#!/usr/bin/env python3
# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved


"""
API for exporting a pytorch model to a predictor, the predictor contains model(s) in
deployable format and predefined functions as glue code. The exported predictor should
generate same output as the original pytorch model. (See predictor/api.py for details of
predictor)

This API defines two customizable methods for the pytorch model:
    prepare_for_export (required by the default export_predictor): returns
        PredictorExportConfig which tells information about how export the predictor.
    export_predictor (optional): the implementation of export process. The default
        implementation is provided to cover the majority of use cases where the
        individual model(s) can be exported in standard way.

NOTE:
    1: There's a difference between predictor type and model type. model type
        refers to predefined deployable format such as caffe2, torchscript(_int8),
        while the predictor type can be anything that "export_predictor" can
        recognize.
    2: The standard model exporting methods are provided by the library code, they're
        meant to be modularized and can be used by customized export_predictor as well.
"""

import json
import logging
import os
import sys
from abc import ABC, abstractmethod
from typing import Callable, Dict, NamedTuple, Optional, Union

if sys.version_info >= (3, 8):
    from typing import final
else:
    # If final decorator not available when using older python version, replace with the
    # dummy implementation that does nothing.
    def final(func):
        return func


import torch
import torch.nn as nn
import torch.quantization.quantize_fx
from d2go.modeling.quantization import post_training_quantize
from detectron2.utils.file_io import PathManager
from mobile_cv.arch.utils import fuse_utils
from mobile_cv.common.misc.file_utils import make_temp_directory
from mobile_cv.common.misc.registry import Registry
from mobile_cv.predictor.api import FuncInfo, ModelInfo, PredictorInfo
from mobile_cv.predictor.builtin_functions import (
    IdentityPostprocess,
    IdentityPreprocess,
    NaiveRunFunc,
)


logger = logging.getLogger(__name__)


class PredictorExportConfig(NamedTuple):
    """
    Storing information for exporting a predictor.

    Args:
        model (any nested iterable structure of nn.Module): the model(s) to be exported
            (via tracing/onnx or scripting). This can be sub-model(s) when the predictor
            consists of multiple models in deployable format, and/or pre/post processing
            is excluded due to requirement of tracing or hardware incompatibility.
        data_generator (Callable): a function to generate all data needed for tracing,
            such that data = data_generator(x), the returned data has the same nested
            structure as model. The data for each model will be treated as positional
            arguments, i.e. model(*data).
        model_export_kwargs (Dict): additional kwargs when exporting each sub-model, it
            follows the same nested structure as the model, and may contains information
            such as scriptable.

        preprocess_info (FuncInfo): info for predictor's preprocess
        postprocess_info (FuncInfo): info for predictor's postprocess
        run_func_info (FuncInfo): info for predictor's run_fun
    """

    model: Union[nn.Module, Dict[str, nn.Module]]
    data_generator: Optional[Callable] = None
    model_export_method: Optional[Union[str, Dict[str, str]]] = None
    model_export_kwargs: Optional[Union[Dict, Dict[str, Dict]]] = None

    preprocess_info: FuncInfo = FuncInfo.gen_func_info(IdentityPreprocess, params={})
    postprocess_info: FuncInfo = FuncInfo.gen_func_info(IdentityPostprocess, params={})
    run_func_info: FuncInfo = FuncInfo.gen_func_info(NaiveRunFunc, params={})


def convert_and_export_predictor(
    cfg,
    pytorch_model,
    predictor_type,
    output_dir,
    data_loader,
):
    """
    Entry point for convert and export model. This involves two steps:
        - convert: converting the given `pytorch_model` to another format, currently
            mainly for quantizing the model.
        - export: exporting the converted `pytorch_model` to predictor. This step
            should not alter the behaviour of model.
    """

    if "int8" in predictor_type:
        if not cfg.QUANTIZATION.QAT.ENABLED:
            logger.info(
                "The model is not quantized during training, running post"
                " training quantization ..."
            )
            pytorch_model = post_training_quantize(cfg, pytorch_model, data_loader)
            # only check bn exists in ptq as qat still has bn inside fused ops
            if fuse_utils.check_bn_exist(pytorch_model):
                logger.warn(f"Post training quantized model has bn inside fused ops")
        logger.info(f"Converting quantized model {cfg.QUANTIZATION.BACKEND}...")

