using SpaceGame.Simulation.Api.Contracts;

namespace SpaceGame.Simulation.Api.Simulation;

public sealed class SimulationEngine
{
  public WorldDelta Tick(SimulationWorld world, float deltaSeconds, long sequence)
  {
    var events = new List<SimulationEventRecord>();

    UpdateStations(world, deltaSeconds, events);

    foreach (var ship in world.Ships)
    {
      var previousPosition = ship.Position;
      var previousState = ship.State;
      var previousBehavior = ship.DefaultBehavior.Kind;
      var previousTask = ship.ControllerTask.Kind;

      RefreshControlLayers(ship);
      PlanControllerTask(ship, world);
      var controllerEvent = UpdateControllerTask(ship, world, deltaSeconds);
      AdvanceControlState(ship, controllerEvent);
      ship.Velocity = ship.Position.Subtract(previousPosition).Divide(deltaSeconds);
      TrackHistory(ship);

      EmitShipStateEvents(ship, previousState, previousBehavior, previousTask, controllerEvent, events);
    }

    world.GeneratedAtUtc = DateTimeOffset.UtcNow;

    return new WorldDelta(
      sequence,
      world.TickIntervalMs,
      world.GeneratedAtUtc,
      false,
      events,
      BuildNodeDeltas(world),
      BuildStationDeltas(world),
      BuildShipDeltas(world),
      BuildFactionDeltas(world));
  }

  public WorldSnapshot BuildSnapshot(SimulationWorld world, long sequence)
  {
    PrimeDeltaBaseline(world);

    return new WorldSnapshot(
      world.Label,
      world.Seed,
      sequence,
      world.TickIntervalMs,
      world.GeneratedAtUtc,
      world.Systems.Select((system) => new SystemSnapshot(
        system.Definition.Id,
        system.Definition.Label,
        ToDto(system.Position),
        system.Definition.StarColor,
        system.Definition.StarSize,
        system.Definition.Planets.Select((planet) => new PlanetSnapshot(
          planet.Label,
          planet.OrbitRadius,
          planet.Size,
          planet.Color,
          planet.HasRing)).ToList())).ToList(),
      world.Nodes.Select(ToNodeDelta).Select((node) => new ResourceNodeSnapshot(
        node.Id,
        node.SystemId,
        node.Position,
        node.OreRemaining,
        node.MaxOre,
        node.ItemId)).ToList(),
      world.Stations.Select(ToStationDelta).Select((station) => new StationSnapshot(
        station.Id,
        station.Label,
        station.Category,
        station.SystemId,
        station.Position,
        station.Color,
        station.DockedShips,
        station.OreStored,
        station.RefinedStock,
        station.FactionId)).ToList(),
      world.Ships.Select(ToShipDelta).Select((ship) => new ShipSnapshot(
        ship.Id,
        ship.Label,
        ship.Role,
        ship.ShipClass,
        ship.SystemId,
        ship.Position,
        ship.Velocity,
        ship.TargetPosition,
        ship.State,
        ship.OrderKind,
        ship.DefaultBehaviorKind,
        ship.ControllerTaskKind,
        ship.Cargo,
        ship.CargoCapacity,
        ship.CargoItemId,
        ship.FactionId,
        ship.Health,
        ship.History)).ToList(),
      world.Factions.Select(ToFactionDelta).Select((faction) => new FactionSnapshot(
        faction.Id,
        faction.Label,
        faction.Color,
        faction.Credits,
        faction.OreMined,
        faction.GoodsProduced,
        faction.ShipsBuilt,
        faction.ShipsLost)).ToList());
  }

  public void PrimeDeltaBaseline(SimulationWorld world)
  {
    foreach (var node in world.Nodes)
    {
      node.LastDeltaSignature = BuildNodeSignature(node);
    }

    foreach (var station in world.Stations)
    {
      station.LastDeltaSignature = BuildStationSignature(station);
    }

    foreach (var ship in world.Ships)
    {
      ship.LastDeltaSignature = BuildShipSignature(ship);
    }

