using System;

using UnityEngine;

namespace Framework.Geometry {

  /// <summary>Helper methods for calculating ballistic trajectories*</summary>
  public static class Trajectory {

/*
    private static Vector3 PlotTrajectoryAtTime (Vector3 start, Vector3 startVelocity, float time) {
      return start + startVelocity*time + Physics.gravity*time*time*0.5f;
    }
*/
/*
    private static float getParabolaY(float width, float height, float x) {
      float a = height / squared(width / 2.0f);
      float b = height;
      float c = width / 2.0f;

      return (a * squared(x - c)) + b;
    }
*/


    /// <summary>Calculates the Y coordinate of a parabola from its X coordinate</summary>
    /// <param name="jumpOffVelocity">Jump off velocity the parabola started with</param>
    /// <param name="x">X coordinate at which the Y coordinate should be calculated</param>
    /// <returns>The parabola's Y coordinate at the specified X coordinate</returns>
    public static float GetParabolaY(float jumpOffVelocity, float x) {
      return 0.5f * -Math.Abs(Physics.gravity.y) * squared(x) + (jumpOffVelocity * x);
    }

    /// <summary>Calculates the initial velocity required to reach a specific height</summary>
    /// <param name="apexHeight">Height the trajectory should reach</param>
    /// <returns>The initial velocity required to reach the specified height</returns>
    public static float GetJumpOffVelocity(float apexHeight) {
      return Mathf.Sqrt(2.0f * Mathf.Abs(Physics.gravity.y) * apexHeight);
    }

    /// <summary>Calculates for how long a projectile will be airborne</summary>
    /// <param name="jumpOffVelocity">Jump off velocity the projectile started from</param>
    /// <returns>The time until the projectile hits the ground again</returns>
    public static float GetTimeInFlight(float jumpOffVelocity) {
      return jumpOffVelocity / Math.Abs(Physics.gravity.y) * 2.0f;
    }

    /// <summary>Returns the square of the input value</summary>
    /// <param name="value">Value that will be squared</param>
    /// <returns>The square of the specified value</returns>
    private static float squared(float value) { return value * value; }

  }

} // namespace Framework.Geometry