using System.Collections.Generic;
using System.Reflection;
using Helpers;
using HarmonyLib;
using Model;
using Model.Physics;
using Track;
using UnityEngine;

namespace RailroaderPhysicsOverhaul;

public static class ConsistLOD
{
    public static bool  Enabled           = true;
    public static float DistanceThreshold = 30f;
    // Must be a power of 2 (1, 2, 4, 8, 16). 1 = full path every tick (no dead-reckoning).
    public static int   ResyncInterval    = 4;

    // Blacklist/whitelist — when enabled, filters which consists get LOD treatment.
    public static bool ExcludeLocomotives = true;
    public static bool BlacklistEnabled   = false;
    public static bool IsBlacklist      = true; // true = listed consists skip LOD; false = only listed use LOD
    public static readonly HashSet<string> RoadNumberList = new(System.StringComparer.OrdinalIgnoreCase);

    public static int _globalTick = 0;
    public static int LastFastPathCount;
    public static int LastFullPathCount;

    // Per-tick sets for debug visualization — cleared at FixedUpdate start, populated by the patch.
    public static readonly HashSet<Car> FastPathCars = new();
    public static readonly HashSet<Car> FullPathCars = new();

    static float DistanceSq => DistanceThreshold * DistanceThreshold;

    // Per-consist LOD eligibility cache — rebuilt lazily, flushed periodically and on settings change.
    // IntegrationSet is not a UnityEngine.Object, so we key by reference identity.
    static readonly Dictionary<IntegrationSet, bool> _consistCache = new();
    public static void InvalidateConsistCache() => _consistCache.Clear();

    internal static bool ShouldUseFastPath(Car car)
    {
        if (!Enabled) return false;
        if (ExcludeLocomotives && car is Model.BaseLocomotive) return false;
        if (!car.EndGearA.IsCoupled || !car.EndGearB.IsCoupled) return false;
        if (car.BodyTransform == null) return false;
        Camera cam = Camera.main;
        if (cam == null) return false;
        if ((car.BodyTransform.position - cam.transform.position).sqrMagnitude <= DistanceSq)
            return false;

        // Blacklist/whitelist — cached per IntegrationSet instance ID to avoid per-car scanning.
        if (BlacklistEnabled && car.set != null)
        {
            if (!_consistCache.TryGetValue(car.set, out bool allowed))
            {
                allowed = IsConsistAllowed(car.set);
                _consistCache[car.set] = allowed;
            }
            if (!allowed) return false;
        }

        return true;
    }

    static bool IsConsistAllowed(IntegrationSet set)
    {
        if (RoadNumberList.Count == 0) return true; // empty list = no filtering
        bool hasMatch = false;
        foreach (Car c in set.Cars)
        {
            // Accept a match against the full display name ("UP 1492"), the road number
            // alone ("1492"), or the reporting mark alone ("UP") — users naturally type
            // whichever they remember, so don't require the exact concatenated string.
            if (RoadNumberList.Contains(c.DisplayName) ||
                RoadNumberList.Contains(c.Ident.RoadNumber) ||
                RoadNumberList.Contains(c.Ident.ReportingMark))
            {
                hasMatch = true;
                break;
            }
        }
        // Blacklist: a match means this consist is NOT allowed to use LOD.
        // Whitelist: no match means this consist is NOT allowed to use LOD.
        return IsBlacklist ? !hasMatch : hasMatch;
    }
}

// Cached accessor for Car._mover (internal field — reflection needed from our assembly).
// CarMover.Move() is public, so once we have the instance we call it directly.
static class CarMoverAccess
{
    static readonly FieldInfo Field =
        typeof(Car).GetField("_mover", BindingFlags.Instance | BindingFlags.NonPublic);

    public static CarMover Get(Car car) => (CarMover)Field.GetValue(car);
}

[HarmonyPatch(typeof(Car), "PositionWheelBoundsFront")]
static class PositionWheelBoundsFrontLODPatch
{
    static int _fastCount;
    static int _fullCount;

    public static void ResetFrameCounts()
    {
        ConsistLOD.LastFastPathCount = _fastCount;
        ConsistLOD.LastFullPathCount = _fullCount;
        _fastCount = 0;
        _fullCount = 0;
    }

    static bool Prefix(Car __instance, Location wheelBoundsF, Graph graph, bool update,
                       ref Location __result)
    {
        if (!update || !ConsistLOD.ShouldUseFastPath(__instance))
        {
            _fullCount++;
            ConsistLOD.FullPathCars.Add(__instance);
            return true; // run original
        }

