# coding=utf-8
# Copyright 2018 Google AI, Google Brain and Carnegie Mellon University Authors and the HuggingFace Inc. team.
# Copyright (c) 2018, NVIDIA CORPORATION.  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.
""" TF 2.0 Transformer XL model.
"""


import logging

import tensorflow as tf

from .configuration_transfo_xl import TransfoXLConfig
from .file_utils import add_start_docstrings, add_start_docstrings_to_callable
from .modeling_tf_transfo_xl_utilities import TFAdaptiveSoftmaxMask
from .modeling_tf_utils import TFPreTrainedModel, get_initializer, keras_serializable, shape_list
from .tokenization_utils import BatchEncoding


logger = logging.getLogger(__name__)

TF_TRANSFO_XL_PRETRAINED_MODEL_ARCHIVE_LIST = [
    "transfo-xl-wt103",
    # See all Transformer XL models at https://huggingface.co/models?filter=transfo-xl
]


class TFPositionalEmbedding(tf.keras.layers.Layer):
    def __init__(self, demb, **kwargs):
        super().__init__(**kwargs)

        self.inv_freq = 1 / (10000 ** (tf.range(0, demb, 2.0) / demb))

    def call(self, pos_seq, bsz=None):
        sinusoid_inp = tf.einsum("i,j->ij", pos_seq, self.inv_freq)
        pos_emb = tf.concat([tf.sin(sinusoid_inp), tf.cos(sinusoid_inp)], -1)

        if bsz is not None:
            return tf.tile(pos_emb[:, None, :], [1, bsz, 1])
        else:
            return pos_emb[:, None, :]


class TFPositionwiseFF(tf.keras.layers.Layer):
    def __init__(self, d_model, d_inner, dropout, pre_lnorm=False, layer_norm_epsilon=1e-5, init_std=0.02, **kwargs):
        super().__init__(**kwargs)

        self.d_model = d_model
        self.d_inner = d_inner
        self.dropout = dropout

        self.layer_1 = tf.keras.layers.Dense(
            d_inner, kernel_initializer=get_initializer(init_std), activation=tf.nn.relu, name="CoreNet_._0"
        )
        self.drop_1 = tf.keras.layers.Dropout(dropout)
        self.layer_2 = tf.keras.layers.Dense(d_model, kernel_initializer=get_initializer(init_std), name="CoreNet_._3")
        self.drop_2 = tf.keras.layers.Dropout(dropout)

        self.layer_norm = tf.keras.layers.LayerNormalization(epsilon=layer_norm_epsilon, name="layer_norm")

        self.pre_lnorm = pre_lnorm

    def call(self, inp, training=False):
        if self.pre_lnorm:
            # layer normalization + positionwise feed-forward
            core_out = self.layer_norm(inp)
            core_out = self.layer_1(core_out)
            core_out = self.drop_1(core_out, training=training)
            core_out = self.layer_2(core_out)
            core_out = self.drop_2(core_out, training=training)

            # residual connection
            output = core_out + inp
        else:
            # positionwise feed-forward
            core_out = self.layer_1(inp)
            core_out = self.drop_1(core_out, training=training)
            core_out = self.layer_2(core_out)
            core_out = self.drop_2(core_out, training=training)

            # residual connection + layer normalization
            output = self.layer_norm(inp + core_out)

        return output


class TFRelPartialLearnableMultiHeadAttn(tf.keras.layers.Layer):
    def __init__(
        self,
        n_head,
        d_model,
        d_head,
        dropout,
        dropatt=0,
        tgt_len=None,
        ext_len=None,
        mem_len=None,
        pre_lnorm=False,
        r_r_bias=None,
        r_w_bias=None,
        output_attentions=False,
        layer_norm_epsilon=1e-5,
        init_std=0.02,
        **kwargs
    ):
        super().__init__(**kwargs)

        self.output_attentions = output_attentions
        self.n_head = n_head
        self.d_model = d_model
        self.d_head = d_head
        self.dropout = dropout

        self.qkv_net = tf.keras.layers.Dense(
            3 * n_head * d_head, kernel_initializer=get_initializer(init_std), use_bias=False, name="qkv_net"
        )

        self.drop = tf.keras.layers.Dropout(dropout)
        self.dropatt = tf.keras.layers.Dropout(dropatt)
        self.o_net = tf.keras.layers.Dense(
            d_model, kernel_initializer=get_initializer(init_std), use_bias=False, name="o_net"
        )

