# Copyright 2002 by Katharine Lindner.  All rights reserved.
# This code is part of the Biopython distribution and governed by its
# license.  Please see the LICENSE file that should have been included
# as part of this package.

"""handles true random numbers supplied from the the web server of fourmilab. Based on atmospheric noise.  The motivation is to support biosimulations that rely on random numbers.
"""

import urllib


def byte_concat( text ):
    val = 0
    numbytes = len( text )
    for i in range( 0, numbytes ):
        val = val * 256
        val = val + ord( text[ i ] )

    return val

class HotCache:

    def __init__( self  ):
#        self.url = 'http://www.fourmilab.ch/cgi-bin/uncgi/Hotbits?num=5000&min=1&max=6&col=1'
        self.url = 'http://www.random.org/cgi-bin/randbyte?'
        self.query = { 'nbytes' : 128, 'fmt' : 'h' }
        self.fill_hot_cache()

    def fill_hot_cache( self ):
        url = self.url + urllib.urlencode( self.query )
        fh = urllib.urlopen( url )
        self.hot_cache = fh.read()
        fh.close()

    def next_num( self, num_digits = 4 ):
        cache = self.hot_cache
        numbytes = num_digits / 2
        if( len( cache ) % numbytes != 0 ):
            print 'len_cache is %d' % len( cache )
            raise ValueError
        if( cache == '' ):
            self.fill_hot_cache()
            cache = self.hot_cache
        hexdigits = cache[ :numbytes ]
        self.hot_cache = cache[ numbytes: ]
        return byte_concat( hexdigits )



class HotRandom:

    def __init__( self ):
        self.hot_cache = HotCache( )

    def hot_rand( self, high, low = 0 ):
        span = high - low
        val = self.hot_cache.next_num()
        val = ( span * val ) >> 16
        val = val + low
        return val


if( __name__ == '__main__' ):
    hot_random = HotRandom()
    for j in range ( 0, 130 ):
        print hot_random.hot_rand( 25 )
    nums = [ '0000', 'abcd', '1234', '5555', '4321', 'aaaa', 'ffff' ]
    for num in nums:
        print hex_convert( num )