        // Fibonacci hash: 4-bit result (0-15) distributes Unity InstanceIDs evenly
        // and supports ResyncInterval 1/2/4/8 via modular comparison.
        int id     = __instance.GetInstanceID();
        int bucket = (int)(((uint)id * 2654435761u) >> 28) & 0xF;
        bool isResync = ConsistLOD.ResyncInterval <= 1 ||
            ConsistLOD._globalTick % ConsistLOD.ResyncInterval == bucket % ConsistLOD.ResyncInterval;

        if (isResync)
        {
            _fullCount++;
            ConsistLOD.FastPathCars.Add(__instance); // logically fast-path, just doing a scheduled sync
            return true; // let original run this tick
        }

        _fastCount++;
        ConsistLOD.FastPathCars.Add(__instance);

        // 1. Update track physics bounds — constraint solver and couplers need these.
        float boundsSpan = __instance.carLength - __instance.wheelInsetF - __instance.wheelInsetR;
        Location wbR = graph.LocationByMoving(wheelBoundsF, -boundsSpan);
        __instance.WheelBoundsF = wheelBoundsF;
        __instance.WheelBoundsR = wbR;
        __result = wbR;

        // Keep LogicalEnd locations in sync — used by CarDidPosition's segment-cache
        // and coupler placement when the culler transitions distance bands.
        __instance.LocationF = graph.LocationByMoving(wheelBoundsF,  __instance.wheelInsetF, false, Graph.EndOfTrackHandling.Unclamped);
        __instance.LocationR = graph.LocationByMoving(wbR,           -__instance.wheelInsetR, false, Graph.EndOfTrackHandling.Unclamped);

        // 2. Replicate SetBodyPosition's chord-based rotation: LookRotation between
        //    the front and rear TRUCK positions, matching the game's exact formula.
        //    Use the same graph instance and the same PositionAccuracy as PositionWheelBoundsFront
        //    would choose (IsVisible ? High : Standard) so the position is byte-for-byte identical
        //    to the full path — preventing a positional jump when the camera closes in.
        float halfTruckSpan = (__instance.carLength - __instance.truckSeparation) / 2f;
        Location truckFLoc  = graph.LocationByMoving(wheelBoundsF, -(halfTruckSpan - __instance.wheelInsetF));
        Location truckRLoc  = graph.LocationByMoving(truckFLoc,    -__instance.truckSeparation);
        PositionAccuracy accuracy = __instance.IsVisible ? PositionAccuracy.High : PositionAccuracy.Standard;
        var prF = graph.GetPositionRotation(truckFLoc, accuracy);
        var prR = graph.GetPositionRotation(truckRLoc, accuracy);

        Vector3 avgUp      = Vector3.Lerp(prF.Rotation * Vector3.up, prR.Rotation * Vector3.up, 0.5f);
        Quaternion bodyRot = Quaternion.LookRotation(prF.Position - prR.Position, avgUp);
        Vector3 gameCenter  = Vector3.Lerp(prF.Position, prR.Position, 0.5f);
        Vector3 worldCenter = WorldTransformer.GameToWorld(gameCenter);

        // 3. Drive _mover.Move() exactly as SetBodyPosition does.
        //    This keeps _moverPosition current every fast-path tick so:
        //    a) Camera-follow code (which reads _moverPosition) sees correct position.
        //    b) On the next resync tick, _velocity = Δpos/dt ≈ actual v, not N×v,
        //       so the rigidbody isn't slammed backward causing a snap.
        CarMoverAccess.Get(__instance).Move(worldCenter, bodyRot, immediate: false);

        // 4. TagCallout is only updated inside SetBodyPosition; keep it in sync here.
        __instance.TagCallout?.SetPosition(worldCenter);

        // 5. Fire OnPosition so TrainController.CarDidPosition runs: this updates the
        //    spatial-hash, car-culler sphere (distance-band gating), and segment cache.
        //    Without this the culler's bounding sphere stays frozen at the last resync
        //    position, causing stale IsVisible / IsNearby states on fast-path ticks.
        __instance.OnPosition?.Invoke(gameCenter, bodyRot);

        return false; // skip original PositionWheelBoundsFront + SetBodyPosition
    }
}

[HarmonyPatch(typeof(TrainController), "FixedUpdate")]
static class TrainControllerFixedUpdateCounterPatch
{
    static void Prefix()
    {
        ConsistLOD._globalTick++;
        ConsistLOD.FastPathCars.Clear();
        ConsistLOD.FullPathCars.Clear();
        PositionWheelBoundsFrontLODPatch.ResetFrameCounts();
        ConsistFreezer.FlushFrameCounts();

        // Periodic consist cache flush — silently handles couple/decouple events
        // without needing to patch the coupler system. ~12 s at 50 Hz.
        if (ConsistLOD._globalTick % 600 == 0)
            ConsistLOD.InvalidateConsistCache();
    }
}