        self.layer_norm = tf.keras.layers.LayerNormalization(epsilon=layer_norm_epsilon, name="layer_norm")

        self.scale = 1 / (d_head ** 0.5)

        self.pre_lnorm = pre_lnorm

        if r_r_bias is not None and r_w_bias is not None:  # Biases are shared
            self.r_r_bias = r_r_bias
            self.r_w_bias = r_w_bias
        else:
            self.r_r_bias = None
            self.r_w_bias = None

        self.r_net = tf.keras.layers.Dense(
            self.n_head * self.d_head, kernel_initializer=get_initializer(init_std), use_bias=False, name="r_net"
        )

    def build(self, input_shape):
        if self.r_r_bias is None or self.r_w_bias is None:  # Biases are not shared
            self.r_r_bias = self.add_weight(
                shape=(self.n_head, self.d_head), initializer="zeros", trainable=True, name="r_r_bias"
            )
            self.r_w_bias = self.add_weight(
                shape=(self.n_head, self.d_head), initializer="zeros", trainable=True, name="r_w_bias"
            )
        super().build(input_shape)

    def _rel_shift(self, x):
        x_size = shape_list(x)

        x = tf.pad(x, [[0, 0], [1, 0], [0, 0], [0, 0]])
        x = tf.reshape(x, [x_size[1] + 1, x_size[0], x_size[2], x_size[3]])
        x = tf.slice(x, [1, 0, 0, 0], [-1, -1, -1, -1])
        x = tf.reshape(x, x_size)

        return x

    def call(self, inputs, training=False):
        w, r, attn_mask, mems, head_mask = inputs
        qlen, rlen, bsz = shape_list(w)[0], shape_list(r)[0], shape_list(w)[1]

        if mems is not None:
            cat = tf.concat([mems, w], 0)
            if self.pre_lnorm:
                w_heads = self.qkv_net(self.layer_norm(cat))
            else:
                w_heads = self.qkv_net(cat)
            r_head_k = self.r_net(r)

            w_head_q, w_head_k, w_head_v = tf.split(w_heads, 3, axis=-1)
            w_head_q = w_head_q[-qlen:]
        else:
            if self.pre_lnorm:
                w_heads = self.qkv_net(self.layer_norm(w))
            else:
                w_heads = self.qkv_net(w)
            r_head_k = self.r_net(r)

            w_head_q, w_head_k, w_head_v = tf.split(w_heads, 3, axis=-1)

        klen = shape_list(w_head_k)[0]

        w_head_q = tf.reshape(w_head_q, (qlen, bsz, self.n_head, self.d_head))  # qlen x bsz x n_head x d_head
        w_head_k = tf.reshape(w_head_k, (klen, bsz, self.n_head, self.d_head))  # qlen x bsz x n_head x d_head
        w_head_v = tf.reshape(w_head_v, (klen, bsz, self.n_head, self.d_head))  # qlen x bsz x n_head x d_head

        r_head_k = tf.reshape(r_head_k, (rlen, self.n_head, self.d_head))  # qlen x n_head x d_head

        # compute attention score
        rw_head_q = w_head_q + self.r_w_bias  # qlen x bsz x n_head x d_head
        AC = tf.einsum("ibnd,jbnd->ijbn", rw_head_q, w_head_k)  # qlen x klen x bsz x n_head

        rr_head_q = w_head_q + self.r_r_bias
        BD = tf.einsum("ibnd,jnd->ijbn", rr_head_q, r_head_k)  # qlen x klen x bsz x n_head
        BD = self._rel_shift(BD)

        # [qlen x klen x bsz x n_head]
        attn_score = AC + BD
        attn_score = attn_score * self.scale

        # compute attention probability
        if attn_mask is not None:
            attn_mask_t = attn_mask[:, :, None, None]
            attn_score = attn_score * (1 - attn_mask_t) - 1e30 * attn_mask_t

        # [qlen x klen x bsz x n_head]
        attn_prob = tf.nn.softmax(attn_score, axis=1)
        attn_prob = self.dropatt(attn_prob, training=training)

        # Mask heads if we want to
        if head_mask is not None:
            attn_prob = attn_prob * head_mask

        # compute attention vector
        attn_vec = tf.einsum("ijbn,jbnd->ibnd", attn_prob, w_head_v)

        # [qlen x bsz x n_head x d_head]
        attn_vec_sizes = shape_list(attn_vec)
        attn_vec = tf.reshape(attn_vec, (attn_vec_sizes[0], attn_vec_sizes[1], self.n_head * self.d_head))