    foreach (var faction in world.Factions)
    {
      faction.LastDeltaSignature = BuildFactionSignature(faction);
    }
  }

  private static IReadOnlyList<ResourceNodeDelta> BuildNodeDeltas(SimulationWorld world)
  {
    var deltas = new List<ResourceNodeDelta>();
    foreach (var node in world.Nodes)
    {
      var signature = BuildNodeSignature(node);
      if (signature == node.LastDeltaSignature)
      {
        continue;
      }

      node.LastDeltaSignature = signature;
      deltas.Add(ToNodeDelta(node));
    }

    return deltas;
  }

  private static IReadOnlyList<StationDelta> BuildStationDeltas(SimulationWorld world)
  {
    var deltas = new List<StationDelta>();
    foreach (var station in world.Stations)
    {
      var signature = BuildStationSignature(station);
      if (signature == station.LastDeltaSignature)
      {
        continue;
      }

      station.LastDeltaSignature = signature;
      deltas.Add(ToStationDelta(station));
    }

    return deltas;
  }

  private static IReadOnlyList<ShipDelta> BuildShipDeltas(SimulationWorld world)
  {
    var deltas = new List<ShipDelta>();
    foreach (var ship in world.Ships)
    {
      var signature = BuildShipSignature(ship);
      if (signature == ship.LastDeltaSignature)
      {
        continue;
      }

      ship.LastDeltaSignature = signature;
      deltas.Add(ToShipDelta(ship));
    }

    return deltas;
  }

  private static IReadOnlyList<FactionDelta> BuildFactionDeltas(SimulationWorld world)
  {
    var deltas = new List<FactionDelta>();
    foreach (var faction in world.Factions)
    {
      var signature = BuildFactionSignature(faction);
      if (signature == faction.LastDeltaSignature)
      {
        continue;
      }

      faction.LastDeltaSignature = signature;
      deltas.Add(ToFactionDelta(faction));
    }

    return deltas;
  }

  private static string BuildNodeSignature(ResourceNodeRuntime node) =>
    $"{node.SystemId}|{node.OreRemaining:0.###}";

  private static string BuildStationSignature(StationRuntime station) =>
    $"{station.SystemId}|{station.OreStored:0.###}|{station.RefinedStock:0.###}|{station.DockedShipIds.Count}";

  private static string BuildShipSignature(ShipRuntime ship) =>
    string.Join("|",
      ship.SystemId,
      ship.Position.X.ToString("0.###"),
      ship.Position.Y.ToString("0.###"),
      ship.Position.Z.ToString("0.###"),
      ship.Velocity.X.ToString("0.###"),
      ship.Velocity.Y.ToString("0.###"),
      ship.Velocity.Z.ToString("0.###"),
      ship.TargetPosition.X.ToString("0.###"),
      ship.TargetPosition.Y.ToString("0.###"),
      ship.TargetPosition.Z.ToString("0.###"),
      ship.State,
      ship.Order?.Kind ?? "none",
      ship.DefaultBehavior.Kind,
      ship.ControllerTask.Kind,
      ship.Cargo.ToString("0.###"),
      ship.Health.ToString("0.###"));

  private static string BuildFactionSignature(FactionRuntime faction) =>
    $"{faction.Credits:0.###}|{faction.OreMined:0.###}|{faction.GoodsProduced:0.###}|{faction.ShipsBuilt}|{faction.ShipsLost}";

  private static ResourceNodeDelta ToNodeDelta(ResourceNodeRuntime node) => new(
    node.Id,
    node.SystemId,
    ToDto(node.Position),
    node.OreRemaining,
    node.MaxOre,
    node.ItemId);

  private static StationDelta ToStationDelta(StationRuntime station) => new(
    station.Id,
    station.Definition.Label,
    station.Definition.Category,
    station.SystemId,
    ToDto(station.Position),
    station.Definition.Color,
    station.DockedShipIds.Count,
    station.OreStored,
    station.RefinedStock,
    station.FactionId);

