"""
Functions used to convert inputs from whatever encoding used in the system to
unicode and back.

Ported to Python 3.

Once Python 2 support is dropped, most of this module will obsolete, since
Unicode is the default everywhere in Python 3.
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

from future.utils import PY2, PY3, native_str
if PY2:
    # We omit str() because that seems too tricky to get right.
    from builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, list, object, range, max, min  # noqa: F401

from past.builtins import unicode

import sys, os, re, locale
import unicodedata
import warnings

from allmydata.util.assertutil import precondition, _assert
from twisted.python import usage
from twisted.python.filepath import FilePath
from allmydata.util import log
from allmydata.util.fileutil import abspath_expanduser_unicode

NoneType = type(None)


def canonical_encoding(encoding):
    if encoding is None:
        log.msg("Warning: falling back to UTF-8 encoding.", level=log.WEIRD)
        encoding = 'utf-8'
    encoding = encoding.lower()
    if encoding == "cp65001":
        encoding = 'utf-8'
    elif encoding == "us-ascii" or encoding == "646" or encoding == "ansi_x3.4-1968":
        encoding = 'ascii'

    return encoding

def check_encoding(encoding):
    # sometimes Python returns an encoding name that it doesn't support for conversion
    # fail early if this happens
    try:
        u"test".encode(encoding)
    except (LookupError, AttributeError):
        raise AssertionError("The character encoding '%s' is not supported for conversion." % (encoding,))

filesystem_encoding = None
io_encoding = None
is_unicode_platform = False
use_unicode_filepath = False

def _reload():
    global filesystem_encoding, io_encoding, is_unicode_platform, use_unicode_filepath

    filesystem_encoding = canonical_encoding(sys.getfilesystemencoding())
    check_encoding(filesystem_encoding)

    if sys.platform == 'win32':
        # On Windows we install UTF-8 stream wrappers for sys.stdout and
        # sys.stderr, and reencode the arguments as UTF-8 (see scripts/runner.py).
        io_encoding = 'utf-8'
    else:
        ioenc = None
        if hasattr(sys.stdout, 'encoding'):
            ioenc = sys.stdout.encoding
        if ioenc is None:
            try:
                ioenc = locale.getpreferredencoding()
            except Exception:
                pass  # work around <http://bugs.python.org/issue1443504>
        io_encoding = canonical_encoding(ioenc)

    check_encoding(io_encoding)

    is_unicode_platform = PY3 or sys.platform in ["win32", "darwin"]

    # Despite the Unicode-mode FilePath support added to Twisted in
    # <https://twistedmatrix.com/trac/ticket/7805>, we can't yet use
    # Unicode-mode FilePaths with INotify on non-Windows platforms due to
    # <https://twistedmatrix.com/trac/ticket/7928>. Supposedly 7928 is fixed,
    # though... and Tahoe-LAFS doesn't use inotify anymore!
    #
    # In the interest of not breaking anything, this logic is unchanged for
    # Python 2, but on Python 3 the paths are always unicode, like it or not.
    use_unicode_filepath = PY3 or sys.platform == "win32"

_reload()


def get_filesystem_encoding():
    """
    Returns expected encoding for local filenames.
    """
    return filesystem_encoding

def get_io_encoding():
    """
    Returns expected encoding for writing to stdout or stderr, and for arguments in sys.argv.
    """
    return io_encoding

def argv_to_unicode(s):
    """
    Decode given argv element to unicode. If this fails, raise a UsageError.
    """
    if isinstance(s, unicode):
        return s

    precondition(isinstance(s, bytes), s)

    try:
        return unicode(s, io_encoding)
    except UnicodeDecodeError:
        raise usage.UsageError("Argument %s cannot be decoded as %s." %
                               (quote_output(s), io_encoding))

def argv_to_abspath(s, **kwargs):
    """
    Convenience function to decode an argv element to an absolute path, with ~ expanded.
    If this fails, raise a UsageError.
    """
    decoded = argv_to_unicode(s)
    if decoded.startswith(u'-'):
        raise usage.UsageError("Path argument %s cannot start with '-'.\nUse %s if you intended to refer to a file."
                               % (quote_output(s), quote_output(os.path.join('.', s))))
    return abspath_expanduser_unicode(decoded, **kwargs)

def unicode_to_argv(s, mangle=False):
    """
    Encode the given Unicode argument as a bytestring.
    If the argument is to be passed to a different process, then the 'mangle' argument
    should be true; on Windows, this uses a mangled encoding that will be reversed by
    code in runner.py.

    On Python 3, just return the string unchanged, since argv is unicode.
    """
    precondition(isinstance(s, unicode), s)
    if PY3:
        warnings.warn("This will be unnecessary once Python 2 is dropped.",
                      DeprecationWarning)
        return s

    if mangle and sys.platform == "win32":
        # This must be the same as 'mangle' in bin/tahoe-script.template.
        return bytes(re.sub(u'[^\\x20-\\x7F]', lambda m: u'\x7F%x;' % (ord(m.group(0)),), s), io_encoding)
    else:
        return s.encode(io_encoding)

def unicode_to_url(s):
    """
    Encode an unicode object used in an URL to bytes.
    """
    # According to RFC 2718, non-ascii characters in URLs must be UTF-8 encoded.