        # linear projection
        attn_out = self.o_net(attn_vec)
        attn_out = self.drop(attn_out, training=training)

        if self.pre_lnorm:
            # residual connection
            outputs = [w + attn_out]
        else:
            # residual connection + layer normalization
            outputs = [self.layer_norm(w + attn_out)]

        if self.output_attentions:
            outputs.append(attn_prob)

        return outputs


class TFRelPartialLearnableDecoderLayer(tf.keras.layers.Layer):
    def __init__(
        self,
        n_head,
        d_model,
        d_head,
        d_inner,
        dropout,
        tgt_len=None,
        ext_len=None,
        mem_len=None,
        dropatt=0.0,
        pre_lnorm=False,
        r_w_bias=None,
        r_r_bias=None,
        output_attentions=False,
        layer_norm_epsilon=1e-5,
        init_std=0.02,
        **kwargs
    ):
        super().__init__(**kwargs)

        self.dec_attn = TFRelPartialLearnableMultiHeadAttn(
            n_head,
            d_model,
            d_head,
            dropout,
            tgt_len=tgt_len,
            ext_len=ext_len,
            mem_len=mem_len,
            dropatt=dropatt,
            pre_lnorm=pre_lnorm,
            r_w_bias=r_w_bias,
            r_r_bias=r_r_bias,
            init_std=init_std,
            output_attentions=output_attentions,
            layer_norm_epsilon=layer_norm_epsilon,
            name="dec_attn",
        )
        self.pos_ff = TFPositionwiseFF(
            d_model,
            d_inner,
            dropout,
            pre_lnorm=pre_lnorm,
            init_std=init_std,
            layer_norm_epsilon=layer_norm_epsilon,
            name="pos_ff",
        )

    def call(self, inputs, training=False):
        dec_inp, r, dec_attn_mask, mems, head_mask = inputs
        attn_outputs = self.dec_attn([dec_inp, r, dec_attn_mask, mems, head_mask], training=training)
        ff_output = self.pos_ff(attn_outputs[0], training=training)

        outputs = [ff_output] + attn_outputs[1:]

        return outputs


class TFAdaptiveEmbedding(tf.keras.layers.Layer):
    def __init__(self, n_token, d_embed, d_proj, cutoffs, div_val=1, init_std=0.02, sample_softmax=False, **kwargs):
        super().__init__(**kwargs)

        self.n_token = n_token
        self.d_embed = d_embed
        self.init_std = init_std

        self.cutoffs = cutoffs + [n_token]
        self.div_val = div_val
        self.d_proj = d_proj

        self.emb_scale = d_proj ** 0.5

        self.cutoff_ends = [0] + self.cutoffs

        self.emb_layers = []
        self.emb_projs = []
        if div_val == 1:
            raise NotImplementedError  # Removed these to avoid maintaining dead code - They are not used in our pretrained checkpoint
        else:
            for i in range(len(self.cutoffs)):
                l_idx, r_idx = self.cutoff_ends[i], self.cutoff_ends[i + 1]
                d_emb_i = d_embed // (div_val ** i)
                self.emb_layers.append(
                    tf.keras.layers.Embedding(
                        r_idx - l_idx,
                        d_emb_i,
                        embeddings_initializer=get_initializer(init_std),
                        name="emb_layers_._{}".format(i),
                    )
                )

    def build(self, input_shape):
        for i in range(len(self.cutoffs)):
            d_emb_i = self.d_embed // (self.div_val ** i)
            self.emb_projs.append(
                self.add_weight(
                    shape=(d_emb_i, self.d_proj),
                    initializer=get_initializer(self.init_std),
                    trainable=True,
                    name="emb_projs_._{}".format(i),
                )
            )
        super().build(input_shape)

    def call(self, inp):
        if self.div_val == 1:
            raise NotImplementedError  # Removed these to avoid maintaining dead code - They are not used in our pretrained checkpoint
        else:
            inp_flat = tf.reshape(inp, (-1,))
            emb_flat = tf.zeros([shape_list(inp_flat)[0], self.d_proj])
            for i in range(len(self.cutoffs)):
                l_idx, r_idx = self.cutoff_ends[i], self.cutoff_ends[i + 1]

                mask_i = (inp_flat >= l_idx) & (inp_flat < r_idx)

