// Copyright (c) FIRST and other WPILib contributors.
// Open Source Software; you can modify and/or share it under the terms of
// the WPILib BSD license file in the root directory of this project.

package edu.wpi.first.math.controller;

import edu.wpi.first.math.controller.proto.ArmFeedforwardProto;
import edu.wpi.first.math.controller.struct.ArmFeedforwardStruct;
import edu.wpi.first.math.jni.ArmFeedforwardJNI;
import edu.wpi.first.util.protobuf.ProtobufSerializable;
import edu.wpi.first.util.struct.StructSerializable;

/**
 * A helper class that computes feedforward outputs for a simple arm (modeled as a motor acting
 * against the force of gravity on a beam suspended at an angle).
 */
public class ArmFeedforward implements ProtobufSerializable, StructSerializable {
  /** The static gain, in volts. */
  private double ks;

  /** The gravity gain, in volts. */
  private double kg;

  /** The velocity gain, in V/(rad/s). */
  private double kv;

  /** The acceleration gain, in V/(rad/s²). */
  private double ka;

  /** The period, in seconds. */
  private final double m_dt;

  /**
   * Creates a new ArmFeedforward with the specified gains and period.
   *
   * @param ks The static gain in volts.
   * @param kg The gravity gain in volts.
   * @param kv The velocity gain in V/(rad/s).
   * @param ka The acceleration gain in V/(rad/s²).
   * @param dt The period in seconds.
   * @throws IllegalArgumentException for kv < zero.
   * @throws IllegalArgumentException for ka < zero.
   * @throws IllegalArgumentException for period ≤ zero.
   */
  public ArmFeedforward(double ks, double kg, double kv, double ka, double dt) {
    this.ks = ks;
    this.kg = kg;
    this.kv = kv;
    this.ka = ka;
    if (kv < 0.0) {
      throw new IllegalArgumentException("kv must be a non-negative number, got " + kv + "!");
    }
    if (ka < 0.0) {
      throw new IllegalArgumentException("ka must be a non-negative number, got " + ka + "!");
    }
    if (dt <= 0.0) {
      throw new IllegalArgumentException("period must be a positive number, got " + dt + "!");
    }
    m_dt = dt;
  }

  /**
   * Creates a new ArmFeedforward with the specified gains. The period is defaulted to 20 ms.
   *
   * @param ks The static gain in volts.
   * @param kg The gravity gain in volts.
   * @param kv The velocity gain in V/(rad/s).
   * @param ka The acceleration gain in V/(rad/s²).
   * @throws IllegalArgumentException for kv &lt; zero.
   * @throws IllegalArgumentException for ka &lt; zero.
   */
  public ArmFeedforward(double ks, double kg, double kv, double ka) {
    this(ks, kg, kv, ka, 0.020);
  }

  /**
   * Creates a new ArmFeedforward with the specified gains. The period is defaulted to 20 ms.
   *
   * @param ks The static gain in volts.
   * @param kg The gravity gain in volts.
   * @param kv The velocity gain in V/(rad/s).
   * @throws IllegalArgumentException for kv &lt; zero.
   */
  public ArmFeedforward(double ks, double kg, double kv) {
    this(ks, kg, kv, 0);
  }

  /**
   * Sets the static gain.
   *
   * @param ks The static gain in volts.
   */
  public void setKs(double ks) {
    this.ks = ks;
  }

  /**
   * Sets the gravity gain.
   *
   * @param kg The gravity gain in volts.
   */
  public void setKg(double kg) {
    this.kg = kg;
  }

  /**
   * Sets the velocity gain.
   *
   * @param kv The velocity gain in V/(rad/s).
   */
  public void setKv(double kv) {
    this.kv = kv;
  }

  /**
   * Sets the acceleration gain.
   *
   * @param ka The acceleration gain in V/(rad/s²).
   */
  public void setKa(double ka) {
    this.ka = ka;
  }

  /**
   * Returns the static gain in volts.
   *
   * @return The static gain in volts.
   */
  public double getKs() {
    return ks;
  }

  /**
   * Returns the gravity gain in volts.
   *
   * @return The gravity gain in volts.
   */
  public double getKg() {
    return kg;
  }

  /**
   * Returns the velocity gain in V/(rad/s).
   *
   * @return The velocity gain.
   */
  public double getKv() {
    return kv;
  }

  /**
   * Returns the acceleration gain in V/(rad/s²).
   *
   * @return The acceleration gain.
   */
  public double getKa() {
    return ka;
  }

  /**
   * Returns the period in seconds.
   *
   * @return The period in seconds.
   */
  public double getDt() {
    return m_dt;
  }

  /**
   * Calculates the feedforward from the gains and velocity setpoint assuming continuous control
   * (acceleration is assumed to be zero).
   *
   * @param position The position setpoint in radians. This angle should be measured from the
   *     horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If
   *     your encoder does not follow this convention, an offset should be added.
   * @param velocity The velocity setpoint in radians per second.
   * @return The computed feedforward.
   */
  public double calculate(double position, double velocity) {
    return ks * Math.signum(velocity) + kg * Math.cos(position) + kv * velocity;
  }

