using System;
using System.Collections.Generic;
using MultiWheelC.TrajectoryPlanning.CoarsePath;
using MultiWheelC.TrajectoryPlanning.Utils;

namespace MultiWheelC.TrajectoryPlanning.EMPlanner;

/// <summary>Independently recomputes and verifies lateral world geometry before a path may be published.</summary>
public sealed class LateralSolutionValidator
{
    public bool TryValidate(LateralPlanningInput input, LateralCandidate candidate, LateralPath path,
        out LateralPath validatedPath, out string failureReason)
    {
        validatedPath = null;
        failureReason = string.Empty;
        if (input == null || candidate == null || path == null)
        {
            failureReason = "Lateral input, candidate, and reconstructed path are required.";
            return false;
        }
        if (path.Points.Count != input.ReferenceStations.Count || candidate.ReferenceStations.Count != path.Points.Count)
        {
            failureReason = "Lateral path point count does not match the candidate stations.";
            return false;
        }

        try
        {
            double spatialTolerance = RequireNonnegative(input.Configuration.Validation.SpatialToleranceMeters,
                "spatial tolerance");
            double kinematicTolerance = RequireNonnegative(input.Configuration.Validation.KinematicTolerance,
                "kinematic tolerance");
            double residualTolerance = RequireNonnegative(input.Configuration.Solver.StrictResidualTolerance,
                "strict residual tolerance");
            if (!ValidateCandidateConstraints(input, candidate, spatialTolerance, kinematicTolerance, residualTolerance,
                    out failureReason))
            {
                return false;
            }

            List<ExpectedSample> expected = ReconstructIndependently(input, candidate, out failureReason);
            if (expected == null)
                return false;
            if (!ComparePath(path, candidate, input.ReferenceStations, expected, spatialTolerance, kinematicTolerance,
                    out failureReason))
            {
                return false;
            }

            validatedPath = new LateralPath(path.Points, true);
            return true;
        }
        catch (ArgumentException exception)
        {
            failureReason = exception.Message;
            return false;
        }
    }

    private static bool ValidateCandidateConstraints(LateralPlanningInput input, LateralCandidate candidate,
        double spatialTolerance, double kinematicTolerance, double residualTolerance, out string failureReason)
    {
        failureReason = string.Empty;
        if (candidate.ReferenceStations.Count != input.ReferenceStations.Count)
        {
            failureReason = "Candidate station count does not match the input.";
            return false;
        }
        if (!candidate.SatisfiesExactDiscreteDynamics(residualTolerance))
        {
            failureReason = "Candidate violates exact lateral dynamics.";
            return false;
        }

        LateralConfiguration lateral = input.Configuration.Lateral;
        double maximumCurvature = GetMaximumVehicleCurvature(input.Vehicle);
        for (int index = 0; index < input.ReferenceStations.Count; index++)
        {
            if (Math.Abs(candidate.ReferenceStations[index] - input.ReferenceStations[index]) > spatialTolerance)
            {
                failureReason = "Candidate reference-S does not match the input at station " + index + ".";
                return false;
            }
            LateralInterval corridor = input.Corridor.Stations[index];
            double l = candidate.L[index];
            double dl = candidate.DL[index];
            double ddl = candidate.DDL[index];
            if (!IsFinite(l) || !IsFinite(dl) || !IsFinite(ddl) || l < corridor.MinimumL - spatialTolerance ||
                l > corridor.MaximumL + spatialTolerance || Math.Abs(l) > input.Configuration.Corridor.MaximumLateralOffsetMeters + spatialTolerance ||
                Math.Abs(dl) > lateral.MaximumLateralSlope + kinematicTolerance ||
                Math.Abs(ddl) > lateral.MaximumLateralSecondDerivativePerMeter + kinematicTolerance)
            {
                failureReason = "Candidate violates lateral corridor or derivative limits at station " + index + ".";
                return false;
            }
            FrenetReferencePoint reference = ReferencePathInterpolator.Interpolate(input.ReferenceSegment,
                input.ReferenceStations[index]);
            double denominator = 1d - reference.GeometricCurvature * l;
            if (!IsFinite(denominator) || denominator < input.Configuration.Frenet.MinimumFrenetDenominator - kinematicTolerance)
            {
                failureReason = "Candidate violates the Frenet denominator at station " + index + ".";
                return false;
            }
            double geometricCurvature = CalculateGeometricCurvature(reference, l, dl, ddl,
                (input.ReferenceSegment.Direction == TravelDirection.Forward ? 1d : -1d) * reference.VehicleCurvatureDerivative);
            double vehicleCurvature = (input.ReferenceSegment.Direction == TravelDirection.Forward ? 1d : -1d) *
                geometricCurvature;
            if (!IsFinite(geometricCurvature) || !IsFinite(vehicleCurvature) ||
                Math.Abs(vehicleCurvature) > maximumCurvature + kinematicTolerance)
            {
                failureReason = "Candidate violates vehicle curvature at station " + index + ".";
                return false;
            }
        }
        for (int index = 0; index < candidate.DDDL.Count; index++)
        {
            if (!IsFinite(candidate.DDDL[index]) ||
                Math.Abs(candidate.DDDL[index]) > lateral.MaximumLateralThirdDerivativePerSquareMeter + kinematicTolerance)
            {
                failureReason = "Candidate violates third-derivative limits at interval " + index + ".";
                return false;
            }
        }

