Create convex hull around points

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

    /// A Boolean value indicating whether the create button can be pressed.
    @State private var createIsDisabled = true

    /// A Boolean indicate whether the reset button can be pressed.
    @State private var resetIsDisabled = true

    var body: some View {
        // Create a map view to display the map.
        MapView(map: model.map, graphicsOverlays: model.graphicsOverlays)
            .onSingleTapGesture { _, mapPoint in
                model.inputPoints.append(mapPoint)
                model.pointsGraphicsOverlay.addGraphic(Graphic(geometry: mapPoint))
                createIsDisabled = false
                resetIsDisabled = false
            }
            .toolbar {
                ToolbarItemGroup(placement: .bottomBar) {
                    Button("Create") {
                        model.createConvexHull()
                        createIsDisabled = true
                    }
                    .disabled(createIsDisabled)
                    Button("Reset") {
                        model.reset()
                        createIsDisabled = true
                        resetIsDisabled = true
                    }
                    .disabled(resetIsDisabled)
                }
            }
    }
}

private extension CreateConvexHullAroundPointsView {
    /// The view model for this sample.
    private class Model: ObservableObject {
        /// A map with a topographic basemap.
        let map: Map

        /// An array of input points to be used in creating the convexHull.
        var inputPoints: [Point] = []

        /// An array that contains the graphics overlays for the sample.
        var graphicsOverlays: [GraphicsOverlay] {
            return [pointsGraphicsOverlay, convexHullGraphicsOverlay]
        }

        /// The graphics overlay for the input points graphics.
        let pointsGraphicsOverlay: GraphicsOverlay

        /// The graphics overlay for the convex hull graphic.
        private let convexHullGraphicsOverlay: GraphicsOverlay

        /// A red simple marker symbol to display where the user tapped on the map.
        private let markerSymbol: SimpleMarkerSymbol

        /// A blue simple line symbol for the outline of the convex hull graphic.
        private let lineSymbol: SimpleLineSymbol

        /// A hollow polygon simple fill symbol for the convex hull graphic.
        private var fillSymbol: SimpleFillSymbol

        init() {
            map = Map(basemapStyle: .arcGISTopographic)

            markerSymbol = SimpleMarkerSymbol(style: .circle, color: .red, size: 10)
            lineSymbol = SimpleLineSymbol(style: .solid, color: .blue, width: 4)
            fillSymbol = SimpleFillSymbol(style: .noFill, outline: lineSymbol)

            pointsGraphicsOverlay = GraphicsOverlay()
            pointsGraphicsOverlay.renderer = SimpleRenderer(symbol: markerSymbol)
            convexHullGraphicsOverlay = GraphicsOverlay()
        }

        /// Reset the points and graphics.
        func reset() {
            inputPoints.removeAll()
            pointsGraphicsOverlay.removeAllGraphics()
            convexHullGraphicsOverlay.removeAllGraphics()
        }

        /// Create the convex hull graphic using the inputPoints.
        func createConvexHull() {
            // Normalize points and create convex hull geometry.
            if let normalizedPoints = GeometryEngine.normalizeCentralMeridian(of: Multipoint(points: inputPoints)),
               let convexHullGeometry = GeometryEngine.convexHull(for: normalizedPoints) {
                // Set the symbol depending on the geometry type of the convex hull.
                let symbol: Symbol?
                switch convexHullGeometry {
                case is Point:
                    symbol = markerSymbol
                case is Polyline:
                    symbol = lineSymbol
                case is ArcGIS.Polygon:
                    symbol = fillSymbol
                default:
                    symbol = nil
                }

                // Remove the existing graphic for convex hull.
                convexHullGraphicsOverlay.removeAllGraphics()

                // Create the convex hull graphic.
                let convexHullGraphic = Graphic(geometry: convexHullGeometry, symbol: symbol)
                convexHullGraphicsOverlay.addGraphic(convexHullGraphic)
            }
        }
    }
}

#Preview {
    NavigationStack {
        CreateConvexHullAroundPointsView()
    }
}