# Copyright 2017, David Wilson
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
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# 1. Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
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# 2. Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
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# POSSIBILITY OF SUCH DAMAGE.

"""
Classes to detect each case from [0] and prepare arguments necessary for the
corresponding Runner class within the target, including preloading requisite
files/modules known missing.

[0] "Ansible Module Architecture", developing_program_flow_modules.html
"""

from __future__ import absolute_import
from __future__ import unicode_literals

import json
import logging
import os
import random

from ansible.executor import module_common
import ansible.errors
import ansible.module_utils
import mitogen.core

import ansible_mitogen.loaders
import ansible_mitogen.target


LOG = logging.getLogger(__name__)
NO_METHOD_MSG = 'Mitogen: no invocation method found for: '
NO_INTERPRETER_MSG = 'module (%s) is missing interpreter line'


def parse_script_interpreter(source):
    """
    Extract the script interpreter and its sole argument from the module
    source code.

    :returns:
        Tuple of `(interpreter, arg)`, where `intepreter` is the script
        interpreter and `arg` is its sole argument if present, otherwise
        :py:data:`None`.
    """
    # Linux requires first 2 bytes with no whitespace, pretty sure it's the
    # same everywhere. See binfmt_script.c.
    if not source.startswith(b'#!'):
        return None, None

    # Find terminating newline. Assume last byte of binprm_buf if absent.
    nl = source.find(b'\n', 0, 128)
    if nl == -1:
        nl = min(128, len(source))

    # Split once on the first run of whitespace. If no whitespace exists,
    # bits just contains the interpreter filename.
    bits = source[2:nl].strip().split(None, 1)
    if len(bits) == 1:
        return mitogen.core.to_text(bits[0]), None
    return mitogen.core.to_text(bits[0]), mitogen.core.to_text(bits[1])


class Invocation(object):
    """
    Collect up a module's execution environment then use it to invoke
    target.run_module() or helpers.run_module_async() in the target context.
    """
    def __init__(self, action, connection, module_name, module_args,
                 task_vars, templar, env, wrap_async, timeout_secs):
        #: ActionBase instance invoking the module. Required to access some
        #: output postprocessing methods that don't belong in ActionBase at
        #: all.
        self.action = action
        #: Ansible connection to use to contact the target. Must be an
        #: ansible_mitogen connection.
        self.connection = connection
        #: Name of the module ('command', 'shell', etc.) to execute.
        self.module_name = module_name
        #: Final module arguments.
        self.module_args = module_args
        #: Task variables, needed to extract ansible_*_interpreter.
        self.task_vars = task_vars
        #: Templar, needed to extract ansible_*_interpreter.
        self.templar = templar
        #: Final module environment.
        self.env = env
        #: Boolean, if :py:data:`True`, launch the module asynchronously.
        self.wrap_async = wrap_async
        #: Integer, if >0, limit the time an asynchronous job may run for.
        self.timeout_secs = timeout_secs
        #: Initially ``None``, but set by :func:`invoke`. The path on the
        #: master to the module's implementation file.
        self.module_path = None
        #: Initially ``None``, but set by :func:`invoke`. The raw source or
        #: binary contents of the module.
        self.module_source = None

    def __repr__(self):
        return 'Invocation(module_name=%s)' % (self.module_name,)


class Planner(object):
    """
    A Planner receives a module name and the contents of its implementation
    file, indicates whether or not it understands how to run the module, and
    exports a method to run the module.
    """
    def __init__(self, invocation):
        self._inv = invocation

    def detect(self):
        """
        Return true if the supplied `invocation` matches the module type
        implemented by this planner.
        """
        raise NotImplementedError()

    def should_fork(self):
        """
        Asynchronous tasks must always be forked.
        """
        return self._inv.wrap_async

    def get_push_files(self):
        """
        Return a list of files that should be propagated to the target context
        using PushFileService. The default implementation pushes nothing.
        """
        return []

    def get_module_deps(self):
        """
        Return a list of the Python module names imported by the module.
        """
        return []

    def get_kwargs(self, **kwargs):
        """
        If :meth:`detect` returned :data:`True`, plan for the module's
        execution, including granting access to or delivering any files to it
        that are known to be absent, and finally return a dict::

            {
                # Name of the class from runners.py that implements the
                # target-side execution of this module type.
                "runner_name": "...",