    # FIXME
    return to_bytes(s)
    #precondition(isinstance(s, unicode), s)
    #return s.encode('utf-8')

def to_bytes(s):
    """Convert unicode to bytes.

    None and bytes are passed through unchanged.
    """
    if s is None or isinstance(s, bytes):
        return s
    return s.encode('utf-8')

def from_utf8_or_none(s):
    precondition(isinstance(s, bytes) or s is None, s)
    if s is None:
        return s
    return s.decode('utf-8')

PRINTABLE_ASCII = re.compile(br'^[\n\r\x20-\x7E]*$',          re.DOTALL)
PRINTABLE_8BIT  = re.compile(br'^[\n\r\x20-\x7E\x80-\xFF]*$', re.DOTALL)

def is_printable_ascii(s):
    return PRINTABLE_ASCII.search(s) is not None

def unicode_to_output(s):
    """
    Encode an unicode object for representation on stdout or stderr.

    On Python 3 just returns the unicode string unchanged, since encoding is
    the responsibility of stdout/stderr, they expect Unicode by default.
    """
    precondition(isinstance(s, unicode), s)
    if PY3:
        warnings.warn("This will be unnecessary once Python 2 is dropped.",
                      DeprecationWarning)
        return s

    try:
        out = s.encode(io_encoding)
    except (UnicodeEncodeError, UnicodeDecodeError):
        raise UnicodeEncodeError(native_str(io_encoding), s, 0, 0,
                                 native_str("A string could not be encoded as %s for output to the terminal:\n%r" %
                                 (io_encoding, repr(s))))

    if PRINTABLE_8BIT.search(out) is None:
        raise UnicodeEncodeError(native_str(io_encoding), s, 0, 0,
                                 native_str("A string encoded as %s for output to the terminal contained unsafe bytes:\n%r" %
                                 (io_encoding, repr(s))))
    return out


def _unicode_escape(m, quote_newlines):
    u = m.group(0)
    if u == u'"' or u == u'$' or u == u'`' or u == u'\\':
        return u'\\' + u
    elif u == u'\n' and not quote_newlines:
        return u
    if len(u) == 2:
        codepoint = (ord(u[0])-0xD800)*0x400 + ord(u[1])-0xDC00 + 0x10000
    else:
        codepoint = ord(u)
    if codepoint > 0xFFFF:
        return u'\\U%08x' % (codepoint,)
    elif codepoint > 0xFF:
        return u'\\u%04x' % (codepoint,)
    else:
        return u'\\x%02x' % (codepoint,)

def _bytes_escape(m, quote_newlines):
    """
    Takes a re match on bytes, the result is escaped bytes of group(0).
    """
    c = m.group(0)
    if c == b'"' or c == b'$' or c == b'`' or c == b'\\':
        return b'\\' + c
    elif c == b'\n' and not quote_newlines:
        return c
    else:
        return b'\\x%02x' % (ord(c),)

MUST_DOUBLE_QUOTE_NL = re.compile(u'[^\\x20-\\x26\\x28-\\x7E\u00A0-\uD7FF\uE000-\uFDCF\uFDF0-\uFFFC]', re.DOTALL)
MUST_DOUBLE_QUOTE    = re.compile(u'[^\\n\\x20-\\x26\\x28-\\x7E\u00A0-\uD7FF\uE000-\uFDCF\uFDF0-\uFFFC]', re.DOTALL)

# if we must double-quote, then we have to escape ", $ and `, but need not escape '
ESCAPABLE_UNICODE = re.compile(u'([\uD800-\uDBFF][\uDC00-\uDFFF])|'  # valid surrogate pairs
                               u'[^ !#\\x25-\\x5B\\x5D-\\x5F\\x61-\\x7E\u00A0-\uD7FF\uE000-\uFDCF\uFDF0-\uFFFC]',
                               re.DOTALL)

ESCAPABLE_8BIT    = re.compile( br'[^ !#\x25-\x5B\x5D-\x5F\x61-\x7E]', re.DOTALL)

def quote_output(s, quotemarks=True, quote_newlines=None, encoding=None):
    """
    Encode either a Unicode string or a UTF-8-encoded bytestring for representation
    on stdout or stderr, tolerating errors. If 'quotemarks' is True, the string is
    always quoted; otherwise, it is quoted only if necessary to avoid ambiguity or
    control bytes in the output. (Newlines are counted as control bytes iff
    quote_newlines is True.)

    Quoting may use either single or double quotes. Within single quotes, all
    characters stand for themselves, and ' will not appear. Within double quotes,
    Python-compatible backslash escaping is used.

    If not explicitly given, quote_newlines is True when quotemarks is True.

