# Copyright 2021 The NetKet Authors - All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import jax

from flax import struct

from netket.hilbert.random import flip_state

from .base import MetropolisRule


@struct.dataclass
class LocalRule(MetropolisRule):
    r"""
    A transition rule acting on the local degree of freedom.

    This transition acts locally only on one local degree of freedom :math:`s_i`,
    and proposes a new state: :math:`s_1 \dots s^\prime_i \dots s_N`,
    where :math:`s^\prime_i \neq s_i`.

    The transition probability associated to this
    sampler can be decomposed into two steps:

    1. One of the site indices :math:`i = 1\dots N` is chosen
    with uniform probability.
    2. Among all the possible (:math:`m`) values that :math:`s_i` can take,
    one of them is chosen with uniform probability.
    """

    def transition(rule, sampler, machine, parameters, state, key, σ):
        key1, key2 = jax.random.split(key, 2)

        n_chains = σ.shape[0]
        hilb = sampler.hilbert

        indxs = jax.random.randint(key1, shape=(n_chains,), minval=0, maxval=hilb.size)
        σp, _ = flip_state(hilb, key2, σ, indxs)

        return σp, None

    def __repr__(self):
        return "LocalRule()"
