"""
This module implements functionality required by master processes, such as
starting new contexts via SSH. Its size is also restricted, since it must be
sent to any context that will be used to establish additional child contexts.
"""

import commands
import getpass
import inspect
import logging
import os
import pkgutil
import re
import socket
import sys
import textwrap
import zlib

import econtext.core


LOG = logging.getLogger('econtext')
IOLOG = logging.getLogger('econtext.io')
RLOG = logging.getLogger('econtext.ctx')

DOCSTRING_RE = re.compile(r'""".+?"""', re.M | re.S)
COMMENT_RE = re.compile(r'^\s*#.*$', re.M)


def minimize_source(source):
    """Remove comments and docstrings from Python `source`, preserving line
    numbers and syntax of empty blocks."""
    subber = lambda match: '""' + ('\n' * match.group(0).count('\n'))
    source = DOCSTRING_RE.sub(subber, source)
    source = COMMENT_RE.sub('\n', source)
    return source.replace('    ', '\t')


def get_child_modules(module, prefix):
    """Return the canonical names of all submodules of a package `module`."""
    it = pkgutil.iter_modules(module.__path__, prefix)
    return [name for _, name, _ in it]


def create_child(*args):
    """Create a child process whose stdin/stdout is connected to a socket,
    returning `(pid, socket_obj)`."""
    parentfp, childfp = socket.socketpair()
    pid = os.fork()
    if not pid:
        os.dup2(childfp.fileno(), 0)
        os.dup2(childfp.fileno(), 1)
        childfp.close()
        parentfp.close()
        os.execvp(args[0], args)
        raise SystemExit

    childfp.close()
    LOG.debug('create_child() child %d fd %d, parent %d, args %r',
              pid, parentfp.fileno(), os.getpid(), args)
    return pid, parentfp


class Listener(econtext.core.BasicStream):
    def __init__(self, broker, address=None, backlog=30):
        self._broker = broker
        self._sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self._sock.bind(address or ('0.0.0.0', 0))
        self._sock.listen(backlog)
        econtext.core.set_cloexec(self._sock.fileno())
        self._listen_addr = self._sock.getsockname()
        self.read_side = econtext.core.Side(self, self._sock.fileno())
        broker.update_stream(self)

    def on_receive(self):
        sock, addr = self._sock.accept()
        context = Context(self._broker, name=addr)
        stream = econtext.core.Stream(context)
        stream.accept(sock.fileno(), sock.fileno())


class LogForwarder(object):
    def __init__(self, context):
        self._context = context
        self._context.add_handle_cb(self.forward_log,
                                    handle=econtext.core.FORWARD_LOG)
        self._log = RLOG.getChild(self._context.name)

    def forward_log(self, data):
        if data == econtext.core._DEAD:
            return

        name, level, s = data
        self._log.log(level, '%s: %s', name, s)


class ModuleResponder(object):
    def __init__(self, context):
        self._context = context
        self._context.add_handle_cb(self.get_module,
                                    handle=econtext.core.GET_MODULE)

    def get_module(self, data):
        if data == econtext.core._DEAD:
            return

        reply_to, fullname = data
        LOG.debug('get_module(%r, %r)', reply_to, fullname)
        try:
            module = __import__(fullname, fromlist=[''])
            is_pkg = getattr(module, '__path__', None) is not None
            path = inspect.getsourcefile(module)
            try:
                source = inspect.getsource(module)
            except IOError:
                if not is_pkg:
                    raise
                source = '\n'

            if is_pkg:
                prefix = module.__name__ + '.'
                present = get_child_modules(module, prefix)
            else:
                present = None

            compressed = zlib.compress(minimize_source(source))
            reply = (is_pkg, present, path, compressed)
            self._context.enqueue(reply_to, reply)
        except Exception:
            LOG.debug('While importing %r', fullname, exc_info=True)
            self._context.enqueue(reply_to, None)


class LocalStream(econtext.core.Stream):
    """
    Base for streams capable of starting new slaves.
    """
    #: The path to the remote Python interpreter.
    python_path = 'python'

    def __init__(self, context):
        super(LocalStream, self).__init__(context)
        self._permitted_classes = set([('econtext.core', 'CallError')])

    def on_shutdown(self):
        """Request the slave gracefully shut itself down."""
        LOG.debug('%r enqueuing SHUTDOWN', self)
        self.enqueue(econtext.core.SHUTDOWN, None)

    def _find_global(self, module_name, class_name):
        """Return the class implementing `module_name.class_name` or raise
        `StreamError` if the module is not whitelisted."""
        if (module_name, class_name) not in self._permitted_classes:
            raise econtext.core.StreamError(
                '%r attempted to unpickle %r in module %r',
                self._context, class_name, module_name)
        return getattr(sys.modules[module_name], class_name)

    def allow_class(self, module_name, class_name):
        """Add `module_name` to the list of permitted modules."""
        self._permitted_modules.add((module_name, class_name))

