"""
Utilities to simplify the boilerplate for native lowering.
"""


import collections
import contextlib
import inspect
import functools
from enum import Enum

from numba.core import typing, types, utils, cgutils
from numba.core.typing.templates import BaseRegistryLoader


class Registry(object):
    """
    A registry of function and attribute implementations.
    """
    def __init__(self, name='unspecified'):
        self.name = name
        self.functions = []
        self.getattrs = []
        self.setattrs = []
        self.casts = []
        self.constants = []

    def lower(self, func, *argtys):
        """
        Decorate an implementation of *func* for the given argument types.
        *func* may be an actual global function object, or any
        pseudo-function supported by Numba, such as "getitem".

        The decorated implementation has the signature
        (context, builder, sig, args).
        """
        def decorate(impl):
            self.functions.append((impl, func, argtys))
            return impl
        return decorate

    def _decorate_attr(self, impl, ty, attr, impl_list, decorator):
        real_impl = decorator(impl, ty, attr)
        impl_list.append((real_impl, attr, real_impl.signature))
        return impl

    def lower_getattr(self, ty, attr):
        """
        Decorate an implementation of __getattr__ for type *ty* and
        the attribute *attr*.

        The decorated implementation will have the signature
        (context, builder, typ, val).
        """
        def decorate(impl):
            return self._decorate_attr(impl, ty, attr, self.getattrs,
                                       _decorate_getattr)
        return decorate

    def lower_getattr_generic(self, ty):
        """
        Decorate the fallback implementation of __getattr__ for type *ty*.

        The decorated implementation will have the signature
        (context, builder, typ, val, attr).  The implementation is
        called for attributes which haven't been explicitly registered
        with lower_getattr().
        """
        return self.lower_getattr(ty, None)

    def lower_setattr(self, ty, attr):
        """
        Decorate an implementation of __setattr__ for type *ty* and
        the attribute *attr*.

        The decorated implementation will have the signature
        (context, builder, sig, args).
        """
        def decorate(impl):
            return self._decorate_attr(impl, ty, attr, self.setattrs,
                                       _decorate_setattr)
        return decorate

    def lower_setattr_generic(self, ty):
        """
        Decorate the fallback implementation of __setattr__ for type *ty*.

        The decorated implementation will have the signature
        (context, builder, sig, args, attr).  The implementation is
        called for attributes which haven't been explicitly registered
        with lower_setattr().
        """
        return self.lower_setattr(ty, None)

    def lower_cast(self, fromty, toty):
        """
        Decorate the implementation of implicit conversion between
        *fromty* and *toty*.

        The decorated implementation will have the signature
        (context, builder, fromty, toty, val).
        """
        def decorate(impl):
            self.casts.append((impl, (fromty, toty)))
            return impl
        return decorate

    def lower_constant(self, ty):
        """
        Decorate the implementation for creating a constant of type *ty*.

        The decorated implementation will have the signature
        (context, builder, ty, pyval).
        """
        def decorate(impl):
            self.constants.append((impl, (ty,)))
            return impl
        return decorate

    def __repr__(self):
        return f"Lowering Registry<{self.name}>"


class RegistryLoader(BaseRegistryLoader):
    """
    An incremental loader for a target registry.
    """
    registry_items = ('functions', 'getattrs', 'setattrs', 'casts', 'constants')


# Global registry for implementations of builtin operations
# (functions, attributes, type casts)
builtin_registry = Registry('builtin_registry')

lower_builtin = builtin_registry.lower
lower_getattr = builtin_registry.lower_getattr
lower_getattr_generic = builtin_registry.lower_getattr_generic
lower_setattr = builtin_registry.lower_setattr
lower_setattr_generic = builtin_registry.lower_setattr_generic
lower_cast = builtin_registry.lower_cast
lower_constant = builtin_registry.lower_constant


def _decorate_getattr(impl, ty, attr):
    real_impl = impl

    if attr is not None:
        def res(context, builder, typ, value, attr):
            return real_impl(context, builder, typ, value)
    else:
        def res(context, builder, typ, value, attr):
            return real_impl(context, builder, typ, value, attr)

    res.signature = (ty,)
    res.attr = attr
    return res

def _decorate_setattr(impl, ty, attr):
    real_impl = impl

    if attr is not None:
        def res(context, builder, sig, args, attr):
            return real_impl(context, builder, sig, args)
    else:
        def res(context, builder, sig, args, attr):
            return real_impl(context, builder, sig, args, attr)