  private static ShipDelta ToShipDelta(ShipRuntime ship) => new(
    ship.Id,
    ship.Definition.Label,
    ship.Definition.Role,
    ship.Definition.ShipClass,
    ship.SystemId,
    ToDto(ship.Position),
    ToDto(ship.Velocity),
    ToDto(ship.TargetPosition),
    ship.State,
    ship.Order?.Kind,
    ship.DefaultBehavior.Kind,
    ship.ControllerTask.Kind,
    ship.Cargo,
    ship.Definition.CargoCapacity,
    ship.Definition.CargoItemId,
    ship.FactionId,
    ship.Health,
    ship.History.ToList());

  private static FactionDelta ToFactionDelta(FactionRuntime faction) => new(
    faction.Id,
    faction.Label,
    faction.Color,
    faction.Credits,
    faction.OreMined,
    faction.GoodsProduced,
    faction.ShipsBuilt,
    faction.ShipsLost);

  private static void EmitShipStateEvents(
    ShipRuntime ship,
    string previousState,
    string previousBehavior,
    string previousTask,
    string controllerEvent,
    ICollection<SimulationEventRecord> events)
  {
    var occurredAtUtc = DateTimeOffset.UtcNow;

    if (previousState != ship.State)
    {
      events.Add(new SimulationEventRecord("ship", ship.Id, "state-changed", $"{ship.Definition.Label} {previousState} -> {ship.State}", occurredAtUtc));
    }

    if (previousBehavior != ship.DefaultBehavior.Kind)
    {
      events.Add(new SimulationEventRecord("ship", ship.Id, "behavior-changed", $"{ship.Definition.Label} behavior {previousBehavior} -> {ship.DefaultBehavior.Kind}", occurredAtUtc));
    }

    if (previousTask != ship.ControllerTask.Kind)
    {
      events.Add(new SimulationEventRecord("ship", ship.Id, "task-changed", $"{ship.Definition.Label} task {previousTask} -> {ship.ControllerTask.Kind}", occurredAtUtc));
    }

    if (controllerEvent != "none")
    {
      events.Add(new SimulationEventRecord("ship", ship.Id, controllerEvent, $"{ship.Definition.Label} {controllerEvent}", occurredAtUtc));
    }
  }

  private void UpdateStations(SimulationWorld world, float deltaSeconds, ICollection<SimulationEventRecord> events)
  {
    foreach (var station in world.Stations)
    {
      if (station.Definition.Category != "refining" || station.OreStored < 60f)
      {
        continue;
      }

      station.ProcessTimer += deltaSeconds;
      if (station.ProcessTimer < 8f)
      {
        continue;
      }

      station.ProcessTimer = 0f;
      station.OreStored -= 60f;
      station.RefinedStock += 60f;
      events.Add(new SimulationEventRecord("station", station.Id, "refined", $"{station.Definition.Label} refined 60 ore", DateTimeOffset.UtcNow));
      var faction = world.Factions.FirstOrDefault((candidate) => candidate.Id == station.FactionId);
      if (faction is not null)
      {
        faction.GoodsProduced += 60f;
        faction.Credits += 18f;
      }
    }
  }

  private void RefreshControlLayers(ShipRuntime ship)
  {
    if (ship.Order is not null && ship.Order.Status == "queued")
    {
      ship.Order.Status = "accepted";
    }
  }

  private void PlanControllerTask(ShipRuntime ship, SimulationWorld world)
  {
    if (ship.Order is not null)
    {
      ship.ControllerTask = new ControllerTaskRuntime
      {
        Kind = "travel",
        TargetEntityId = null,
        TargetSystemId = ship.Order.DestinationSystemId,
        TargetPosition = ship.Order.DestinationPosition,
        Threshold = world.Balance.ArrivalThreshold,
      };
      return;
    }

    if (ship.DefaultBehavior.Kind == "auto-mine")
    {
      PlanAutoMine(ship, world);
      return;
    }

    if (ship.DefaultBehavior.Kind == "patrol" && ship.DefaultBehavior.PatrolPoints.Count > 0)
    {
      ship.ControllerTask = new ControllerTaskRuntime
      {
        Kind = "travel",
        TargetPosition = ship.DefaultBehavior.PatrolPoints[ship.DefaultBehavior.PatrolIndex],
        TargetSystemId = ship.SystemId,
        Threshold = 18f,
      };
      return;
    }

