/// @file
/// @brief Task3: implementation

#include "task3.hpp"      // sample_to_csv
#include "iue-io/csv.hpp" // iue::io::savetxt
#include "task2.hpp"      // range|sample|numint|numdiff

/// @todo Include standard library headers as needed
#include <functional> // std::function
#include <vector>     // std::vector

/// @brief This function
/// - samples a one-dimensional scalar function (f) in a provided interval and resolution,
//  - approximates its derivative (df) and antiderivative (F) numerically, and
/// - produces a csv-file holding the discrete values in this form:
///   - csv-column layout: x, f, F, df
/// @param filepath
/// @param del Delimiter
/// @param comment Character designating a line as a comment
/// @param func Callable with a signature compatible with f(double) -> double
/// @param start Start of the interval
/// @param end End of the interval
/// @param N Number of values; assumption: N >= 2
void sample_to_csv(std::filesystem::path filepath, char del, char comments, std::function<double(double)> func,
                   double start, double end, unsigned int N) {
  // Create a sequence of equidistant values in the interval [start, end]
  std::vector<double> x = range(start, end, N);
  // Sample the function 'func' at the locations 'x'
  std::vector<double> f = sample(x, func);
  // Approximate the derivative of 'f' at the locations 'x'
  std::vector<double> df = numdiff(x, f);
  // Approximate the antiderivative of 'f' at the locations 'x'
  std::vector<double> F = numint(x, f, 0.0);
  // Create a matrix holding the discrete values of 'x', 'f', 'F', and 'df'
  std::vector<std::vector<double>> data(N, std::vector<double>(4));
  for (unsigned int i = 0; i < N; ++i) {
    data[i][0] = x[i];
    data[i][1] = f[i];
    data[i][2] = F[i];
    data[i][3] = df[i];
  }
    // Save the matrix to a csv-file
    iue::io::savetxt(filepath, data, del);

}