using System.Security.Cryptography;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using SatelliteProvider.Common.Configs;
using SatelliteProvider.Common.Interfaces;
using SatelliteProvider.Common.Utils;
using SatelliteProvider.DataAccess.Models;
using SatelliteProvider.DataAccess.Repositories;

namespace SatelliteProvider.Services.RouteManagement.TileProvision;

public sealed class RouteTileDeliveryOrchestrator
{
    private readonly RouteTileExpander _expander;
    private readonly ITileRepository _tileRepository;
    private readonly ITileService _tileService;
    private readonly MapConfig _mapConfig;
    private readonly ProcessingConfig _processingConfig;
    private readonly TileProvisionConfig _provisionConfig;
    private readonly ILogger<RouteTileDeliveryOrchestrator> _logger;

    public RouteTileDeliveryOrchestrator(
        RouteTileExpander expander,
        ITileRepository tileRepository,
        ITileService tileService,
        IOptions<MapConfig> mapConfig,
        IOptions<ProcessingConfig> processingConfig,
        IOptions<TileProvisionConfig> provisionConfig,
        ILogger<RouteTileDeliveryOrchestrator> logger)
    {
        _expander = expander;
        _tileRepository = tileRepository;
        _tileService = tileService;
        _mapConfig = mapConfig.Value;
        _processingConfig = processingConfig.Value;
        _provisionConfig = provisionConfig.Value;
        _logger = logger;
    }

    public async Task DeliverAsync(
        RouteTileDeliveryJob job,
        IRouteTileDeliverySink sink,
        CancellationToken cancellationToken)
    {
        ValidateJob(job);

        var jobStartedAt = DateTime.UtcNow;
        var candidates = _expander.Expand(
            job.Waypoints,
            job.RegionSizeMeters,
            job.Zoom,
            job.GeofenceVertices,
            job.IncludeGeofenceTiles);

        var clientIndex = ClientTileCatalog.IndexByZxy(job.ClientTiles);
        var locationHashes = candidates
            .Select(c => Uuidv5.LocationHashForTile(c.Z, c.X, c.Y))
            .Distinct()
            .ToArray();
        var dbTiles = await _tileRepository.GetTilesByLocationHashesAsync(locationHashes);

        var workItems = new List<TileWorkItem>(candidates.Count);
        var skippedByClient = 0u;

        foreach (var candidate in candidates)
        {
            var hash = Uuidv5.LocationHashForTile(candidate.Z, candidate.X, candidate.Y);
            dbTiles.TryGetValue(hash, out var dbTile);
            var prospect = BuildServerProspect(candidate, dbTile, jobStartedAt);
            clientIndex.TryGetValue((candidate.Z, candidate.X, candidate.Y), out var clientTile);

            if (ClientTileCatalog.ShouldSkipForClient(clientTile, prospect))
            {
                skippedByClient++;
                continue;
            }

            workItems.Add(new TileWorkItem(candidate, dbTile));
        }

        var totalCandidates = (uint)candidates.Count;
        var toDeliver = (uint)workItems.Count;
        await sink.WriteManifestAsync(totalCandidates, skippedByClient, toDeliver, cancellationToken);

        if (toDeliver == 0)
        {
            await sink.WriteCompleteAsync(0, skippedByClient, 0, cancellationToken);
            return;
        }

        var delivered = 0u;
        var batchSeq = 0u;
        var pendingBatch = new List<PreparedTileDelivery>(_provisionConfig.MaxTilesPerBatch);

        async Task FlushBatchAsync()
        {
            if (pendingBatch.Count == 0)
            {
                return;
            }

            pendingBatch.Sort((a, b) => a.Candidate.RoutePriority.CompareTo(b.Candidate.RoutePriority));
            await sink.WriteBatchAsync(batchSeq++, pendingBatch.ToList(), cancellationToken);
            delivered += (uint)pendingBatch.Count;
            pendingBatch.Clear();
        }

        var cachedItems = workItems.Where(w => w.DbTile is not null).ToList();
        var missingItems = workItems.Where(w => w.DbTile is null).ToList();

        foreach (var item in cachedItems.OrderBy(w => w.Candidate.RoutePriority))
        {
            cancellationToken.ThrowIfCancellationRequested();
            var prepared = await TryPrepareFromDatabaseAsync(item.Candidate, item.DbTile!, cancellationToken);
            if (prepared is null)
            {
                missingItems.Add(item);
                continue;
            }

            pendingBatch.Add(prepared);
            if (pendingBatch.Count >= _provisionConfig.MaxTilesPerBatch)
            {
                await FlushBatchAsync();
            }
        }

        await FlushBatchAsync();

        if (missingItems.Count > 0)
        {
            var downloadChannel = System.Threading.Channels.Channel.CreateBounded<PreparedTileDelivery>(
                new System.Threading.Channels.BoundedChannelOptions(_provisionConfig.MaxTilesPerBatch * 2)
                {
                    FullMode = System.Threading.Channels.BoundedChannelFullMode.Wait,
                    SingleReader = true,
                    SingleWriter = false,
                });

            var inFlight = 0;
            var lastProgressAt = DateTime.UtcNow;

            async Task EmitProgressIfDueAsync()
            {
                var now = DateTime.UtcNow;
                if ((now - lastProgressAt).TotalSeconds < _provisionConfig.ProgressEmitIntervalSeconds)
                {
                    return;
                }

                lastProgressAt = now;
                await sink.WriteProgressAsync(delivered, toDeliver, (uint)Volatile.Read(ref inFlight), cancellationToken);
            }