    On Python 3, returns Unicode strings.
    """
    precondition(isinstance(s, (bytes, unicode)), s)
    encoding = encoding or io_encoding

    if quote_newlines is None:
        quote_newlines = quotemarks

    def _encode(s):
        if isinstance(s, bytes):
            try:
                s = s.decode('utf-8')
            except UnicodeDecodeError:
                return b'b"%s"' % (ESCAPABLE_8BIT.sub(lambda m: _bytes_escape(m, quote_newlines), s),)

        must_double_quote = quote_newlines and MUST_DOUBLE_QUOTE_NL or MUST_DOUBLE_QUOTE
        if must_double_quote.search(s) is None:
            try:
                out = s.encode(encoding)
                if quotemarks or out.startswith(b'"'):
                    return b"'%s'" % (out,)
                else:
                    return out
            except (UnicodeDecodeError, UnicodeEncodeError):
                pass

        escaped = ESCAPABLE_UNICODE.sub(lambda m: _unicode_escape(m, quote_newlines), s)
        return b'"%s"' % (escaped.encode(encoding, 'backslashreplace'),)

    result = _encode(s)
    if PY3:
        # On Python 3 half of what this function does is unnecessary, since
        # sys.stdout typically expects Unicode. To ensure no encode errors, one
        # can do:
        #
        # sys.stdout.reconfigure(encoding=sys.stdout.encoding, errors="backslashreplace")
        #
        # Although the problem is that doesn't work in Python 3.6, only 3.7 or
        # later... For now not thinking about it, just returning unicode since
        # that is the right thing to do on Python 3.
        result = result.decode(encoding)
    return result


def quote_path(path, quotemarks=True):
    return quote_output(b"/".join(map(to_bytes, path)), quotemarks=quotemarks, quote_newlines=True)

def quote_local_unicode_path(path, quotemarks=True):
    precondition(isinstance(path, unicode), path)

    if sys.platform == "win32" and path.startswith(u"\\\\?\\"):
        path = path[4 :]
        if path.startswith(u"UNC\\"):
            path = u"\\\\" + path[4 :]

    return quote_output(path, quotemarks=quotemarks, quote_newlines=True)

def quote_filepath(path, quotemarks=True):
    return quote_local_unicode_path(unicode_from_filepath(path), quotemarks=quotemarks)

def extend_filepath(fp, segments):
    # We cannot use FilePath.preauthChild, because
    # * it has the security flaw described in <https://twistedmatrix.com/trac/ticket/6527>;
    # * it may return a FilePath in the wrong mode.

    for segment in segments:
        fp = fp.child(segment)

    if isinstance(fp.path, unicode) and not use_unicode_filepath:
        return FilePath(fp.path.encode(filesystem_encoding))
    else:
        return fp

def to_filepath(path):
    precondition(isinstance(path, unicode if use_unicode_filepath else (bytes, unicode)),
                 path=path)

    if isinstance(path, unicode) and not use_unicode_filepath:
        path = path.encode(filesystem_encoding)

    if sys.platform == "win32":
        _assert(isinstance(path, unicode), path=path)
        if path.startswith(u"\\\\?\\") and len(path) > 4:
            # FilePath normally strips trailing path separators, but not in this case.
            path = path.rstrip(u"\\")

    return FilePath(path)

def _decode(s):
    precondition(isinstance(s, (bytes, unicode)), s=s)

    if isinstance(s, bytes):
        return s.decode(filesystem_encoding)
    else:
        return s

def unicode_from_filepath(fp):
    precondition(isinstance(fp, FilePath), fp=fp)
    return _decode(fp.path)

def unicode_segments_from(base_fp, ancestor_fp):
    precondition(isinstance(base_fp, FilePath), base_fp=base_fp)
    precondition(isinstance(ancestor_fp, FilePath), ancestor_fp=ancestor_fp)

    return base_fp.asTextMode().segmentsFrom(ancestor_fp.asTextMode())

def unicode_platform():
    """
    Does the current platform handle Unicode filenames natively?
    """
    return is_unicode_platform

class FilenameEncodingError(Exception):
    """
    Filename cannot be encoded using the current encoding of your filesystem
    (%s). Please configure your locale correctly or rename this file.
    """
    pass

def listdir_unicode_fallback(path):
    """
    This function emulates a fallback Unicode API similar to one available
    under Windows or MacOS X.

    If badly encoded filenames are encountered, an exception is raised.
    """
    precondition(isinstance(path, unicode), path)

    try:
        byte_path = path.encode(filesystem_encoding)
    except (UnicodeEncodeError, UnicodeDecodeError):
        raise FilenameEncodingError(path)

    try:
        return [unicode(fn, filesystem_encoding) for fn in os.listdir(byte_path)]
    except UnicodeDecodeError as e:
        raise FilenameEncodingError(e.object)

def listdir_unicode(path):
    """
    Wrapper around listdir() which provides safe access to the convenient
    Unicode API even under platforms that don't provide one natively.
    """
    precondition(isinstance(path, unicode), path)

    # On Windows and MacOS X, the Unicode API is used
    # On other platforms (ie. Unix systems), the byte-level API is used

    if is_unicode_platform:
        return os.listdir(path)
    else:
        return listdir_unicode_fallback(path)

def listdir_filepath(fp):
    return listdir_unicode(unicode_from_filepath(fp))


# 'x' at the end of a variable name indicates that it holds a Unicode string that may not
# be NFC-normalized.
def normalize(namex):
    return unicodedata.normalize('NFC', namex)