  /**
   * Calculates the feedforward from the gains and setpoints assuming continuous control.
   *
   * @param currentAngle The current angle in radians. This angle should be measured from the
   *     horizontal (i.e. if the provided angle is 0, the arm should be parallel to the floor). If
   *     your encoder does not follow this convention, an offset should be added.
   * @param currentVelocity The current velocity setpoint in radians per second.
   * @param nextVelocity The next velocity setpoint in radians per second.
   * @return The computed feedforward in volts.
   */
  public double calculate(double currentAngle, double currentVelocity, double nextVelocity) {
    return ArmFeedforwardJNI.calculate(
        ks, kv, ka, kg, currentAngle, currentVelocity, nextVelocity, m_dt);
  }

  // Rearranging the main equation from the calculate() method yields the
  // formulas for the methods below:

  /**
   * Calculates the maximum achievable velocity given a maximum voltage supply, a position, and an
   * acceleration. Useful for ensuring that velocity and acceleration constraints for a trapezoidal
   * profile are simultaneously achievable - enter the acceleration constraint, and this will give
   * you a simultaneously-achievable velocity constraint.
   *
   * @param maxVoltage The maximum voltage that can be supplied to the arm.
   * @param angle The angle of the arm, in radians. This angle should be measured from the
   *     horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If
   *     your encoder does not follow this convention, an offset should be added.
   * @param acceleration The acceleration of the arm, in (rad/s²).
   * @return The maximum possible velocity in (rad/s) at the given acceleration and angle.
   */
  public double maxAchievableVelocity(double maxVoltage, double angle, double acceleration) {
    // Assume max velocity is positive
    return (maxVoltage - ks - Math.cos(angle) * kg - acceleration * ka) / kv;
  }

  /**
   * Calculates the minimum achievable velocity given a maximum voltage supply, a position, and an
   * acceleration. Useful for ensuring that velocity and acceleration constraints for a trapezoidal
   * profile are simultaneously achievable - enter the acceleration constraint, and this will give
   * you a simultaneously-achievable velocity constraint.
   *
   * @param maxVoltage The maximum voltage that can be supplied to the arm, in volts.
   * @param angle The angle of the arm, in radians. This angle should be measured from the
   *     horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If
   *     your encoder does not follow this convention, an offset should be added.
   * @param acceleration The acceleration of the arm, in (rad/s²).
   * @return The minimum possible velocity in (rad/s) at the given acceleration and angle.
   */
  public double minAchievableVelocity(double maxVoltage, double angle, double acceleration) {
    // Assume min velocity is negative, ks flips sign
    return (-maxVoltage + ks - Math.cos(angle) * kg - acceleration * ka) / kv;
  }

  /**
   * Calculates the maximum achievable acceleration given a maximum voltage supply, a position, and
   * a velocity. Useful for ensuring that velocity and acceleration constraints for a trapezoidal
   * profile are simultaneously achievable - enter the velocity constraint, and this will give you a
   * simultaneously-achievable acceleration constraint.
   *
   * @param maxVoltage The maximum voltage that can be supplied to the arm, in volts.
   * @param angle The angle of the arm, in radians. This angle should be measured from the
   *     horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If
   *     your encoder does not follow this convention, an offset should be added.
   * @param velocity The velocity of the elevator, in (rad/s)
   * @return The maximum possible acceleration in (rad/s²) at the given velocity.
   */
  public double maxAchievableAcceleration(double maxVoltage, double angle, double velocity) {
    return (maxVoltage - ks * Math.signum(velocity) - Math.cos(angle) * kg - velocity * kv) / ka;
  }

  /**
   * Calculates the minimum achievable acceleration given a maximum voltage supply, a position, and
   * a velocity. Useful for ensuring that velocity and acceleration constraints for a trapezoidal
   * profile are simultaneously achievable - enter the velocity constraint, and this will give you a
   * simultaneously-achievable acceleration constraint.
   *
   * @param maxVoltage The maximum voltage that can be supplied to the arm, in volts.
   * @param angle The angle of the arm, in radians. This angle should be measured from the
   *     horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If
   *     your encoder does not follow this convention, an offset should be added.
   * @param velocity The velocity of the elevator, in (rad/s)
   * @return The maximum possible acceleration in (rad/s²) at the given velocity.
   */
  public double minAchievableAcceleration(double maxVoltage, double angle, double velocity) {
    return maxAchievableAcceleration(-maxVoltage, angle, velocity);
  }

  /** Arm feedforward struct for serialization. */
  public static final ArmFeedforwardStruct struct = new ArmFeedforwardStruct();

  /** Arm feedforward protobuf for serialization. */
  public static final ArmFeedforwardProto proto = new ArmFeedforwardProto();
}