# 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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# 3. Neither the name of the copyright holder nor the names of its contributors
# may be used to endorse or promote products derived from this software without
# specific prior written permission.
#
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# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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# POSSIBILITY OF SUCH DAMAGE.

"""
Classes in this file define Mitogen 'services' that run (initially) within the
connection multiplexer process that is forked off the top-level controller
process.

Once a worker process connects to a multiplexer process
(Connection._connect()), it communicates with these services to establish new
connections, grant access to files by children, and register for notification
when a child has completed a job.
"""

from __future__ import absolute_import
import logging
import os
import os.path
import sys
import threading

import mitogen
import mitogen.service
import ansible_mitogen.module_finder
import ansible_mitogen.target


LOG = logging.getLogger(__name__)


class Error(Exception):
    pass


class ContextService(mitogen.service.Service):
    """
    Used by workers to fetch the single Context instance corresponding to a
    connection configuration, creating the matching connection if it does not
    exist.

    For connection methods and their parameters, see:
        https://mitogen.readthedocs.io/en/latest/api.html#context-factories

    This concentrates connections in the top-level process, which may become a
    bottleneck. The bottleneck can be removed using per-CPU connection
    processes and arranging for the worker to select one according to a hash of
    the connection parameters (sharding).
    """
    max_interpreters = int(os.getenv('MITOGEN_MAX_INTERPRETERS', '20'))

    def __init__(self, *args, **kwargs):
        super(ContextService, self).__init__(*args, **kwargs)
        self._lock = threading.Lock()
        #: Records the :meth:`get` result dict for successful calls, returned
        #: for identical subsequent calls. Keyed by :meth:`key_from_kwargs`.
        self._response_by_key = {}
        #: List of :class:`mitogen.core.Latch` awaiting the result for a
        #: particular key.
        self._latches_by_key = {}
        #: Mapping of :class:`mitogen.core.Context` -> reference count. Each
        #: call to :meth:`get` increases this by one. Calls to :meth:`put`
        #: decrease it by one.
        self._refs_by_context = {}
        #: List of contexts in creation order by via= parameter. When
        #: :attr:`max_interpreters` is reached, the most recently used context
        #: is destroyed to make room for any additional context.
        self._lru_by_via = {}
        #: :meth:`key_from_kwargs` result by Context.
        self._key_by_context = {}

    @mitogen.service.expose(mitogen.service.AllowParents())
    @mitogen.service.arg_spec({
        'context': mitogen.core.Context
    })
    def put(self, context):
        """
        Return a reference, making it eligable for recycling once its reference
        count reaches zero.
        """
        LOG.debug('%r.put(%r)', self, context)
        if self._refs_by_context.get(context, 0) == 0:
            LOG.warning('%r.put(%r): refcount was 0. shutdown_all called?',
                        self, context)
            return
        self._refs_by_context[context] -= 1

    def key_from_kwargs(self, **kwargs):
        """
        Generate a deduplication key from the request.
        """
        out = []
        stack = [kwargs]
        while stack:
            obj = stack.pop()
            if isinstance(obj, dict):
                stack.extend(sorted(obj.iteritems()))
            elif isinstance(obj, (list, tuple)):
                stack.extend(obj)
            else:
                out.append(str(obj))
        return ''.join(out)

    def _produce_response(self, key, response):
        """
        Reply to every waiting request matching a configuration key with a
        response dictionary, deleting the list of waiters when done.

        :param str key:
            Result of :meth:`key_from_kwargs`
        :param dict response:
            Response dictionary
        :returns:
            Number of waiters that were replied to.
        """
        self._lock.acquire()
        try:
            latches = self._latches_by_key.pop(key)
            count = len(latches)
            for latch in latches:
                latch.put(response)
        finally:
            self._lock.release()
        return count

    def _shutdown(self, context, lru=None, new_context=None):
        """
        Arrange for `context` to be shut down, and optionally add `new_context`
        to the LRU list while holding the lock.
        """
        LOG.info('%r._shutdown(): shutting down %r', self, context)
        context.shutdown()