            var downloadLimiter = new SemaphoreSlim(
                _processingConfig.MaxConcurrentDownloads,
                _processingConfig.MaxConcurrentDownloads);

            try
            {
                var producer = Task.Run(async () =>
                {
                    try
                    {
                        var tasks = missingItems
                            .OrderBy(w => w.Candidate.RoutePriority)
                            .Select(async item =>
                            {
                                await downloadLimiter.WaitAsync(cancellationToken);
                                Interlocked.Increment(ref inFlight);
                                try
                                {
                                    var prepared = await TryDownloadAndPrepareAsync(item.Candidate, cancellationToken);
                                    if (prepared is not null)
                                    {
                                        await downloadChannel.Writer.WriteAsync(prepared, cancellationToken);
                                    }
                                }
                                finally
                                {
                                    Interlocked.Decrement(ref inFlight);
                                    downloadLimiter.Release();
                                }
                            });

                        await Task.WhenAll(tasks);
                    }
                    finally
                    {
                        downloadChannel.Writer.Complete();
                    }
                }, cancellationToken);

                await foreach (var prepared in downloadChannel.Reader.ReadAllAsync(cancellationToken))
                {
                    await EmitProgressIfDueAsync();
                    pendingBatch.Add(prepared);
                    if (pendingBatch.Count >= _provisionConfig.MaxTilesPerBatch)
                    {
                        await FlushBatchAsync();
                    }
                }

                await producer;
            }
            finally
            {
                downloadLimiter.Dispose();
            }
        }

        await FlushBatchAsync();
        var serverFiltered = toDeliver - delivered;
        await sink.WriteCompleteAsync(delivered, skippedByClient, serverFiltered, cancellationToken);
    }

    private void ValidateJob(RouteTileDeliveryJob job)
    {
        if (job.RouteId == Guid.Empty)
        {
            throw new ArgumentException("route_id must be a non-empty UUID", nameof(job));
        }

        if (job.Waypoints.Count < 2)
        {
            throw new ArgumentException("Route must have at least 2 waypoints", nameof(job));
        }

        if (job.RegionSizeMeters <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(job), "region_size_meters must be positive");
        }

        if (!_mapConfig.AllowedZoomLevels.Contains(job.Zoom))
        {
            throw new ArgumentException(
                $"zoom {job.Zoom} is not allowed. Allowed: {string.Join(", ", _mapConfig.AllowedZoomLevels)}",
                nameof(job));
        }
    }

    private ServerTileProspect BuildServerProspect(
        RouteTileCandidate candidate,
        TileEntity? dbTile,
        DateTime jobStartedAtUtc)
    {
        var center = GeoUtils.TileToWorldPos(candidate.X, candidate.Y, candidate.Z);
        var resolution = TileResolutionHelper.ResolutionMetersPerPixel(
            candidate.Z,
            center.Lat,
            _mapConfig.TileSizePixels);

        if (dbTile is null)
        {
            return new ServerTileProspect(resolution, jobStartedAtUtc, null);
        }

        return new ServerTileProspect(
            dbTile.TileSizePixels > 0 ? dbTile.TileSizeMeters / dbTile.TileSizePixels : resolution,
            dbTile.CapturedAt,
            dbTile.ContentSha256);
    }

    private async Task<PreparedTileDelivery?> TryPrepareFromDatabaseAsync(
        RouteTileCandidate candidate,
        TileEntity dbTile,
        CancellationToken cancellationToken)
    {
        if (!File.Exists(dbTile.FilePath))
        {
            return null;
        }

        try
        {
            var jpeg = await File.ReadAllBytesAsync(dbTile.FilePath, cancellationToken);
            var hash = dbTile.ContentSha256 is { Length: 32 } existingHash
                ? existingHash
                : SHA256.HashData(jpeg);
            var resolution = dbTile.TileSizePixels > 0
                ? dbTile.TileSizeMeters / dbTile.TileSizePixels
                : TileResolutionHelper.ResolutionMetersPerPixel(
                    candidate.Z,
                    dbTile.Latitude,
                    _mapConfig.TileSizePixels);

            return new PreparedTileDelivery(
                candidate,
                jpeg,
                hash,
                resolution,
                dbTile.CapturedAt,
                dbTile.Source);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Failed to read cached tile ({Z}, {X}, {Y})", candidate.Z, candidate.X, candidate.Y);
            return null;
        }
    }

    private async Task<PreparedTileDelivery?> TryDownloadAndPrepareAsync(
        RouteTileCandidate candidate,
        CancellationToken cancellationToken)
    {
        try
        {
            var center = GeoUtils.TileToWorldPos(candidate.X, candidate.Y, candidate.Z);
            await _tileService.DownloadAndStoreSingleTileAsync(
                center.Lat,
                center.Lon,
                candidate.Z,
                cancellationToken);

            var dbTile = await _tileRepository.GetByTileCoordinatesAsync(candidate.Z, candidate.X, candidate.Y);
            if (dbTile is null || !File.Exists(dbTile.FilePath))
            {
                return null;
            }

            return await TryPrepareFromDatabaseAsync(candidate, dbTile, cancellationToken);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(
                ex,
                "Failed to download tile ({Z}, {X}, {Y}) for route delivery",
                candidate.Z,
                candidate.X,
                candidate.Y);
            return null;
        }
    }

    private sealed record TileWorkItem(RouteTileCandidate Candidate, TileEntity? DbTile);
}