    res.signature = (ty, types.Any)
    res.attr = attr
    return res


def fix_returning_optional(context, builder, sig, status, retval):
    # Reconstruct optional return type
    if isinstance(sig.return_type, types.Optional):
        value_type = sig.return_type.type
        optional_none = context.make_optional_none(builder, value_type)
        retvalptr = cgutils.alloca_once_value(builder, optional_none)
        with builder.if_then(builder.not_(status.is_none)):
            optional_value = context.make_optional_value(
                builder, value_type, retval,
                )
            builder.store(optional_value, retvalptr)
        retval = builder.load(retvalptr)
    return retval

def user_function(fndesc, libs):
    """
    A wrapper inserting code calling Numba-compiled *fndesc*.
    """

    def imp(context, builder, sig, args):
        func = context.declare_function(builder.module, fndesc)
        # env=None assumes this is a nopython function
        status, retval = context.call_conv.call_function(
            builder, func, fndesc.restype, fndesc.argtypes, args)
        with cgutils.if_unlikely(builder, status.is_error):
            context.call_conv.return_status_propagate(builder, status)
        assert sig.return_type == fndesc.restype
        # Reconstruct optional return type
        retval = fix_returning_optional(context, builder, sig, status, retval)
        # If the data representations don't match up
        if retval.type != context.get_value_type(sig.return_type):
            msg = "function returned {0} but expect {1}"
            raise TypeError(msg.format(retval.type, sig.return_type))

        return impl_ret_new_ref(context, builder, fndesc.restype, retval)

    imp.signature = fndesc.argtypes
    imp.libs = tuple(libs)
    return imp


def user_generator(gendesc, libs):
    """
    A wrapper inserting code calling Numba-compiled *gendesc*.
    """

    def imp(context, builder, sig, args):
        func = context.declare_function(builder.module, gendesc)
        # env=None assumes this is a nopython function
        status, retval = context.call_conv.call_function(
            builder, func, gendesc.restype, gendesc.argtypes, args)
        # Return raw status for caller to process StopIteration
        return status, retval

    imp.libs = tuple(libs)
    return imp


def iterator_impl(iterable_type, iterator_type):
    """
    Decorator a given class as implementing *iterator_type*
    (by providing an `iternext()` method).
    """

    def wrapper(cls):
        # These are unbound methods
        iternext = cls.iternext

        @iternext_impl(RefType.BORROWED)
        def iternext_wrapper(context, builder, sig, args, result):
            (value,) = args
            iterobj = cls(context, builder, value)
            return iternext(iterobj, context, builder, result)

        lower_builtin('iternext', iterator_type)(iternext_wrapper)
        return cls

    return wrapper


class _IternextResult(object):
    """
    A result wrapper for iteration, passed by iternext_impl() into the
    wrapped function.
    """
    __slots__ = ('_context', '_builder', '_pairobj')

    def __init__(self, context, builder, pairobj):
        self._context = context
        self._builder = builder
        self._pairobj = pairobj

    def set_exhausted(self):
        """
        Mark the iterator as exhausted.
        """
        self._pairobj.second = self._context.get_constant(types.boolean, False)

    def set_valid(self, is_valid=True):
        """
        Mark the iterator as valid according to *is_valid* (which must
        be either a Python boolean or a LLVM inst).
        """
        if is_valid in (False, True):
            is_valid = self._context.get_constant(types.boolean, is_valid)
        self._pairobj.second = is_valid

    def yield_(self, value):
        """
        Mark the iterator as yielding the given *value* (a LLVM inst).
        """
        self._pairobj.first = value

    def is_valid(self):
        """
        Return whether the iterator is marked valid.
        """
        return self._context.get_argument_value(self._builder,
                                                types.boolean,
                                                self._pairobj.second)

    def yielded_value(self):
        """
        Return the iterator's yielded value, if any.
        """
        return self._pairobj.first

class RefType(Enum):
    """
    Enumerate the reference type
    """
    """
    A new reference
    """
    NEW = 1
    """
    A borrowed reference
    """
    BORROWED = 2
    """
    An untracked reference
    """
    UNTRACKED = 3

def iternext_impl(ref_type=None):
    """
    Wrap the given iternext() implementation so that it gets passed
    an _IternextResult() object easing the returning of the iternext()
    result pair.

    ref_type: a numba.targets.imputils.RefType value, the reference type used is
    that specified through the RefType enum.

