feat: annotation placer

package earth.maps.cardinal.ui.util

import android.util.Log

import earth.maps.cardinal.data.LatLng

import uniffi.ferrostar.GeographicCoordinate

import uniffi.ferrostar.Route

import javax.inject.Inject

import kotlin.math.abs

/**

 * Utility class for determining optimal placement of route duration annotations on a map.

 * 

 * This class solves the problem of placing annotations (such as route duration text) on polylines

 * in a way that users can clearly identify which annotation applies to which route. The primary

 * challenge is avoiding placement on route segments where multiple routes overlap, as this would

 * create visual ambiguity.

 * 

 * The algorithm works by:

 * 1. Analyzing all routes to identify overlapping segments

 * 2. Finding divergent segments (where only one route exists) for each route

 * 3. Selecting the longest divergent segment for optimal visibility

 * 4. Placing the annotation at the midpoint of that segment

 * 

 * @constructor Creates an instance of AnnotationPlacer using dependency injection

 */

class AnnotationPlacer @Inject constructor() {

    fun placeAnnotations(routes: List<List<LatLng>>): List<LatLng> {

        return emptyList()

    /**

     * Determines optimal annotation placement points for a collection of routes.

     * 

     * This method analyzes the geometry of all provided routes to find non-overlapping

     * segments where annotations can be placed without visual ambiguity. For each route,

     * it identifies the longest segment that doesn't overlap with any other route and

     * places the annotation at the midpoint of that segment.

     * 

     * The algorithm follows these steps:

     * 1. Count overlapping points across all routes

     * 2. For each route, identify contiguous segments where overlap count == 1 (diverged)

     * 3. Track cumulative distance along each divergent segment

     * 4. Select the longest divergent segment for each route

     * 5. Place annotation at the midpoint of the selected segment

     * 

     * @param routes A list of Route objects containing geographic coordinate data

     * @return A Map where each Route is mapped to its optimal annotation placement LatLng coordinate.

     *         Routes with no divergent segments will be excluded from the result.

     * 

     * @see Route for the route data structure

     * @see LatLng for the coordinate representation

     * 

     * Example usage:

     * ```kotlin

     * val annotationPlacer = AnnotationPlacer()

     * val routes = listOf(route1, route2, route3)

     * val placements = annotationPlacer.placeAnnotations(routes)

     * 

     * placements.forEach { (route, position) ->

     *     // Place annotation at 'position' for 'route'

     * }

     * ```

     */

    fun placeAnnotations(routes: List<Route>): Map<Route, LatLng> {

        val routeOverlapCount: MutableMap<LatLng, Int> = mutableMapOf()

        val routesLatLng = routes.map { route -> route.geometry.map { LatLng(it.lat, it.lng) } }

        val placements: MutableMap<Route, LatLng> = mutableMapOf()

        // Step 1: Count how many routes pass through each point

        for (route in routesLatLng) {

            for (point in route) {

                routeOverlapCount.merge(point, 1, Int::plus)

            }

        }

        // Step 2: For each route, find divergent segments and place annotations

        routesLatLng.forEachIndexed { index, route ->

            val segments: MutableList<List<Pair<LatLng, Double>>> = mutableListOf()

            var currentSegment: MutableList<Pair<LatLng, Double>>? = null

            var currentSegmentLengthMeters: Double? = null

            // Step 2a: Identify contiguous divergent segments

            for (point in route) {

                val isDiverged = routeOverlapCount[point] == 1

                if (isDiverged) {

                    if (currentSegment != null) {

                        // Continue current segment

                        currentSegmentLengthMeters = currentSegmentLengthMeters?.plus(

                            currentSegment.lastOrNull()?.first?.fastDistanceTo(point) ?: 0.0

                        )

                        currentSegment.add(Pair(point, currentSegmentLengthMeters ?: 0.0))

                    } else {

                        // Start new segment

                        currentSegment = mutableListOf(Pair(point, 0.0))

                        currentSegmentLengthMeters = 0.0

                    }

                } else {

                    // End current segment if we hit an overlapping point

                    if (currentSegment != null) {

                        segments.add(currentSegment)

                        currentSegment = null

                        currentSegmentLengthMeters = null

                    }

                }

            }

            // Add the final segment if the route ends while diverged

            if (currentSegment != null) {

                segments.add(currentSegment)

            }

            // Step 2b: Select the longest divergent segment

            val bestSegment =

                segments.sortedByDescending { segment -> segment.lastOrNull()?.second }

                    .firstOrNull()

            if (bestSegment == null) {

                Log.w(TAG, "Route with zero divergent segments found, skipping")

                return@forEachIndexed

            }

            val bestSegmentLength = bestSegment.lastOrNull()?.second

            if (bestSegmentLength == null) {

                Log.w(TAG, "Empty divergent segment found, skipping. This is a logic error.")

                return@forEachIndexed

            }

            // Step 2c: Find the midpoint of the selected segment

            val segmentMidpoint =

                bestSegment.minByOrNull { abs(it.second - bestSegmentLength / 2.0) }

            if (segmentMidpoint == null) {

                Log.w(TAG, "Empty divergent segment found after sorting, skipping. This is a logic error.")

                return@forEachIndexed

            }

            // Step 2d: Store the placement for this route

            placements.put(routes[index], segmentMidpoint.first)

        }

        return placements

    }

    companion object {

        /** Tag used for logging debug and warning messages */

        const val TAG = "AnnotationPlacer"

    }

}