# Copyright 2017, David Wilson
#
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"""
Helper functions intended to be executed on the target. These are entrypoints
for file transfer, module execution and sundry bits like changing file modes.
"""

from __future__ import absolute_import
import cStringIO
import json
import logging
import operator
import os
import pwd
import random
import re
import stat
import subprocess
import tempfile
import traceback
import zlib

import ansible.module_utils.json_utils
import ansible_mitogen.runner
import ansible_mitogen.services
import mitogen.core
import mitogen.fork
import mitogen.parent
import mitogen.service


LOG = logging.getLogger(__name__)

#: Caching of fetched file data.
_file_cache = {}

#: Initialized to an econtext.parent.Context pointing at a pristine fork of
#: the target Python interpreter before it executes any code or imports.
_fork_parent = None


def _get_file(context, path, out_fp):
    """
    Streamily download a file from the connection multiplexer process in the
    controller.

    :param mitogen.core.Context context:
        Reference to the context hosting the FileService that will be used to
        fetch the file.
    :param bytes in_path:
        FileService registered name of the input file.
    :param bytes out_path:
        Name of the output path on the local disk.
    :returns:
        :data:`True` on success, or :data:`False` if the transfer was
        interrupted and the output should be discarded.
    """
    LOG.debug('_get_file(): fetching %r from %r', path, context)
    recv = mitogen.core.Receiver(router=context.router)
    size = mitogen.service.call(
        context=context,
        handle=ansible_mitogen.services.FileService.handle,
        method='fetch',
        kwargs={
            'path': path,
            'sender': recv.to_sender()
        }
    )

    for chunk in recv:
        s = chunk.unpickle()
        LOG.debug('_get_file(%r): received %d bytes', path, len(s))
        out_fp.write(s)

    if out_fp.tell() != size:
        LOG.error('get_file(%r): receiver was closed early, controller '
                  'is likely shutting down.', path)

    LOG.debug('target.get_file(): fetched %d bytes of %r from %r',
              size, path, context)
    return out_fp.tell() == size


def get_file(context, path):
    """
    Basic in-memory caching module fetcher. This generates an one roundtrip for
    every previously unseen file, so it is only a temporary solution.

    :param context:
        Context we should direct FileService requests to. For now (and probably
        forever) this is just the top-level Mitogen connection manager process.
    :param path:
        Path to fetch from FileService, must previously have been registered by
        a privileged context using the `register` command.
    :returns:
        Bytestring file data.
    """
    if path not in _file_cache:
        io = cStringIO.StringIO()
        if not _get_file(context, path, io):
            raise IOError('transfer of %r was interrupted.' % (path,))
        _file_cache[path] = io.getvalue()
    return _file_cache[path]


def transfer_file(context, in_path, out_path):
    """
    Streamily download a file from the connection multiplexer process in the
    controller.

    :param mitogen.core.Context context:
        Reference to the context hosting the FileService that will be used to
        fetch the file.
    :param bytes in_path:
        FileService registered name of the input file.
    :param bytes out_path:
        Name of the output path on the local disk.
    """
    fp = open(out_path+'.tmp', 'wb', mitogen.core.CHUNK_SIZE)
    try:
        try:
            if not _get_file(context, in_path, fp):
                raise IOError('transfer of %r was interrupted.' % (in_path,))
        except Exception:
            os.unlink(fp.name)
            raise
    finally:
        fp.close()

    os.rename(out_path + '.tmp', out_path)


@mitogen.core.takes_econtext
def start_fork_parent(econtext):
    """
    Called by ContextService immediately after connection; arranges for the
    (presently) spotless Python interpreter to be forked, where the newly
    forked interpreter becomes the parent of any newly forked future
    interpreters.