        if cfg.QUANTIZATION.EAGER_MODE:
            # TODO(T93870278): move this logic to prepare_for_quant_convert
            pytorch_model = torch.quantization.convert(pytorch_model, inplace=False)
        else:  # FX graph mode quantization
            if hasattr(pytorch_model, "prepare_for_quant_convert"):
                pytorch_model = pytorch_model.prepare_for_quant_convert(cfg)
            else:
                # TODO(T93870381): move this to a default function
                pytorch_model = torch.quantization.quantize_fx.convert_fx(pytorch_model)

        logger.info("Quantized Model:\n{}".format(pytorch_model))
    else:
        pytorch_model = fuse_utils.fuse_model(pytorch_model)
        logger.info("Fused Model:\n{}".format(pytorch_model))
        if fuse_utils.count_bn_exist(pytorch_model) > 0:
            logger.warning("BN existed in pytorch model after fusing.")

    return export_predictor(cfg, pytorch_model, predictor_type, output_dir, data_loader)


def export_predictor(cfg, pytorch_model, predictor_type, output_dir, data_loader):
    """
    Interface for exporting a pytorch model to predictor of given type. This function
    can be override to achieve customized exporting procedure, eg. using non-default
    optimization passes, composing traced models, etc.

    Args:
        cfg (CfgNode): the config
        pytorch_model (nn.Module): a pytorch model, mostly also a meta-arch
        predictor_type (str): a string which specifies the type of predictor, note that
            the definition of type is interpreted by "export_predictor", the default
            implementation uses the deployable model format (eg. caffe2_fp32,
            torchscript_int8) as predictor type.
        output_dir (str): the parent directory where the predictor will be saved
        data_loader: data loader for the pytorch model

    Returns:
        predictor_path (str): the directory of exported predictor, a sub-directory of
            "output_dir"
    """
    # predictor exporting can be customized by implement "export_predictor" of meta-arch
    if hasattr(pytorch_model, "export_predictor"):
        return pytorch_model.export_predictor(
            cfg, predictor_type, output_dir, data_loader
        )
    else:
        return default_export_predictor(
            cfg, pytorch_model, predictor_type, output_dir, data_loader
        )


def _export_single_model(
    predictor_path,
    model,
    input_args,
    save_path,
    model_export_method,
    model_export_kwargs,
):
    assert isinstance(model, nn.Module), model
    # model_export_method either inherits ModelExportMethod or is a key in the registry
    model_export_method_str = None
    if isinstance(model_export_method, str):
        model_export_method_str = model_export_method
        model_export_method = ModelExportMethodRegistry.get(model_export_method)
    assert issubclass(model_export_method, ModelExportMethod), model_export_method
    logger.info("Using model export method: {}".format(model_export_method))

    load_kwargs = model_export_method.export(
        model=model,
        input_args=input_args,
        save_path=save_path,
        export_method=model_export_method_str,
        **model_export_kwargs,
    )
    assert isinstance(load_kwargs, dict)
    model_rel_path = os.path.relpath(save_path, predictor_path)
    return ModelInfo(
        path=model_rel_path,
        export_method="{}.{}".format(
            model_export_method.__module__, model_export_method.__qualname__
        ),
        load_kwargs=load_kwargs,
    )


def default_export_predictor(
    cfg, pytorch_model, predictor_type, output_dir, data_loader
):
    # The default implementation acts based on the PredictorExportConfig returned by
    # calling "prepare_for_export". It'll export all sub models in standard way
    # according to the "predictor_type".
    assert hasattr(pytorch_model, "prepare_for_export"), pytorch_model
    inputs = next(iter(data_loader))
    export_config = pytorch_model.prepare_for_export(cfg, inputs, predictor_type)
    model_inputs = (
        export_config.data_generator(inputs)
        if export_config.data_generator is not None
        else (inputs,)
    )