    ship.ControllerTask = new ControllerTaskRuntime
    {
      Kind = "idle",
      Threshold = world.Balance.ArrivalThreshold,
    };
  }

  private void PlanAutoMine(ShipRuntime ship, SimulationWorld world)
  {
    var behavior = ship.DefaultBehavior;
    var refinery = world.Stations.FirstOrDefault((station) => station.Id == behavior.RefineryId);
    var node = behavior.NodeId is null
      ? world.Nodes
        .Where((candidate) => candidate.SystemId == behavior.AreaSystemId)
        .OrderByDescending((candidate) => candidate.OreRemaining)
        .FirstOrDefault()
      : world.Nodes.FirstOrDefault((candidate) => candidate.Id == behavior.NodeId);

    if (refinery is null || node is null)
    {
      behavior.Kind = "idle";
      ship.ControllerTask = new ControllerTaskRuntime { Kind = "idle", Threshold = world.Balance.ArrivalThreshold };
      return;
    }

    behavior.NodeId ??= node.Id;
    switch (behavior.Phase)
    {
      case "extract":
        ship.ControllerTask = new ControllerTaskRuntime
        {
          Kind = "extract",
          TargetEntityId = node.Id,
          TargetSystemId = node.SystemId,
          TargetPosition = node.Position,
          Threshold = 14f,
        };
        break;
      case "travel-to-station":
        ship.ControllerTask = new ControllerTaskRuntime
        {
          Kind = "travel",
          TargetEntityId = refinery.Id,
          TargetSystemId = refinery.SystemId,
          TargetPosition = refinery.Position,
          Threshold = refinery.Definition.Radius + 8f,
        };
        break;
      case "dock":
        ship.ControllerTask = new ControllerTaskRuntime
        {
          Kind = "dock",
          TargetEntityId = refinery.Id,
          TargetSystemId = refinery.SystemId,
          TargetPosition = refinery.Position,
          Threshold = refinery.Definition.Radius + 4f,
        };
        break;
      case "unload":
        ship.ControllerTask = new ControllerTaskRuntime
        {
          Kind = "unload",
          TargetEntityId = refinery.Id,
          TargetSystemId = refinery.SystemId,
          TargetPosition = refinery.Position,
          Threshold = 0f,
        };
        break;
      case "undock":
        ship.ControllerTask = new ControllerTaskRuntime
        {
          Kind = "undock",
          TargetEntityId = refinery.Id,
          TargetSystemId = refinery.SystemId,
          TargetPosition = new Vector3(refinery.Position.X + world.Balance.UndockDistance, refinery.Position.Y, refinery.Position.Z),
          Threshold = 8f,
        };
        break;
      default:
        ship.ControllerTask = new ControllerTaskRuntime
        {
          Kind = "travel",
          TargetEntityId = node.Id,
          TargetSystemId = node.SystemId,
          TargetPosition = node.Position,
          Threshold = 18f,
        };
        behavior.Phase = "travel-to-node";
        break;
    }
  }

  private string UpdateControllerTask(ShipRuntime ship, SimulationWorld world, float deltaSeconds)
  {
    var task = ship.ControllerTask;
    switch (task.Kind)
    {
      case "idle":
        ship.State = "idle";
        ship.TargetPosition = ship.Position;
        return "none";
      case "travel":
        return UpdateTravel(ship, world, deltaSeconds);
      case "extract":
        return UpdateExtract(ship, world, deltaSeconds);
      case "dock":
        return UpdateDock(ship, world, deltaSeconds);
      case "unload":
        return UpdateUnload(ship, world, deltaSeconds);
      case "undock":
        return UpdateUndock(ship, world, deltaSeconds);
      default:
        ship.State = "idle";
        ship.TargetPosition = ship.Position;
        return "none";
    }
  }