                # Remaining keys are passed to the constructor of the class
                # named by `runner_name`.
            }
        """
        new = dict((mitogen.core.UnicodeType(k), kwargs[k])
                   for k in kwargs)
        new.setdefault('emulate_tty', True)
        new.setdefault('service_context', self._inv.connection.parent)
        return new

    def __repr__(self):
        return '%s()' % (type(self).__name__,)


class BinaryPlanner(Planner):
    """
    Binary modules take their arguments and will return data to Ansible in the
    same way as want JSON modules.
    """
    runner_name = 'BinaryRunner'

    def detect(self):
        return module_common._is_binary(self._inv.module_source)

    def get_push_files(self):
        return [self._inv.module_path]

    def get_kwargs(self, **kwargs):
        return super(BinaryPlanner, self).get_kwargs(
            runner_name=self.runner_name,
            module=self._inv.module_name,
            path=self._inv.module_path,
            json_args=json.dumps(self._inv.module_args),
            env=self._inv.env,
            **kwargs
        )


class ScriptPlanner(BinaryPlanner):
    """
    Common functionality for script module planners -- handle interpreter
    detection and rewrite.
    """
    def _get_interpreter(self):
        interpreter, arg = parse_script_interpreter(
            self._inv.module_source
        )
        if interpreter is None:
            raise ansible.errors.AnsibleError(NO_INTERPRETER_MSG % (
                self._inv.module_name,
            ))

        key = u'ansible_%s_interpreter' % os.path.basename(interpreter).strip()
        try:
            template = self._inv.task_vars[key].strip()
            return self._inv.templar.template(template), arg
        except KeyError:
            return interpreter, arg

    def get_kwargs(self, **kwargs):
        interpreter, arg = self._get_interpreter()
        return super(ScriptPlanner, self).get_kwargs(
            interpreter_arg=arg,
            interpreter=interpreter,
            **kwargs
        )


class JsonArgsPlanner(ScriptPlanner):
    """
    Script that has its interpreter directive and the task arguments
    substituted into its source as a JSON string.
    """
    runner_name = 'JsonArgsRunner'

    def detect(self):
        return module_common.REPLACER_JSONARGS in self._inv.module_source


class WantJsonPlanner(ScriptPlanner):
    """
    If a module has the string WANT_JSON in it anywhere, Ansible treats it as a
    non-native module that accepts a filename as its only command line
    parameter. The filename is for a temporary file containing a JSON string
    containing the module's parameters. The module needs to open the file, read
    and parse the parameters, operate on the data, and print its return data as
    a JSON encoded dictionary to stdout before exiting.

    These types of modules are self-contained entities. As of Ansible 2.1,
    Ansible only modifies them to change a shebang line if present.
    """
    runner_name = 'WantJsonRunner'

    def detect(self):
        return b'WANT_JSON' in self._inv.module_source


class NewStylePlanner(ScriptPlanner):
    """
    The Ansiballz framework differs from module replacer in that it uses real
    Python imports of things in ansible/module_utils instead of merely
    preprocessing the module.
    """
    runner_name = 'NewStyleRunner'
    marker = b'from ansible.module_utils.'

    def detect(self):
        return self.marker in self._inv.module_source

    def _get_interpreter(self):
        return None, None

    def get_push_files(self):
        return super(NewStylePlanner, self).get_push_files() + [
            path
            for fullname, path, is_pkg in self.get_module_map()['custom']
        ]

    def get_module_deps(self):
        return self.get_module_map()['builtin']

    #: Module names appearing in this set always require forking, usually due
    #: to some terminal leakage that cannot be worked around in any sane
    #: manner.
    ALWAYS_FORK_MODULES = frozenset([
        'dnf',  # issue #280; py-dnf/hawkey need therapy
    ])

    def should_fork(self):
        """
        In addition to asynchronous tasks, new-style modules should be forked
        if:

        * the user specifies mitogen_task_isolation=fork, or
        * the new-style module has a custom module search path, or
        * the module is known to leak like a sieve.
        """
        return (
            super(NewStylePlanner, self).should_fork() or
            (self._inv.task_vars.get('mitogen_task_isolation') == 'fork') or
            (self._inv.module_name in self.ALWAYS_FORK_MODULES) or
            (len(self.get_module_map()['custom']) > 0)
        )

    def get_search_path(self):
        return tuple(
            path
            for path in ansible_mitogen.loaders.module_utils_loader._get_paths(
                subdirs=False
            )
            if os.path.isdir(path)
        )