    The wrapped function will be called with the following signature:
        (context, builder, sig, args, iternext_result)
    """
    if ref_type not in [x for x in RefType]:
        raise ValueError("ref_type must be an enum member of imputils.RefType")

    def outer(func):
        def wrapper(context, builder, sig, args):
            pair_type = sig.return_type
            pairobj = context.make_helper(builder, pair_type)
            func(context, builder, sig, args,
                _IternextResult(context, builder, pairobj))
            if ref_type == RefType.NEW:
                impl_ret = impl_ret_new_ref
            elif ref_type == RefType.BORROWED:
                impl_ret = impl_ret_borrowed
            elif ref_type == RefType.UNTRACKED:
                impl_ret = impl_ret_untracked
            else:
                raise ValueError("Unknown ref_type encountered")
            return impl_ret(context, builder,
                                    pair_type, pairobj._getvalue())
        return wrapper
    return outer


def call_getiter(context, builder, iterable_type, val):
    """
    Call the `getiter()` implementation for the given *iterable_type*
    of value *val*, and return the corresponding LLVM inst.
    """
    getiter_sig = typing.signature(iterable_type.iterator_type, iterable_type)
    getiter_impl = context.get_function('getiter', getiter_sig)
    return getiter_impl(builder, (val,))


def call_iternext(context, builder, iterator_type, val):
    """
    Call the `iternext()` implementation for the given *iterator_type*
    of value *val*, and return a convenience _IternextResult() object
    reflecting the results.
    """
    itemty = iterator_type.yield_type
    pair_type = types.Pair(itemty, types.boolean)
    iternext_sig = typing.signature(pair_type, iterator_type)
    iternext_impl = context.get_function('iternext', iternext_sig)
    val = iternext_impl(builder, (val,))
    pairobj = context.make_helper(builder, pair_type, val)
    return _IternextResult(context, builder, pairobj)


def call_len(context, builder, ty, val):
    """
    Call len() on the given value.  Return None if len() isn't defined on
    this type.
    """
    try:
        len_impl = context.get_function(len, typing.signature(types.intp, ty,))
    except NotImplementedError:
        return None
    else:
        return len_impl(builder, (val,))


_ForIterLoop = collections.namedtuple('_ForIterLoop',
                                      ('value', 'do_break'))


@contextlib.contextmanager
def for_iter(context, builder, iterable_type, val):
    """
    Simulate a for loop on the given iterable.  Yields a namedtuple with
    the given members:
    - `value` is the value being yielded
    - `do_break` is a callable to early out of the loop
    """
    iterator_type = iterable_type.iterator_type
    iterval = call_getiter(context, builder, iterable_type, val)

    bb_body = builder.append_basic_block('for_iter.body')
    bb_end = builder.append_basic_block('for_iter.end')

    def do_break():
        builder.branch(bb_end)

    builder.branch(bb_body)

    with builder.goto_block(bb_body):
        res = call_iternext(context, builder, iterator_type, iterval)
        with builder.if_then(builder.not_(res.is_valid()), likely=False):
            builder.branch(bb_end)
        yield _ForIterLoop(res.yielded_value(), do_break)
        builder.branch(bb_body)

    builder.position_at_end(bb_end)
    if context.enable_nrt:
        context.nrt.decref(builder, iterator_type, iterval)


def impl_ret_new_ref(ctx, builder, retty, ret):
    """
    The implementation returns a new reference.
    """
    return ret


def impl_ret_borrowed(ctx, builder, retty, ret):
    """
    The implementation returns a borrowed reference.
    This function automatically incref so that the implementation is
    returning a new reference.
    """
    if ctx.enable_nrt:
        ctx.nrt.incref(builder, retty, ret)
    return ret


def impl_ret_untracked(ctx, builder, retty, ret):
    """
    The return type is not a NRT object.
    """
    return ret


@contextlib.contextmanager
def force_error_model(context, model_name='numpy'):
    """
    Temporarily change the context's error model.
    """
    from numba.core import callconv

    old_error_model = context.error_model
    context.error_model = callconv.create_error_model(model_name, context)
    try:
        yield
    finally:
        context.error_model = old_error_model


def numba_typeref_ctor(*args, **kwargs):
    """A stub for use internally by Numba when a call is emitted
    on a TypeRef.
    """
    raise NotImplementedError("This function should not be executed.")