user_input.h

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#ifndef USER_INPUT_H
#define USER_INPUT_H
 
#include <functional>
#include <iostream>
#include <limits>
#include <string>
 
/**
 * @file user_input.h
 * @brief Utility functions for safe user input from the console.
 *
 * Provides generic and typed functions to read and validate numeric values
 * from the standard input stream, with customizable prompts and validation rules.
 */
 
/**
 * @brief Generic template for asking a numeric value from the user.
 *
 * This function continuously asks the user for input until a valid number
 * is provided and passes the validation rule.
 *
 * @tparam T Type of number (int, double, etc.)
 * @param prompt Message shown before user input.
 * @param isValid Validation function returning true if the input is acceptable.
 * @param errorMessage Message displayed when validation fails.
 * @return T The valid numeric value entered by the user.
 */
template <typename T>
T askForNumber(const std::string& prompt,
               const std::function<bool(T)>& isValid,
               const std::string& errorMessage)
{
    T value;
    while (true)
    {
        std::cout << prompt;
 
        if (!(std::cin >> value))
        {
            if (std::cin.eof())
            {
                throw std::runtime_error("End of input stream reached.");
            }
            std::cin.clear(); // reset input stream
            std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
            std::cout << "Invalid input. Please enter a number." << std::endl;
            continue;
        }
 
        if (isValid(value))
            return value;
 
        std::cout << errorMessage << std::endl;
    }
}
 
/**
 * @brief Ask for an integer value from the user.
 *
 * @param prompt Message shown before user input.
 * @param isValid Validation function returning true if the input is acceptable.
 * @param errorMessage Message displayed when validation fails.
 * @return int The valid integer entered by the user.
 */
int askForInteger(const std::string& prompt,
                  const std::function<bool(int)>& isValid,
                  const std::string& errorMessage);
 
/**
 * @brief Ask for a floating-point value from the user.
 *
 * @param prompt Message shown before user input.
 * @param isValid Validation function returning true if the input is acceptable.
 * @param errorMessage Message displayed when validation fails.
 * @return double The valid floating-point number entered by the user.
 */
double askForDouble(const std::string& prompt,
                    const std::function<bool(double)>& isValid,
                    const std::string& errorMessage);
 
#endif // USER_INPUT_H