    _module_map = None

    def get_module_map(self):
        if self._module_map is None:
            self._module_map = self._inv.connection.parent.call_service(
                service_name='ansible_mitogen.services.ModuleDepService',
                method_name='scan',

                module_name='ansible_module_%s' % (self._inv.module_name,),
                module_path=self._inv.module_path,
                search_path=self.get_search_path(),
                builtin_path=module_common._MODULE_UTILS_PATH,
                context=self._inv.connection.context,
            )
        return self._module_map

    def get_kwargs(self):
        return super(NewStylePlanner, self).get_kwargs(
            module_map=self.get_module_map(),
        )


class ReplacerPlanner(NewStylePlanner):
    """
    The Module Replacer framework is the original framework implementing
    new-style modules. It is essentially a preprocessor (like the C
    Preprocessor for those familiar with that programming language). It does
    straight substitutions of specific substring patterns in the module file.
    There are two types of substitutions.

    * Replacements that only happen in the module file. These are public
      replacement strings that modules can utilize to get helpful boilerplate
      or access to arguments.

      "from ansible.module_utils.MOD_LIB_NAME import *" is replaced with the
      contents of the ansible/module_utils/MOD_LIB_NAME.py. These should only
      be used with new-style Python modules.

      "#<<INCLUDE_ANSIBLE_MODULE_COMMON>>" is equivalent to
      "from ansible.module_utils.basic import *" and should also only apply to
      new-style Python modules.

      "# POWERSHELL_COMMON" substitutes the contents of
      "ansible/module_utils/powershell.ps1". It should only be used with
      new-style Powershell modules.
    """
    runner_name = 'ReplacerRunner'

    def detect(self):
        return module_common.REPLACER in self._inv.module_source


class OldStylePlanner(ScriptPlanner):
    runner_name = 'OldStyleRunner'

    def detect(self):
        # Everything else.
        return True


_planners = [
    BinaryPlanner,
    # ReplacerPlanner,
    NewStylePlanner,
    JsonArgsPlanner,
    WantJsonPlanner,
    OldStylePlanner,
]


def get_module_data(name):
    path = ansible_mitogen.loaders.module_loader.find_plugin(name, '')
    with open(path, 'rb') as fp:
        source = fp.read()
    return mitogen.core.to_text(path), source


def _propagate_deps(invocation, planner, context):
    invocation.connection.parent.call_service(
        service_name='mitogen.service.PushFileService',
        method_name='propagate_paths_and_modules',
        context=context,
        paths=planner.get_push_files(),
        modules=planner.get_module_deps(),
    )


def _invoke_async_task(invocation, planner):
    job_id = '%016x' % random.randint(0, 2**64)
    context = invocation.connection.create_fork_child()
    _propagate_deps(invocation, planner, context)
    context.call_no_reply(
        ansible_mitogen.target.run_module_async,
        job_id=job_id,
        timeout_secs=invocation.timeout_secs,
        kwargs=planner.get_kwargs(),
    )

    return {
        'stdout': json.dumps({
            # modules/utilities/logic/async_wrapper.py::_run_module().
            'changed': True,
            'started': 1,
            'finished': 0,
            'ansible_job_id': job_id,
        })
    }


def _invoke_forked_task(invocation, planner):
    context = invocation.connection.create_fork_child()
    _propagate_deps(invocation, planner, context)
    try:
        return context.call(
            ansible_mitogen.target.run_module,
            kwargs=planner.get_kwargs(),
        )
    finally:
        context.shutdown()


def _get_planner(invocation):
    for klass in _planners:
        planner = klass(invocation)
        if planner.detect():
            LOG.debug('%r accepted %r (filename %r)', planner,
                      invocation.module_name, invocation.module_path)
            return planner
        LOG.debug('%r rejected %r', planner, invocation.module_name)
    raise ansible.errors.AnsibleError(NO_METHOD_MSG + repr(invocation))


def invoke(invocation):
    """
    Find a Planner subclass corresnding to `invocation` and use it to invoke
    the module.

    :param Invocation invocation:
    :returns:
        Module return dict.
    :raises ansible.errors.AnsibleError:
        Unrecognized/unsupported module type.
    """
    (invocation.module_path,
     invocation.module_source) = get_module_data(invocation.module_name)
    planner = _get_planner(invocation)

    if invocation.wrap_async:
        response = _invoke_async_task(invocation, planner)
    elif planner.should_fork():
        response = _invoke_forked_task(invocation, planner)
    else:
        _propagate_deps(invocation, planner, invocation.connection.context)
        response = invocation.connection.call(
            ansible_mitogen.target.run_module,
            kwargs=planner.get_kwargs(),
        )

    return invocation.action._postprocess_response(response)