Project geometry

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// Copyright 2022 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 ProjectGeometryView: View {
    /// A location callout placement.
    @State private var calloutPlacement: LocationCalloutPlacement?

    /// The point where the map was tapped in its original spatial reference (Web Mercator).
    @State private var originalPoint: Point?

    /// A map with a topographic basemap style and an initial viewpoint.
    @StateObject private var map: Map = {
        let map = Map(basemapStyle: .arcGISTopographic)
        map.initialViewpoint = Viewpoint(
            center: Point(x: -1.2e7, y: 5e6, spatialReference: .webMercator),
            scale: 4e7
        )
        return map
    }()

    /// A graphics overlay containing a graphic with a circular, red marker symbol.
    @StateObject private var graphicsOverlay = GraphicsOverlay(graphics: [
        Graphic(symbol: SimpleMarkerSymbol(color: .red, size: 8))
    ])

    /// The graphic with a circular, red marker symbol.
    private var pointGraphic: Graphic { graphicsOverlay.graphics.first! }

    var body: some View {
        MapView(map: map, graphicsOverlays: [graphicsOverlay])
            .onSingleTapGesture { _, mapPoint in
                if calloutPlacement == nil {
                    // Sets the original point to where the map was tapped.
                    originalPoint = GeometryEngine.normalizeCentralMeridian(of: mapPoint) as? Point

                    // Projects the original point from Web Mercator to WGS 84.
                    let projectedPoint = GeometryEngine.project(originalPoint!, into: .wgs84)!

                    // Updates the geometry of the point graphic.
                    pointGraphic.geometry = projectedPoint

                    // Updates the location callout placement.
                    calloutPlacement = LocationCalloutPlacement(location: projectedPoint)
                } else {
                    // Hides the callout and point graphic.
                    calloutPlacement = nil
                    pointGraphic.geometry = nil
                }
            }
            .callout(placement: $calloutPlacement.animation(.default.speed(4))) { callout in
                VStack(alignment: .leading) {
                    Group {
                        Text("Coordinates")
                            .fontWeight(.medium)
                        Text("Original: \(originalPoint!.xyCoordinates)")
                        Text("Projected: \(callout.location.xyCoordinates)")
                    }
                    .font(.callout)
                }
                .padding(6)
            }
            .overlay(alignment: .top) {
                Text("Tap on the map.")
                    .frame(maxWidth: .infinity)
                    .padding(.vertical, 6)
                    .background(.thinMaterial, ignoresSafeAreaEdges: .horizontal)
            }
    }
}

private extension FormatStyle where Self == FloatingPointFormatStyle<Double> {
    /// Formats the double with four decimals places of precision.
    static var decimal: Self {
        Self.number.precision(.fractionLength(4))
    }
}

private extension Point {
    /// The point's decimal-formatted x and y coordinates.
    var xyCoordinates: Text {
        Text("\(self.x, format: .decimal), \(self.y, format: .decimal)")
    }
}