                inp_i = tf.boolean_mask(inp_flat, mask_i) - l_idx
                emb_i = self.emb_layers[i](inp_i)
                emb_i = tf.einsum("id,de->ie", emb_i, self.emb_projs[i])

                mask_idx = tf.cast(tf.where(mask_i), dtype=tf.int64)
                emb_flat += tf.scatter_nd(mask_idx, emb_i, tf.cast(shape_list(emb_flat), dtype=tf.int64))

            embed_shape = shape_list(inp) + [self.d_proj]
            embed = tf.reshape(emb_flat, embed_shape)

        embed *= self.emb_scale

        return embed


@keras_serializable
class TFTransfoXLMainLayer(tf.keras.layers.Layer):
    config_class = TransfoXLConfig

    def __init__(self, config, **kwargs):
        super().__init__(**kwargs)
        self.output_attentions = config.output_attentions
        self.output_hidden_states = config.output_hidden_states

        self.n_token = config.vocab_size

        self.d_embed = config.d_embed
        self.d_model = config.d_model
        self.n_head = config.n_head
        self.d_head = config.d_head
        self.untie_r = config.untie_r

        self.word_emb = TFAdaptiveEmbedding(
            config.vocab_size,
            config.d_embed,
            config.d_model,
            config.cutoffs,
            div_val=config.div_val,
            init_std=config.init_std,
            name="word_emb",
        )

        self.drop = tf.keras.layers.Dropout(config.dropout)

        self.n_layer = config.n_layer

        self.tgt_len = config.tgt_len
        self.mem_len = config.mem_len
        self.ext_len = config.ext_len
        self.max_klen = config.tgt_len + config.ext_len + config.mem_len

        self.attn_type = config.attn_type

        self.layers = []
        if config.attn_type == 0:  # the default attention
            for i in range(config.n_layer):
                self.layers.append(
                    TFRelPartialLearnableDecoderLayer(
                        config.n_head,
                        config.d_model,
                        config.d_head,
                        config.d_inner,
                        config.dropout,
                        tgt_len=config.tgt_len,
                        ext_len=config.ext_len,
                        mem_len=config.mem_len,
                        dropatt=config.dropatt,
                        pre_lnorm=config.pre_lnorm,
                        r_w_bias=None if self.untie_r else self.r_w_bias,
                        r_r_bias=None if self.untie_r else self.r_r_bias,
                        output_attentions=self.output_attentions,
                        layer_norm_epsilon=config.layer_norm_epsilon,
                        init_std=config.init_std,
                        name="layers_._{}".format(i),
                    )
                )
        else:  # learnable embeddings and absolute embeddings
            raise NotImplementedError  # Removed these to avoid maintaining dead code - They are not used in our pretrained checkpoint

        self.same_length = config.same_length
        self.clamp_len = config.clamp_len

        if self.attn_type == 0:  # default attention
            self.pos_emb = TFPositionalEmbedding(self.d_model, name="pos_emb")
        else:  # learnable embeddings and absolute embeddings
            raise NotImplementedError  # Removed these to avoid maintaining dead code - They are not used in our pretrained checkpoint

    def build(self, input_shape):
        if not self.untie_r:
            self.r_w_bias = self.add_weight(
                shape=(self.n_head, self.d_head), initializer="zeros", trainable=True, name="r_w_bias"
            )
            self.r_r_bias = self.add_weight(
                shape=(self.n_head, self.d_head), initializer="zeros", trainable=True, name="r_r_bias"
            )
        super().build(input_shape)

    def get_input_embeddings(self):
        return self.word_emb

    def _resize_token_embeddings(self, new_num_tokens):
        return self.word_emb

    def backward_compatible(self):
        self.sample_softmax = -1

    def reset_length(self, tgt_len, ext_len, mem_len):
        self.tgt_len = tgt_len
        self.mem_len = mem_len
        self.ext_len = ext_len

    def _prune_heads(self, heads):
        raise NotImplementedError

    def init_mems(self, bsz):
        if self.mem_len > 0:
            mems = []
            for i in range(self.n_layer):
                empty = tf.zeros([self.mem_len, bsz, self.d_model])
                mems.append(empty)

            return mems
        else:
            return None

    def _update_mems(self, hids, mems, mlen, qlen):
        # does not deal with None
        if mems is None:
            return None