    This is necessary to prevent modules that are executed in-process from
    polluting the global interpreter state in a way that effects explicitly
    isolated modules.
    """
    global _fork_parent
    mitogen.parent.upgrade_router(econtext)
    _fork_parent = econtext.router.fork()


@mitogen.core.takes_econtext
def start_fork_child(wrap_async, kwargs, econtext):
    mitogen.parent.upgrade_router(econtext)
    context = econtext.router.fork()
    if not wrap_async:
        try:
            return context.call(run_module, kwargs)
        finally:
            context.shutdown()

    job_id = '%016x' % random.randint(0, 2**64)
    context.call_async(run_module_async, job_id, kwargs)
    return {
        'stdout': json.dumps({
            # modules/utilities/logic/async_wrapper.py::_run_module().
            'changed': True,
            'started': 1,
            'finished': 0,
            'ansible_job_id': job_id,
        })
    }


@mitogen.core.takes_econtext
def run_module(kwargs, econtext):
    """
    Set up the process environment in preparation for running an Ansible
    module. This monkey-patches the Ansible libraries in various places to
    prevent it from trying to kill the process on completion, and to prevent it
    from reading sys.stdin.
    """
    should_fork = kwargs.pop('should_fork', False)
    wrap_async = kwargs.pop('wrap_async', False)
    if should_fork:
        return _fork_parent.call(start_fork_child, wrap_async, kwargs)

    runner_name = kwargs.pop('runner_name')
    klass = getattr(ansible_mitogen.runner, runner_name)
    impl = klass(**kwargs)
    return impl.run()


def _get_async_dir():
    return os.path.expanduser(
        os.environ.get('ANSIBLE_ASYNC_DIR', '~/.ansible_async')
    )


def _write_job_status(job_id, dct):
    """
    Update an async job status file.
    """
    LOG.info('_write_job_status(%r, %r)', job_id, dct)
    dct.setdefault('ansible_job_id', job_id)
    dct.setdefault('data', '')

    async_dir = _get_async_dir()
    if not os.path.exists(async_dir):
        os.makedirs(async_dir)

    path = os.path.join(async_dir, job_id)
    with open(path + '.tmp', 'w') as fp:
        fp.write(json.dumps(dct))
    os.rename(path + '.tmp', path)


def _run_module_async(job_id, kwargs, econtext):
    """
    Body on run_module_async().

    1. Immediately updates the status file to mark the job as started.
    2. Installs a timer/signal handler to implement the time limit.
    3. Runs as with run_module(), writing the result to the status file.
    """
    _write_job_status(job_id, {
        'started': 1,
        'finished': 0
    })

    kwargs['emulate_tty'] = False
    dct = run_module(kwargs, econtext)
    if mitogen.core.PY3:
        for key in 'stdout', 'stderr':
            dct[key] = dct[key].decode('utf-8', 'surrogateescape')

    try:
        filtered, warnings = (
            ansible.module_utils.json_utils.
            _filter_non_json_lines(dct['stdout'])
        )
        result = json.loads(filtered)
        result.setdefault('warnings', []).extend(warnings)
        result['stderr'] = dct['stderr']
        _write_job_status(job_id, result)
    except Exception:
        _write_job_status(job_id, {
            "failed": 1,
            "msg": traceback.format_exc(),
            "data": dct['stdout'],  # temporary notice only
            "stderr": dct['stderr']
        })


@mitogen.core.takes_econtext
def run_module_async(job_id, kwargs, econtext):
    """
    Since run_module_async() is invoked with .call_async(), with nothing to
    read the result from the corresponding Receiver, wrap the body in an
    exception logger, and wrap that in something that tears down the context on
    completion.
    """
    try:
        try:
            _run_module_async(job_id, kwargs, econtext)
        except Exception:
            LOG.exception('_run_module_async crashed')
    finally:
        econtext.broker.shutdown()


def make_temp_directory(base_dir):
    """
    Handle creation of `base_dir` if it is absent, in addition to a unique
    temporary directory within `base_dir`.

    :returns:
        Newly created temporary directory.
    """
    if not os.path.exists(base_dir):
        os.makedirs(base_dir, mode=int('0700', 8))
    return tempfile.mkdtemp(
        dir=base_dir,
        prefix='ansible-mitogen-tmp-',
    )


def get_user_shell():
    """
    For commands executed directly via an SSH command-line, SSH looks up the
    user's shell via getpwuid() and only defaults to /bin/sh if that field is
    missing or empty.
    """
    try:
        pw_shell = pwd.getpwuid(os.geteuid()).pw_shell
    except KeyError:
        pw_shell = None

    return pw_shell or '/bin/sh'


def exec_args(args, in_data='', chdir=None, shell=None, emulate_tty=False):
    """
    Run a command in a subprocess, emulating the argument handling behaviour of
    SSH.