        double startDenominator = 1d - input.StartProjection.ReferencePoint.GeometricCurvature *
            input.StartProjection.LateralOffset;
        double expectedStartDL = startDenominator * Math.Tan(input.StartProjection.HeadingError);
        if (!IsFinite(expectedStartDL) || Math.Abs(candidate.L[0] - input.StartProjection.LateralOffset) > spatialTolerance ||
            Math.Abs(candidate.DL[0] - expectedStartDL) > kinematicTolerance)
        {
            failureReason = "Candidate violates the lateral start state.";
            return false;
        }
        if (input.TerminalType != EmTerminalType.RollingSafetyStop &&
            (Math.Abs(candidate.L[candidate.L.Count - 1]) > spatialTolerance ||
             Math.Abs(candidate.DL[candidate.DL.Count - 1]) > kinematicTolerance))
        {
            failureReason = "Candidate violates the exact terminal lateral state.";
            return false;
        }
        return true;
    }

    private static List<ExpectedSample> ReconstructIndependently(LateralPlanningInput input, LateralCandidate candidate,
        out string failureReason)
    {
        failureReason = string.Empty;
        double minimumDenominator = input.Configuration.Frenet.MinimumFrenetDenominator;
        double directionSign = input.ReferenceSegment.Direction == TravelDirection.Forward ? 1d : -1d;
        var samples = new List<ExpectedSample>(candidate.ReferenceStations.Count);
        for (int index = 0; index < candidate.ReferenceStations.Count; index++)
        {
            FrenetReferencePoint reference = ReferencePathInterpolator.Interpolate(input.ReferenceSegment,
                candidate.ReferenceStations[index]);
            double l = candidate.L[index];
            double dl = candidate.DL[index];
            double ddl = candidate.DDL[index];
            double denominator = 1d - reference.GeometricCurvature * l;
            if (!IsFinite(denominator) || denominator < minimumDenominator)
            {
                failureReason = "Independent reconstruction found a Frenet denominator violation at station " + index + ".";
                return null;
            }
            double travelYaw = reference.TravelYaw + Math.Atan2(dl, denominator);
            double vehicleYaw = input.ReferenceSegment.Direction == TravelDirection.Forward
                ? AngleMath.NormalizeRadians(travelYaw)
                : AngleMath.NormalizeRadians(travelYaw + Math.PI);
            double geometricCurvature = CalculateGeometricCurvature(reference, l, dl, ddl,
                directionSign * reference.VehicleCurvatureDerivative);
            double vehicleCurvature = directionSign * geometricCurvature;
            double x = reference.X - l * Math.Sin(reference.TravelYaw);
            double y = reference.Y + l * Math.Cos(reference.TravelYaw);
            if (!IsFinite(x) || !IsFinite(y) || !IsFinite(travelYaw) || !IsFinite(vehicleYaw) ||
                !IsFinite(geometricCurvature) || !IsFinite(vehicleCurvature))
            {
                failureReason = "Independent reconstruction produced non-finite geometry at station " + index + ".";
                return null;
            }
            samples.Add(new ExpectedSample(candidate.ReferenceStations[index], x, y, vehicleYaw, geometricCurvature,
                vehicleCurvature));
        }

        samples[0].PathS = 0d;
        for (int index = 1; index < samples.Count; index++)
        {
            double dx = samples[index].X - samples[index - 1].X;
            double dy = samples[index].Y - samples[index - 1].Y;
            double chord = Math.Sqrt(dx * dx + dy * dy);
            if (!IsFinite(chord) || chord <= 0d)
            {
                failureReason = "Independent reconstruction found non-increasing PathS at station " + index + ".";
                return null;
            }
            samples[index].PathS = samples[index - 1].PathS + chord;
        }
        for (int index = 0; index < samples.Count; index++)
        {
            int lower = index == 0 ? 0 : index - 1;
            int upper = index == samples.Count - 1 ? samples.Count - 1 : index + 1;
            double span = samples[upper].PathS - samples[lower].PathS;
            if (!IsFinite(span) || span <= 0d)
            {
                failureReason = "Independent curvature derivative span is invalid at station " + index + ".";
                return null;
            }
            samples[index].VehicleCurvatureDerivative =
                (samples[upper].VehicleCurvature - samples[lower].VehicleCurvature) / span;
        }
        return samples;
    }