    # base64'd and passed to 'python -c'. It forks, dups 0->100, creates a
    # pipe, then execs a new interpreter with a custom argv. CONTEXT_NAME is
    # replaced with the context name. Optimized for size.
    def _first_stage():
        import os,sys,zlib
        R,W=os.pipe()
        if os.fork():
            os.dup2(0,100)
            os.dup2(R,0)
            os.close(R)
            os.close(W)
            os.execv(sys.executable,('econtext:'+CONTEXT_NAME,))
        else:
            os.fdopen(W,'wb',0).write(zlib.decompress(sys.stdin.read(input())))
            print 'OK'
            sys.exit(0)

    def get_boot_command(self):
        name = self._context.remote_name
        if name is None:
            name = '%s@%s:%d'
            name %= (getpass.getuser(), socket.gethostname(), os.getpid())

        source = inspect.getsource(self._first_stage)
        source = textwrap.dedent('\n'.join(source.strip().split('\n')[1:]))
        source = source.replace('    ', '\t')
        source = source.replace('CONTEXT_NAME', repr(name))
        encoded = source.encode('base64').replace('\n', '')
        return [self.python_path, '-c',
                'exec "%s".decode("base64")' % (encoded,)]

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

    def get_preamble(self):
        source = inspect.getsource(econtext.core)
        source += '\nExternalContext().main%r\n' % ((
            self._context.key,
            LOG.level or logging.getLogger().level or logging.INFO,
        ),)

        compressed = zlib.compress(minimize_source(source))
        return str(len(compressed)) + '\n' + compressed

    def connect(self):
        LOG.debug('%r.connect()', self)
        pid, sock = create_child(*self.get_boot_command())
        self.read_side = econtext.core.Side(self, os.dup(sock.fileno()))
        self.write_side = econtext.core.Side(self, os.dup(sock.fileno()))
        sock.close()
        LOG.debug('%r.connect(): child process stdin/stdout=%r',
                  self, self.read_side.fd)

        econtext.core.write_all(self.write_side.fd, self.get_preamble())
        s = os.read(self.read_side.fd, 4096)
        if s != 'OK\n':
            raise econtext.core.StreamError('Bootstrap failed; stdout: %r', s)


class SSHStream(LocalStream):
    #: The path to the SSH binary.
    ssh_path = 'ssh'

    def get_boot_command(self):
        bits = [self.ssh_path]
        if self._context.username:
            bits += ['-l', self._context.username]
        bits.append(self._context.hostname)
        base = super(SSHStream, self).get_boot_command()
        return bits + map(commands.mkarg, base)


class Broker(econtext.core.Broker):
    #: Always allow time for slaves to drain.
    graceful_count = 1

    def create_listener(self, address=None, backlog=30):
        """Listen on `address `for connections from newly spawned contexts."""
        self._listener = Listener(self, address, backlog)

    def get_local(self, name='default', python_path=None):
        """Get the named context running on the local machine, creating it if
        it does not exist."""
        context = Context(self, name)
        context.stream = LocalStream(context)
        if python_path:
            context.stream.python_path = python_path
        context.stream.connect()
        return self.register(context)

    def get_remote(self, hostname, username=None, name=None, python_path=None):
        """Get the named remote context, creating it if it does not exist."""
        if name is None:
            name = hostname

        context = Context(self, name, hostname, username)
        context.stream = SSHStream(context)
        if python_path:
            context.stream.python_path = python_path
        context.stream.connect()
        return self.register(context)


class Context(econtext.core.Context):
    def __init__(self, *args, **kwargs):
        super(Context, self).__init__(*args, **kwargs)
        self.responder = ModuleResponder(self)
        self.log_forwarder = LogForwarder(self)

    def on_disconnect(self):
        self.stream = None