#!/usr/bin/env python3.5

import sys
import random
import os
import math

prefix = os.getcwd() + "/Challenges/SD/"

def eprint(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)

def usage():
    eprint("ERROR the script expects 2 integer arguments: 'n' and 'seed'.")
    eprint("\b - 'n' is an integer corresponding to the size of the matrix: H will be of size n//2 * n")
    eprint("\b - 'seed' is an integer corresponding to the initial value of the random seed")
    eprint("This script generates an instance of the syndrome decoding problem.")
    eprint("This matrix H is given in systematic form. The identity part is omitted.")
    eprint("The instance is stored in 'Challenges/SD/SD_n_seed'.")

def dGV(n, k):
    d = 0
    aux = 2**(n-k)
    b = 1
    while aux >= 0:
        aux -= b
        d += 1
        b *= (n-d+1)
        b /= d
    return d 
    
def main(n, seed):
    w = math.ceil(1.05 * dGV(n,n//2))
    random.seed(seed)
    text = ""
    text += "# n\n"
    text += str(n)
    text += "\n"
    text += "# seed\n"
    text += str(seed)
    text += "\n"
    text += "# w\n"
    text += str(w)
    text += "\n"
    text += "# H^transpose (each line corresponds to column of H, the identity part is omitted)\n"
    for i in range(n-n//2):
        line = ""
        for j in range(n//2):
            line += str(random.randint(0,1))
        line += "\n"
        text += line
    text += "# s^transpose\n"
    line = ""
    for j in range(n//2):
        line += str(random.randint(0,1))
    line += "\n"
    text += line
    filename = prefix + "SD_" + str(n) + "_" + str(seed)
    file  = open(filename, "w")
    file.write(text)
    file.close()

if __name__ == "__main__":
    # execute only if run as a script
    if len(sys.argv)!=3:
        usage()
        exit(1)
    try:
        n = int(sys.argv[1])
        seed = int(sys.argv[2])
    except:
        usage()
        exit(1)
    main(n, seed)