        key = self._key_by_context[context]

        self._lock.acquire()
        try:
            del self._response_by_key[key]
            del self._refs_by_context[context]
            del self._key_by_context[context]
            if lru and context in lru:
                lru.remove(context)
            if new_context:
                lru.append(new_context)
        finally:
            self._lock.release()

    def _update_lru(self, new_context, spec, via):
        """
        Update the LRU ("MRU"?) list associated with the connection described
        by `kwargs`, destroying the most recently created context if the list
        is full. Finally add `new_context` to the list.
        """
        lru = self._lru_by_via.setdefault(via, [])
        if len(lru) < self.max_interpreters:
            lru.append(new_context)
            return

        for context in reversed(lru):
            if self._refs_by_context[context] == 0:
                break
        else:
            LOG.warning('via=%r reached maximum number of interpreters, '
                        'but they are all marked as in-use.', via)
            return

        self._shutdown(context, lru=lru, new_context=new_context)

    @mitogen.service.expose(mitogen.service.AllowParents())
    def shutdown_all(self):
        """
        For testing use, arrange for all connections to be shut down.
        """
        for context in list(self._key_by_context):
            self._shutdown(context)
        self._lru_by_via = {}

    def _on_stream_disconnect(self, stream):
        """
        Respond to Stream disconnection by deleting any record of contexts
        reached via that stream. This method runs in the Broker thread and must
        not to block.
        """
        # TODO: there is a race between creation of a context and disconnection
        # of its related stream. An error reply should be sent to any message
        # in _latches_by_key below.
        self._lock.acquire()
        try:
            for context, key in list(self._key_by_context.items()):
                if context.context_id in stream.routes:
                    LOG.info('Dropping %r due to disconnect of %r',
                             context, stream)
                    self._response_by_key.pop(key, None)
                    self._latches_by_key.pop(key, None)
                    self._refs_by_context.pop(context, None)
                    self._lru_by_via.pop(context, None)
                    self._refs_by_context.pop(context, None)
        finally:
            self._lock.release()

    ALWAYS_PRELOAD = (
        'ansible.module_utils.basic',
        'ansible.module_utils.json_utils',
        'ansible.release',
        'ansible_mitogen.runner',
        'ansible_mitogen.target',
        'mitogen.fork',
        'mitogen.service',
    )

    def _send_module_forwards(self, context):
        for fullname in self.ALWAYS_PRELOAD:
            self.router.responder.forward_module(context, fullname)

    def _connect(self, key, spec, via=None):
        """
        Actual connect implementation. Arranges for the Mitogen connection to
        be created and enqueues an asynchronous call to start the forked task
        parent in the remote context.

        :param key:
            Deduplication key representing the connection configuration.
        :param spec:
            Connection specification.
        :returns:
            Dict like::

                {
                    'context': mitogen.core.Context or None,
                    'home_dir': str or None,
                    'msg': str or None
                }

            Where either `msg` is an error message and the remaining fields are
            :data:`None`, or `msg` is :data:`None` and the remaining fields are
            set.
        """
        try:
            method = getattr(self.router, spec['method'])
        except AttributeError:
            raise Error('unsupported method: %(transport)s' % spec)

        context = method(via=via, unidirectional=True, **spec['kwargs'])
        if via and spec.get('enable_lru'):
            self._update_lru(context, spec, via)
        else:
            # For directly connected contexts, listen to the associated
            # Stream's disconnect event and use it to invalidate dependent
            # Contexts.
            stream = self.router.stream_by_id(context.context_id)
            mitogen.core.listen(stream, 'disconnect',
                                lambda: self._on_stream_disconnect(stream))

        self._send_module_forwards(context)
        home_dir = context.call(os.path.expanduser, '~')

