from __future__ import absolute_import, print_function, division

import re

try:
    from collections.abc import MutableMapping
except ImportError:  # pragma: no cover
    from collections import MutableMapping  # Workaround for Python < 3.3

import six
from ..multidict import MultiDict
from ..utils import always_bytes

# See also: http://lucumr.pocoo.org/2013/7/2/the-updated-guide-to-unicode/

if six.PY2:  # pragma: no cover
    _native = lambda x: x
    _always_bytes = lambda x: x
else:
    # While headers _should_ be ASCII, it's not uncommon for certain headers to be utf-8 encoded.
    _native = lambda x: x.decode("utf-8", "surrogateescape")
    _always_bytes = lambda x: always_bytes(x, "utf-8", "surrogateescape")


class Headers(MultiDict):
    """
    Header class which allows both convenient access to individual headers as well as
    direct access to the underlying raw data. Provides a full dictionary interface.

    Example:

    .. code-block:: python

        # Create headers with keyword arguments
        >>> h = Headers(host="example.com", content_type="application/xml")

        # Headers mostly behave like a normal dict.
        >>> h["Host"]
        "example.com"

        # HTTP Headers are case insensitive
        >>> h["host"]
        "example.com"

        # Headers can also be created from a list of raw (header_name, header_value) byte tuples
        >>> h = Headers([
            (b"Host",b"example.com"),
            (b"Accept",b"text/html"),
            (b"accept",b"application/xml")
        ])

        # Multiple headers are folded into a single header as per RFC7230
        >>> h["Accept"]
        "text/html, application/xml"

        # Setting a header removes all existing headers with the same name.
        >>> h["Accept"] = "application/text"
        >>> h["Accept"]
        "application/text"

        # bytes(h) returns a HTTP1 header block.
        >>> print(bytes(h))
        Host: example.com
        Accept: application/text

        # For full control, the raw header fields can be accessed
        >>> h.fields

    Caveats:
        For use with the "Set-Cookie" header, see :py:meth:`get_all`.
    """

    def __init__(self, fields=None, **headers):
        """
        Args:
            fields: (optional) list of ``(name, value)`` header byte tuples,
                e.g. ``[(b"Host", b"example.com")]``. All names and values must be bytes.
            **headers: Additional headers to set. Will overwrite existing values from `fields`.
                For convenience, underscores in header names will be transformed to dashes -
                this behaviour does not extend to other methods.
                If ``**headers`` contains multiple keys that have equal ``.lower()`` s,
                the behavior is undefined.
        """
        super(Headers, self).__init__(fields)

        for key, value in self.fields:
            if not isinstance(key, bytes) or not isinstance(value, bytes):
                raise TypeError("Header fields must be bytes.")

        # content_type -> content-type
        headers = {
            _always_bytes(name).replace(b"_", b"-"): _always_bytes(value)
            for name, value in six.iteritems(headers)
            }
        self.update(headers)

    @staticmethod
    def _reduce_values(values):
        # Headers can be folded
        return ", ".join(values)

    @staticmethod
    def _kconv(key):
        # Headers are case-insensitive
        return key.lower()

    def __bytes__(self):
        if self.fields:
            return b"\r\n".join(b": ".join(field) for field in self.fields) + b"\r\n"
        else:
            return b""

    if six.PY2:  # pragma: no cover
        __str__ = __bytes__

    def __delitem__(self, key):
        key = _always_bytes(key)
        super(Headers, self).__delitem__(key)

    def __iter__(self):
        for x in super(Headers, self).__iter__():
            yield _native(x)

    def get_all(self, name):
        """
        Like :py:meth:`get`, but does not fold multiple headers into a single one.
        This is useful for Set-Cookie headers, which do not support folding.
        See also: https://tools.ietf.org/html/rfc7230#section-3.2.2
        """
        name = _always_bytes(name)
        return [
            _native(x) for x in
            super(Headers, self).get_all(name)
        ]

    def set_all(self, name, values):
        """
        Explicitly set multiple headers for the given key.
        See: :py:meth:`get_all`
        """
        name = _always_bytes(name)
        values = [_always_bytes(x) for x in values]
        return super(Headers, self).set_all(name, values)

    def insert(self, index, key, value):
        key = _always_bytes(key)
        value = _always_bytes(value)
        super(Headers, self).insert(index, key, value)

    def replace(self, pattern, repl, flags=0):
        """
        Replaces a regular expression pattern with repl in each "name: value"
        header line.

        Returns:
            The number of replacements made.
        """
        pattern = _always_bytes(pattern)
        repl = _always_bytes(repl)
        pattern = re.compile(pattern, flags)
        replacements = 0

        fields = []
        for name, value in self.fields:
            line, n = pattern.subn(repl, name + b": " + value)
            try:
                name, value = line.split(b": ", 1)
            except ValueError:
                # We get a ValueError if the replacement removed the ": "
                # There's not much we can do about this, so we just keep the header as-is.
                pass
            else:
                replacements += n
            fields.append([name, value])
        self.fields = fields
        return replacements