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# Copyright 2014 Joe Gregorio

#

# Licensed under the MIT License

"""MIME-Type Parser

This module provides basic functions for handling mime-types. It can handle

matching mime-types against a list of media-ranges. See section 14.1 of the

HTTP specification [RFC 2616] for a complete explanation.

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1

Contents:

- parse_mime_type(): Parses a mime-type into its component parts.

- parse_media_range(): Media-ranges are mime-types with wild-cards and a 'q'

quality parameter.

- quality(): Determines the quality ('q') of a mime-type when

compared against a list of media-ranges.

- quality_parsed(): Just like quality() except the second parameter must be

pre-parsed.

- best_match(): Choose the mime-type with the highest quality ('q')

from a list of candidates.

"""

from __future__ import absolute_import

from functools import reduce

import six

__version__ = '0.1.3'

__author__ = 'Joe Gregorio'

__email__ = 'joe@bitworking.org'

__license__ = 'MIT License'

__credits__ = ''

def parse_mime_type(mime_type):

"""Parses a mime-type into its component parts.

Carves up a mime-type and returns a tuple of the (type, subtype, params)

where 'params' is a dictionary of all the parameters for the media range.

For example, the media range 'application/xhtml;q=0.5' would get parsed

into:

('application', 'xhtml', {'q', '0.5'})

"""

parts = mime_type.split(';')

params = dict([tuple([s.strip() for s in param.split('=', 1)])\

for param in parts[1:]

])

full_type = parts[0].strip()

# Java URLConnection class sends an Accept header that includes a

# single '*'. Turn it into a legal wildcard.

if full_type == '*':

full_type = '*/*'

(type, subtype) = full_type.split('/')

return (type.strip(), subtype.strip(), params)

def parse_media_range(range):

"""Parse a media-range into its component parts.

Carves up a media range and returns a tuple of the (type, subtype,

params) where 'params' is a dictionary of all the parameters for the media

range. For example, the media range 'application/*;q=0.5' would get parsed

into:

('application', '*', {'q', '0.5'})

In addition this function also guarantees that there is a value for 'q'

in the params dictionary, filling it in with a proper default if

necessary.

"""

(type, subtype, params) = parse_mime_type(range)

if 'q' not in params or not params['q'] or \

not float(params['q']) or float(params['q']) > 1\

or float(params['q']) < 0:

params['q'] = '1'

return (type, subtype, params)

def fitness_and_quality_parsed(mime_type, parsed_ranges):

"""Find the best match for a mime-type amongst parsed media-ranges.

Find the best match for a given mime-type against a list of media_ranges

that have already been parsed by parse_media_range(). Returns a tuple of

the fitness value and the value of the 'q' quality parameter of the best

match, or (-1, 0) if no match was found. Just as for quality_parsed(),

'parsed_ranges' must be a list of parsed media ranges.

"""

best_fitness = -1

best_fit_q = 0

(target_type, target_subtype, target_params) =\

parse_media_range(mime_type)

for (type, subtype, params) in parsed_ranges:

type_match = (type == target_type or\

type == '*' or\

target_type == '*')

subtype_match = (subtype == target_subtype or\

subtype == '*' or\

target_subtype == '*')

if type_match and subtype_match:

param_matches = reduce(lambda x, y: x + y, [1 for (key, value) in \

six.iteritems(target_params) if key != 'q' and \

key in params and value == params[key]], 0)

fitness = (type == target_type) and 100 or 0

fitness += (subtype == target_subtype) and 10 or 0

fitness += param_matches

if fitness > best_fitness:

best_fitness = fitness

best_fit_q = params['q']

return best_fitness, float(best_fit_q)

def quality_parsed(mime_type, parsed_ranges):

"""Find the best match for a mime-type amongst parsed media-ranges.

Find the best match for a given mime-type against a list of media_ranges

that have already been parsed by parse_media_range(). Returns the 'q'

quality parameter of the best match, 0 if no match was found. This function

bahaves the same as quality() except that 'parsed_ranges' must be a list of

parsed media ranges.

"""

return fitness_and_quality_parsed(mime_type, parsed_ranges)[1]

def quality(mime_type, ranges):

"""Return the quality ('q') of a mime-type against a list of media-ranges.

Returns the quality 'q' of a mime-type when compared against the

media-ranges in ranges. For example:

>>> quality('text/html','text/*;q=0.3, text/html;q=0.7,

text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5')

0.7

"""

parsed_ranges = [parse_media_range(r) for r in ranges.split(',')]

return quality_parsed(mime_type, parsed_ranges)

def best_match(supported, header):

"""Return mime-type with the highest quality ('q') from list of candidates.

Takes a list of supported mime-types and finds the best match for all the

media-ranges listed in header. The value of header must be a string that

conforms to the format of the HTTP Accept: header. The value of 'supported'

is a list of mime-types. The list of supported mime-types should be sorted

in order of increasing desirability, in case of a situation where there is

a tie.

>>> best_match(['application/xbel+xml', 'text/xml'],

'text/*;q=0.5,*/*; q=0.1')

'text/xml'

"""

split_header = _filter_blank(header.split(','))

parsed_header = [parse_media_range(r) for r in split_header]

weighted_matches = []

pos = 0

for mime_type in supported:

weighted_matches.append((fitness_and_quality_parsed(mime_type,

parsed_header), pos, mime_type))

pos += 1

weighted_matches.sort()

return weighted_matches[-1][0][1] and weighted_matches[-1][2] or ''

def _filter_blank(i):

for s in i:

if s.strip():

yield s