    predictor_path = os.path.join(output_dir, predictor_type)
    PathManager.mkdirs(predictor_path)

    predictor_init_kwargs = {
        "preprocess_info": export_config.preprocess_info,
        "postprocess_info": export_config.postprocess_info,
        "run_func_info": export_config.run_func_info,
    }

    if isinstance(export_config.model, dict):
        models_info = {}
        for name, model in export_config.model.items():
            save_path = os.path.join(predictor_path, name)
            model_info = _export_single_model(
                predictor_path=predictor_path,
                model=model,
                input_args=model_inputs[name] if model_inputs is not None else None,
                save_path=save_path,
                model_export_method=(
                    predictor_type
                    if export_config.model_export_method is None
                    else export_config.model_export_method[name]
                ),
                model_export_kwargs=(
                    {}
                    if export_config.model_export_kwargs is None
                    else export_config.model_export_kwargs[name]
                ),
            )
            models_info[name] = model_info
        predictor_init_kwargs["models"] = models_info
    else:
        save_path = predictor_path  # for single model exported files are put under `predictor_path` together with predictor_info.json
        model_info = _export_single_model(
            predictor_path=predictor_path,
            model=export_config.model,
            input_args=model_inputs,
            save_path=save_path,
            model_export_method=export_config.model_export_method or predictor_type,
            model_export_kwargs=export_config.model_export_kwargs or {},
        )
        predictor_init_kwargs["model"] = model_info

    # assemble predictor
    predictor_info = PredictorInfo(**predictor_init_kwargs)
    with PathManager.open(
        os.path.join(predictor_path, "predictor_info.json"), "w"
    ) as f:
        json.dump(predictor_info.to_dict(), f, indent=4)

    return predictor_path


class ModelExportMethod(ABC):
    """
    Base class for "model export method". Each model export method can export a pytorch
    model to a certain deployable format, such as torchscript or caffe2. It consists
    with `export` and `load` methods.
    """

    @classmethod
    @abstractmethod
    def export(cls, model, input_args, save_path, export_method, **export_kwargs):
        """
        Export the model to deployable format.

        Args:
            model (nn.Module): a pytorch model to export
            input_args (Tuple[Any]): inputs of model, called as model(*input_args)
            save_path (str): directory where the model will be exported
            export_method (str): string name for the export method
            export_kwargs (Dict): additional parameters for exporting model defined
                by each model export method.
        Return:
            load_kwargs (Dict): additional information (besides save_path) needed in
                order to load the exported model. This needs to be JSON serializable.
        """
        pass

    @classmethod
    @abstractmethod
    def load(cls, save_path, **load_kwargs):
        """
        Load the exported model back for inference.

        Args:
            save_path (str): directory where the model is stored.
            load_kwargs (Dict): addtional information to load the exported model.
        Returns:
            model (nn.Module): a nn.Module (often time a wrapper for non torchscript
                types like caffe2), it works the same as the original pytorch model,
                i.e. getting the same output when called as model(*input_args)
        """
        pass

    @classmethod
    @final
    def test_export_and_load(
        cls, model, input_args, export_method, export_kwargs, output_checker
    ):
        """
        Illustrate the life-cycle of export and load, used for testing.
        """
        with make_temp_directory("test_export_and_load") as save_path:
            # run the orginal model
            assert isinstance(model, nn.Module), model
            assert isinstance(input_args, (list, tuple)), input_args
            original_output = model(*input_args)
            # export the model
            model.eval()  # TODO: decide where eval() should be called
            load_kwargs = cls.export(
                model, input_args, save_path, export_method, **export_kwargs
            )
            # sanity check for load_kwargs
            assert isinstance(load_kwargs, dict), load_kwargs
            assert json.dumps(load_kwargs), load_kwargs
            # loaded model back
            loaded_model = cls.load(save_path, **load_kwargs)
            # run the loaded model
            assert isinstance(loaded_model, nn.Module), loaded_model
            new_output = loaded_model(*input_args)
            # compare outputs
            output_checker(new_output, original_output)


ModelExportMethodRegistry = Registry("ModelExportMethod", allow_override=True)
