satellite-provider/SatelliteProvider/SatelliteDownloader.cs

using System.Collections.Concurrent;
using Microsoft.Extensions.Options;
using Newtonsoft.Json;
using SatelliteProvider.Configs;
using SatelliteProvider.DTO;
using SixLabors.ImageSharp;

namespace SatelliteProvider;

public interface ISatelliteDownloader
{
    Task GetTiles(GeoPoint geoPoint, double radiusM, int zoomLevel, CancellationToken token = default);
}

public class SatelliteDownloader(ILogger<SatelliteDownloader> logger, IOptions<MapConfig> mapConfig, IHttpClientFactory httpClientFactory)
    : ISatelliteDownloader
{
    private const string TILE_URL_TEMPLATE = "https://mt{0}.google.com/vt/lyrs=s&x={1}&y={2}&z={3}&token={4}";
    private const int NUM_SERVERS = 4;
    private readonly string _apiKey = mapConfig.Value.ApiKey;

    private readonly string _satDirectory = Path.Combine(Directory.GetCurrentDirectory(), "maps");


    private record SessionResponse(string Session);

    private async Task<string?> GetSessionToken()
    {
        var url = $"https://tile.googleapis.com/v1/createSession?key={_apiKey}";
        using var httpClient = httpClientFactory.CreateClient();
        try
        {
            var str = JsonConvert.SerializeObject(new { mapType = "satellite" });
            var response = await httpClient.PostAsync(url, new StringContent(str));
            response.EnsureSuccessStatusCode();
            var sessionResponse = await response.Content.ReadFromJsonAsync<SessionResponse>();
            return sessionResponse?.Session;
        }
        catch (Exception e)
        {
            logger.LogError(e, e.Message);
            throw;
        }
    }

    public async Task GetTiles(GeoPoint centerGeoPoint, double radiusM, int zoomLevel, CancellationToken token = default)
    {
        var (latMin, latMax, lonMin, lonMax) = GeoUtils.GetBoundingBox(centerGeoPoint, radiusM);

        var (xMin, yMin) = GeoUtils.WorldToTilePos(latMax, lonMin, zoomLevel); // Top-left corner
        var (xMax, yMax) = GeoUtils.WorldToTilePos(latMin, lonMax, zoomLevel); // Bottom-right corner

        var tilesToDownload = new ConcurrentQueue<SatTile>();
        var server = 0;
        var sessionToken = await GetSessionToken();

        for (var y = yMin; y <= yMax + 1; y++)
            for (var x = xMin; x <= xMax + 1; x++)
            {
                token.ThrowIfCancellationRequested();
                var url = string.Format(TILE_URL_TEMPLATE, server, x, y, zoomLevel, sessionToken);

                tilesToDownload.Enqueue(new SatTile(x, y, zoomLevel, url));
                server = (server + 1) % NUM_SERVERS;
            }

        var downloadTasks = new List<Task>();
        int downloadedCount = 0;


        for (int i = 0; i < NUM_SERVERS; i++)
        {
            downloadTasks.Add(Task.Run(async () =>
            {
                using var httpClient = httpClientFactory.CreateClient();

                while (tilesToDownload.TryDequeue(out var tileInfo))
                {
                    if (token.IsCancellationRequested) break;
                    try
                    {
                        httpClient.DefaultRequestHeaders.UserAgent.ParseAdd("Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.0.0 Safari/537.36");
                        var response = await httpClient.GetAsync(tileInfo.Url, token);
                        response.EnsureSuccessStatusCode();
                        var tileData = await response.Content.ReadAsByteArrayAsync(token);
                        using var tileImage = Image.Load(tileData);
                        await tileImage.SaveAsync(Path.Combine(_satDirectory, tileInfo.FileName), token);
                        if (tileData.Length > 0)
                        {
                            Interlocked.Increment(ref downloadedCount);
                        }
                    }
                    catch (HttpRequestException requestException)
                    {
                        logger.LogError(requestException, $"Fail to download tile! Url: {tileInfo.Url}. {requestException.Message}");
                    }
                    catch (Exception e)
                    {
                        logger.LogError(e, $"Fail to download tile! {e.Message}");
                    }
                }
            }, token));
        }

        await Task.WhenAll(downloadTasks);
    }
}