Show line of sight analysis in map

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// Copyright 2026 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 ShowLineOfSightAnalysisInMapView: View {
    /// The view model for the sample.
    @State private var model = Model()
    /// The placement of the visibility description callout.
    @State private var calloutPlacement: CalloutPlacement?
    /// A Boolean value indicating whether the obstructed line of sight graphics are showing.
    @State private var isShowingObstructed = true
    /// The error shown in the error alert.
    @State private var error: (any Error)?

    /// The states of the sample.
    private enum SampleState: Equatable {
        /// A line of sight analysis is being run.
        case evaluatingLinesOfSight
        /// The given tap point is being identified.
        case identifying(tapPoint: CGPoint)
    }

    /// The current state of the sample.
    @State private var sampleState: SampleState? = .evaluatingLinesOfSight

    var body: some View {
        MapViewReader { mapViewProxy in
            MapView(map: model.map, graphicsOverlays: model.graphicOverlays)
                .callout(placement: $calloutPlacement.animation(.default.speed(2))) { placement in
                    if let attributes = placement.geoElement?.attributes,
                       let visibilityDescription = attributes[.visibilityDescription] as? String {
                        Text(visibilityDescription)
                            .padding(6)
                    }
                }
                .onSingleTapGesture { screenPoint, _ in
                    guard sampleState == nil else { return }
                    sampleState = .identifying(tapPoint: screenPoint)
                }
                .task(id: sampleState) {
                    guard let sampleState else { return }
                    defer { self.sampleState = nil }

                    do {
                        switch sampleState {
                        case .evaluatingLinesOfSight:
                            try await model.evaluateLinesOfSight()
                        case let .identifying(tapPoint):
                            calloutPlacement = nil

                            let identifyResult = try await mapViewProxy.identify(
                                on: model.observerGraphicsOverlay,
                                screenPoint: tapPoint,
                                tolerance: 10
                            )

                            guard let observerGraphic = identifyResult.graphics.first else { return }
                            calloutPlacement = .geoElement(observerGraphic)
                        }
                    } catch {
                        self.error = error
                    }
                }
                .errorAlert(presentingError: $error)
        }
        .overlay(alignment: .top) {
            Text("Raster data copyright Scottish Government and SEPA (2014)")
                .font(.caption)
                .frame(maxWidth: .infinity)
                .padding(.vertical, 6)
                .background(.thinMaterial, ignoresSafeAreaEdges: .horizontal)
        }
        .toolbar {
            ToolbarItem(placement: .bottomBar) {
                Menu("Settings", systemImage: "gear") {
                    Toggle("Show Obstructed", isOn: $isShowingObstructed)
                        .onChange(of: isShowingObstructed) {
                            model.setObstructedVisibility(isVisible: isShowingObstructed)
                        }
                }
            }
        }
    }
}

// MARK: Model

/// The view model for this sample.
@Observable
private final class Model {
    /// A map with a dark hillshade basemap initially centered on the Isle of Arran, Scotland.
    let map: Map = {
        let map = Map(basemapStyle: .arcGISHillshadeDark)
        let initialExtent = Envelope(xRange: -585030 ... -570890, yRange: 7472900 ... 7495670)
        map.initialViewpoint = Viewpoint(boundingGeometry: initialExtent)
        return map
    }()

    /// The overlays containing the graphics to display on the map.
    var graphicOverlays: [GraphicsOverlay] {
        return [lineOfSightGraphicsOverlay, targetGraphicsOverlay, observerGraphicsOverlay]
    }

    /// The overlay containing the observer position graphics.
    let observerGraphicsOverlay = GraphicsOverlay()

    /// The overlay containing the target position graphic.
    private let targetGraphicsOverlay = GraphicsOverlay()

    /// The overlay containing the line of sight analysis result graphics.
    private let lineOfSightGraphicsOverlay = GraphicsOverlay()

    /// The height of the target and observer position points.
    private static let positionHeight = 5.0

    /// The target observer's location on the map.
    private let targetPoint = Point(
        x: -577955.365,
        y: 7484288.220,
        z: positionHeight,
        spatialReference: .webMercator
    )

    /// An observer of a line of sight analysis.
    private struct Observer {
        /// The observer's location on the map in Web Mercator.
        let point: Point
        /// The observer's symbol for its graphic.
        let symbol: SimpleMarkerSymbol

        init(x: Double, y: Double, color: UIColor) {
            point = Point(x: x, y: y, z: positionHeight, spatialReference: .webMercator)
            symbol = SimpleMarkerSymbol(style: .triangle, color: color, size: 15)
        }
    }

    /// The observers to evaluate lines of sight for.
    private let observers = [
        Observer(x: -580893.546, y: 7489102.890, color: .green),
        Observer(x: -583446.004, y: 7483567.462, color: .white),
        Observer(x: -577665.236, y: 7490792.908, color: .orange),
        Observer(x: -576452.981, y: 7487071.388, color: .yellow),
        Observer(x: -576650.067, y: 7481479.772, color: .purple),
        Observer(x: -571683.896, y: 7492017.864, color: .blue)
    ]

    init() {
        // Creates graphics to display the target and observer positions on the map.
        let beaconSymbol = PictureMarkerSymbol(image: .beacon)
        beaconSymbol.width = 22
        beaconSymbol.height = 22

        let targetGraphic = Graphic(geometry: targetPoint, symbol: beaconSymbol)
        targetGraphicsOverlay.addGraphic(targetGraphic)

        let observerGraphics = observers.map { Graphic(geometry: $0.point, symbol: $0.symbol) }
        observerGraphicsOverlay.addGraphics(observerGraphics)
    }

