namespace ReactorMaintenance.Simulation;

public sealed class SimulationEngine(IEnumerable<ISimulationEffect> effects, IEnumerable<IAreaSimulationEffect> areaEffects, IEnumerable<Hazard> hazards)
{
    private sealed record ForecastKey(EFailureKind Kind, GridPosition? Position);

    public SimulationEngine()
        : this(
            [new PipeLeakEffect(), new MachineEffect(), new FireAndElectricalHazardEffect(), new CellIntegrityEffect()],
            [new SmokeSpreadEffect()],
            [new PipeBurstHazard(), new IgnitionHazard(), new MeltdownHazard(), new StabilityCollapseHazard()])
    {
    }

    public LevelState AdvanceTurn(LevelState level)
    {
        return AdvanceTurn(level, true);
    }

    public IReadOnlyList<Forecast> Forecast(LevelState level)
    {
        var forecasts = new List<Forecast>();
        var seen = new HashSet<ForecastKey>();
        var forecastLevel = level with { Cells = level.Cells.ToArray(), Forecasts = Array.Empty<Forecast>() };
        if (forecastLevel.Global.Lost)
            AddHazardForecasts(forecasts, seen, forecastLevel, Balancing.CurrentForecastTurn);

        AddReactorReadyForecast(forecasts, seen, forecastLevel, Balancing.CurrentForecastTurn);

        if (IsReactorReady(forecastLevel) || forecastLevel.Global.Lost || forecastLevel.Global.ReactorActivated)
            return forecasts.OrderBy(f => f.Turns).ThenBy(f => f.Message).ToArray();

        for (var step = Balancing.TurnIncrement; step <= Balancing.MaxForecastStepCount; step++)
        {
            forecastLevel = AdvanceTurn(forecastLevel, false);
            AddHazardForecasts(forecasts, seen, forecastLevel, step);
            AddReactorReadyForecast(forecasts, seen, forecastLevel, step);

            if (forecastLevel.Global.Lost || IsReactorReady(forecastLevel) || forecastLevel.Global.ReactorActivated)
                break;
        }

        return forecasts.OrderBy(f => f.Turns).ThenBy(f => f.Message).ToArray();
    }

    public LevelState ActivateReactor(LevelState level)
    {
        if (!IsReactorReady(level))
            return level with { Global = level.Global with { Status = "REACTOR NOT READY" } };

        return level with {
            Global = level.Global with {
                ReactorActivated = true,
                Status = "REACTOR ONLINE"
            }
        };
    }

    private LevelState AdvanceTurn(LevelState level, bool updateForecasts)
    {
        var cells = level.Cells.ToArray();

        for (var y = Balancing.FirstGridCoordinate; y < level.Height; y++)
        {
            for (var x = Balancing.FirstGridCoordinate; x < level.Width; x++)
            {
                var position = new GridPosition(x, y);
                var index = level.Index(position);
                var cell = cells[index];

                if (!cell.IsWalkable)
                    continue;

                foreach (var effect in m_Effects)
                    cell = effect.Apply(cell);

                cells[index] = cell with { Hazards = cell.Hazards.Clamp() };
            }
        }

        foreach (var areaEffect in m_AreaEffects)
            cells = areaEffect.Apply(level, cells);

        var global = UpdateGlobal(level, cells);
        var next = level with {
            Cells = cells,
            Global = global with { Turn = level.Global.Turn + Balancing.TurnIncrement }
        };

        return updateForecasts ? next with { Forecasts = Forecast(next) } : next;
    }

    private void AddHazardForecasts(List<Forecast> forecasts, HashSet<ForecastKey> seen, LevelState level, int turns)
    {
        foreach (var hazard in m_Hazards)
        {
            foreach (var forecast in hazard.Predict(level, turns))
                AddForecast(forecasts, seen, forecast);
        }
    }

    private static void AddReactorReadyForecast(List<Forecast> forecasts, HashSet<ForecastKey> seen, LevelState level, int turns)
    {
        if (IsReactorReady(level))
            AddForecast(forecasts, seen, new(EFailureKind.ReactorReady, null, turns, "REACTOR READY"));
    }

    private static void AddForecast(List<Forecast> forecasts, HashSet<ForecastKey> seen, Forecast forecast)
    {
        if (seen.Add(new(forecast.Kind, forecast.Position)))
            forecasts.Add(forecast);
    }

    private static GlobalState UpdateGlobal(LevelState level, CellState[] cells)
    {
        var reactorHeat = cells.Where(c => c.Kind == ECellKind.Reactor).Select(c => c.Hazards.Heat).DefaultIfEmpty(level.Global.CoreHeat).Max();
        var poweredGenerators = cells.Count(c => c is { Kind: ECellKind.Generator, Powered: true, Hazards.Fire: false });
        var poweredPumps = cells.Count(c => c is { Kind: ECellKind.CoolingPump, Powered: true, Hazards.Fire: false });
        var damagedCriticalCells = cells.Count(c => c.Kind is ECellKind.Reactor or ECellKind.Generator or ECellKind.CoolingPump && c.Hazards.Stability <= Balancing.CriticalCellStabilityThreshold);
        var stability = Rules.Clamp(level.Global.FacilityStability - damagedCriticalCells);
        var lost = reactorHeat >= Balancing.MeltdownCoreHeatThreshold || stability <= Balancing.StabilityCollapseThreshold;
        var status = lost ? reactorHeat >= Balancing.MeltdownCoreHeatThreshold ? "CORE MELTDOWN" : "FACILITY STABILITY COLLAPSE" : "STABILIZE SYSTEMS";
        var global = level.Global with {
            CoreHeat = Rules.Clamp(reactorHeat - poweredPumps),
            Power = Rules.Clamp(poweredGenerators * Balancing.GeneratorPowerOutput),
            Cooling = Rules.Clamp(poweredPumps * Balancing.CoolingPumpOutput),
            FacilityStability = stability,
            Lost = lost,
            Status = status
        };

        return IsReactorReady(level with { Cells = cells, Global = global }) ? global with { Status = "REACTOR READY" } : global;
    }

    private static bool IsReactorReady(LevelState level)
    {
        var hasReactor = level.Cells.Any(c => c.Kind == ECellKind.Reactor);
        var hasStablePower = level.Global.Power >= Balancing.ReactorReadyPowerThreshold || level.Cells.Any(c => c is { Kind: ECellKind.Generator, Powered: true, Hazards.Fire: false });
        var hasCooling = level.Global.Cooling >= Balancing.ReactorReadyCoolingThreshold || level.Cells.Any(c => c is { Kind: ECellKind.CoolingPump, Powered: true, Hazards.Fire: false });
        var reactorStable = level.Global.CoreHeat < Balancing.ReactorReadyCoreHeatThreshold;
        return hasReactor && hasStablePower && hasCooling && reactorStable && !level.Global.Lost;
    }

    private readonly IReadOnlyList<IAreaSimulationEffect> m_AreaEffects = areaEffects.ToArray();
    private readonly IReadOnlyList<ISimulationEffect> m_Effects = effects.ToArray();
    private readonly IReadOnlyList<Hazard> m_Hazards = hazards.ToArray();
}