# Copyright 2018 Amazon.com, Inc. or its affiliates. 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.
# A copy of the License is located at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# or in the "license" file accompanying this file. This file 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.

from typing import Any, Dict, Iterable, List, Optional

from gluonts.core.component import validated
from gluonts.dataset.common import Dataset
from gluonts.dataset.field_names import FieldName
from gluonts.dataset.loader import as_stacked_batches
from gluonts.dataset.stat import calculate_dataset_statistics
from gluonts.itertools import Cyclic
from gluonts.time_feature import TimeFeature, time_features_from_frequency_str
from gluonts.torch.distributions import DistributionOutput
from gluonts.torch.model.estimator import PyTorchLightningEstimator
from gluonts.torch.model.predictor import PyTorchPredictor
from gluonts.torch.modules.loss import DistributionLoss, NegativeLogLikelihood
from gluonts.transform import (
    AddAgeFeature,
    AddObservedValuesIndicator,
    AddTimeFeatures,
    AsNumpyArray,
    Chain,
    DummyValueImputation,
    ExpectedNumInstanceSampler,
    InstanceSplitter,
    MissingValueImputation,
    RemoveFields,
    SetField,
    TestSplitSampler,
    Transformation,
    ValidationSplitSampler,
    VstackFeatures,
)
from gluonts.transform.sampler import InstanceSampler
import torch

from .lightning_module import TransformerLightningModule
from ...modules import StudentTOutput

PREDICTION_INPUT_NAMES = [
    "feat_static_cat",
    "feat_static_real",
    "past_time_feat",
    "past_target",
    "past_observed_values",
    "future_time_feat",
]

TRAINING_INPUT_NAMES = PREDICTION_INPUT_NAMES + [
    "future_target",
    "future_observed_values",
]


class TransformerEstimator(PyTorchLightningEstimator):
    @validated()
    def __init__(
        self,
        freq: str,
        prediction_length: int,
        input_size: int = 1,
        context_length: Optional[int] = None,
        dropout: float = 0.1,
        lr: float = 1e-3,
        weight_decay: float = 1e-8,
        d_model: int = 32,
        dim_feedforward: int = 64,
        activation: str = "gelu",
        nhead: int = 4,
        num_encoder_layers: int = 2,
        num_decoder_layers: int = 2,
        lags_seq: Optional[List[int]] = None,
        time_features: Optional[List[TimeFeature]] = None,
        scaling: Optional[str] = "mean",
        default_scale: float = 0.0,
        num_feat_dynamic_real: int = 0,
        num_feat_static_cat: int = 0,
        num_feat_static_real: int = 0,
        cardinality: Optional[List[int]] = None,
        embedding_dimension: Optional[List[int]] = None,
        distr_output: DistributionOutput = StudentTOutput(),
        loss: DistributionLoss = NegativeLogLikelihood(),
        num_parallel_samples: int = 100,
        batch_size: int = 32,
        num_batches_per_epoch: int = 50,
        patience: int = 10,
        imputation_method: Optional[MissingValueImputation] = None,
        trainer_kwargs: Optional[Dict[str, Any]] = None,
        train_sampler: Optional[InstanceSampler] = None,
        validation_sampler: Optional[InstanceSampler] = None,
    ) -> None:
        default_trainer_kwargs = {
            "max_epochs": 100,
            "gradient_clip_val": 10.0,
        }
        if trainer_kwargs is not None:
            default_trainer_kwargs.update(trainer_kwargs)
        super().__init__(trainer_kwargs=default_trainer_kwargs)

        self.input_size = input_size
        self.freq = freq
        self.prediction_length = prediction_length
        self.context_length = (
            context_length if context_length is not None else prediction_length
        )
        self.distr_output = distr_output
        self.loss = loss
        self.lr = lr
        self.weight_decay = weight_decay
        self.patience = patience

        self.num_feat_dynamic_real = num_feat_dynamic_real
        self.num_feat_static_cat = num_feat_static_cat
        self.num_feat_static_real = num_feat_static_real
        self.cardinality = (
            cardinality if cardinality and num_feat_static_cat > 0 else [1]
        )
        self.embedding_dimension = embedding_dimension
        self.lags_seq = lags_seq

        self.time_features = (
            time_features
            if time_features is not None
            else time_features_from_frequency_str(self.freq)
        )
        self.scaling = scaling
        self.default_scale = default_scale

        self.dropout = dropout
        self.d_model = d_model
        self.nhead = nhead
        self.activation = activation
        self.dim_feedforward = dim_feedforward
        self.num_encoder_layers = num_encoder_layers
        self.num_decoder_layers = num_decoder_layers

        self.num_parallel_samples = num_parallel_samples
        self.batch_size = batch_size
        self.num_batches_per_epoch = num_batches_per_epoch

        self.imputation_method = (
            imputation_method
            if imputation_method is not None
            else DummyValueImputation(self.distr_output.value_in_support)
        )

        self.train_sampler = train_sampler or ExpectedNumInstanceSampler(
            num_instances=1.0, min_future=prediction_length
        )
        self.validation_sampler = validation_sampler or ValidationSplitSampler(
            min_future=prediction_length
        )

