/* CSCI 200: Lab 1A (Math Equation Solver): Tyler Beckman
 *
 * Author: Tyler Beckman
 *
 * A C++ program to interactively solve 10 different mathmatical equations,
 * using the appropriate constants where relevant. I decided to implement all 10
 * rather than just 2 because it sounded interesting and I wanted to challenge
 * myself. It also will keep prompting for the equation to solve until you
 * explicitly respond with a 0 or CTRL+C it, rather than just exit once the
 * equation is calculated.
 */
#include <iostream>

#include <cmath>

double const MOLAR_GAS_CONSTANT = 8.314'462'618'153'24;
double const GRAVITATIONAL_CONSTANT = 0.000'000'000'066'740'8;
double const SPHERE_VOLUME_RATIO = 4.0 / 3;
double const VACUUM_PERMITTIVITY = 0.000'000'000'008'854'187'818'8;

double ideal_gas_law(double moles, double gas_absolute_temperature,
                     double volume) {
  return (moles * MOLAR_GAS_CONSTANT * gas_absolute_temperature) / volume;
}

double average_acceleration(double pos_start, double pos_end, double time_start,
                            double time_end) {
  return (pos_end - pos_start) / std::pow(time_end - time_start, 2);
}

double ohms_law(double voltage, double resistance) {
  return voltage / resistance;
}

double universal_gravitation(double mass_one, double mass_two,
                             double distance) {
  return GRAVITATIONAL_CONSTANT *
         ((mass_one * mass_two) / std::pow(distance, 2));
}

double pythagorean_theorem(double x, double y) {
  return std::sqrt(std::pow(x, 2) + std::pow(y, 2));
}

double sphere_volume(double radius) {
  return SPHERE_VOLUME_RATIO * M_PI * std::pow(radius, 3);
}

double deflection(double weight, double length, double elasticity_modulus,
                  double moment_of_inertia) {
  return (weight * std::pow(length, 3)) /
         (3 * elasticity_modulus * moment_of_inertia);
}

double heat_transfer_rate(double transfer_coefficient, double surface_area,
                          double temperature_change) {
  return transfer_coefficient * surface_area * temperature_change;
}

double stress(double force, double area) { return force / area; }

double shear_stress(double sigma_x, double sigma_y, double tau_xy,
                    double theta) {
  return -0.5 * (sigma_x - sigma_y) * sin(2 * theta) + tau_xy * cos(2 * theta);
}

double coulombs_law(double charge_1, double charge_2,
                    double relative_static_permittivity, double distance) {
  return std::fabs(charge_1 * charge_2) /
         (4 * M_PI * VACUUM_PERMITTIVITY * relative_static_permittivity *
          std::pow(distance, 2));
}

double input_double(std::string prompt) {
  double out;
  while (true) {
    std::cout << prompt + ": ";
    std::cin >> out;

    if (std::cin.fail()) {
      // The clear and ignore are necessary because otherwise it seems to keep
      // reusing the first input a person enters
      std::cin.clear();
      std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
      std::cout << "Invalid number, please make sure your number is formatted "
                   "correctly."
                << std::endl;
    } else {
      break;
    }
  }

  return out;
}

int main() {
  while (true) {
    std::cout << "[0] Quit program" << std::endl
              << "[1] Ideal gas law" << std::endl
              << "[2] Average acceleration" << std::endl
              << "[3] Ohm's law" << std::endl
              << "[4] Universal gravitation" << std::endl
              << "[5] Pythagorean theorem" << std::endl
              << "[6] Sphere volume" << std::endl
              << "[7] Deflection" << std::endl
              << "[8] Heat transfer rate" << std::endl
              << "[9] Stress" << std::endl
              << "[10] Shear Stress" << std::endl
              << "[11] Coulomb's law" << std::endl;
    int equation_choice =
        input_double("Which equation would you like to calculate?");

    double calculated_value;

    switch (equation_choice) {
      case 0:
        return 0;
      case 1:
        calculated_value = ideal_gas_law(
            input_double("Please enter amount of moles"),
            input_double("Please enter the gas absolute temperate"),
            input_double("Please enter the volume"));
        break;
      case 2:
        calculated_value = average_acceleration(
            input_double("Please enter the starting position"),
            input_double("Please enter the ending position"),
            input_double("Please enter the starting time"),
            input_double("Please enter the ending time"));
        break;
      case 3:
        calculated_value =
            ohms_law(input_double("Please input the voltage"),
                     input_double("Please input the resistance"));
        break;
      case 4:
        calculated_value = universal_gravitation(
            input_double("Please input the mass of object 1"),
            input_double("Please input the mass of object 2"),
            input_double("Please input the distance between objects"));
        break;
      case 5:
        calculated_value =
            pythagorean_theorem(input_double("Please input the x distance"),
                                input_double("Please input the y distance"));
        break;
      case 6:
        calculated_value =
            sphere_volume(input_double("Please input the sphere radius"));
        break;
      case 7:
        calculated_value =
            deflection(input_double("Please input the force of weight"),
                       input_double("Please input the length"),
                       input_double("Please input the elasticity modulus"),
                       input_double("Please input the moment of inertia"));
        break;
      case 8:
        calculated_value = heat_transfer_rate(
            input_double("Please input the transfer coefficient"),
            input_double("Please input the surface area"),
            input_double("Please input the change in temperature"));
        break;
      case 9:
        calculated_value =
            stress(input_double("Please input the amount of force"),
                   input_double("Please input the surface area"));
        break;
      case 10:
        calculated_value = shear_stress(
            input_double("Please enter σ_x"), input_double("Please enter σ_y"),
            input_double("Please enter τ_xy"),
            input_double("Please enter θ (in radians)"));
        break;
      case 11:
        calculated_value = coulombs_law(
            input_double("Please input the first charge"),
            input_double("Please input the second charge"),
            input_double("Please input the relative static permittivity"),
            input_double("Please input the distance between charges"));
        break;
      default:
        std::cout << "That is not a valid equation choice. Please try again."
                  << std::endl;
        continue;
    }
    std::cout << "The result of that calculation is: " << calculated_value
              << std::endl;
  }
}