import os

PRIORITY = 60
GHC_PATH = '/opt/ghc/'
CABAL_PATH = '/opt/cabal/'
LINK_PATH = '/usr/bin/'

ghc_executables = [
    'ghc',
    'ghc-pkg',
    'ghci',
    'haddock',
    'hp2ps',
    'hpc',
    'hsc2hs'
    'runghc',
    'runhaskell'
]

cabal_executables = [
    'cabal'
]

def update_alternatives(path, exes, ver):

    origin_path = path + ver + '/bin/'
    command = "sudo update-alternatives --install %s %s %s %d " % \
        (LINK_PATH + exes[0], exes[0], origin_path + exes[0], PRIORITY)
    for exe in exes[1:]:
        command += "--slave %s %s %s " % (LINK_PATH + exe, exe, origin_path + exe)
    os.system(command)

if __name__ == '__main__':
    ghc_version = raw_input("input GHC version: ")
    update_alternatives(GHC_PATH, ghc_executables, ghc_version)
    cabal_version = raw_input("input Cabal version: ")
    update_alternatives(CABAL_PATH, cabal_executables, cabal_version)