from typing import (
    Any, Callable, Dict, Iterable, List, NamedTuple, Optional, Sequence,
    TYPE_CHECKING, Tuple, Union,
)

import click

from ._core import Constraint
from .common import join_param_labels
from .._util import first_bool
from ..typing import Decorator, F

if TYPE_CHECKING:
    from cloup import HelpFormatter, OptionGroup


class BoundConstraintSpec(NamedTuple):
    """A NamedTuple storing a ``Constraint`` and the **names of the parameters**
    it has to check."""
    constraint: Constraint
    param_names: Union[Sequence[str]]

    def resolve_params(self, cmd: 'ConstraintMixin') -> 'BoundConstraint':
        return BoundConstraint(
            self.constraint,
            cmd.get_params_by_name(self.param_names)
        )


def _constraint_memo(
    f: Any, constr: Union[BoundConstraintSpec, 'BoundConstraint']
) -> None:
    if not hasattr(f, '__cloup_constraints__'):
        f.__cloup_constraints__ = []
    f.__cloup_constraints__.append(constr)


def constraint(constr: Constraint, params: Iterable[str]) -> Callable[[F], F]:
    """Register a constraint on a list of parameters specified by (destination) name
    (e.g. the default name of ``--input-file`` is ``input_file``)."""
    spec = BoundConstraintSpec(constr, tuple(params))

    def decorator(f: F) -> F:
        _constraint_memo(f, spec)
        return f

    return decorator


def constrained_params(
    constr: Constraint,
    *param_adders: Decorator,
) -> Callable[[F], F]:
    """
    Return a decorator that adds the given parameters and applies a constraint
    to them. Equivalent to::

        @param_adders[0]
        ...
        @param_adders[-1]
        @constraint(constr, <param names>)

    This decorator saves you to manually (re)type the parameter names.
    It can also be used inside ``@option_group``.

    Instead of using this decorator, you can also call the constraint itself::

        @constr(*param_adders)

    but remember that:

    - Python 3.9 is the first that allows arbitrary expressions on the right of ``@``;
    - using a long conditional/composite constraint as decorator may be less
      readable.

    In these cases, you may consider using ``@constrained_params``.

    .. versionadded:: 0.9.0

    :param constr: an instance of :class:`Constraint`
    :param param_adders:
        function decorators, each attaching a single parameter to the decorated
        function.
    """

    def decorator(f: F) -> F:
        reversed_params = []
        for add_param in reversed(param_adders):
            add_param(f)
            param = f.__click_params__[-1]  # type: ignore
            reversed_params.append(param)
        bound_constr = BoundConstraint(constr, tuple(reversed_params[::-1]))
        _constraint_memo(f, bound_constr)
        return f

    return decorator


class BoundConstraint(NamedTuple):
    """Internal utility ``NamedTuple`` that represents a ``Constraint``
    bound to a collection of ``click.Parameter`` instances.
    Note: this is not a subclass of Constraint."""

    constraint: Constraint
    params: Sequence[click.Parameter]

    def check_consistency(self) -> None:
        self.constraint.check_consistency(self.params)

    def check_values(self, ctx: click.Context) -> None:
        self.constraint.check_values(self.params, ctx)

    def get_help_record(self, ctx: click.Context) -> Optional[Tuple[str, str]]:
        constr_help = self.constraint.help(ctx)
        if not constr_help:
            return None
        param_list = '{%s}' % join_param_labels(self.params)
        return param_list, constr_help


class ConstraintMixin:
    """Provides support for constraints."""

    def __init__(
        self, *args: Any,
        constraints: Sequence[Union[BoundConstraintSpec, BoundConstraint]] = (),
        show_constraints: Optional[bool] = None,
        **kwargs: Any,
    ):
        """
        :param constraints:
            sequence of constraints bound to specific groups of parameters.
            Note that constraints applied to option groups are collected from
            the option groups themselves, so they don't need to be included in
            this argument.
        :param show_constraints:
            whether to include a "Constraint" section in the command help. This
            is also available as a context setting having a lower priority than
            this attribute.
        :param args:
            positional arguments forwarded to the next class in the MRO
        :param kwargs:
            keyword arguments forwarded to the next class in the MRO
        """
        super().__init__(*args, **kwargs)

        self.show_constraints = show_constraints

        # This allows constraints to efficiently access parameters by name
        self._params_by_name: Dict[str, click.Parameter] = {
            param.name: param for param in self.params  # type: ignore
        }

        # Collect constraints applied to option groups and bind them to the
        # corresponding Option instances
        option_groups: Tuple[OptionGroup, ...] = getattr(self, 'option_groups', tuple())
        self.optgroup_constraints = tuple(
            BoundConstraint(grp.constraint, grp.options)
            for grp in option_groups
            if grp.constraint is not None
        )
        """Constraints applied to ``OptionGroup`` instances."""

        # Bind constraints defined via @constraint to click.Parameter instances
        self.param_constraints: Tuple[BoundConstraint, ...] = tuple(
            (
                constr if isinstance(constr, BoundConstraint)
                else constr.resolve_params(self)
            )
            for constr in constraints
        )
        """Constraints registered using ``@constraint`` (or equivalent method)."""

        self.all_constraints = self.optgroup_constraints + self.param_constraints
        """All constraints applied to parameter/option groups of this command."""

    def parse_args(self, ctx: click.Context, args: List[str]) -> List[str]:
        # Check constraints' consistency *before* parsing
        if not ctx.resilient_parsing and Constraint.must_check_consistency(ctx):
            for constr in self.all_constraints:
                constr.check_consistency()

        args = super().parse_args(ctx, args)  # type: ignore

        # Skip constraints checking if the user wants to see --help for subcommand
        # or if resilient parsing is enabled
        should_show_subcommand_help = isinstance(ctx.command, click.Group) and any(
            help_flag in args for help_flag in ctx.help_option_names
        )
        if ctx.resilient_parsing or should_show_subcommand_help:
            return args

        # Check constraints
        for constr in self.all_constraints:
            constr.check_values(ctx)
        return args

    def get_param_by_name(self, name: str) -> click.Parameter:
        try:
            return self._params_by_name[name]
        except KeyError:
            raise KeyError(f"there's no CLI parameter named '{name}'")

    def get_params_by_name(self, names: Iterable[str]) -> Sequence[click.Parameter]:
        return tuple(self.get_param_by_name(name) for name in names)

    def format_constraints(self, ctx: click.Context, formatter: "HelpFormatter") -> None:
        records_gen = (constr.get_help_record(ctx) for constr in self.param_constraints)
        records = [rec for rec in records_gen if rec is not None]
        if records:
            with formatter.section('Constraints'):
                formatter.write_dl(records)

    def must_show_constraints(self, ctx: click.Context) -> bool:
        # By default, don't show constraints
        return first_bool(
            self.show_constraints,
            getattr(ctx, "show_constraints", None),
            False,
        )


def ensure_constraints_support(command: click.Command) -> ConstraintMixin:
    if isinstance(command, ConstraintMixin):
        return command
    raise TypeError(
        'a Command must inherits from ConstraintMixin to support constraints')