#!/usr/bin/python2.5

#

# Copyright 2008 the Melange authors.

#

# Licensed under the Apache License, Version 2.0 (the "License");

# you may not use this file except in compliance with the License.

# You may obtain a copy of the License at

#

#   http://www.apache.org/licenses/LICENSE-2.0

#

# Unless required by applicable law or agreed to in writing, software

# distributed under the License is distributed on an "AS IS" BASIS,

# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

# See the License for the specific language governing permissions and

# limitations under the License.

"""Helpers for manipulating HTTP requests.

"""

__authors__ = [

  '"Todd Larsen" <tlarsen@google.com>',

  ]

def getSingleIndexedParamValue(request, param_name, values=()):

  """Returns a value indexed by a query parameter in the HTTP request.

  Args:

    request: the Django HTTP request object

    param_name: name of the query parameter in the HTTP request

    values: list (or tuple) of ordered values; one of which is

      retrieved by the index value of the param_name argument in

      the HTTP request

  Returns:

    None if the query parameter was not present, was not an integer, or

      was an integer that is not a valid [0..len(values)-1] index into

      the values list.

    Otherwise, returns values[int(param_name value)]

  """

  value_idx = request.GET.get(param_name)

  if isinstance(value_idx, (tuple, list)):

    # keep only the first argument if multiple are present

    value_idx = value_idx[0]

  try:

    # GET parameter 'param_name' should be an integer value index

    value_idx = int(value_idx)

  except:

    # ignore bogus or missing parameter values, so return None (no message)

    return None

  if value_idx < 0:

    # value index out of range, so return None (no value)

    return None

  if value_idx >= len(values):

    # value index out of range, so return None (no value)

    return None

  # return value associated with valid value index

  return values[value_idx]

def getSingleIndexedParamValueIfMissing(value, request, param_name,

                                        values=()):

  """Returns missing value indexed by a query parameter in the HTTP request.

  Args:

    value: an existing value, or a "False" value such as None

    request, param_name, values: see getSingleIndexParamValue()

  Returns:

    value, if value is "non-False"

    Otherwise, returns getSingleIndexedParamValue() result.

  """

  if value:

    # value already present, so return it

    return value

  return getSingleIndexedParamValue(request, param_name, values=values)

# TODO(tlarsen):  write getMultipleIndexParamValues() that returns a

#   list of values if present, omitting those values that are

#   out of range