from collections import defaultdict
from functools import wraps
from types import FunctionType
from typing import (
    Any,
    Callable,
    Dict,
    Generic,
    List,
    Optional,
    Sequence,
    TypeVar,
    Union,
    cast,
    overload,
)

import ujson
from django.http import HttpRequest, HttpResponse
from django.utils.translation import ugettext as _
from typing_extensions import Literal

from zerver.lib.exceptions import ErrorCode, InvalidJSONError, JsonableError
from zerver.lib.types import Validator, ViewFuncT


class RequestConfusingParmsError(JsonableError):
    code = ErrorCode.REQUEST_CONFUSING_VAR
    data_fields = ['var_name1', 'var_name2']

    def __init__(self, var_name1: str, var_name2: str) -> None:
        self.var_name1: str = var_name1
        self.var_name2: str = var_name2

    @staticmethod
    def msg_format() -> str:
        return _("Can't decide between '{var_name1}' and '{var_name2}' arguments")

class RequestVariableMissingError(JsonableError):
    code = ErrorCode.REQUEST_VARIABLE_MISSING
    data_fields = ['var_name']

    def __init__(self, var_name: str) -> None:
        self.var_name: str = var_name

    @staticmethod
    def msg_format() -> str:
        return _("Missing '{var_name}' argument")

class RequestVariableConversionError(JsonableError):
    code = ErrorCode.REQUEST_VARIABLE_INVALID
    data_fields = ['var_name', 'bad_value']

    def __init__(self, var_name: str, bad_value: Any) -> None:
        self.var_name: str = var_name
        self.bad_value = bad_value

    @staticmethod
    def msg_format() -> str:
        return _("Bad value for '{var_name}': {bad_value}")

# Used in conjunction with @has_request_variables, below
ResultT = TypeVar('ResultT')

class _REQ(Generic[ResultT]):
    # NotSpecified is a sentinel value for determining whether a
    # default value was specified for a request variable.  We can't
    # use None because that could be a valid, user-specified default
    class _NotSpecified:
        pass
    NotSpecified = _NotSpecified()

    def __init__(
        self,
        whence: Optional[str] = None,
        *,
        converter: Optional[Callable[[str], ResultT]] = None,
        default: Union[_NotSpecified, ResultT, None] = NotSpecified,
        validator: Optional[Validator] = None,
        str_validator: Optional[Validator] = None,
        argument_type: Optional[str] = None,
        intentionally_undocumented: bool=False,
        documentation_pending: bool=False,
        aliases: Sequence[str] = [],
        path_only: bool=False
    ) -> None:
        """whence: the name of the request variable that should be used
        for this parameter.  Defaults to a request variable of the
        same name as the parameter.

        converter: a function that takes a string and returns a new
        value.  If specified, this will be called on the request
        variable value before passing to the function

        default: a value to be used for the argument if the parameter
        is missing in the request

        validator: similar to converter, but takes an already parsed JSON
        data structure.  If specified, we will parse the JSON request
        variable value before passing to the function

        str_validator: Like validator, but doesn't parse JSON first.

        argument_type: pass 'body' to extract the parsed JSON
        corresponding to the request body

        aliases: alternate names for the POST var

        path_only: Used for parameters included in the URL that we still want
        to validate via REQ's hooks.
        """

        self.post_var_name = whence
        self.func_var_name: Optional[str] = None
        self.converter = converter
        self.validator = validator
        self.str_validator = str_validator
        self.default = default
        self.argument_type = argument_type
        self.aliases = aliases
        self.intentionally_undocumented = intentionally_undocumented
        self.documentation_pending = documentation_pending
        self.path_only = path_only

        if converter and (validator or str_validator):
            # Not user-facing, so shouldn't be tagged for translation
            raise AssertionError('converter and validator are mutually exclusive')
        if validator and str_validator:
            # Not user-facing, so shouldn't be tagged for translation
            raise AssertionError('validator and str_validator are mutually exclusive')

# This factory function ensures that mypy can correctly analyze REQ.
#
# Note that REQ claims to return a type matching that of the parameter
# of which it is the default value, allowing type checking of view
# functions using has_request_variables. In reality, REQ returns an
# instance of class _REQ to enable the decorator to scan the parameter
# list for _REQ objects and patch the parameters as the true types.

# Overload 1: converter
@overload
def REQ(
    whence: Optional[str] = ...,
    *,
    converter: Callable[[str], ResultT],
    default: ResultT = ...,
    intentionally_undocumented: bool = ...,
    documentation_pending: bool = ...,
    aliases: Sequence[str] = ...,
    path_only: bool = ...
) -> ResultT:
    ...

# Overload 2: validator
@overload
def REQ(
    whence: Optional[str] = ...,
    *,
    default: ResultT = ...,
    validator: Validator,
    intentionally_undocumented: bool = ...,
    documentation_pending: bool = ...,
    aliases: Sequence[str] = ...,
    path_only: bool = ...
) -> ResultT:
    ...

# Overload 3: no converter/validator, default: str or unspecified, argument_type=None
@overload
def REQ(
    whence: Optional[str] = ...,
    *,
    default: str = ...,
    str_validator: Optional[Validator] = ...,
    intentionally_undocumented: bool = ...,
    documentation_pending: bool = ...,
    aliases: Sequence[str] = ...,
    path_only: bool = ...
) -> str:
    ...

# Overload 4: no converter/validator, default=None, argument_type=None
@overload
def REQ(
    whence: Optional[str] = ...,
    *,
    default: None,
    str_validator: Optional[Validator] = ...,
    intentionally_undocumented: bool = ...,
    documentation_pending: bool = ...,
    aliases: Sequence[str] = ...,
    path_only: bool = ...
) -> Optional[str]:
    ...

