#!/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 used to render lists.

"""

__authors__ = [

  '"Chen Lunpeng" <forever.clp@gmail.com>',

  '"Pawel Solyga" <pawel.solyga@gmail.com>',

  ]

import itertools

from soc.logic import dicts

import soc.views.helper.forms

DEF_PAGINATION = 50

MAX_PAGINATION = 100

DEF_PAGINATION_CHOICES = (

  ('10', '10 items per page'),

  ('25', '25 items per page'),

  ('50', '50 items per page'),

  ('100', '100 items per page'),

)

def getPreferredListPagination(user=None):

  """Returns User's preferred list pagination limit.

  Args:

    user: User entity containing the list pagination preference;

      default is None, to use the current logged-in User

  """

  # TODO: eventually this limit should be a User profile preference

  #   (stored in the site-wide User Model) preference 

  return DEF_PAGINATION

def getLimitAndOffset(request, offset_key, limit_key):

  """Retrieves, converts and validates offset and limit values

  Args:

    offset: offset in list which defines first item to return

    limit: max amount of items per page

  Returns:

    updated offset and limit values

  """

  offset = request.GET.get(offset_key)

  limit = request.GET.get(limit_key)

  if offset is None:

    offset = ''

  if limit is None:

    limit = ''

  try:

    offset = int(offset)

  except ValueError:

    offset = 0

  try:

    limit = int(limit)

  except ValueError:

    limit = getPreferredListPagination()

  offset = max(0, offset)

  limit = max(1, limit)

  limit = min(MAX_PAGINATION, limit)

  return limit, offset

def generateLinkFromGetArgs(request, offset_and_limits):

  """Constructs the get args for the url.

  """

  args = ["%s=%s" % (k, v) for k, v in offset_and_limits.iteritems()]

  link_suffix = '?' + '&'.join(args)

  return request.path + link_suffix

def getListContent(request, params, filter=None, order=None,

                   idx=0, need_content=False):

  """Returns a dict with fields used for rendering lists.

  Args:

    request: the Django HTTP request object

    params: a dict with params for the View this list belongs to

    filter: a filter for this list

    order: the order which should be used for the list (in getForFields format)

    idx: the index of this list

    need_content: iff True will return None if there is no data

  Returns:

    A a dictionary with the following values set:

    {

      'data': list data to be displayed

      'main': url to list main template

      'pagination': url to list pagination template

      'row': url to list row template

      'heading': url to list heading template

      'limit': max amount of items per page,

      'newest': url to first page of the list 

      'prev': url to previous page 

      'next': url to next page

      'first': offset of the first item in the list

      'last': offest of the lst item in the list

    }

  """

  logic = params['logic']

  offset_key = 'offset_%d' % idx

  limit_key = 'limit_%d' % idx

  limit, offset = getLimitAndOffset(request, offset_key, limit_key)

  pagination_form = makePaginationForm(request, limit, limit_key)

  # Fetch one more to see if there should be a 'next' link

  data = logic.getForFields(filter=filter, limit=limit+1, offset=offset,

                            order=order)

  if need_content and not data:

    return None

  more = len(data) > limit

  if more:

    del data[limit:]

  newest = next = prev = ''

  get_args = request.GET

  offset_and_limits = {}

  for key, value in get_args.iteritems():

    if key.startswith('offset_') or key.startswith('limit_'):

      offset_and_limits[key] = value

  if more:

    offset_and_limits[offset_key] = offset+limit

    offset_and_limits[limit_key] = limit

    next = generateLinkFromGetArgs(request, offset_and_limits)

  if offset > 0:

    offset_and_limits[offset_key] = max(0, offset-limit)

    offset_and_limits[limit_key] = limit

    prev = generateLinkFromGetArgs(request, offset_and_limits)

  if offset > limit:

    del offset_and_limits[offset_key]

    offset_and_limits[limit_key] = limit

    newest = generateLinkFromGetArgs(request, offset_and_limits)

  content = {

      'data': data,

      'first': offset+1,

      'last': len(data) > 1 and offset+len(data) or None,

      'logic': logic,

      'limit': limit,

      'newest': newest, 

      'next': next,

      'pagination_form': pagination_form,

      'prev': prev, 

      }

  updates = dicts.rename(params, params['list_params'])

  content.update(updates)

  return content

def makePaginationForm(

  request, limit, arg_name, choices=DEF_PAGINATION_CHOICES,

  field_name_fmt=soc.views.helper.forms.DEF_SELECT_QUERY_ARG_FIELD_NAME_FMT):

  """Returns a customized pagination limit selection form.

  Args:

    request: the standard Django HTTP request object

    limit: the initial value of the selection control

    arg_name: see soc.views.helper.forms.makeSelectQueryArgForm(); default is 'limit'

    choices: see soc.views.helper.forms.makeSelectQueryArgForm(); default is

      DEF_PAGINATION_CHOICES

    field_name_fmt: see soc.views.helper.forms.makeSelectQueryArgForm()

  """

  choices = makeNewPaginationChoices(limit=limit, choices=choices)

  return soc.views.helper.forms.makeSelectQueryArgForm(

      request, arg_name, limit, choices)

def makeNewPaginationChoices(limit=DEF_PAGINATION,

                             choices=DEF_PAGINATION_CHOICES):

  """Updates the pagination limit selection form.

  Args:

    limit: the initial value of the selection control;

      default is DEF_PAGINATION

    choices: see soc.views.helper.forms.makeSelectQueryArgForm();

      default is DEF_PAGINATION_CHOICES

  Returns:

    a new pagination choices list if limit is not in

    DEF_PAGINATION_CHOICES, or DEF_PAGINATION_CHOICES otherwise

  """

  # determine where to insert the new limit into choices

  new_choices = []

  for index, (pagination, label) in enumerate(choices):

    items = int(pagination)

    if limit == items:

      # limit is already present, so just return existing choices

      return choices

    if limit < items:

      # limit needs to be inserted before the current pagination,

      # so assemble a new choice tuple and append it 

      choice = (str(limit), '%s items per page' % limit)

      new_choices.append(choice)

      # append the remainder of the original list and exit early

      # (avoiding unnecessary remaining type conversions, etc.)

      new_choices.extend(choices[index:])

      return new_choices

    # append the existing choice

    new_choices.append((pagination, label))

  # new choice must go last, past all other existing choices

  choice = (str(limit), '%s items per page' % limit)

  new_choices.append(choice)

  return new_choices