Show viewshed from point on map

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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
 *
 *    http://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.
 *
 */

package com.esri.arcgismaps.sample.showviewshedfrompointonmap.components

import android.app.Application
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.viewModelScope
import com.arcgismaps.Color
import com.arcgismaps.data.FeatureCollectionTable
import com.arcgismaps.geometry.GeodeticCurveType
import com.arcgismaps.geometry.GeometryEngine
import com.arcgismaps.geometry.GeometryType
import com.arcgismaps.geometry.LinearUnit
import com.arcgismaps.geometry.Point
import com.arcgismaps.mapping.ArcGISMap
import com.arcgismaps.mapping.BasemapStyle
import com.arcgismaps.mapping.Viewpoint
import com.arcgismaps.mapping.symbology.SimpleFillSymbol
import com.arcgismaps.mapping.symbology.SimpleFillSymbolStyle
import com.arcgismaps.mapping.symbology.SimpleMarkerSymbol
import com.arcgismaps.mapping.symbology.SimpleMarkerSymbolStyle
import com.arcgismaps.mapping.symbology.SimpleRenderer
import com.arcgismaps.mapping.view.Graphic
import com.arcgismaps.mapping.view.GraphicsOverlay
import com.arcgismaps.mapping.view.SingleTapConfirmedEvent
import com.arcgismaps.tasks.geoprocessing.GeoprocessingExecutionType
import com.arcgismaps.tasks.geoprocessing.GeoprocessingJob
import com.arcgismaps.tasks.geoprocessing.GeoprocessingParameters
import com.arcgismaps.tasks.geoprocessing.GeoprocessingTask
import com.arcgismaps.tasks.geoprocessing.geoprocessingparameters.GeoprocessingFeatures
import com.arcgismaps.tasks.geoprocessing.geoprocessingparameters.GeoprocessingLinearUnit
import com.arcgismaps.toolkit.geoviewcompose.MapViewProxy
import com.esri.arcgismaps.sample.sampleslib.components.MessageDialogViewModel
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.launch

class ShowViewshedFromPointOnMapViewModel(application: Application) :
    AndroidViewModel(application) {

    // ArcGISMap with a topographic basemap
    val arcGISMap: ArcGISMap = ArcGISMap(BasemapStyle.ArcGISTopographic).apply {
        initialViewpoint = Viewpoint(
            latitude = 45.379,
            longitude = 6.849,
            scale = 144447.0
        )
    }

    // Used by the composable MapView for viewpoint changes
    val mapviewProxy = MapViewProxy()

    // Graphics overlay for the red marker at the tapped location
    val inputGraphicsOverlay = GraphicsOverlay().apply {
        renderer = SimpleRenderer(
            symbol = SimpleMarkerSymbol(
                style = SimpleMarkerSymbolStyle.Circle,
                color = Color.red,
                size = 10f
            )
        )
    }

    // Graphics overlay for displaying the resulting viewshed polygons
    val resultGraphicsOverlay = GraphicsOverlay().apply {
        renderer = SimpleRenderer(
            symbol = SimpleFillSymbol(
                style = SimpleFillSymbolStyle.Solid,
                color = Color.fromRgba(r = 255, g = 165, b = 0, a = 100)
            )
        )
    }

    // Graphics overlay for displaying the 15 km buffer range
    val bufferGraphicsOverlay = GraphicsOverlay().apply {
        renderer = SimpleRenderer(
            symbol = SimpleFillSymbol(
                style = SimpleFillSymbolStyle.Solid,
                color = Color.fromRgba(r = 0, g = 0, b = 255, a = 50)
            )
        )
    }

    // GeoprocessingTask pointing to the Viewshed service URL
    private val geoprocessingTask = GeoprocessingTask(
        url = "https://sampleserver6.arcgisonline.com/arcgis/rest/services/Elevation/ESRI_Elevation_World/GPServer/Viewshed"
    )

    // Running GeoprocessingJob for cancellation/cleanup
    private var geoprocessingJob: GeoprocessingJob? = null

    // State flows for controlling UI
    private val _isGeoprocessingInProgress = MutableStateFlow(false)
    val isGeoprocessingInProgress = _isGeoprocessingInProgress.asStateFlow()

    // Message dialog view model for handling error messages
    val messageDialogVM = MessageDialogViewModel()

    init {
        viewModelScope.launch {
            arcGISMap.load().onFailure { messageDialogVM.showMessageDialog(it) }
        }
    }