# Overload 5: argument_type="body"
@overload
def REQ(
    whence: Optional[str] = ...,
    *,
    default: ResultT = ...,
    str_validator: Optional[Validator] = ...,
    argument_type: Literal["body"],
    intentionally_undocumented: bool = ...,
    documentation_pending: bool = ...,
    aliases: Sequence[str] = ...,
    path_only: bool = ...
) -> ResultT:
    ...

# Implementation
def REQ(
    whence: Optional[str] = None,
    *,
    converter: Optional[Callable[[str], ResultT]] = None,
    default: Union[_REQ._NotSpecified, ResultT] = _REQ.NotSpecified,
    validator: Optional[Validator] = None,
    str_validator: Optional[Validator] = None,
    argument_type: Optional[str] = None,
    intentionally_undocumented: bool=False,
    documentation_pending: bool=False,
    aliases: Sequence[str] = [],
    path_only: bool = False
) -> ResultT:
    return cast(ResultT, _REQ(
        whence,
        converter=converter,
        default=default,
        validator=validator,
        str_validator=str_validator,
        argument_type=argument_type,
        intentionally_undocumented=intentionally_undocumented,
        documentation_pending=documentation_pending,
        aliases=aliases,
        path_only=path_only,
    ))

arguments_map: Dict[str, List[str]] = defaultdict(list)

# Extracts variables from the request object and passes them as
# named function arguments.  The request object must be the first
# argument to the function.
#
# To use, assign a function parameter a default value that is an
# instance of the _REQ class.  That parameter will then be automatically
# populated from the HTTP request.  The request object must be the
# first argument to the decorated function.
#
# This should generally be the innermost (syntactically bottommost)
# decorator applied to a view, since other decorators won't preserve
# the default parameter values used by has_request_variables.
#
# Note that this can't be used in helper functions which are not
# expected to call json_error or json_success, as it uses json_error
# internally when it encounters an error
def has_request_variables(view_func: ViewFuncT) -> ViewFuncT:
    num_params = view_func.__code__.co_argcount
    default_param_values = cast(FunctionType, view_func).__defaults__
    if default_param_values is None:
        default_param_values = ()
    num_default_params = len(default_param_values)
    default_param_names = view_func.__code__.co_varnames[num_params - num_default_params:]

    post_params = []

    view_func_full_name = '.'.join([view_func.__module__, view_func.__name__])

    for (name, value) in zip(default_param_names, default_param_values):
        if isinstance(value, _REQ):
            value.func_var_name = name
            if value.post_var_name is None:
                value.post_var_name = name
            post_params.append(value)

            # Record arguments that should be documented so that our
            # automated OpenAPI docs tests can compare these against the code.
            if (not value.intentionally_undocumented
                    and not value.documentation_pending
                    and not value.path_only):
                arguments_map[view_func_full_name].append(value.post_var_name)

    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: Any, **kwargs: Any) -> HttpResponse:
        for param in post_params:
            func_var_name = param.func_var_name
            if param.path_only:
                # For path_only parameters, they should already have
                # been passed via the URL, so there's no need for REQ
                # to do anything.
                #
                # TODO: Either run validators for path_only parameters
                # or don't declare them using REQ.
                assert func_var_name in kwargs
            if func_var_name in kwargs:
                continue
            assert func_var_name is not None

            if param.argument_type == 'body':
                try:
                    val = ujson.loads(request.body)
                except ValueError:
                    raise InvalidJSONError(_("Malformed JSON"))
                kwargs[func_var_name] = val
                continue
            elif param.argument_type is not None:
                # This is a view bug, not a user error, and thus should throw a 500.
                raise Exception(_("Invalid argument type"))

            post_var_names = [param.post_var_name]
            post_var_names += param.aliases

            default_assigned = False

            post_var_name: Optional[str] = None

            for req_var in post_var_names:
                if req_var in request.POST:
                    val = request.POST[req_var]
                elif req_var in request.GET:
                    val = request.GET[req_var]
                else:
                    # This is covered by test_REQ_aliases, but coverage.py
                    # fails to recognize this for some reason.
                    continue  # nocoverage
                if post_var_name is not None:
                    assert req_var is not None
                    raise RequestConfusingParmsError(post_var_name, req_var)
                post_var_name = req_var

            if post_var_name is None:
                post_var_name = param.post_var_name
                assert post_var_name is not None
                if param.default is _REQ.NotSpecified:
                    raise RequestVariableMissingError(post_var_name)
                val = param.default
                default_assigned = True

            if param.converter is not None and not default_assigned:
                try:
                    val = param.converter(val)
                except JsonableError:
                    raise
                except Exception:
                    raise RequestVariableConversionError(post_var_name, val)

            # Validators are like converters, but they don't handle JSON parsing; we do.
            if param.validator is not None and not default_assigned:
                try:
                    val = ujson.loads(val)
                except Exception:
                    raise JsonableError(_('Argument "{}" is not valid JSON.').format(post_var_name))

                error = param.validator(post_var_name, val)
                if error:
                    raise JsonableError(error)

            # str_validators is like validator, but for direct strings (no JSON parsing).
            if param.str_validator is not None and not default_assigned:
                error = param.str_validator(post_var_name, val)
                if error:
                    raise JsonableError(error)

            kwargs[func_var_name] = val

        return view_func(request, *args, **kwargs)

    return cast(ViewFuncT, _wrapped_view_func)