using Machines.Race;

namespace Machines.Player;

/// <summary>
/// Handles drift decisions for bots; simple but effective
/// </summary>
public sealed class BotDriftController
{
	private bool _isDrifting;
	private float _driftTimer;
	private int _driftDirection;
	private float _cooldown;

	/// <summary>
	/// Look-ahead time (s) when scanning for corners
	/// </summary>
	private const float ScanTimeAhead = 0.8f;

	/// <summary>
	/// Force drift on every detected corner regardless of arc length
	/// </summary>
	[ConVar( "bot_force_drift" )]
	public static bool ForceDrift { get; set; } = false;

	/// <summary>
	/// Updates drift decision for this frame, writing <see cref="CarInputData.Drift"/>
	/// </summary>
	public void Update( ref CarInputData data, float speed, RacingLine line, float pathDistance, bool canStart, Car car = null, float driftChance = 1f )
	{
		if ( _cooldown > 0f )
			_cooldown -= Time.Delta;

		if ( _isDrifting )
		{
			_driftTimer += Time.Delta;

			// Sample curvature ahead of the bot - exit early before the corner ends
			var lookAhead = MathF.Max( speed * 0.15f, 50f );
			var curvAhead = line?.GetCurvatureAtDistance( pathDistance + lookAhead ) ?? 0f;
			var curvNow = line?.GetCurvatureAtDistance( pathDistance ) ?? 0f;

			// Exit when the road ahead is straightening out
			var exitThreshold = 0.001f;
			var cornerEnding = _driftTimer > 0.25f && curvAhead < exitThreshold;

			// Exit if heading diverges too far from the racing line
			var headingBad = false;
			if ( car?.Movement != null && line != null && _driftTimer > 0.3f )
			{
				var carForward = car.Movement.GameObject.WorldRotation.Forward.WithZ( 0f ).Normal;
				var lineTangent = line.GetTangentAtDistance( pathDistance + lookAhead );
				var dot = Vector3.Dot( carForward, lineTangent );
				headingBad = dot < 0.6f;
			}

			var tooSlow = speed < 80f;
			var maxDuration = _driftTimer >= 1.5f;

			if ( cornerEnding || headingBad || tooSlow || maxDuration )
			{
				_isDrifting = false;
				_driftTimer = 0f;
				data.Drift = false;
				_cooldown = car?.Drift?.DriftCooldown ?? 0.5f;
			}
			else
			{
				data.Drift = true;
				var steerPush = MathF.Min( 0.3f, curvNow * 150f );
				data.Steer = (data.Steer + _driftDirection * steerPush).Clamp( -1f, 1f );
			}
		}
		else if ( canStart && _cooldown <= 0f && speed > 100f && line != null && car?.ActiveStats != null )
		{
			TryInitiateDrift( ref data, speed, line, pathDistance, car, driftChance );
		}
	}

	private void TryInitiateDrift( ref CarInputData data, float speed, RacingLine line, float pathDistance, Car car, float driftChance )
	{
		var stats = car.ActiveStats;

		var scanDist = speed * ScanTimeAhead;
		var step = RacingLine.CurvatureStep;
		var steps = (int)(scanDist / step);
		if ( steps < 2 ) return;

		// Force mode: near-zero catches any bend; normal mode: >15% steer input
		var steerForDrift = ForceDrift ? 0.02f : 0.15f;
		var driftThreshold = (steerForDrift * stats.TurnRate * MathF.PI / 180f) / MathF.Max( speed, 100f );

		// Find contiguous corner section
		float cornerStart = 0f, cornerEnd = 0f;
		bool inCorner = false;

		for ( int i = 1; i <= steps; i++ )
		{
			var d = pathDistance + i * step;
			var curv = line.GetCurvatureAtDistance( d );

			if ( curv >= driftThreshold )
			{
				if ( !inCorner )
				{
					inCorner = true;
					cornerStart = d;
				}
				cornerEnd = d;
			}
			else if ( inCorner )
			{
				break;
			}
		}

		if ( !inCorner ) return;

		var arcLength = cornerEnd - cornerStart;

		// Arc must be long enough to charge boost (skipped in force mode)
		if ( !ForceDrift )
		{
			var minArc = speed * stats.MinDriftTimeForBoost;
			if ( arcLength < minArc * 0.7f ) return;
		}

		// Determine corner direction from tangent change
		var mid = cornerStart + MathF.Max( arcLength * 0.5f, 10f );
		var t1 = line.GetTangentAtDistance( mid - 20f );
		var t2 = line.GetTangentAtDistance( mid + 20f );
		var direction = Vector3.Cross( t1, t2 ).z > 0f ? 1 : -1;

		// Wait until near corner entry
		var distToEntry = cornerStart - pathDistance;
		if ( distToEntry < 0f ) distToEntry += line.TotalLength;

		var entryLead = speed * 0.15f;
		if ( distToEntry > entryLead )
			return;

		// Skip based on driver's drift chance
		if ( !ForceDrift && Game.Random.Float() > driftChance )
		{
			_cooldown = 0.5f; // Avoid re-checking the same corner every frame
			return;
		}

		// Commit
		_isDrifting = true;
		_driftTimer = 0f;
		_driftDirection = direction;
		data.Drift = true;
		data.Steer = (data.Steer + _driftDirection * 0.3f).Clamp( -1f, 1f );
	}

	/// <summary>
	/// Clears drift state after a respawn/teleport
	/// </summary>
	public void Reset()
	{
		_isDrifting = false;
		_driftTimer = 0f;
		_cooldown = 0f;
		_driftDirection = 0;
	}
}