        # mems is not None
        assert len(hids) == len(mems), "len(hids) != len(mems)"

        # There are `mlen + qlen` steps that can be cached into mems
        # For the next step, the last `ext_len` of the `qlen` tokens
        # will be used as the extended context. Hence, we only cache
        # the tokens from `mlen + qlen - self.ext_len - self.mem_len`
        # to `mlen + qlen - self.ext_len`.
        new_mems = []
        end_idx = mlen + max(0, qlen - 0 - self.ext_len)
        beg_idx = max(0, end_idx - self.mem_len)
        for i in range(len(hids)):

            cat = tf.concat([mems[i], hids[i]], axis=0)
            tf.stop_gradient(cat)
            new_mems.append(cat[beg_idx:end_idx])

        return new_mems

    def call(self, inputs, mems=None, head_mask=None, inputs_embeds=None, training=False):
        if isinstance(inputs, (tuple, list)):
            input_ids = inputs[0]
            mems = inputs[1] if len(inputs) > 1 else mems
            head_mask = inputs[2] if len(inputs) > 2 else head_mask
            inputs_embeds = inputs[3] if len(inputs) > 3 else inputs_embeds
            assert len(inputs) <= 4, "Too many inputs."
        elif isinstance(inputs, (dict, BatchEncoding)):
            input_ids = inputs.get("input_ids")
            mems = inputs.get("mems", mems)
            head_mask = inputs.get("head_mask", head_mask)
            inputs_embeds = inputs.get("inputs_embeds", inputs_embeds)
            assert len(inputs) <= 4, "Too many inputs."
        else:
            input_ids = inputs

        # the original code for Transformer-XL used shapes [len, bsz] but we want a unified interface in the library
        # so we transpose here from shape [bsz, len] to shape [len, bsz]
        if input_ids is not None and inputs_embeds is not None:
            raise ValueError("You cannot specify both input_ids and inputs_embeds at the same time")
        elif input_ids is not None:
            input_ids = tf.transpose(input_ids, perm=(1, 0))
            qlen, bsz = shape_list(input_ids)
        elif inputs_embeds is not None:
            inputs_embeds = tf.transpose(inputs_embeds, perm=(1, 0, 2))
            qlen, bsz = shape_list(inputs_embeds)[:2]
        else:
            raise ValueError("You have to specify either input_ids or inputs_embeds")

        if mems is None:
            mems = self.init_mems(bsz)

        # Prepare head mask if needed
        # 1.0 in head_mask indicate we keep the head
        # attention_probs has shape bsz x n_heads x N x N
        # input head_mask has shape [num_heads] or [num_hidden_layers x num_heads] (a head_mask for each layer)
        # and head_mask is converted to shape [num_hidden_layers x qlen x klen x bsz x n_head]
        if head_mask is not None:
            raise NotImplementedError
        else:
            head_mask = [None] * self.n_layer

        if inputs_embeds is not None:
            word_emb = inputs_embeds
        else:
            word_emb = self.word_emb(input_ids)

        mlen = shape_list(mems[0])[0] if mems is not None else 0
        klen = mlen + qlen

        attn_mask = tf.ones([qlen, qlen])
        mask_u = tf.linalg.band_part(attn_mask, 0, -1)
        mask_dia = tf.linalg.band_part(attn_mask, 0, 0)
        attn_mask_pad = tf.zeros([qlen, mlen])
        dec_attn_mask = tf.concat([attn_mask_pad, mask_u - mask_dia], 1)
        if self.same_length:
            mask_l = tf.linalg.band_part(attn_mask, -1, 0)
            dec_attn_mask = tf.concat([dec_attn_mask[:, :qlen] + mask_l - mask_dia, dec_attn_mask[:, qlen:]], 1)
        # ::: PyTorch masking code for reference :::
        # if self.same_length:
        #     all_ones = word_emb.new_ones((qlen, klen), dtype=torch.uint8)
        #     mask_len = klen - self.mem_len
        #     if mask_len > 0:
        #         mask_shift_len = qlen - mask_len
        #     else:
        #         mask_shift_len = qlen
        #     dec_attn_mask = (torch.triu(all_ones, 1+mlen)
        #             + torch.tril(all_ones, -mask_shift_len))[:, :, None] # -1
        # else:
        #     dec_attn_mask = torch.triu(
        #         word_emb.new_ones((qlen, klen), dtype=torch.uint8), diagonal=1+mlen)[:,:,None]

