import java.util.Objects;

public class Main {
    public static void main(String[] args) {
        byte a = 1, b = 1, n = 10, m = 10;
        boolean simplify_math = true;
        int iteration_amount = 1;
        byte verbosity = 1;
        int p = 0;
        boolean run_safe = false;

        while (p < args.length) {
            try {
            if (Objects.equals(args[p], "-h")) {
                System.out.print("Usage: java Main [options]\nOptions:\n    -v <byte>   Sets verbosity level (0-2, default is 1\n    -a, -b, -n, -m <byte>   Sets default values for a, b, n and m variables respectively\n    -s <bool>   Use simplified algorithm to calculate the desired value (true/false, default is true)\n    -t <int>    Enables benchmarking mode and performs selected calculation <int> times\n");
                System.exit(0);
            }
            else if (Objects.equals(args[p], "-v")) {
                verbosity = (byte) Integer.parseInt(args[p+1]);
                p += 2;
            }
            else if (Objects.equals(args[p], "-a")) {
                a = (byte) Integer.parseInt(args[p+1]);
                p += 2;
            }
            else if (Objects.equals(args[p], "-b")) {
                b = (byte) Integer.parseInt(args[p+1]);
                p += 2;
            }
            else if (Objects.equals(args[p], "-n")) {
                n = (byte) Integer.parseInt(args[p+1]);
                p += 2;
            }
            else if (Objects.equals(args[p], "-m")) {
                m = (byte) Integer.parseInt(args[p+1]);
                p += 2;
            }
            else if (Objects.equals(args[p], "-t")) {
                iteration_amount = Integer.parseInt(args[p+1]);
                p += 2;
            }
            else if (Objects.equals(args[p], "-s")) {
                simplify_math = Boolean.parseBoolean(args[p+1]);
                p += 2;
            }
            else if (Objects.equals(args[p], "--safe")) {
                run_safe = true;
                p++;
            }
            else {
                if (verbosity >= 1) {
                    System.err.println("Unknown argument found: " + args[p] + "\nPlease, use 'java Main -h' for help");
                }
                System.exit(1);
            }
            }
            catch (Exception e) {
                System.err.println("Exception while parsing CLI arguments: " + e);
                System.err.println("Aborting execution.");
                System.exit(1);
            }
        }

        if (verbosity >= 2) {
            System.out.println(String.format("Using arguments: a=%d, b=%d, n=%d, m=%d", a, b, n, m));
        }

        if (simplify_math == true) {
            if (b <= 0 && m >= 0) {
                System.err.println("Preventing division by zero!\nAborting calculations.");
                System.exit(1);
            }
            else
            {
                if (a <= 0 && n >= 0) {
                    System.err.println("Bypassing division by zero with fast math; expect wrong calculations");
                    if (run_safe) {
                        System.err.println("--safe flag is set, preventing further execution");
                        System.exit(1);
                    }
                }

                for (int g = 0; g < iteration_amount; g++) {
                    double result = calc_quick(verbosity, a, n, b, m);
                    if (iteration_amount == 1) {
                        if (verbosity >= 1) {
                            System.out.println(String.format("Result is %.3f", result));
                        }
                        else
                        {
                            System.out.print(result);
                        }
                    }
                }
            }
        }
        else
        {
            if ((a <= 0 && n >= 0) || (b <= 0 && m >= 0)) {
                System.err.println("Preventing division by zero!\nAborting calculations.");
                System.exit(1);
            }
            else
            {
                for (int g = 0; g < iteration_amount; g++) {
                    double result = calc_generic(verbosity, a, n, b, m);
                    if (iteration_amount == 1) {
                        if (verbosity >= 1) {
                            System.out.println(String.format("Result is %.3f", result));
                        }
                        else
                        {
                            System.out.print(result);
                        }
                    }
                }
            }
        }
    }

    private static double calc_generic(byte verbosity, byte a, byte n, byte b, byte m) {
        double result = 0;
        for (byte i = a; i <= n; i++) {
            for (byte j = b; j <= m; j++) {
                if (verbosity >= 3) {
                    System.out.print(result);
                }

                result += ((double) i / (double) j) / ((double) i - (double) 0);

                if (verbosity >= 3) {
                    System.out.println(" + " + (((double)i / (double)j) / ((double)i-(double)0)) + " = " + result);
                }
            }
        }
        return result;
    }

    private static double calc_quick(byte verbosity, byte a, byte n, byte b, byte m) {
        double t = 0;
        for (byte j = b; j <= m; j++) {if (verbosity >= 3) {System.out.print(t);}; t += (double)1/(double)j; if (verbosity >= 3) {System.out.println(" + " + (double)1/(double)j + " = " + t);} }
        return (double) (t * ((double)n-(double)a + (double) 1));
    }
}