# Character encoding routines
# Copyright 2010-2015 Kurt McKee <contactme@kurtmckee.org>
# Copyright 2002-2008 Mark Pilgrim
# All rights reserved.
#
# This file is a part of feedparser.
#
# Redistribution and use in source and binary forms, with or without modification,
# are permitted provided that the following conditions are met:
#
# * Redistributions of source code must retain the above copyright notice,
#   this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright notice,
#   this list of conditions and the following disclaimer in the documentation
#   and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 'AS IS'
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.

from __future__ import absolute_import, unicode_literals

import cgi
import codecs
import collections
import re

try:
    import chardet
except ImportError:
    chardet = None
    lazy_chardet_encoding = None
else:
    def lazy_chardet_encoding(data):
        chardet_encoding = chardet.detect(data)['encoding']
        if not chardet_encoding:
            chardet_encoding = ''
        if isinstance(chardet_encoding, bytes_):
            chardet_encoding = chardet_encoding.encode('ascii', 'ignore')
        return chardet_encoding

from .exceptions import (
    CharacterEncodingOverride, CharacterEncodingUnknown, NonXMLContentType,
)

bytes_ = type(b'')
unicode_ = type('')

# Each marker represents some of the characters of the opening XML
# processing instruction ('<?xm') in the specified encoding.
EBCDIC_MARKER = b'\x4C\x6F\xA7\x94'
UTF16BE_MARKER = b'\x00\x3C\x00\x3F'
UTF16LE_MARKER = b'\x3C\x00\x3F\x00'
UTF32BE_MARKER = b'\x00\x00\x00\x3C'
UTF32LE_MARKER = b'\x3C\x00\x00\x00'

ZERO_BYTES = '\x00\x00'

# Match the opening XML declaration.
# Example: <?xml version="1.0" encoding="utf-8"?>
RE_XML_DECLARATION = re.compile('^<\?xml[^>]*?>')

# Capture the value of the XML processing instruction's encoding attribute.
# Example: <?xml version="1.0" encoding="utf-8"?>
RE_XML_PI_ENCODING = re.compile(b'^<\?.*encoding=[\'"](.*?)[\'"].*\?>')

def convert_to_utf8(http_headers, data, result):
    '''Detect and convert the character encoding to UTF-8.

    http_headers is a dictionary
    data is a raw string (not Unicode)'''

    # This is so much trickier than it sounds, it's not even funny.
    # According to RFC 3023 ('XML Media Types'), if the HTTP Content-Type
    # is application/xml, application/*+xml,
    # application/xml-external-parsed-entity, or application/xml-dtd,
    # the encoding given in the charset parameter of the HTTP Content-Type
    # takes precedence over the encoding given in the XML prefix within the
    # document, and defaults to 'utf-8' if neither are specified.  But, if
    # the HTTP Content-Type is text/xml, text/*+xml, or
    # text/xml-external-parsed-entity, the encoding given in the XML prefix
    # within the document is ALWAYS IGNORED and only the encoding given in
    # the charset parameter of the HTTP Content-Type header should be
    # respected, and it defaults to 'us-ascii' if not specified.

    # Furthermore, discussion on the atom-syntax mailing list with the
    # author of RFC 3023 leads me to the conclusion that any document
    # served with a Content-Type of text/* and no charset parameter
    # must be treated as us-ascii.  (We now do this.)  And also that it
    # must always be flagged as non-well-formed.  (We now do this too.)

    # If Content-Type is unspecified (input was local file or non-HTTP source)
    # or unrecognized (server just got it totally wrong), then go by the
    # encoding given in the XML prefix of the document and default to
    # 'iso-8859-1' as per the HTTP specification (RFC 2616).

    # Then, assuming we didn't find a character encoding in the HTTP headers
    # (and the HTTP Content-type allowed us to look in the body), we need
    # to sniff the first few bytes of the XML data and try to determine
    # whether the encoding is ASCII-compatible.  Section F of the XML
    # specification shows the way here:
    # http://www.w3.org/TR/REC-xml/#sec-guessing-no-ext-info

    # If the sniffed encoding is not ASCII-compatible, we need to make it
    # ASCII compatible so that we can sniff further into the XML declaration
    # to find the encoding attribute, which will tell us the true encoding.

    # Of course, none of this guarantees that we will be able to parse the
    # feed in the declared character encoding (assuming it was declared
    # correctly, which many are not).  iconv_codec can help a lot;
    # you should definitely install it if you can.
    # http://cjkpython.i18n.org/

    bom_encoding = ''
    xml_encoding = ''
    rfc3023_encoding = ''

    # Look at the first few bytes of the document to guess what
    # its encoding may be. We only need to decode enough of the
    # document that we can use an ASCII-compatible regular
    # expression to search for an XML encoding declaration.
    # The heuristic follows the XML specification, section F:
    # http://www.w3.org/TR/REC-xml/#sec-guessing-no-ext-info
    # Check for BOMs first.
    if data[:4] == codecs.BOM_UTF32_BE:
        bom_encoding = 'utf-32be'
        data = data[4:]
    elif data[:4] == codecs.BOM_UTF32_LE:
        bom_encoding = 'utf-32le'
        data = data[4:]
    elif data[:2] == codecs.BOM_UTF16_BE and data[2:4] != ZERO_BYTES:
        bom_encoding = 'utf-16be'
        data = data[2:]
    elif data[:2] == codecs.BOM_UTF16_LE and data[2:4] != ZERO_BYTES:
        bom_encoding = 'utf-16le'
        data = data[2:]
    elif data[:3] == codecs.BOM_UTF8:
        bom_encoding = 'utf-8'
        data = data[3:]
    # Check for the characters '<?xm' in several encodings.
    elif data[:4] == EBCDIC_MARKER:
        bom_encoding = 'cp037'
    elif data[:4] == UTF16BE_MARKER:
        bom_encoding = 'utf-16be'
    elif data[:4] == UTF16LE_MARKER:
        bom_encoding = 'utf-16le'
    elif data[:4] == UTF32BE_MARKER:
        bom_encoding = 'utf-32be'
    elif data[:4] == UTF32LE_MARKER:
        bom_encoding = 'utf-32le'

