using System;
using System.Collections.Generic;
using Godot.Collections;

namespace Pong.Scripts.Objects;

public partial class Enemy : RigidBody2D
{
	/// <summary>
	/// draw shapes to the screen (like <see cref="_scanArea"/>).
	/// </summary>
	[Export] private bool _drawDebugShapes;
	[Export] private double _moveSpeed;

	private CollisionShape2D _collisionShape;
	private Rect2 _scanArea;
	
	private PhysicsDirectSpaceState2D _spaceState;
	private readonly Variant _collider = "collider";
	private PhysicsShapeQueryParameters2D _query;

	public override void _Ready()
	{
		_collisionShape = GetNode<CollisionShape2D>("CollisionShape2D");
		GenerateCastArea();
		
		_spaceState = GetWorld2D().DirectSpaceState;
		_query = new PhysicsShapeQueryParameters2D
		{
			Shape = new RectangleShape2D { Size = _scanArea.Size },
			Exclude = new Array<Rid>(new[] { GetRid() })
		};
	}

	public override void _PhysicsProcess(double delta)
	{
		Scan(delta);
	}

	public override void _Draw()
	{
		if (!_drawDebugShapes) return;
		DrawRect(_scanArea, Colors.Aqua);
	}

	private void Scan(double delta)
	{
		var result = _spaceState.IntersectShape(_query);

		if (result.Count <= 0)
		{
			LinearVelocity = Vector2.Zero;
			return;
		}

		TrackBall(delta, result);
	}

	/// <summary>
	/// track the distance between the ball and the enemy paddle on the y axis and move velocity accordingly.
	/// </summary>
	/// <param name="delta">how long it took to complete the last frame in seconds. this should be constant as
	/// should be executed in the physics process method which should be separate from the main frame rate.</param>
	/// <param name="result">a dictionary of objects that collided with the cast. this method only works if
	/// theres an object that has the Ball class.</param>
	private void TrackBall(double delta, IReadOnlyList<Dictionary> result)
	{
		// checks if the collider is a ball, if not, return.
		if (result[0][_collider].As<Ball>() is not { } ball) return;

		// gets the sign of the distance between the ball and the paddle on the y axis
		var normalisedDistance = new Vector2 { Y = Mathf.Sign(ball.Position.Y - Position.Y) };
		var linearVelocity = normalisedDistance * _moveSpeed * Constants.Meter;

		// lerp the velocity to smooth out jerky movement.
		LinearVelocity = LinearVelocity.Lerp(linearVelocity, delta);
	}

	/// <summary>
	/// generate the shape that the cast uses to detect collisions.
	/// </summary>
	/// <exception cref="InvalidOperationException">if the collision shape is not a rectangle shape.</exception>
	private void GenerateCastArea()
	{
		if (_collisionShape.Shape is not RectangleShape2D shape)
			throw new InvalidOperationException("the collision shape needs to be a rectangle shape");

		// grow the area the enemy can see by around half of the screen area.
		_scanArea = shape.GetRect().GrowSide(Side.Left, 400).GrowIndividual(0, 190, 0, 190);
	}
}