    /**
     * Handles the [singleTapConfirmedEvent] by retrieving the tapped [Point] to
     * cancel and run a new viewshed geoprocessing job.
     */
    fun onMapTapped(singleTapConfirmedEvent: SingleTapConfirmedEvent) {
        val tapPoint = singleTapConfirmedEvent.mapPoint
            ?: return messageDialogVM.showMessageDialog("Unable to retrieve tapped point")
        viewModelScope.launch {
            // Clear existing overlays and cancel any running job
            clearOverlays()
            geoprocessingJob?.cancel()
            // Add a new red marker to the map at the tapped point
            addTapMarker(tapPoint)
            // Show a 15 km buffer to visualize the visibility range
            addBufferGraphic(tapPoint)
            // Start the geoprocessing job to obtain the viewshed polygons
            _isGeoprocessingInProgress.value = true
            calculateViewshed(tapPoint)
            _isGeoprocessingInProgress.value = false
        }
    }

    /**
     * Perform the viewshed calculation on the geoprocessing service
     * for the given [tapPoint].
     */
    private suspend fun calculateViewshed(tapPoint: Point) {
        // Create an empty FeatureCollectionTable for the tapped location
        val table = FeatureCollectionTable(
            fields = emptyList(),
            geometryType = GeometryType.Point,
            spatialReference = tapPoint.spatialReference
        )

        // Create a new feature with the tapped geometry and add to the table
        val newFeature = table.createFeature().also { it.geometry = tapPoint }
        table.addFeature(newFeature)

        // Create geoprocessing parameters for a synchronous execution
        val geoprocessingParameters = GeoprocessingParameters(
            geoprocessingExecutionType = GeoprocessingExecutionType.SynchronousExecute
        ).apply {
            processSpatialReference = tapPoint.spatialReference
            outputSpatialReference = tapPoint.spatialReference
            // Provide the tapped point as "Input_Observation_Point"
            inputs["Input_Observation_Point"] = GeoprocessingFeatures(featureSet = table)
            inputs["Viewshed_Distance"] = GeoprocessingLinearUnit(distance = 15000.0)
        }

        // Create a new job
        geoprocessingJob = geoprocessingTask.createJob(geoprocessingParameters)

        // Start and await the result
        geoprocessingJob?.start()

        val gpResult = geoprocessingJob?.result()?.getOrElse {
            return messageDialogVM.showMessageDialog(it)
        }

        // Get the output features for the viewshed polygon
        val viewshedFeatureSet = gpResult?.outputs?.get("Viewshed_Result") as? GeoprocessingFeatures
            ?: return messageDialogVM.showMessageDialog("No viewshed result found in the geoprocessing job.")
        val featureSet = viewshedFeatureSet.features
            ?: return messageDialogVM.showMessageDialog("Geoprocessing feature set is null.")

        // Add each resulting feature geometry as a graphic to resultGraphicsOverlay
        val resultGraphics = featureSet.mapNotNull { feature ->
            feature.geometry?.let { Graphic(it) }
        }

        // Add the graphics to the overlay and set the map's viewpoint to its extent
        resultGraphicsOverlay.graphics.addAll(resultGraphics)
        resultGraphicsOverlay.extent?.let { resultExtent ->
            mapviewProxy.setViewpointGeometry(
                boundingGeometry = resultExtent,
                paddingInDips = 20.0
            )
        }
    }

    /**
     * Place a simple red marker graphic at the tapped location.
     */
    private fun addTapMarker(tapPoint: Point) {
        val graphic = Graphic(tapPoint)
        inputGraphicsOverlay.graphics.add(graphic)
    }

    /**
     * Add a 15 km buffer graphic around [tapPoint].
     */
    private fun addBufferGraphic(tapPoint: Point, radiusMeters: Double = 15000.0) {
        // Use the geometry engine to build a geodesic planar buffer
        val bufferGeometry = GeometryEngine.bufferGeodeticOrNull(
            geometry = tapPoint,
            distance = radiusMeters,
            distanceUnit = LinearUnit.meters,
            maxDeviation = Double.NaN,
            curveType = GeodeticCurveType.Geodesic
        )
        // Create a graphic from the buffered geometry
        val bufferGraphic = Graphic(bufferGeometry)
        // Add it to the buffer graphics overlay
        bufferGraphicsOverlay.graphics.add(bufferGraphic)
    }

    /**
     * Clear any previous marker or result polygons from the map.
     */
    private fun clearOverlays() {
        inputGraphicsOverlay.graphics.clear()
        resultGraphicsOverlay.graphics.clear()
        bufferGraphicsOverlay.graphics.clear()
    }
}