# Copyright (c) 2021 PaddlePaddle 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 json
import os
import re
from typing import Union

import paddle
from paddle import distributed as dist
from paddle.optimizer import Optimizer

from deepspeech.utils import mp_tools
from deepspeech.utils.log import Log

logger = Log(__name__).getlog()

__all__ = ["load_parameters", "save_parameters"]


def _load_latest_checkpoint(checkpoint_dir: str) -> int:
    """Get the iteration number corresponding to the latest saved checkpoint.
    Args:
        checkpoint_dir (str): the directory where checkpoint is saved.
    Returns:
        int: the latest iteration number. -1 for no checkpoint to load.
    """
    checkpoint_record = os.path.join(checkpoint_dir, "checkpoint")
    if not os.path.isfile(checkpoint_record):
        return -1

    # Fetch the latest checkpoint index.
    with open(checkpoint_record, "rt") as handle:
        latest_checkpoint = handle.readlines()[-1].strip()
        iteration = int(latest_checkpoint.split(":")[-1])
    return iteration


def _save_record(checkpoint_dir: str, iteration: int):
    """Save the iteration number of the latest model to be checkpoint record.
    Args:
        checkpoint_dir (str): the directory where checkpoint is saved.
        iteration (int): the latest iteration number.
    Returns:
        None
    """
    checkpoint_record = os.path.join(checkpoint_dir, "checkpoint")
    # Update the latest checkpoint index.
    with open(checkpoint_record, "a+") as handle:
        handle.write("model_checkpoint_path:{}\n".format(iteration))


def load_parameters(model,
                    optimizer=None,
                    checkpoint_dir=None,
                    checkpoint_path=None):
    """Load a specific model checkpoint from disk. 
    Args:
        model (Layer): model to load parameters.
        optimizer (Optimizer, optional): optimizer to load states if needed.
            Defaults to None.
        checkpoint_dir (str, optional): the directory where checkpoint is saved.
        checkpoint_path (str, optional): if specified, load the checkpoint
            stored in the checkpoint_path(prefix) and the argument 'checkpoint_dir' will 
            be ignored. Defaults to None. 
    Returns:
        configs (dict): epoch or step, lr and other meta info should be saved.
    """
    configs = {}

    if checkpoint_path is not None:
        tag = os.path.basename(checkpoint_path).split(":")[-1]
    elif checkpoint_dir is not None:
        iteration = _load_latest_checkpoint(checkpoint_dir)
        if iteration == -1:
            return configs
        checkpoint_path = os.path.join(checkpoint_dir, "{}".format(iteration))
    else:
        raise ValueError(
            "At least one of 'checkpoint_dir' and 'checkpoint_path' should be specified!"
        )

    rank = dist.get_rank()

    params_path = checkpoint_path + ".pdparams"
    model_dict = paddle.load(params_path)
    model.set_state_dict(model_dict)
    logger.info("Rank {}: loaded model from {}".format(rank, params_path))

    optimizer_path = checkpoint_path + ".pdopt"
    if optimizer and os.path.isfile(optimizer_path):
        optimizer_dict = paddle.load(optimizer_path)
        optimizer.set_state_dict(optimizer_dict)
        logger.info("Rank {}: loaded optimizer state from {}".format(
            rank, optimizer_path))

    info_path = re.sub('.pdparams$', '.json', params_path)
    if os.path.exists(info_path):
        with open(info_path, 'r') as fin:
            configs = json.load(fin)
    return configs


@mp_tools.rank_zero_only
def save_parameters(checkpoint_dir: str,
                    tag_or_iteration: Union[int, str],
                    model: paddle.nn.Layer,
                    optimizer: Optimizer=None,
                    infos: dict=None):
    """Checkpoint the latest trained model parameters.
    Args:
        checkpoint_dir (str): the directory where checkpoint is saved.
        tag_or_iteration (int or str): the latest iteration(step or epoch) number.
        model (Layer): model to be checkpointed.
        optimizer (Optimizer, optional): optimizer to be checkpointed.
            Defaults to None.
        infos (dict or None): any info you want to save.
    Returns:
        None
    """
    checkpoint_path = os.path.join(checkpoint_dir,
                                   "{}".format(tag_or_iteration))

    model_dict = model.state_dict()
    params_path = checkpoint_path + ".pdparams"
    paddle.save(model_dict, params_path)
    logger.info("Saved model to {}".format(params_path))

    if optimizer:
        opt_dict = optimizer.state_dict()
        optimizer_path = checkpoint_path + ".pdopt"
        paddle.save(opt_dict, optimizer_path)
        logger.info("Saved optimzier state to {}".format(optimizer_path))

    info_path = re.sub('.pdparams$', '.json', params_path)
    infos = {} if infos is None else infos
    with open(info_path, 'w') as fout:
        data = json.dumps(infos)
        fout.write(data)

    if isinstance(tag_or_iteration, int):
        _save_record(checkpoint_dir, tag_or_iteration)