        hids = []
        attentions = []
        if self.attn_type == 0:  # default
            pos_seq = tf.range(klen - 1, -1, -1.0)
            if self.clamp_len > 0:
                pos_seq = tf.minimum(pos_seq, self.clamp_len)
            pos_emb = self.pos_emb(pos_seq)

            core_out = self.drop(word_emb, training=training)
            pos_emb = self.drop(pos_emb, training=training)

            for i, layer in enumerate(self.layers):
                hids.append(core_out)
                mems_i = None if mems is None else mems[i]
                layer_outputs = layer([core_out, pos_emb, dec_attn_mask, mems_i, head_mask[i]], training=training)
                core_out = layer_outputs[0]
                if self.output_attentions:
                    attentions.append(layer_outputs[1])
        else:  # learnable embeddings and absolute embeddings
            raise NotImplementedError  # Removed these to avoid maintaining dead code - They are not used in our pretrained checkpoint

        core_out = self.drop(core_out, training=training)

        new_mems = self._update_mems(hids, mems, mlen, qlen)

        # We transpose back here to shape [bsz, len, hidden_dim]
        outputs = [tf.transpose(core_out, perm=(1, 0, 2)), new_mems]
        if self.output_hidden_states:
            # Add last layer and transpose to library standard shape [bsz, len, hidden_dim]
            hids.append(core_out)
            hids = list(tf.transpose(t, perm=(1, 0, 2)) for t in hids)
            outputs.append(hids)
        if self.output_attentions:
            # Transpose to library standard shape [bsz, n_heads, query_seq_len, key_seq_len]
            attentions = list(tf.transpose(t, perm=(2, 3, 0, 1)) for t in attentions)
            outputs.append(attentions)
        return outputs  # last hidden state, new_mems, (all hidden states), (all attentions)


class TFTransfoXLPreTrainedModel(TFPreTrainedModel):
    """ An abstract class to handle weights initialization and
        a simple interface for downloading and loading pretrained models.
    """

    config_class = TransfoXLConfig
    base_model_prefix = "transformer"


TRANSFO_XL_START_DOCSTRING = r"""

    .. note::

        TF 2.0 models accepts two formats as inputs:

            - having all inputs as keyword arguments (like PyTorch models), or
            - having all inputs as a list, tuple or dict in the first positional arguments.

        This second option is useful when using :obj:`tf.keras.Model.fit()` method which currently requires having
        all the tensors in the first argument of the model call function: :obj:`model(inputs)`.

        If you choose this second option, there are three possibilities you can use to gather all the input Tensors
        in the first positional argument :

        - a single Tensor with input_ids only and nothing else: :obj:`model(inputs_ids)`
        - a list of varying length with one or several input Tensors IN THE ORDER given in the docstring:
          :obj:`model([input_ids, attention_mask])` or :obj:`model([input_ids, attention_mask, token_type_ids])`
        - a dictionary with one or several input Tensors associated to the input names given in the docstring:
          :obj:`model({'input_ids': input_ids, 'token_type_ids': token_type_ids})`

    Parameters:
        config (:class:`~transformers.TransfoXLConfig`): Model configuration class with all the parameters of the model.
            Initializing with a config file does not load the weights associated with the model, only the configuration.
            Check out the :meth:`~transformers.PreTrainedModel.from_pretrained` method to load the model weights.
"""

TRANSFO_XL_INPUTS_DOCSTRING = r"""
    Args:
        input_ids (:obj:`tf.Tensor` or :obj:`Numpy array` of shape :obj:`(batch_size, sequence_length)`):
            Indices of input sequence tokens in the vocabulary.

            Indices can be obtained using :class:`transformers.TransfoXLTokenizer`.
            See :func:`transformers.PreTrainedTokenizer.encode` and
            :func:`transformers.PreTrainedTokenizer.encode_plus` for details.

            `What are input IDs? <../glossary.html#input-ids>`__
        mems (:obj:`List[tf.Tensor]` of length :obj:`config.n_layers`):
            Contains pre-computed hidden-states (key and values in the attention blocks) as computed by the model
            (see `mems` output below). Can be used to speed up sequential decoding. The token ids which have their mems
            given to this model should not be passed as input ids as they have already been computed.
        head_mask (:obj:`tf.Tensor` or :obj:`Numpy array` of shape :obj:`(num_heads,)` or :obj:`(num_layers, num_heads)`, `optional`, defaults to :obj:`None`):
            Mask to nullify selected heads of the self-attention modules.
            Mask values selected in ``[0, 1]``:
            :obj:`1` indicates the head is **not masked**, :obj:`0` indicates the head is **masked**.
        inputs_embeds (:obj:`tf.Tensor` or :obj:`Numpy array` of shape :obj:`(batch_size, sequence_length, hidden_size)`, `optional`, defaults to :obj:`None`):
            Optionally, instead of passing :obj:`input_ids` you can choose to directly pass an embedded representation.
            This is useful if you want more control over how to convert `input_ids` indices into associated vectors
            than the model's internal embedding lookup matrix.
"""


