from abc import ABCMeta
from abc import abstractmethod
from typing import Iterator
from typing import List
from typing import MutableMapping
from typing import Sequence
from typing import Tuple
from typing import TypeVar

from _internal_mitmproxy.coretypes import serializable

KT = TypeVar('KT')
VT = TypeVar('VT')


class _MultiDict(MutableMapping[KT, VT], metaclass=ABCMeta):
    """
    A MultiDict is a dictionary-like data structure that supports multiple values per key.
    """

    fields: Tuple[Tuple[KT, VT], ...]
    """The underlying raw datastructure."""

    def __repr__(self):
        fields = (
            repr(field)
            for field in self.fields
        )
        return "{cls}[{fields}]".format(
            cls=type(self).__name__,
            fields=", ".join(fields)
        )

    @staticmethod
    @abstractmethod
    def _reduce_values(values: Sequence[VT]) -> VT:
        """
        If a user accesses multidict["foo"], this method
        reduces all values for "foo" to a single value that is returned.
        For example, HTTP headers are folded, whereas we will just take
        the first cookie we found with that name.
        """

    @staticmethod
    @abstractmethod
    def _kconv(key: KT) -> KT:
        """
        This method converts a key to its canonical representation.
        For example, HTTP headers are case-insensitive, so this method returns key.lower().
        """

    def __getitem__(self, key: KT) -> VT:
        values = self.get_all(key)
        if not values:
            raise KeyError(key)
        return self._reduce_values(values)

    def __setitem__(self, key: KT, value: VT) -> None:
        self.set_all(key, [value])

    def __delitem__(self, key: KT) -> None:
        if key not in self:
            raise KeyError(key)
        key = self._kconv(key)
        self.fields = tuple(
            field for field in self.fields
            if key != self._kconv(field[0])
        )

    def __iter__(self) -> Iterator[KT]:
        seen = set()
        for key, _ in self.fields:
            key_kconv = self._kconv(key)
            if key_kconv not in seen:
                seen.add(key_kconv)
                yield key

    def __len__(self) -> int:
        return len({self._kconv(key) for key, _ in self.fields})

    def __eq__(self, other) -> bool:
        if isinstance(other, MultiDict):
            return self.fields == other.fields
        return False

    def get_all(self, key: KT) -> List[VT]:
        """
        Return the list of all values for a given key.
        If that key is not in the MultiDict, the return value will be an empty list.
        """
        key = self._kconv(key)
        return [
            value
            for k, value in self.fields
            if self._kconv(k) == key
        ]

    def set_all(self, key: KT, values: List[VT]) -> None:
        """
        Remove the old values for a key and add new ones.
        """
        key_kconv = self._kconv(key)

        new_fields: List[Tuple[KT, VT]] = []
        for field in self.fields:
            if self._kconv(field[0]) == key_kconv:
                if values:
                    new_fields.append(
                        (field[0], values.pop(0))
                    )
            else:
                new_fields.append(field)
        while values:
            new_fields.append(
                (key, values.pop(0))
            )
        self.fields = tuple(new_fields)

    def add(self, key: KT, value: VT) -> None:
        """
        Add an additional value for the given key at the bottom.
        """
        self.insert(len(self.fields), key, value)

    def insert(self, index: int, key: KT, value: VT) -> None:
        """
        Insert an additional value for the given key at the specified position.
        """
        item = (key, value)
        self.fields = self.fields[:index] + (item,) + self.fields[index:]

    def keys(self, multi: bool = False):
        """
        Get all keys.

        If `multi` is True, one key per value will be returned.
        If `multi` is False, duplicate keys will only be returned once.
        """
        return (
            k
            for k, _ in self.items(multi)
        )

    def values(self, multi: bool = False):
        """
        Get all values.

        If `multi` is True, all values will be returned.
        If `multi` is False, only the first value per key will be returned.
        """
        return (
            v
            for _, v in self.items(multi)
        )

    def items(self, multi: bool = False):
        """
        Get all (key, value) tuples.

        If `multi` is True, all `(key, value)` pairs will be returned.
        If False, only one tuple per key is returned.
        """
        if multi:
            return self.fields
        else:
            return super().items()


class MultiDict(_MultiDict[KT, VT], serializable.Serializable):
    """A concrete MultiDict, storing its own data."""

    def __init__(self, fields=()):
        super().__init__()
        self.fields = tuple(
            tuple(i) for i in fields
        )

    @staticmethod
    def _reduce_values(values):
        return values[0]

    @staticmethod
    def _kconv(key):
        return key

    def get_state(self):
        return self.fields

    def set_state(self, state):
        self.fields = tuple(tuple(x) for x in state)

    @classmethod
    def from_state(cls, state):
        return cls(state)


class MultiDictView(_MultiDict[KT, VT]):
    """
    The MultiDictView provides the MultiDict interface over calculated data.
    The view itself contains no state - data is retrieved from the parent on
    request, and stored back to the parent on change.
    """

    def __init__(self, getter, setter):
        self._getter = getter
        self._setter = setter
        super().__init__()

    @staticmethod
    def _kconv(key):
        # All request-attributes are case-sensitive.
        return key

    @staticmethod
    def _reduce_values(values):
        # We just return the first element if
        # multiple elements exist with the same key.
        return values[0]

    @property  # type: ignore
    def fields(self):
        return self._getter()

    @fields.setter
    def fields(self, value):
        self._setter(value)

    def copy(self) -> "MultiDict[KT,VT]":
        return MultiDict(self.fields)