  private string UpdateTravel(ShipRuntime ship, SimulationWorld world, float deltaSeconds)
  {
    var task = ship.ControllerTask;
    if (task.TargetPosition is null || task.TargetSystemId is null)
    {
      ship.State = "idle";
      ship.TargetPosition = ship.Position;
      return "none";
    }

    ship.TargetPosition = task.TargetPosition.Value;
    var distance = ship.Position.DistanceTo(task.TargetPosition.Value);
    if (distance <= task.Threshold)
    {
      ship.Position = task.TargetPosition.Value;
      ship.TargetPosition = ship.Position;
      ship.SystemId = task.TargetSystemId;
      ship.State = "arriving";
      return "arrived";
    }

    var speed = ship.Definition.Speed;
    if (ship.SystemId != task.TargetSystemId)
    {
      ship.State = distance > 800f ? "ftl" : "spooling-ftl";
      speed = ship.Definition.FtlSpeed;
    }
    else if (distance > 200f)
    {
      ship.State = distance > 500f ? "warping" : "spooling-warp";
      speed = ship.Definition.Speed * 4.5f;
    }
    else
    {
      ship.State = "approaching";
      speed = ship.Definition.Speed;
    }

    ship.Position = ship.Position.MoveToward(task.TargetPosition.Value, speed * deltaSeconds);
    return "none";
  }

  private string UpdateExtract(ShipRuntime ship, SimulationWorld world, float deltaSeconds)
  {
    var task = ship.ControllerTask;
    var node = world.Nodes.FirstOrDefault((candidate) => candidate.Id == task.TargetEntityId);
    if (node is null || task.TargetPosition is null)
    {
      ship.State = "idle";
      ship.TargetPosition = ship.Position;
      return "none";
    }

    ship.TargetPosition = task.TargetPosition.Value;
    var distance = ship.Position.DistanceTo(task.TargetPosition.Value);
    if (distance > task.Threshold)
    {
      ship.State = "mining-approach";
      ship.Position = ship.Position.MoveToward(task.TargetPosition.Value, ship.Definition.Speed * deltaSeconds);
      return "none";
    }

    ship.State = "mining";
    ship.ActionTimer += deltaSeconds;
    if (ship.ActionTimer < 1f)
    {
      return "none";
    }

    ship.ActionTimer = 0f;
    var mined = MathF.Min(world.Balance.MiningRate, ship.Definition.CargoCapacity - ship.Cargo);
    mined = MathF.Min(mined, node.OreRemaining);
    ship.Cargo += mined;
    node.OreRemaining -= mined;
    if (node.OreRemaining <= 0f)
    {
      node.OreRemaining = node.MaxOre;
    }

    return ship.Cargo >= ship.Definition.CargoCapacity ? "cargo-full" : "none";
  }

  private string UpdateDock(ShipRuntime ship, SimulationWorld world, float deltaSeconds)
  {
    var task = ship.ControllerTask;
    var station = world.Stations.FirstOrDefault((candidate) => candidate.Id == task.TargetEntityId);
    if (station is null || task.TargetPosition is null)
    {
      ship.State = "idle";
      ship.TargetPosition = ship.Position;
      return "none";
    }

    ship.TargetPosition = task.TargetPosition.Value;
    var distance = ship.Position.DistanceTo(task.TargetPosition.Value);
    if (distance > task.Threshold)
    {
      ship.State = "docking-approach";
      ship.Position = ship.Position.MoveToward(task.TargetPosition.Value, ship.Definition.Speed * deltaSeconds);
      return "none";
    }

    ship.State = "docking";
    ship.ActionTimer += deltaSeconds;
    if (ship.ActionTimer < world.Balance.DockingDuration)
    {
      return "none";
    }

    ship.ActionTimer = 0f;
    ship.State = "docked";
    ship.DockedStationId = station.Id;
    station.DockedShipIds.Add(ship.Id);
    ship.Position = station.Position;
    ship.TargetPosition = station.Position;
    return "docked";
  }

  private string UpdateUnload(ShipRuntime ship, SimulationWorld world, float deltaSeconds)
  {
    if (ship.DockedStationId is null)
    {
      ship.State = "idle";
      ship.TargetPosition = ship.Position;
      return "none";
    }