@add_start_docstrings(
    "The bare Bert Model transformer outputing raw hidden-states without any specific head on top.",
    TRANSFO_XL_START_DOCSTRING,
)
class TFTransfoXLModel(TFTransfoXLPreTrainedModel):
    def __init__(self, config, *inputs, **kwargs):
        super().__init__(config, *inputs, **kwargs)
        self.transformer = TFTransfoXLMainLayer(config, name="transformer")

    @add_start_docstrings_to_callable(TRANSFO_XL_INPUTS_DOCSTRING)
    def call(self, inputs, **kwargs):
        r"""
    Return:
        :obj:`tuple(tf.Tensor)` comprising various elements depending on the configuration (:class:`~transformers.TransfoXLConfig`) and inputs:
        last_hidden_state (:obj:`tf.Tensor` of shape :obj:`(batch_size, sequence_length, hidden_size)`):
            Sequence of hidden-states at the last layer of the model.
        mems (:obj:`List[tf.Tensor]` of length :obj:`config.n_layers`):
            Contains pre-computed hidden-states (key and values in the attention blocks).
            Can be used (see `mems` input) to speed up sequential decoding. The token ids which have their past given to this model
            should not be passed as input ids as they have already been computed.
        hidden_states (:obj:`tuple(tf.Tensor)`, `optional`, returned when ``config.output_hidden_states=True``):
            Tuple of :obj:`tf.Tensor` (one for the output of the embeddings + one for the output of each layer)
            of shape :obj:`(batch_size, sequence_length, hidden_size)`.

            Hidden-states of the model at the output of each layer plus the initial embedding outputs.
        attentions (:obj:`tuple(tf.Tensor)`, `optional`, returned when ``config.output_attentions=True``):
            Tuple of :obj:`tf.Tensor` (one for each layer) of shape
            :obj:`(batch_size, num_heads, sequence_length, sequence_length)`.

            Attentions weights after the attention softmax, used to compute the weighted average in the self-attention
            heads.

    Examples::

        import tensorflow as tf
        from transformers import TransfoXLTokenizer, TFTransfoXLModel

        tokenizer = TransfoXLTokenizer.from_pretrained('transfo-xl-wt103')
        model = TFTransfoXLModel.from_pretrained('transfo-xl-wt103')
        input_ids = tf.constant(tokenizer.encode("Hello, my dog is cute", add_special_tokens=True))[None, :]  # Batch size 1
        outputs = model(input_ids)
        last_hidden_states, mems = outputs[:2]

        """
        outputs = self.transformer(inputs, **kwargs)
        return outputs


class TFTransfoXLLMHead(tf.keras.layers.Layer):
    def __init__(self, config, input_embeddings, **kwargs):
        super().__init__(**kwargs)
        self.vocab_size = config.vocab_size

        # The output weights are the same as the input embeddings, but there is
        # an output-only bias for each token.
        self.input_embeddings = input_embeddings

    def build(self, input_shape):
        self.bias = self.add_weight(shape=(self.vocab_size,), initializer="zeros", trainable=True, name="bias")
        super().build(input_shape)

    def call(self, hidden_states):
        hidden_states = self.input_embeddings(hidden_states, mode="linear")
        hidden_states = hidden_states + self.bias
        return hidden_states


@add_start_docstrings(
    """The Transformer-XL Model with a language modeling head on top
    (adaptive softmax with weights tied to the adaptive input embeddings)""",
    TRANSFO_XL_START_DOCSTRING,
)
class TFTransfoXLLMHeadModel(TFTransfoXLPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)
        self.transformer = TFTransfoXLMainLayer(config, name="transformer")
        self.sample_softmax = config.sample_softmax
        assert (
            self.sample_softmax <= 0
        ), "Sampling from the softmax is not implemented yet. Please look at issue: #3310: https://github.com/huggingface/transformers/issues/3310"

        self.crit = TFAdaptiveSoftmaxMask(
            config.vocab_size, config.d_embed, config.d_model, config.cutoffs, div_val=config.div_val, name="crit"
        )

    def get_output_embeddings(self):
        """ Double-check if you are using adaptive softmax.
        """
        if len(self.crit.out_layers) > 0:
            return self.crit.out_layers[-1]
        return None

    def reset_length(self, tgt_len, ext_len, mem_len):
        self.transformer.reset_length(tgt_len, ext_len, mem_len)

    def init_mems(self, bsz):
        return self.transformer.init_mems(bsz)

