using CounterStrikeSharp.API;
using CounterStrikeSharp.API.Core;
using Vector = CounterStrikeSharp.API.Modules.Utils.Vector;

namespace NoGoZones;

// Logical barrier: CSS can't give a spawned entity a custom-size collision shape (see README), so
// zones are enforced by moving players back out every tick.
//
// Works on the player's origin against the zone box grown by the player's hull (Minkowski sum),
// so the whole hull is kept out, not just the feet. Each tick it compares last tick's origin to
// this tick's: if the step crossed into a zone, the player is put back on the face they came
// through, keeping their movement along the face (so walls slide, and the top can be stood on).
// Sweeping the step also stops fast players from skipping over a thin zone between two ticks.
public class Blocker
{
    private const float Epsilon = 0.05f;

    // Used if a pawn's collision property isn't readable.
    private static readonly Point3 DefaultHullMins = new(-16f, -16f, 0f);
    private static readonly Point3 DefaultHullMaxs = new(16f, 16f, 72f);

    private readonly Dictionary<uint, Point3> _lastOrigin = [];

    public void Reset() => _lastOrigin.Clear();

    public void Forget(uint pawnIndex) => _lastOrigin.Remove(pawnIndex);

    public void Tick(IReadOnlyList<Zone> zones, bool ignoreNoclip)
    {
        if (zones.Count == 0)
        {
            _lastOrigin.Clear();
            return;
        }

        foreach (var player in Utilities.GetPlayers())
        {
            if (player is not { IsValid: true, PawnIsAlive: true })
                continue;
            var pawn = player.PlayerPawn.Value;
            if (pawn is not { IsValid: true } || pawn.AbsOrigin is not { } absOrigin)
                continue;

            var origin = Point3.From(absOrigin);
            var index = pawn.Index;

            if (ignoreNoclip && pawn.MoveType == MoveType_t.MOVETYPE_NOCLIP)
            {
                _lastOrigin[index] = origin;
                continue;
            }

            var (hullMins, hullMaxs) = Hull(pawn);
            var previous = _lastOrigin.TryGetValue(index, out var last) ? last : origin;
            var velocity = pawn.AbsVelocity;
            var v = new Point3(velocity.X, velocity.Y, velocity.Z);
            var moved = false;

            // Horizontal hull half-widths; the hull is centred on the origin in X/Y.
            float hx = MathF.Max(MathF.Abs(hullMins.X), MathF.Abs(hullMaxs.X));
            float hy = MathF.Max(MathF.Abs(hullMins.Y), MathF.Abs(hullMaxs.Y));

            foreach (var zone in zones)
            {
                if (!zone.Active)
                    continue;

                // Work in the zone's own frame. A turned zone sees the (world-aligned) hull as wider,
                // so grow it by the hull's extent along each local axis.
                var shape = zone.Shape;
                float c = MathF.Abs(shape.Cos), s = MathF.Abs(shape.Sin);
                float ex = hx * c + hy * s, ey = hx * s + hy * c;

                // Region the origin must stay out of.
                var lo = new Point3(shape.Mins.X - ex, shape.Mins.Y - ey, shape.Mins.Z - hullMaxs.Z);
                var hi = new Point3(shape.Maxs.X + ex, shape.Maxs.Y + ey, shape.Maxs.Z - hullMins.Z);

                var localOrigin = shape.ToLocal(origin);
                var localV = shape.ToLocal(v);
                if (Resolve(shape.ToLocal(previous), ref localOrigin, ref localV, lo, hi))
                {
                    origin = shape.ToWorld(localOrigin);
                    v = shape.ToWorld(localV);
                    moved = true;
                }
            }

            if (moved)
                pawn.Teleport(origin.ToVector(), null, v.ToVector());

            _lastOrigin[index] = origin;
        }
    }

    private static (Point3, Point3) Hull(CCSPlayerPawn pawn)
    {
        var collision = pawn.Collision;
        if (collision == null)
            return (DefaultHullMins, DefaultHullMaxs);
        var mins = Point3.From(collision.Mins);
        var maxs = Point3.From(collision.Maxs);
        // A zero-size hull means the property wasn't populated; don't let that shrink the zone.
        return maxs.X - mins.X < 1f ? (DefaultHullMins, DefaultHullMaxs) : (mins, maxs);
    }

    private static bool Inside(Point3 p, Point3 lo, Point3 hi) =>
        p.X > lo.X && p.X < hi.X && p.Y > lo.Y && p.Y < hi.Y && p.Z > lo.Z && p.Z < hi.Z;

    // Returns true if origin/velocity were changed.
    private static bool Resolve(Point3 from, ref Point3 to, ref Point3 v, Point3 lo, Point3 hi)
    {
        if (Inside(from, lo, hi))
        {
            // Already inside last tick (zone created on top of them, spawn, teleport): push out
            // along the shallowest face.
            if (!Inside(to, lo, hi))
                return false;
            PushOutShallowest(ref to, ref v, lo, hi);
            return true;
        }

        // Slab test on the segment from -> to: find where it enters the box, and through which face.
        float tEnter = 0f, tExit = 1f;
        int axis = -1;
        bool fromLow = false;
        for (var a = 0; a < 3; a++)
        {
            float p0 = Get(from, a), d = Get(to, a) - p0, l = Get(lo, a), h = Get(hi, a);
            if (MathF.Abs(d) < 1e-6f)
            {
                if (p0 <= l || p0 >= h)
                    return false; // parallel to this slab and outside it
                continue;
            }
            float t1 = (l - p0) / d, t2 = (h - p0) / d;
            bool enterLow = t1 < t2;
            if (!enterLow)
                (t1, t2) = (t2, t1);
            if (t1 > tEnter)
            {
                tEnter = t1;
                axis = a;
                fromLow = enterLow;
            }
            tExit = MathF.Min(tExit, t2);
            if (tEnter > tExit)
                return false;
        }
        if (axis < 0)
            return false;

        // Clamp just outside the entry face and kill velocity into it; the other two axes keep
        // this tick's movement, so the player slides along the face.
        Set(ref to, axis, fromLow ? Get(lo, axis) - Epsilon : Get(hi, axis) + Epsilon);
        var va = Get(v, axis);
        if (fromLow ? va > 0 : va < 0)
            Set(ref v, axis, 0f);
        return true;
    }

    private static void PushOutShallowest(ref Point3 p, ref Point3 v, Point3 lo, Point3 hi)
    {
        int best = 0;
        bool toLow = true;
        float bestDepth = float.MaxValue;
        for (var a = 0; a < 3; a++)
        {
            float down = Get(p, a) - Get(lo, a), up = Get(hi, a) - Get(p, a);
            if (down < bestDepth) { bestDepth = down; best = a; toLow = true; }
            if (up < bestDepth) { bestDepth = up; best = a; toLow = false; }
        }
        Set(ref p, best, toLow ? Get(lo, best) - Epsilon : Get(hi, best) + Epsilon);
        Set(ref v, best, 0f);
    }

    private static float Get(Point3 p, int axis) => axis switch { 0 => p.X, 1 => p.Y, _ => p.Z };

    private static void Set(ref Point3 p, int axis, float value)
    {
        switch (axis)
        {
            case 0: p.X = value; break;
            case 1: p.Y = value; break;
            default: p.Z = value; break;
        }
    }
}