    var station = world.Stations.FirstOrDefault((candidate) => candidate.Id == ship.DockedStationId);
    if (station is null)
    {
      ship.DockedStationId = null;
      ship.State = "idle";
      ship.TargetPosition = ship.Position;
      return "none";
    }

    ship.TargetPosition = station.Position;
    ship.State = "transferring";
    var moved = MathF.Min(ship.Cargo, world.Balance.TransferRate * deltaSeconds);
    ship.Cargo -= moved;
    station.OreStored += moved;
    var faction = world.Factions.FirstOrDefault((candidate) => candidate.Id == ship.FactionId);
    if (faction is not null)
    {
      faction.OreMined += moved;
      faction.Credits += moved * 0.4f;
    }

    return ship.Cargo <= 0.01f ? "unloaded" : "none";
  }

  private string UpdateUndock(ShipRuntime ship, SimulationWorld world, float deltaSeconds)
  {
    var task = ship.ControllerTask;
    if (ship.DockedStationId is null || task.TargetPosition is null)
    {
      ship.State = "idle";
      ship.TargetPosition = ship.Position;
      return "none";
    }

    ship.TargetPosition = task.TargetPosition.Value;
    var station = world.Stations.FirstOrDefault((candidate) => candidate.Id == ship.DockedStationId);
    station?.DockedShipIds.Remove(ship.Id);
    ship.DockedStationId = null;
    ship.State = "undocking";
    ship.Position = ship.Position.MoveToward(task.TargetPosition.Value, ship.Definition.Speed * deltaSeconds);
    return ship.Position.DistanceTo(task.TargetPosition.Value) <= task.Threshold ? "undocked" : "none";
  }

  private void AdvanceControlState(ShipRuntime ship, string controllerEvent)
  {
    if (ship.Order is not null && controllerEvent == "arrived")
    {
      ship.Order = null;
      ship.ControllerTask.Kind = "idle";
      return;
    }

    if (ship.DefaultBehavior.Kind == "auto-mine")
    {
      switch (ship.DefaultBehavior.Phase, controllerEvent)
      {
        case ("travel-to-node", "arrived"):
          ship.DefaultBehavior.Phase = ship.Cargo >= ship.Definition.CargoCapacity ? "travel-to-station" : "extract";
          break;
        case ("extract", "cargo-full"):
          ship.DefaultBehavior.Phase = "travel-to-station";
          break;
        case ("travel-to-station", "arrived"):
          ship.DefaultBehavior.Phase = "dock";
          break;
        case ("dock", "docked"):
          ship.DefaultBehavior.Phase = "unload";
          break;
        case ("unload", "unloaded"):
          ship.DefaultBehavior.Phase = "undock";
          break;
        case ("undock", "undocked"):
          ship.DefaultBehavior.Phase = "travel-to-node";
          ship.DefaultBehavior.NodeId = null;
          break;
      }
    }

    if (ship.DefaultBehavior.Kind == "patrol" && controllerEvent == "arrived" && ship.DefaultBehavior.PatrolPoints.Count > 0)
    {
      ship.DefaultBehavior.PatrolIndex = (ship.DefaultBehavior.PatrolIndex + 1) % ship.DefaultBehavior.PatrolPoints.Count;
    }
  }

  private static void TrackHistory(ShipRuntime ship)
  {
    var signature = $"{ship.State}|{ship.DefaultBehavior.Kind}|{ship.ControllerTask.Kind}|{ship.Cargo:0.0}";
    if (signature == ship.LastSignature)
    {
      return;
    }

    ship.LastSignature = signature;
    ship.History.Add($"{DateTimeOffset.UtcNow:HH:mm:ss}  state={ship.State} behavior={ship.DefaultBehavior.Kind} task={ship.ControllerTask.Kind} cargo={ship.Cargo:0.#}");
    if (ship.History.Count > 18)
    {
      ship.History.RemoveAt(0);
    }
  }

  private static Vector3Dto ToDto(Vector3 value) => new(value.X, value.Y, value.Z);
}