using System.Collections;
using UnityEngine;

public class BallLauncher : MonoBehaviour
{

	public Rigidbody ball;
	public Transform target;

	public float h = 25;
	public float gravity = -18;

	public bool debugPath;

	public LineRenderer line;

	void Start ()
	{
		ball.useGravity = false;
	}

	void Update ()
	{
		if (Input.GetKeyDown (KeyCode.Space))
		{
			Launch ();
		}

		if (debugPath)
		{
			DrawPath ();
		}
	}

	void Launch ()
	{
		Physics.gravity = Vector3.up * gravity;
		ball.useGravity = true;
		ball.velocity = CalculateLaunchData ().initialVelocity;
	}

	LaunchData CalculateLaunchData ()
	{
		float displacementY = target.position.y - ball.position.y;
		Vector3 displacementXZ = new Vector3 (target.position.x - ball.position.x, 0, target.position.z - ball.position.z);
		float time = Mathf.Sqrt (-2 * h / gravity) + Mathf.Sqrt (2 * (displacementY - h) / gravity);
		Vector3 velocityY = Vector3.up * Mathf.Sqrt (-2 * gravity * h);
		Vector3 velocityXZ = displacementXZ / time;

		return new LaunchData (velocityXZ + velocityY * -Mathf.Sign (gravity), time);
	}

	void DrawPath ()
	{
		LaunchData launchData = CalculateLaunchData ();
		Vector3 previousDrawPoint = ball.position;

		int resolution = 30;
		for (int i = 1; i <= resolution; i++)
		{
			float simulationTime = i / (float) resolution * launchData.timeToTarget;
			Vector3 displacement = launchData.initialVelocity * simulationTime + Vector3.up * gravity * simulationTime * simulationTime / 2f;
			Vector3 drawPoint = ball.position + displacement;

			Debug.DrawLine (previousDrawPoint, drawPoint, Color.green);
			previousDrawPoint = drawPoint;
		}
	}

	struct LaunchData
	{
		public readonly Vector3 initialVelocity;
		public readonly float timeToTarget;

		public LaunchData (Vector3 initialVelocity, float timeToTarget)
		{
			this.initialVelocity = initialVelocity;
			this.timeToTarget = timeToTarget;
		}

	}
}