#!/usr/bin/env python3
## Call with "--help" for documentation.

import argparse, configparser, itertools, os, os.path, sys, subprocess, datetime

## Helper functions
def readConfig(fname, defSection = 'DEFAULT'):
    config = configparser.ConfigParser()
    with open(fname) as file:
        stream = itertools.chain(("["+defSection+"]\n",), file)
        config.read_file(stream)
    return config

def certfile(name, suff = None):
    global config
    return os.path.join(config['dirs']['certs'], name + ".crt" + ('' if suff is None else '+'+suff) )

def keyfile(name):
    global config
    return os.path.join(config['dirs']['keys'], name + ".key")

def csrfile(name):
    global config
    return os.path.join(config['dirs']['csrs'], name + ".csr")

def make_backup(fname):
    if os.path.exists(fname):
        backupname = os.path.basename(fname) + "." + str(datetime.date.today())
        i = 0
        while True:
            backupfile = os.path.join(config['dirs']['backups'], backupname + "." + str(i))
            if not os.path.exists(backupfile):
                os.rename(fname, backupfile)
                break
            elif i >= 100:
                print("Somehow it's really hard to find a name for the backup file...")
            i += 1
    assert not os.path.exists(fname)

def trigger_hook(hook):
    global config
    exe = config['hooks'][hook]
    if exe is not None:
        subprocess.check_call([exe])

## The interesting work
def gencsr(name, domains):
    # This is done by a shell script
    exe = os.path.join(os.path.dirname(__file__), 'gencsr')
    csr = subprocess.check_output([exe, keyfile(name)] + domains)
    with open(csrfile(name), 'wb') as file:
        file.write(csr)

def acme(name, domains):
    global config
    print("Obtaining certificate {} for domains {}".format(name, ' '.join(domains)))
    gencsr(name, domains)
    # call acme-tiny as a script
    acme_tiny = os.path.join(config['acme']['acme-tiny'], 'acme_tiny.py')
    signed_crt = subprocess.check_output([acme_tiny, "--quiet", "--account-key", config['acme']['account-key'], "--csr", csrfile(name), "--acme-dir", config['acme']['challenge-dir']])
    # save new certificate
    make_backup(certfile(name))
    with open(certfile(name), 'wb') as file:
        file.write(signed_crt)
    # append DH params
    dhfile = config['DEFAULT']['dh-params']
    if dhfile is not None:
        with open(dhfile, 'rb') as file:
            dh = file.read()
        make_backup(certfile(name, 'dh'))
        with open(certfile(name, 'dh'), 'wb') as file:
            file.write(signed_crt)
            file.write(dh)

def getcert(name):
    global config
    if not os.path.exists(keyfile(name)):
        raise Exception("No such key: {}".format(name))
    domains = config['DEFAULT']['domains'].split()
    acme(name, domains)
    trigger_hook('post-cert')

## Main
if __name__ == "__main__":
    # allow overwriting some values on the command-line
    parser = argparse.ArgumentParser(description='Generate and (automatically) renew certificates, optionally providing staging for new keys')
    parser.add_argument("-c", "--config",
                        dest="config",
                        help="The configuration file")
    parser.add_argument
    parser.add_argument("action", metavar='ACTION', nargs=1,
                        help="The action to perform. Possible values: renew, cron")
    args = parser.parse_args()
    
    # read config
    if not os.path.isfile(args.config):
        raise Exception("The config file does not exist: "+args.config)
    global config
    config = readConfig(args.config)
    
    if args.action[0] == 'renew':
        getcert(config['files']['live'])
        # We may also have to renew the staging
        staging = config['files']['staging']
        if staging is not None and os.path.exists(keyfile(staging)):
            getcert(staging)
    else:
        raise Exception("Unknown action {}".format(args.action))