    private static bool ComparePath(LateralPath path, LateralCandidate candidate, IReadOnlyList<double> stations,
        IReadOnlyList<ExpectedSample> expected, double spatialTolerance, double kinematicTolerance,
        out string failureReason)
    {
        failureReason = string.Empty;
        for (int index = 0; index < path.Points.Count; index++)
        {
            LateralPathPoint actual = path.Points[index];
            ExpectedSample sample = expected[index];
            double dddl = candidate.DDDL[Math.Min(index, candidate.DDDL.Count - 1)];
            if (!AreClose(actual.ReferenceS, stations[index], spatialTolerance) ||
                !AreClose(actual.PathS, sample.PathS, spatialTolerance) ||
                !AreClose(actual.L, candidate.L[index], spatialTolerance) ||
                !AreClose(actual.DL, candidate.DL[index], kinematicTolerance) ||
                !AreClose(actual.DDL, candidate.DDL[index], kinematicTolerance) ||
                !AreClose(actual.DDDL, dddl, kinematicTolerance) ||
                !AreClose(actual.X, sample.X, spatialTolerance) || !AreClose(actual.Y, sample.Y, spatialTolerance) ||
                Math.Abs(AngleMath.NormalizeRadians(actual.VehicleYaw - sample.VehicleYaw)) > kinematicTolerance ||
                !AreClose(actual.GeometricCurvature, sample.GeometricCurvature, kinematicTolerance) ||
                !AreClose(actual.VehicleCurvature, sample.VehicleCurvature, kinematicTolerance) ||
                !AreClose(actual.VehicleCurvatureDerivative, sample.VehicleCurvatureDerivative, kinematicTolerance))
            {
                failureReason = "Independent lateral geometry validation failed at station " + index + ".";
                return false;
            }
            if (index == 0 && Math.Abs(actual.PathS) > spatialTolerance)
            {
                failureReason = "PathS must start at zero.";
                return false;
            }
            if (index > 0 && actual.PathS <= path.Points[index - 1].PathS + spatialTolerance)
            {
                failureReason = "PathS must be strictly increasing.";
                return false;
            }
        }
        return true;
    }

    private static double CalculateGeometricCurvature(FrenetReferencePoint reference, double l, double dl, double ddl,
        double referenceCurvatureDerivative)
    {
        double a = 1d - reference.GeometricCurvature * l;
        double denominatorSquared = a * a + dl * dl;
        double numerator = a * a * reference.GeometricCurvature + a * ddl +
            referenceCurvatureDerivative * l * dl + 2d * reference.GeometricCurvature * dl * dl;
        return numerator / (denominatorSquared * Math.Sqrt(denominatorSquared));
    }

    private static double GetMaximumVehicleCurvature(VehicleParameters vehicle)
    {
        if (vehicle == null)
            throw new ArgumentNullException(nameof(vehicle));
        if (vehicle.MaximumCurvaturePerMeter.HasValue)
            return RequirePositive(vehicle.MaximumCurvaturePerMeter.Value, "vehicle maximum curvature");
        if (vehicle.MinimumTurningRadiusMeters.HasValue)
            return 1d / RequirePositive(vehicle.MinimumTurningRadiusMeters.Value, "vehicle minimum turning radius");
        throw new ArgumentException("Vehicle maximum curvature is required.", nameof(vehicle));
    }

    private static bool AreClose(double actual, double expected, double tolerance)
    {
        return IsFinite(actual) && IsFinite(expected) && Math.Abs(actual - expected) <= tolerance;
    }

    private static double RequirePositive(double value, string name)
    {
        if (!IsFinite(value) || value <= 0d)
            throw new ArgumentOutOfRangeException(name);
        return value;
    }

    private static double RequireNonnegative(double value, string name)
    {
        if (!IsFinite(value) || value < 0d)
            throw new ArgumentOutOfRangeException(name);
        return value;
    }

    private static bool IsFinite(double value)
    {
        return !double.IsNaN(value) && !double.IsInfinity(value);
    }

    private sealed class ExpectedSample
    {
        public ExpectedSample(double referenceS, double x, double y, double vehicleYaw, double geometricCurvature,
            double vehicleCurvature)
        {
            ReferenceS = referenceS;
            X = x;
            Y = y;
            VehicleYaw = vehicleYaw;
            GeometricCurvature = geometricCurvature;
            VehicleCurvature = vehicleCurvature;
        }

        public double ReferenceS { get; }
        public double X { get; }
        public double Y { get; }
        public double VehicleYaw { get; }
        public double GeometricCurvature { get; }
        public double VehicleCurvature { get; }
        public double PathS { get; set; }
        public double VehicleCurvatureDerivative { get; set; }
    }
}