Query table statistics

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// Copyright 2025 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 QueryTableStatisticsView: View {
    /// The view model for the sample.
    @State private var model = Model()

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

    /// The statistic records resulting from a query.
    @State private var statisticRecords: [StatisticRecord] = []

    /// A Boolean value indicating whether queries will include cities outside
    /// of the map view's current extent.
    @State private var includesCitiesOutsideExtent = false

    /// A Boolean value indicating whether queries will include cities with
    /// populations under 5 million.
    @State private var includesCitiesUnder5M = false

    /// A Boolean value indicating whether there is an ongoing query operation.
    @State private var isQuerying = false

    /// A Boolean value indicating whether the settings view is showing.
    @State private var isShowingSettings = false

    /// A Boolean value indicating whether the statistic list is showing.
    @State private var isShowingStatistics = false

    /// An error thrown from a query.
    @State private var queryError: (any Error)?

    var body: some View {
        MapView(map: model.map, viewpoint: viewpoint)
            .onViewpointChanged(kind: .boundingGeometry) { viewpoint = $0 }
            .toolbar {
                ToolbarItemGroup(placement: .bottomBar) {
                    Button("Query Statistics") {
                        isQuerying = true
                    }
                    .disabled(isQuerying)
                    .task(id: isQuerying) {
                        // Queries the statistics when the button is pressed.
                        guard isQuerying else {
                            return
                        }
                        defer { isQuerying = false }

                        do {
                            let extent = includesCitiesOutsideExtent ? nil : viewpoint?.targetGeometry
                            statisticRecords = try await model.queryStatistics(
                                within: extent,
                                includesCitiesUnder5M: includesCitiesUnder5M
                            )

                            isShowingStatistics = true
                        } catch {
                            self.queryError = error
                        }
                    }
                    .sheet(isPresented: $isShowingStatistics) {
                        StatisticList(records: statisticRecords)
                            .presentationDetents([.medium, .large])
                    }

                    Spacer()

                    Button("Settings", systemImage: "gear") {
                        isShowingSettings = true
                    }
                    .labelStyle(.iconOnly)
                    .popover(isPresented: $isShowingSettings) {
                        Form {
                            Toggle("Include Cities Outside Extent", isOn: $includesCitiesOutsideExtent)
                            Toggle("Include Cities Under 5M", isOn: $includesCitiesUnder5M)
                        }
                        .frame(idealWidth: 320, idealHeight: 160)
                        .presentationCompactAdaptation(.popover)
                    }
                }
            }
            .errorAlert(presentingError: $queryError)
    }
}

/// A view that displays the statistics from a given list of statistic records.
private struct StatisticList: View {
    /// The statistic records containing the statistics to display.
    let records: [StatisticRecord]

    /// The action to dismiss the view.
    @Environment(\.dismiss) private var dismiss

    var body: some View {
        NavigationStack {
            List(records, id: \.objectID) { record in
                Section {
                    let statistics = record.statistics.sorted(by: { $0.key < $1.key })
                    ForEach(statistics, id: \.key) { name, value in
                        if let integer = value as? Int {
                            LabeledContent(name, value: integer, format: .number)
                        } else if let double = value as? Double {
                            LabeledContent(name, value: double, format: .number)
                        }
                    }
                    .textSelection(.enabled)
                }
            }
            .navigationTitle("Statistics")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .confirmationAction) {
                    Button("Done") {
                        dismiss()
                    }
                }
            }
        }
    }
}

/// The view model for this sample.
@Observable
private final class Model: Sendable {
    /// A map with a streets basemap.
    let map: Map = {
        let map = Map(basemapStyle: .arcGISStreets)

        let envelope = Envelope(
            xRange: -14_803_800...5_233_700,
            yRange: -15_950_300...17_262_800,
            spatialReference: .webMercator
        )
        map.initialViewpoint = Viewpoint(boundingGeometry: envelope)

        return map
    }()

    /// The service feature table containing the data to query.
    private let serviceFeatureTable = ServiceFeatureTable(url: .sampleWorldCitiesLayer)

    /// The parameters to use in the statistics query.
    private let statisticsQueryParameters = StatisticsQueryParameters(
        // Creates a statistic definition for the "POP" field and each of the statistic types.
        statisticDefinitions: StatisticDefinition.StatisticType.allCases
            .map { .init(fieldName: "POP", statisticType: $0) }
    )

    init() {
        // Adds the table to the map as an operational layer.
        let featureLayer = FeatureLayer(featureTable: serviceFeatureTable)
        map.addOperationalLayer(featureLayer)
    }

    /// Queries the statistics of the data in the given extent.
    /// - Parameters:
    ///   - extent: The geometry to query within.
    ///   - includesCitiesUnder5M: A Boolean value indicating whether queries
    ///   will include cities with populations under 5 million.
    /// - Returns: The statistic records resulting from the query.
    func queryStatistics(
        within extent: Geometry?,
        includesCitiesUnder5M: Bool
    ) async throws -> [StatisticRecord] {
        // Sets up the parameters for the query.
        statisticsQueryParameters.geometry = extent
        statisticsQueryParameters.whereClause = includesCitiesUnder5M ? "" : "POP_RANK = 1"

        // Queries the feature table using the parameters.
        let result = try await serviceFeatureTable.queryStatistics(using: statisticsQueryParameters)

        // Gets the statistic records from the query result.
        let statisticRecords = Array(result.statisticRecords())

        return statisticRecords
    }
}

private extension StatisticRecord {
    /// The object identifier for this statistic record.
    var objectID: ObjectIdentifier { .init(self) }
}

private extension StatisticDefinition.StatisticType {
    /// All the statistic types.
    static var allCases: [Self] {
        return [average, count, maximum, minimum, standardDeviation, sum, variance]
    }
}

private extension URL {
    /// The URL to the "Cities" layer on the "SampleWorldCities" map service.
    static var sampleWorldCitiesLayer: URL {
        URL(string: "https://sampleserver6.arcgisonline.com/arcgis/rest/services/SampleWorldCities/MapServer/0")!
    }
}

#Preview {
    QueryTableStatisticsView()
}