    :param list[str]:
        Argument vector.
    :param bytes in_data:
        Optional standard input for the command.
    :param bool emulate_tty:
        If :data:`True`, arrange for stdout and stderr to be merged into the
        stdout pipe and for LF to be translated into CRLF, emulating the
        behaviour of a TTY.
    :return:
        (return code, stdout bytes, stderr bytes)
    """
    LOG.debug('exec_args(%r, ..., chdir=%r)', args, chdir)
    assert isinstance(args, list)

    if emulate_tty:
        stderr = subprocess.STDOUT
    else:
        stderr = subprocess.PIPE

    proc = subprocess.Popen(
        args=args,
        stdout=subprocess.PIPE,
        stderr=stderr,
        stdin=subprocess.PIPE,
        cwd=chdir,
    )
    stdout, stderr = proc.communicate(in_data)

    if emulate_tty:
        stdout = stdout.replace('\n', '\r\n')
    return proc.returncode, stdout, stderr or ''


def exec_command(cmd, in_data='', chdir=None, shell=None, emulate_tty=False):
    """
    Run a command in a subprocess, emulating the argument handling behaviour of
    SSH.

    :param bytes cmd:
        String command line, passed to user's shell.
    :param bytes in_data:
        Optional standard input for the command.
    :return:
        (return code, stdout bytes, stderr bytes)
    """
    assert isinstance(cmd, basestring)
    return exec_args(
        args=[get_user_shell(), '-c', cmd],
        in_data=in_data,
        chdir=chdir,
        shell=shell,
        emulate_tty=emulate_tty,
    )


def read_path(path):
    """
    Fetch the contents of a filesystem `path` as bytes.
    """
    return open(path, 'rb').read()


def write_path(path, s):
    """
    Writes bytes `s` to a filesystem `path`.
    """
    open(path, 'wb').write(s)


CHMOD_CLAUSE_PAT = re.compile(r'([uoga]*)([+\-=])([ugo]|[rwx]*)')
CHMOD_MASKS = {
    'u': stat.S_IRWXU,
    'g': stat.S_IRWXG,
    'o': stat.S_IRWXO,
    'a': (stat.S_IRWXU | stat.S_IRWXG | stat.S_IRWXO),
}
CHMOD_BITS = {
    'u': {'r': stat.S_IRUSR, 'w': stat.S_IWUSR, 'x': stat.S_IXUSR},
    'g': {'r': stat.S_IRGRP, 'w': stat.S_IWGRP, 'x': stat.S_IXGRP},
    'o': {'r': stat.S_IROTH, 'w': stat.S_IWOTH, 'x': stat.S_IXOTH},
    'a': {
        'r': (stat.S_IRUSR | stat.S_IRGRP | stat.S_IROTH),
        'w': (stat.S_IWUSR | stat.S_IWGRP | stat.S_IWOTH),
        'x': (stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH)
    }
}


def apply_mode_spec(spec, mode):
    """
    Given a symbolic file mode change specification in the style of chmod(1)
    `spec`, apply changes in the specification to the numeric file mode `mode`.
    """
    for clause in spec.split(','):
        match = CHMOD_CLAUSE_PAT.match(clause)
        who, op, perms = match.groups()
        for ch in who or 'a':
            mask = CHMOD_MASKS[ch]
            bits = CHMOD_BITS[ch]
            cur_perm_bits = mode & mask
            new_perm_bits = reduce(operator.or_, (bits[p] for p in perms), 0)
            mode &= ~mask
            if op == '=':
                mode |= new_perm_bits
            elif op == '+':
                mode |= new_perm_bits | cur_perm_bits
            else:
                mode |= cur_perm_bits & ~new_perm_bits
    return mode


def set_file_mode(path, spec):
    """
    Update the permissions of a file using the same syntax as chmod(1).
    """
    mode = os.stat(path).st_mode

    if spec.isdigit():
        new_mode = int(spec, 8)
    else:
        new_mode = apply_mode_spec(spec, mode)

    os.chmod(path, new_mode)