/*max_functions.c*/

#include"max_functions.h"

int set_output_voltage(double setpoint_voltage, ESeries E_resistors) {

    bool solution_found = false;
    int decade_max = 6;
    int decade_min = 1;

    double R_high_resistance = 0.0;
    double R_low_resistance = 0.0;

    //start at 10k for low resistor and at minimum for high resistor
    int R_high_decade = decade_min;
    int R_low_decade = 4;
    double R_high_value = 1.00;
    double R_low_value = 1.00;

    // voltage computed from resistor configuration used to compare new result to previous optimum
    double output_voltage = 0.0;
    double output_voltage_w = 0.0;

    // set the max array index for given e series
    unsigned int e_max_values = get_E_MAX(E_resistors);
    if (e_max_values == E_NIL) {
        printf("max668_calc:max_functions:set_output_voltage: Unknown E series.\n");
        return EXIT_FAILURE;
    }

    // working variables
    int R_high_decade_w = R_high_decade;
    int R_low_decade_w = R_low_decade;
    double R_high_value_w = R_high_value;
    double R_low_value_w = R_low_value;

    /*
     * start at minimum given Rlow from datasheet and select optimal Rhigh for given Rlow and Vout.
     * do this for all possible Rlows and choose the optimal combination
     * (minimize |setpoint_voltage - output_voltage|)
     */
    for(int i_low = R_low_decade; i_low <= 6; i_low++) {

        R_low_decade_w = i_low;

        for (int j_low = 0; j_low <= e_max_values; j_low++) {

            // in the 6th decate only examine R_low = 1M, then stop
            if ( i_low == 6 && j_low > 0 )
                break;

            // select new R_low
            R_low_value_w = E_values[E_resistors][j_low];
            R_low_resistance = R_low_value_w * exp(log(10)*R_low_decade_w);

            // calculate corresponding R_high
            R_high_resistance = R_low_resistance *((setpoint_voltage/1.25)-1);
            R_high_decade_w = floor(log10(R_high_resistance));
            R_high_value_w = round_to_E_series((R_high_resistance / exp(log(10)*R_high_decade_w)), E_resistors);

            // calculate the acchieved outputvoltage for resistor combination from the given E series
            output_voltage_w = 1.25 * ((R_high_resistance/R_low_resistance) + 1);

            // if the calculated resistance is too small or too great, ignore it
            if (R_high_decade_w > decade_max || R_high_decade_w < decade_min)
                continue;

            // if a new optimum is found -> save the values
            if (fabs(output_voltage - setpoint_voltage) > fabs(output_voltage_w - setpoint_voltage)) {
                R_high_decade = R_high_decade_w;
                R_high_value = R_high_value_w;
                R_low_decade = R_low_decade_w;
                R_low_value = R_low_value_w;
                output_voltage = output_voltage_w;
                solution_found = true;
            }
        }
    }

    // report the found optimal resistor combination in the given E series
    if (solution_found) {
        printf("Found optimal combination for R_high / R_low: \n");
        printf("R_low: %5.2fE%i ohms\n",R_low_resistance,R_low_decade);
        printf("R_high: %4.2fE%i ohms\n",R_high_resistance,R_high_decade);
        printf("Achieved output_voltage:");
        printf("V_out: %4.2f",output_voltage);
    }
    else {
        printf("max668_calc:max_functions:set_output_voltage: Unable to find valid resistance combination within given range.\n");
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}