    @classmethod
    def derive_auto_fields(cls, train_iter):
        stats = calculate_dataset_statistics(train_iter)

        return {
            "num_feat_dynamic_real": stats.num_feat_dynamic_real,
            "num_feat_static_cat": len(stats.feat_static_cat),
            "cardinality": [len(cats) for cats in stats.feat_static_cat],
        }

    def create_transformation(self) -> Transformation:
        remove_field_names = []
        if self.num_feat_static_real == 0:
            remove_field_names.append(FieldName.FEAT_STATIC_REAL)
        if self.num_feat_dynamic_real == 0:
            remove_field_names.append(FieldName.FEAT_DYNAMIC_REAL)

        return Chain(
            [RemoveFields(field_names=remove_field_names)]
            + (
                [SetField(output_field=FieldName.FEAT_STATIC_CAT, value=[0])]
                if not self.num_feat_static_cat > 0
                else []
            )
            + (
                [SetField(output_field=FieldName.FEAT_STATIC_REAL, value=[0.0])]
                if not self.num_feat_static_real > 0
                else []
            )
            + [
                AsNumpyArray(
                    field=FieldName.FEAT_STATIC_CAT,
                    expected_ndim=1,
                    dtype=int,
                ),
                AsNumpyArray(
                    field=FieldName.FEAT_STATIC_REAL,
                    expected_ndim=1,
                ),
                AsNumpyArray(
                    field=FieldName.TARGET,
                    # in the following line, we add 1 for the time dimension
                    expected_ndim=1 + len(self.distr_output.event_shape),
                ),
                AddObservedValuesIndicator(
                    target_field=FieldName.TARGET,
                    output_field=FieldName.OBSERVED_VALUES,
                    imputation_method=self.imputation_method,
                ),
                AddTimeFeatures(
                    start_field=FieldName.START,
                    target_field=FieldName.TARGET,
                    output_field=FieldName.FEAT_TIME,
                    time_features=self.time_features,
                    pred_length=self.prediction_length,
                ),
                AddAgeFeature(
                    target_field=FieldName.TARGET,
                    output_field=FieldName.FEAT_AGE,
                    pred_length=self.prediction_length,
                    log_scale=True,
                ),
                VstackFeatures(
                    output_field=FieldName.FEAT_TIME,
                    input_fields=[FieldName.FEAT_TIME, FieldName.FEAT_AGE]
                    + (
                        [FieldName.FEAT_DYNAMIC_REAL]
                        if self.num_feat_dynamic_real > 0
                        else []
                    ),
                ),
                AsNumpyArray(FieldName.FEAT_TIME, expected_ndim=2),
            ]
        )

    def _create_instance_splitter(self, module: TransformerLightningModule, mode: str):
        assert mode in ["training", "validation", "test"]

        instance_sampler = {
            "training": self.train_sampler,
            "validation": self.validation_sampler,
            "test": TestSplitSampler(),
        }[mode]

        return InstanceSplitter(
            target_field=FieldName.TARGET,
            is_pad_field=FieldName.IS_PAD,
            start_field=FieldName.START,
            forecast_start_field=FieldName.FORECAST_START,
            instance_sampler=instance_sampler,
            past_length=module.model._past_length,
            future_length=self.prediction_length,
            time_series_fields=[
                FieldName.FEAT_TIME,
                FieldName.OBSERVED_VALUES,
            ],
            dummy_value=self.distr_output.value_in_support,
        )

    def create_training_data_loader(
        self,
        data: Dataset,
        module: TransformerLightningModule,
        shuffle_buffer_length: Optional[int] = None,
        **kwargs,
    ) -> Iterable:
        data = Cyclic(data).stream()
        instances = self._create_instance_splitter(module, "training").apply(
            data, is_train=True
        )
        return as_stacked_batches(
            instances,
            batch_size=self.batch_size,
            shuffle_buffer_length=shuffle_buffer_length,
            field_names=TRAINING_INPUT_NAMES,
            output_type=torch.tensor,
            num_batches_per_epoch=self.num_batches_per_epoch,
        )

    def create_validation_data_loader(
        self,
        data: Dataset,
        module: TransformerLightningModule,
        **kwargs,
    ) -> Iterable:
        instances = self._create_instance_splitter(module, "validation").apply(
            data, is_train=True
        )
        return as_stacked_batches(
            instances,
            batch_size=self.batch_size,
            field_names=TRAINING_INPUT_NAMES,
            output_type=torch.tensor,
        )

    def create_lightning_module(self) -> TransformerLightningModule:
        return TransformerLightningModule(
            loss=self.loss,
            lr=self.lr,
            weight_decay=self.weight_decay,
            patience=self.patience,
            model_kwargs={
                "freq": self.freq,
                "context_length": self.context_length,
                "prediction_length": self.prediction_length,
                "input_size": self.input_size,
                "num_feat_dynamic_real": (
                    1 + self.num_feat_dynamic_real + len(self.time_features)
                ),
                "num_feat_static_real": max(1, self.num_feat_static_real),
                "num_feat_static_cat": max(1, self.num_feat_static_cat),
                "cardinality": self.cardinality,
                "embedding_dimension": self.embedding_dimension,
                "distr_output": self.distr_output,
                "dropout": self.dropout,
                "lags_seq": self.lags_seq,
                "scaling": self.scaling,
                "default_scale": self.default_scale,
                "num_parallel_samples": self.num_parallel_samples,
                "d_model": self.d_model,
                "dim_feedforward": self.dim_feedforward,
                "activation": self.activation,
                "nhead": self.nhead,
                "num_encoder_layers": self.num_encoder_layers,
                "num_decoder_layers": self.num_decoder_layers,
            },
        )

    def create_predictor(
        self,
        transformation: Transformation,
        module: TransformerLightningModule,
    ) -> PyTorchPredictor:
        prediction_splitter = self._create_instance_splitter(module, "test")

        return PyTorchPredictor(
            input_transform=transformation + prediction_splitter,
            input_names=PREDICTION_INPUT_NAMES,
            prediction_net=module,
            batch_size=self.batch_size,
            prediction_length=self.prediction_length,
            device=torch.device("cuda" if torch.cuda.is_available() else "cpu"),
        )