        # We don't need to wait for the result of this. Ideally we'd check its
        # return value somewhere, but logs will catch a failure anyway.
        context.call_async(ansible_mitogen.target.init_child)

        if os.environ.get('MITOGEN_DUMP_THREAD_STACKS'):
            from mitogen import debug
            context.call(debug.dump_to_logger)

        self._key_by_context[context] = key
        self._refs_by_context[context] = 0
        return {
            'context': context,
            'home_dir': home_dir,
            'msg': None,
        }

    def _wait_or_start(self, spec, via=None):
        latch = mitogen.core.Latch()
        key = self.key_from_kwargs(via=via, **spec)
        self._lock.acquire()
        try:
            response = self._response_by_key.get(key)
            if response is not None:
                self._refs_by_context[response['context']] += 1
                latch.put(response)
                return latch

            latches = self._latches_by_key.setdefault(key, [])
            first = len(latches) == 0
            latches.append(latch)
        finally:
            self._lock.release()

        if first:
            # I'm the first requestee, so I will create the connection.
            try:
                response = self._connect(key, spec, via=via)
                count = self._produce_response(key, response)
                # Only record the response for non-error results.
                self._response_by_key[key] = response
                # Set the reference count to the number of waiters.
                self._refs_by_context[response['context']] += count
            except Exception:
                self._produce_response(key, sys.exc_info())

        return latch

    @mitogen.service.expose(mitogen.service.AllowParents())
    @mitogen.service.arg_spec({
        'stack': list
    })
    def get(self, msg, stack):
        """
        Return a Context referring to an established connection with the given
        configuration, establishing new connections as necessary.

        :param list stack:
            Connection descriptions. Each element is a dict containing 'method'
            and 'kwargs' keys describing the Router method and arguments.
            Subsequent elements are proxied via the previous.

        :returns dict:
            * context: mitogen.master.Context or None.
            * homedir: Context's home directory or None.
            * msg: StreamError exception text or None.
            * method_name: string failing method name.
        """
        via = None
        for spec in stack:
            try:
                result = self._wait_or_start(spec, via=via).get()
                if isinstance(result, tuple):  # exc_info()
                    e1, e2, e3 = result
                    raise e1, e2, e3
                via = result['context']
            except mitogen.core.StreamError as e:
                return {
                    'context': None,
                    'home_dir': None,
                    'method_name': spec['method'],
                    'msg': str(e),
                }

        return result


class ModuleDepService(mitogen.service.Service):
    """
    Scan a new-style module and produce a cached mapping of module_utils names
    to their resolved filesystem paths.
    """
    def __init__(self, file_service, **kwargs):
        super(ModuleDepService, self).__init__(**kwargs)
        self._file_service = file_service
        self._cache = {}

    def _get_builtin_names(self, builtin_path, resolved):
        return [
            fullname
            for fullname, path, is_pkg in resolved
            if os.path.abspath(path).startswith(builtin_path)
        ]

    def _get_custom_tups(self, builtin_path, resolved):
        return [
            (fullname, path, is_pkg)
            for fullname, path, is_pkg in resolved
            if not os.path.abspath(path).startswith(builtin_path)
        ]

    @mitogen.service.expose(policy=mitogen.service.AllowParents())
    @mitogen.service.arg_spec({
        'module_name': basestring,
        'module_path': basestring,
        'search_path': tuple,
        'builtin_path': basestring,
        'context': mitogen.core.Context,
    })
    def scan(self, module_name, module_path, search_path, builtin_path, context):
        key = (module_name, search_path)
        if key not in self._cache:
            resolved = ansible_mitogen.module_finder.scan(
                module_name=module_name,
                module_path=module_path,
                search_path=tuple(search_path) + (builtin_path,),
            )
            builtin_path = os.path.abspath(builtin_path)
            builtin = self._get_builtin_names(builtin_path, resolved)
            custom = self._get_custom_tups(builtin_path, resolved)
            self._cache[key] = {
                'builtin': builtin,
                'custom': custom,
            }

            # Grant FileService access to paths in here to avoid another 2 IPCs
            # from WorkerProcess.
            self._file_service.register(path=module_path)
            for fullname, path, is_pkg in custom:
                self._file_service.register(path=path)

        for name in self._cache[key]['builtin']:
            self.router.responder.forward_module(context, name)
        return self._cache[key]['custom']