    tempdata = data
    try:
        if bom_encoding:
            tempdata = data.decode(bom_encoding).encode('utf-8')
    except (UnicodeDecodeError, LookupError):
        # feedparser recognizes UTF-32 encodings that aren't
        # available in Python 2.4 and 2.5, so it's possible to
        # encounter a LookupError during decoding.
        xml_encoding_match = None
    else:
        xml_encoding_match = RE_XML_PI_ENCODING.match(tempdata)

    if xml_encoding_match:
        xml_encoding = xml_encoding_match.groups()[0].decode('utf-8').lower()
        # Normalize the xml_encoding if necessary.
        if bom_encoding and (xml_encoding in (
            'u16', 'utf-16', 'utf16', 'utf_16',
            'u32', 'utf-32', 'utf32', 'utf_32',
            'iso-10646-ucs-2', 'iso-10646-ucs-4',
            'csucs4', 'csunicode', 'ucs-2', 'ucs-4'
        )):
            xml_encoding = bom_encoding

    # Find the HTTP Content-Type and, hopefully, a character
    # encoding provided by the server. The Content-Type is used
    # to choose the "correct" encoding among the BOM encoding,
    # XML declaration encoding, and HTTP encoding, following the
    # heuristic defined in RFC 3023.
    http_content_type = http_headers.get('content-type') or ''
    http_content_type, params = cgi.parse_header(http_content_type)
    http_encoding = params.get('charset', '').replace("'", "")
    if isinstance(http_encoding, bytes_):
        http_encoding = http_encoding.decode('utf-8', 'ignore')

    acceptable_content_type = 0
    application_content_types = ('application/xml', 'application/xml-dtd',
                                 'application/xml-external-parsed-entity')
    text_content_types = ('text/xml', 'text/xml-external-parsed-entity')
    if (http_content_type in application_content_types) or \
       (http_content_type.startswith('application/') and
        http_content_type.endswith('+xml')):
        acceptable_content_type = 1
        rfc3023_encoding = http_encoding or xml_encoding or 'utf-8'
    elif (http_content_type in text_content_types) or \
         (http_content_type.startswith('text/') and
          http_content_type.endswith('+xml')):
        acceptable_content_type = 1
        rfc3023_encoding = http_encoding or 'us-ascii'
    elif http_content_type.startswith('text/'):
        rfc3023_encoding = http_encoding or 'us-ascii'
    elif http_headers and 'content-type' not in http_headers:
        rfc3023_encoding = xml_encoding or 'iso-8859-1'
    else:
        rfc3023_encoding = xml_encoding or 'utf-8'
    # gb18030 is a superset of gb2312, so always replace gb2312
    # with gb18030 for greater compatibility.
    if rfc3023_encoding.lower() == 'gb2312':
        rfc3023_encoding = 'gb18030'
    if xml_encoding.lower() == 'gb2312':
        xml_encoding = 'gb18030'

    # there are four encodings to keep track of:
    # - http_encoding is the encoding declared in the Content-Type HTTP header
    # - xml_encoding is the encoding declared in the <?xml declaration
    # - bom_encoding is the encoding sniffed from the first 4 bytes of the XML data
    # - rfc3023_encoding is the actual encoding, as per RFC 3023 and a variety of other conflicting specifications
    error = None

    if http_headers and (not acceptable_content_type):
        if 'content-type' in http_headers:
            msg = '%s is not an XML media type' % http_headers['content-type']
        else:
            msg = 'no Content-type specified'
        error = NonXMLContentType(msg)

    # determine character encoding
    known_encoding = 0
    tried_encodings = []
    # try: HTTP encoding, declared XML encoding, encoding sniffed from BOM
    for proposed_encoding in (rfc3023_encoding, xml_encoding, bom_encoding,
                              lazy_chardet_encoding, 'utf-8', 'windows-1252', 'iso-8859-2'):
        if isinstance(proposed_encoding, collections.Callable):
            proposed_encoding = proposed_encoding(data)
        if not proposed_encoding:
            continue
        if proposed_encoding in tried_encodings:
            continue
        tried_encodings.append(proposed_encoding)
        try:
            data = data.decode(proposed_encoding)
        except (UnicodeDecodeError, LookupError):
            pass
        else:
            known_encoding = 1
            # Update the encoding in the opening XML processing instruction.
            new_declaration = '''<?xml version='1.0' encoding='utf-8'?>'''
            if RE_XML_DECLARATION.search(data):
                data = RE_XML_DECLARATION.sub(new_declaration, data)
            else:
                data = new_declaration + '\n' + data
            data = data.encode('utf-8')
            break
    # if still no luck, give up
    if not known_encoding:
        error = CharacterEncodingUnknown(
            'document encoding unknown, I tried ' +
            '%s, %s, utf-8, windows-1252, and iso-8859-2 but nothing worked' %
            (rfc3023_encoding, xml_encoding))
        rfc3023_encoding = ''
    elif proposed_encoding != rfc3023_encoding:
        error = CharacterEncodingOverride(
            'document declared as %s, but parsed as %s' %
            (rfc3023_encoding, proposed_encoding))
        rfc3023_encoding = proposed_encoding

    result['encoding'] = rfc3023_encoding
    if error:
        result['bozo'] = True
        result['bozo_exception'] = error
    return data