    /// Runs a line of sight analysis.
    @MainActor
    func evaluateLinesOfSight() async throws {
        // Creates a continuous field using a TIF file containing elevation data.
        let elevationField = try await ContinuousField.field(fromFilesAt: [.arranTIF], bandIndex: 0)

        // Creates line of sight parameters with target and observer positions.
        let parameters = LineOfSightParameters()
        let targetPosition = LineOfSightPosition(position: targetPoint, heightOrigin: .relative)
        let observerPositions = observers.map { observer in
            LineOfSightPosition(position: observer.point, heightOrigin: .relative)
        }
        parameters.observerTargetPairs = ObserverTargetPairs(
            observers: observerPositions,
            targets: [targetPosition],
        )

        // Creates and evaluates a line of sight function to get the lines of sight.
        let lineOfSightFunction = LineOfSightFunction(
            elevation: elevationField,
            parameters: parameters,
        )
        let lineOfSightResults = try await lineOfSightFunction.evaluate()

        // Creates and adds graphics for the results to show the lines of sight on the map.
        let lineOfSightGraphics = makeLineOfSightGraphics(lineOfSightResults)
        lineOfSightGraphicsOverlay.addGraphics(lineOfSightGraphics)

        // Adds descriptions of the results' visibility to the corresponding observer graphics.
        let lineOfSightObserverPairs = zip(lineOfSightResults, observerGraphicsOverlay.graphics)
        for (lineOfSight, observerGraphic) in lineOfSightObserverPairs {
            let visibilityDescription = lineOfSight.visibilityDescription
            observerGraphic.setAttributeValue(visibilityDescription, forKey: .visibilityDescription)
        }
    }

    /// Sets the visibility of the obstructed line of sight graphics.
    /// - Parameter isVisible: A Boolean value indicating whether the graphics should be visible.
    func setObstructedVisibility(isVisible: Bool) {
        for graphic in lineOfSightGraphicsOverlay.graphics {
            guard let targetVisibility = graphic.attributes[.targetVisibility] as? Float,
                  targetVisibility != 1 else {
                continue
            }
            graphic.isVisible = isVisible
        }
    }

    /// Creates graphics for displaying line of sight visibilities.
    /// - Parameter linesOfSight: The lines of sight results to create graphics for.
    private func makeLineOfSightGraphics(_ linesOfSight: [LineOfSight]) -> [Graphic] {
        let visibleLineSymbol = SimpleLineSymbol(color: .green, width: 2)
        let notVisibleLineSymbol = SimpleLineSymbol(style: .longDash, color: .gray)
        return linesOfSight.flatMap { linesOfSight in
            let visibleLineGraphic = Graphic(
                geometry: linesOfSight.visibleLine,
                attributes: [.targetVisibility: linesOfSight.targetVisibility],
                symbol: visibleLineSymbol
            )
            let notVisibleLineGraphic = Graphic(
                geometry: linesOfSight.notVisibleLine,
                attributes: [.targetVisibility: linesOfSight.targetVisibility],
                symbol: notVisibleLineSymbol
            )
            return [visibleLineGraphic, notVisibleLineGraphic]
        }
    }
}

// MARK: Extensions

private extension LineOfSight {
    /// A description of the line of sight's visibility.
    var visibilityDescription: String {
        if let error {
            // Uses the error as the description if line of sight could not be evaluated.
            let illegalStateError = error as? IllegalStateError
            return illegalStateError?.details ?? error.localizedDescription
        } else {
            // Calculates the visible distance from the observer in meters.
            let visibleMeters = if let visibleLine {
                GeometryEngine.geodeticLength(of: visibleLine, lengthUnit: .meters, curveType: .geodesic)
            } else {
                0.0
            }
            let visibleMeasurement = Measurement(value: visibleMeters, unit: UnitLength.meters)

            // Uses `notVisibleLine` to determine if the target is visible from the observer.
            return if notVisibleLine == nil {
                "Target visible from observer after \(visibleMeasurement.formatted())."
            } else {
                "Target obstructed from observer after \(visibleMeasurement.formatted())."
            }
        }
    }
}

private extension String {
    /// A key for an attribute that describes a line of sight's visibility.
    static var visibilityDescription: String { "visibilityDescription" }
    /// A key for an attribute that contains a line of sight's target visibility.
    static var targetVisibility: String { "targetVisibility" }
}

private extension URL {
    /// A URL to a local GeoTIFF file containing elevation data of the Isle of Arran, Scotland.
    static var arranTIF: URL {
        Bundle.main.url(forResource: "arran", withExtension: "tif", subdirectory: "arran")!
    }
}