#!/usr/bin/python
# Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import logging


class Error(Exception):
  pass


_DefaultAlwaysCheck = False


class _ErrorCheckerContext(object):
    """Reference-count our error-checking state and only check for
    errors when we take the first ref or drop the last ref.

    This way, we can minimize the number of checks; each one takes a
    bit of time.  You will likely want to set always_check to True when
    debugging new SCPI interactions.

    On first entry, we check for errors, but do not stop if we find
    them; these are errors that were accumulated on the device before
    this test ran.
    """

    def __init__(self, scpi):
        self.always_check = _DefaultAlwaysCheck
        self.scpi = scpi
        self.depth = 0
        self.ignore_errors_once = True

    def __enter__(self):
        if self.depth == 0 or self.always_check:
            errors = self.scpi._WaitAndFetchErrors(
                raise_on_error=not self.ignore_errors_once)
            self.ignore_errors_once = False
        self.depth += 1
        return self

    def __exit__(self, type, value, traceback):
        self.depth -= 1
        if self.depth <= 0 or self.always_check:
            self.scpi._WaitAndFetchErrors()
        return


class Scpi(object):
  """Wrapper for SCPI.

  SCPI = "standard commands for programmable instruments",
  a relative of GPIB.

  The SCPI driver must export:  Query, Send, Reset and Close
  """

  def __init__(self, driver, opc_on_stanza=False):
    self.driver = driver
    self.opc_on_stanza = opc_on_stanza
    self.scpi_logger = logging.getLogger('SCPI')
    self.checker_context = _ErrorCheckerContext(self)

  def Query(self, command):
    """Send the SCPI command and return the response."""
    self.scpi_logger.info('] %s', command)
    response = self.driver.Query(command)
    self.scpi_logger.info('[ %s', response)
    return response

  def Send(self, command):
    """Send the SCPI command."""
    self.scpi_logger.info('] %s', command)
    self.driver.Send(command)

  def Reset(self):
    """Tell the device to reset with *RST."""
    # Some devices (like the prologix) require special handling for
    # reset.
    self.driver.Reset()

  def Close(self):
    """Close the device."""
    self.driver.Close()

  def RetrieveErrors(self):
    """Retrieves all SYSTem:ERRor messages from the device."""
    errors = []
    while True:
      error = self.Query('SYSTem:ERRor?')
      if '+0,"No error"' in error:
        # We've reached the end of the error stack
        break
      if '-420' in error and 'Query UNTERMINATED' in error:
        # This is benign; the GPIB bridge asked for a response when
        # the device didn't have one to give.

        # TODO(rochberg): This is a layering violation; we should
        # really only accept -420 if the underlying driver is in a
        # mode that is known to cause this
        continue
      if '+292' in error and 'Data arrived on unknown SAPI' in error:
        # This may be benign; It is known to occur when we do a switch
        # from GPRS to WCDMA
        continue

      else:
        errors.append(error)
    self.Send('*CLS')           # Clear status
    errors.reverse()
    return errors

  def _WaitAndFetchErrors(self, raise_on_error=True):
    """Waits for command completion, returns errors."""
    self.Query('*OPC?')      # Wait for operation complete
    errors = self.RetrieveErrors()
    if errors and raise_on_error:
      raise Error('\n'.join(errors))
    return errors

  def SimpleVerify(self, command, arg):
    """Sends "command arg", then "command?", expecting arg back.

    Arguments:
      command: SCPI command
      arg: Argument.  We currently check for exact equality: you should
        send strings quoted with " because that's what the 8960 returns.
        We also fail if you send 1 and receive +1 back.

    Raises:
      Error:  Verification failed
    """
    with self.checker_context:
        self.Send('%s %s' % (command, arg))
        result = self.Query('%s?' % (command,))
        if result != arg:
          raise Error('Error on %s: sent %s, got %s' % (command, arg, result))

  def SendStanza(self, commands):
    """Sends a list of commands, checks to see that they complete correctly."""
    with self.checker_context:
        for c in commands:
          if self.opc_on_stanza:
            self.Query(c + ';*OPC?')
          else:
            self.Send(c)