    @add_start_docstrings_to_callable(TRANSFO_XL_INPUTS_DOCSTRING)
    def call(self, inputs, mems=None, head_mask=None, inputs_embeds=None, labels=None, training=False):
        r"""
    Return:
        :obj:`tuple(tf.Tensor)` comprising various elements depending on the configuration (:class:`~transformers.TransfoXLConfig`) and inputs:
        prediction_scores (:obj:`tf.Tensor` of shape :obj:`(batch_size, sequence_length, config.vocab_size)`):
            Prediction scores of the language modeling head (scores for each vocabulary token before SoftMax).
        mems (:obj:`List[tf.Tensor]` of length :obj:`config.n_layers`):
            Contains pre-computed hidden-states (key and values in the attention blocks).
            Can be used (see `past` input) to speed up sequential decoding. The token ids which have their past given to this model
            should not be passed as input ids as they have already been computed.
        hidden_states (:obj:`tuple(tf.Tensor)`, `optional`, returned when ``config.output_hidden_states=True``):
            Tuple of :obj:`tf.Tensor` (one for the output of the embeddings + one for the output of each layer)
            of shape :obj:`(batch_size, sequence_length, hidden_size)`.

            Hidden-states of the model at the output of each layer plus the initial embedding outputs.
        attentions (:obj:`tuple(tf.Tensor)`, `optional`, returned when ``config.output_attentions=True``):
            Tuple of :obj:`tf.Tensor` (one for each layer) of shape
            :obj:`(batch_size, num_heads, sequence_length, sequence_length)`.

            Attentions weights after the attention softmax, used to compute the weighted average in the self-attention
            heads.

    Examples::

        import tensorflow as tf
        from transformers import TransfoXLTokenizer, TFTransfoXLLMHeadModel

        tokenizer = TransfoXLTokenizer.from_pretrained('transfo-xl-wt103')
        model = TFTransfoXLLMHeadModel.from_pretrained('transfo-xl-wt103')
        input_ids = tf.constant(tokenizer.encode("Hello, my dog is cute", add_special_tokens=True))[None, :]  # Batch size 1
        outputs = model(input_ids)
        prediction_scores, mems = outputs[:2]

        """
        if isinstance(inputs, (tuple, list)):
            input_ids = inputs[0]
            mems = inputs[1] if len(inputs) > 1 else mems
            head_mask = inputs[2] if len(inputs) > 2 else head_mask
            inputs_embeds = inputs[3] if len(inputs) > 3 else inputs_embeds
            labels = inputs[4] if len(inputs) > 4 else labels
            assert len(inputs) <= 5, "Too many inputs."
        elif isinstance(inputs, dict):
            input_ids = inputs.get("input_ids")
            mems = inputs.get("mems", mems)
            head_mask = inputs.get("head_mask", head_mask)
            inputs_embeds = inputs.get("inputs_embeds", inputs_embeds)
            labels = inputs.get("labels", labels)
            assert len(inputs) <= 5, "Too many inputs."
        else:
            input_ids = inputs

        if input_ids is not None:
            bsz, tgt_len = shape_list(input_ids)[:2]
        else:
            bsz, tgt_len = shape_list(inputs_embeds)[:2]

        transformer_outputs = self.transformer([input_ids, mems, head_mask, inputs_embeds], training=training)

        last_hidden = transformer_outputs[0]
        pred_hid = last_hidden[:, -tgt_len:]
        outputs = transformer_outputs[1:]

        softmax_output = self.crit([pred_hid, labels], training=training)
        outputs = [softmax_output] + outputs

        return outputs  # logits, new_mems, (all hidden states), (all attentions)

    def prepare_inputs_for_generation(self, inputs, past, **model_kwargs):
        inputs = {"inputs": inputs}

        # if past is defined in model kwargs then use it for faster decoding
        if past:
            inputs["mems"] = past

        return inputs
