI", "WY"
        ]

        init() {
            featureTable = ServiceFeatureTable(url: .medicareHospitalSpendLayer)
            featureLayer = FeatureLayer(featureTable: featureTable)
            map.addOperationalLayer(featureLayer)
        }

        /// Queries the extent for the specified state.
        /// - Parameter stateAbbreviation: The state abbreviation to query.
        /// - Returns: The combined extent of the queried features or `nil` if no features are found.
        /// - Throws: An error if the query fails.
        func queryExtent(stateAbbreviation: String) async throws -> Envelope? {
            guard !stateAbbreviation.isEmpty else { return nil }
            featureLayer.clearSelection()
            let queryParameters = QueryParameters()
            queryParameters.whereClause = "State LIKE '%\(stateAbbreviation)%'"

            let queryResult = try await featureTable.queryFeatures(using: queryParameters)
            let queryResultFeatures = Array(queryResult.features())

            if !queryResultFeatures.isEmpty {
                return GeometryEngine.combineExtents(
                    of: queryResultFeatures.compactMap(\.geometry)
                )
            } else {
                return nil
            }
        }

        /// Counts the number of features within the specified extent.
        /// - Parameter extent: The geometry defining the extent to query.
        /// - Returns: The count of features within the specified extent.
        /// - Throws: An error if the count operation fails.
        func countFeaturesWithinExtent(extent: Geometry) async throws -> Int {
            let queryParameters = QueryParameters()
            queryParameters.geometry = extent
            queryParameters.spatialRelationship = .intersects
            return try await featureLayer.featureTable!.queryFeatureCount(
                using: queryParameters
            )
        }
    }
}

private extension URL {
    /// The URL for the Medicare Hospital Spending layer service.
    static var medicareHospitalSpendLayer: URL {
        URL(string: "https://services1.arcgis.com/4yjifSiIG17X0gW4/arcgis/rest/services/Medicare_Hospital_Spending_per_Patient/FeatureServer/0")!
    }
}

#Preview {
    QueryFeatureCountAndExtentView()
}