"""
Evaluates a given set of MAGMA commands using
http://magma.maths.usyd.edu.au/calc/ the free online MAGMA calculator.

AUTHOR: Martin Albrecht <malb@informatik.uni-bremen.de>
"""

import urllib

def magma_remote_eval(cmd):
    """
    Evaluates cmd using http://magma.maths.usyd.edu.au/calc/ . No
    state is preserved remotely so all definitions must be in one
    command. Also the remote execution is terminated after 20 seconds.

    EXAMPLES:
        sage: s = 'R<x> := PolynomialRing(GF(2^8));\n f := x^2 + x; f'
        sage: magma_remote_eval(s)
         'x^2 + x'

    TODO: It could be possible to provide a full backend for SAGE's Magma
        class using this approach. Is this a copyright problem?
    """
    start_string = "<textarea name=\"output\" cols=\"80\" rows=\"15\" id=\"output\">"
    #Magma V2.13-4     Sun Oct 22 2006 23:14:27    [Seed = 2030523014]
    #-------------------------------------
    #
    # <output> 
    #
    #Total time: <val> seconds, Total memory usage: <val>MB
    end_string= "</textarea>"

    url = "http://magma.maths.usyd.edu.au/calc/?input=%s"%urllib.quote(cmd)

    fp = urllib.urlopen(url)
    answer = fp.read()

    i = answer.index(start_string)
    j = answer.rindex(end_string)
    answer = answer[i+len(start_string):j]
    answer = answer.splitlines()
    return "\n".join(answer[3:-2]) # strip MAGMA version string etc.