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

import argparse, configparser, itertools, stat, 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(src = fname, dst = 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])

def key_mtime(name):
    return datetime.datetime.fromtimestamp(os.stat(keyfile(name)).st_mtime)

def cert_expiry(name):
    from certcheck import cert_expiry_date
    return cert_expiry_date(certfile(name))

## The interesting work
def acme(name, domains):
    global config
    # Generating the CSR 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)
    # call acme-tiny as a script
    acme_tiny = os.path.join(config['acme']['acme-tiny'], 'acme_tiny.py')
    signed_crt = subprocess.check_output(["python", 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 f:
        f.write(signed_crt)
    # append DH params
    dhfile = config['DEFAULT'].get('dh-params')
    if dhfile is not None:
        with open(dhfile, 'rb') as f:
            dh = f.read()
        with open(certfile(name, 'dh'), 'wb') as f:
            f.write(signed_crt)
            f.write(dh)
    # append chain
    chainfile = config['DEFAULT'].get('chain')
    if chainfile is not None:
        with open(chainfile, 'rb') as f:
            chain = f.read()
        with open(certfile(name, 'chain'), 'wb') as f:
            f.write(signed_crt)
            f.write(chain)

def request_cert(name):
    global config
    if not os.path.exists(keyfile(name)):
        raise Exception("No such key: {}".format(name))
    domains = config['DEFAULT']['domains'].split()
    print("Obtaining certificate '{}' for domains: {}".format(name, ' '.join(domains)))
    acme(name, domains)

def generate_key(name):
    print("Generating new private key '{}'".format(name))
    with subprocess.Popen(["openssl", "genrsa", str(int(config['DEFAULT']['key-length']))], stdout=subprocess.PIPE, stderr=subprocess.PIPE) as f:
        (stdout, stderr) = f.communicate()
        if f.returncode:
            sys.stderr.write(stderr)
            raise Exception("Error while generating private key")
    # now we have a key, save it
    make_backup(keyfile(name))
    with open(keyfile(name), 'wb') as f:
        f.write(stdout)

def check_staging():
    '''Returns 0 if nothing was done, 1 if a stage key is present but has to be kept, 2 is a stage key was unstaged.'''
    live = config['files']['live']
    staging = config['files'].get('staging')
    if staging is None or not os.path.exists(keyfile(staging)):
        return 0
    
    staging_time = datetime.timedelta(hours = int(config['timing']['staging-hours']))
    key_age = datetime.datetime.now() - key_mtime(staging)
    if key_age < staging_time:
        return 1
    print("Unstaging '{}' to '{}'".format(staging, live))
    # unstage the key!
    make_backup(keyfile(live))
    os.rename(src = keyfile(staging), dst = keyfile(live))
    make_backup(certfile(live))
    os.rename(src = certfile(staging), dst = certfile(live))
    try:
        os.rename(src = certfile(staging, 'dh'), dst = certfile(live, 'dh'))
    except FileNotFoundError:
        pass
    try:
        os.rename(src = certfile(staging, 'chain'), dst = certfile(live, 'chain'))
    except FileNotFoundError:
        pass
    return 2

def auto_renewal():
    '''Returns 0 if nothing was done, 1 if only certs were changed, 2 if certs and keys were changed.'''
    live = config['files']['live']
    staging = config['files'].get('staging')
    
    max_key_age = datetime.timedelta(days = int(config['timing']['max-key-age-days']))
    renew_cert_time = datetime.timedelta(days = int(config['timing']['renew-cert-before-expiry-days']))
    
    # determine what to do
    now = datetime.datetime.now()
    key_age = now - key_mtime(live)
    cert_validity = cert_expiry(live) - now
    need_new_key = key_age >= max_key_age
    need_new_cert = cert_validity <= renew_cert_time
    if need_new_cert and key_age + renew_cert_time >= max_key_age:
        # We are about to request a new certificate, and within <renew_cert_time>, we need a new key: Get the new key now
        need_new_key = True
    
    # Do it
    if need_new_key:
        new_key_name = (live if staging is None else staging)
        generate_key(new_key_name)
        request_cert(new_key_name)
        return 2
    elif need_new_cert:
        request_cert(live)
        return 1
    else:
        return 0

## 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("-k", "--hooks",
                        dest="hooks", action="store_true",
                        help="Trigger hooks.")
    parser.add_argument("action", metavar='ACTION', nargs=1,
                        help="The action to perform. Possible values: init, 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':
        live = config['files']['live']
        staging = config['files'].get('staging')
        
        request_cert(live)
        if staging is not None and os.path.exists(keyfile(staging)):
            request_cert(staging)
        # trigger the "new cert" hook
        if args.hooks:
            trigger_hook('post-certchange')
    elif args.action[0] == 'cron':
        # First, check if we need to unstage a staging key
        unstaged = check_staging()
        if unstaged >= 1:
            # A staging eky is present, do *not* check for renewal
            if unstaged >= 2 and args.hooks:
                # trigger all the hooks
                trigger_hook('post-certchange')
                trigger_hook('post-keychange')
        else:
            # Check if we need to renew anything
            renewed = auto_renewal()
            if args.hooks:
                if renewed >= 1:
                    trigger_hook('post-certchange')
                if renewed >= 2:
                    trigger_hook('post-keychange')
    elif args.action[0] == 'init':
        # create directories with appropriate permissions
        try:
            os.makedirs(config['dirs']['certs'], mode = 0o755, exist_ok = True)
            os.makedirs(config['dirs']['keys'], mode = 0o710, exist_ok = True)
            os.makedirs(config['dirs']['csrs'], mode = 0o755, exist_ok = True)
            os.makedirs(config['dirs']['backups'], mode = 0o700, exist_ok = True)
        except OSError:
            pass
        # if necessary, generate key + certificate
        live = config['files']['live']
        if not os.path.exists(keyfile(live)):
            generate_key(live)
            request_cert(live)
            if args.hooks:
                trigger_hook('post-certchange')
                trigger_hook('post-keychange')
    else:
        raise Exception("Unknown action {}".format(args.action))