#!/usr/bin/env python3

class Letter2Bitmask:
    "A class that handles translation of letters to bitmask bits and reverse."

    def _dicts_from_letters(letters):
        """Return c2b and b2c dictonaries from an array of letters.
        
        The argument is an array containing all 26 letters from the ASCII alphabet
        (each letter exactly once).
        
        The function returns a pair of maps:
        - The first map, c2b, has the characters as keys 
          and the corresponding bitmap as values.
        - The second map, b2c, is the reverse."""
        c2b = {}
        b2c = {}
        bitmask = 1
        for c in letters:
            c2b[c] = bitmask
            b2c[bitmask] = c
            bitmask <<= 1
        return [c2b, b2c]


    def __init__(self, letters):
        self._c2b, self._b2c = Letter2Bitmask._dicts_from_letters(letters)

    def bit(self, c):
        return self._c2b[c]
        
    def char(self, bit):
        return self._b2c[bit]

    def number(self, chars):
        result = 0
        for c in chars:
            result |= self._c2b[c]
        return result

    def chars(self, number):
        result = set()
        bitmask = 1 << number.bit_length()
        while bitmask:
            if number & bitmask:
               result.add(self._b2c[bitmask])
            bitmask >>= 1
        return sorted(result)

if __name__ == "__main__":
    import argparse
    from letters_rare_first import from_lettercount_file
    parser = argparse.ArgumentParser(description="Show map keys used for \"database\" files.")
    parser.add_argument("--lettercount",
                        default="lettercount",
                        type=argparse.FileType("r", encoding="UTF8"),
                        help="The input lettercount file as generated by lettercount")
    args = parser.parse_args()
    with args.lettercount as lettercount_file:
        l2b = Letter2Bitmask(from_lettercount_file(lettercount_file))
        print("We use this translation of letters to single-bit-bitmasks:\n{}".format(l2b._c2b))