"""
Implements the python side of the data engine sandbox, which allows us to register functions on
the python side and call them from Node.js.

Usage:
  import sandbox
  sandbox.register(func_name, func)
  sandbox.call_external("hello", 1, 2, 3)
  sandbox.run()
"""

import os
import marshal
import sys
import traceback

class CarefulReader(object):
  """
  Wrap a pipe when reading from Pyodide, to work around marshaling
  panicking if fewer bytes are read in a block than it was expecting.
  Just wait for more.
  """

  def __init__(self, file_):
    self._file = file_

  def write(self, data):
    return self._file.write(data)

  def read(self, size):
    return self._file.read(size)

  def readinto(self, b):
    result = self._file.readinto(b)
    while result is not None and result < len(b):
      bview = memoryview(b)
      result += self._file.readinto(bview[result:])
    return result

  def __getattr__(self, attr):
    return getattr(self._file, attr)

def log(msg):
  sys.stderr.write(str(msg) + "\n")
  sys.stderr.flush()

class Sandbox(object):
  """
  This class works in conjunction with Sandbox.js to allow function calls
  between the Node process and this sandbox.

  The sandbox provides two pipes to send data to and from the sandboxed
  process. Data on these is serialized using `marshal` module. All messages are comprised of a
  msgCode followed immediatedly by msgBody, with the following msgCodes:
    CALL = call to the other side. The data must be an array of [func_name, arguments...]
    DATA = data must be a value to return to a call from the other side
    EXC = data must be an exception to return to a call from the other side

  Optionally, a callback can be supplied instead of an output pipe.
  """

  CALL = None
  DATA = True
  EXC = False

  def __init__(self, external_input, external_output, external_output_method=None):
    self._functions = {}
    self._external_input = external_input
    self._external_output = external_output
    self._external_output_method = external_output_method

  @classmethod
  def connected_to_js_pipes(cls):
    """
    Send data on two specially-opened side channels.
    """
    external_input = os.fdopen(3, "rb", 64 * 1024)
    external_output = os.fdopen(4, "wb", 64 * 1024)
    return cls(external_input, external_output)

  @classmethod
  def use_common_pipes(cls):
    """
    Send data via stdin/stdout, rather than specially-opened side channels.
    Duplicate stdin/stdout, close, and reopen as binary file objects.
    """
    os.dup2(0, 3)
    os.dup2(1, 4)
    os.close(0)
    os.close(1)
    sys.stdout = sys.stderr
    return Sandbox.connected_to_js_pipes()

  @classmethod
  def use_pyodide(cls):
    import js  # Get pyodide object.
    external_input = CarefulReader(sys.stdin.buffer)
    external_output_method = lambda data: js.sendFromSandbox(data)
    sys.stdout = sys.stderr
    return cls(external_input, None, external_output_method)

  def _send_to_js(self, msgCode, msgBody):
    # (Note that marshal version 2 is the default; we specify it explicitly for clarity. The
    # difference with version 0 is that version 2 uses a faster binary format for floats.)

    # For large data, JS's Unmarshaller is very inefficient parsing it if it gets it piecewise.
    # It's much better to ensure the whole blob is sent as one write. We marshal the resulting
    # buffer again so that the reader can quickly tell how many bytes to expect.
    buf = marshal.dumps((msgCode, msgBody), 2)
    if self._external_output:
      marshal.dump(buf, self._external_output, 2)
      self._external_output.flush()
    elif self._external_output_method:
      buf = marshal.dumps(buf, 2)
      self._external_output_method(buf)
    else:
      raise Exception('no data output method')

  def call_external(self, name, *args):
    self._send_to_js(Sandbox.CALL, (name,) + args)
    (msgCode, data) = self.run(break_on_response=True)
    if msgCode == Sandbox.EXC:
      raise Exception(data)
    return data

  def register(self, func_name, func):
    self._functions[func_name] = func

  def run(self, break_on_response=False):
    while True:
      try:
        msgCode = marshal.load(self._external_input)
        data = marshal.load(self._external_input)
      except EOFError:
        break
      if msgCode != Sandbox.CALL:
        if break_on_response:
          return (msgCode, data)
        continue

      if not isinstance(data, list) or len(data) < 1:
        raise ValueError("Bad call " + data)
      try:
        fname = data[0]
        args = data[1:]
        ret = self._functions[fname](*args)
        self._send_to_js(Sandbox.DATA, ret)
      except Exception as e:
        traceback.print_exc()
        self._send_to_js(Sandbox.EXC, "%s %s" % (type(e).__name__, e))
    if break_on_response:
      raise Exception("Sandbox disconnected unexpectedly")

default_sandbox = None

def get_default_sandbox():
  global default_sandbox
  if default_sandbox is None:
    if os.environ.get('PIPE_MODE') == 'minimal':
      default_sandbox = Sandbox.use_common_pipes()
    elif os.environ.get('PIPE_MODE') == 'pyodide':
      default_sandbox = Sandbox.use_pyodide()
    else:
      default_sandbox = Sandbox.connected_to_js_pipes()
  return default_sandbox

def call_external(name, *args):
  return get_default_sandbox().call_external(name, *args)

def register(func_name, func):
  get_default_sandbox().register(func_name, func)

def run():
  get_default_sandbox().run()