# Copyright (c) 2021 The Regents of The University of California
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from json.decoder import JSONDecodeError
from .simstat import SimStat
from .statistic import Scalar, Distribution, Accumulator, Statistic
from .group import Group, Vector
import json
from typing import IO, Union

class JsonLoader(json.JSONDecoder):
    """
    Subclass of JSONDecoder that overrides 'object_hook'. Converts JSON object
    into a SimStat object.

    Usage
    -----
    ```
    from m5.ext.pystats.jsonloader import JsonLoader

    with open(path) as f:
        simstat_object = json.load(f, cls=JsonLoader)
    ```
    """

    def __init__(self):
        super(JsonLoader, self).__init__(self,
            object_hook=self.__json_to_simstat
        )

    def __json_to_simstat(self, d: dict) -> Union[SimStat,Statistic,Group]:
        if 'type' in d:
            if d['type'] == 'Scalar':
                d.pop('type', None)
                return Scalar(**d)

            elif d['type'] == 'Distribution':
                d.pop('type', None)
                return Distribution(**d)

            elif d['type'] == 'Accumulator':
                d.pop('type', None)
                return Accumulator(**d)

            elif d['type'] == 'Group':
                return Group(**d)

            elif d['type'] == 'Vector':
                d.pop('type', None)
                d.pop('time_conversion', None)
                return Vector(d)

            else:
                raise ValueError(
                    f"SimStat object has invalid type {d['type']}"
                )
        else:
            return SimStat(**d)

def load(json_file: IO) -> SimStat:
    """
    Wrapper function that provides a cleaner interface for using the
    JsonLoader class.

    Usage
    -----
    ```
    import m5.ext.pystats as pystats

    with open(path) as f:
        pystats.jsonloader.load(f)
    ```
    """

    simstat_object = json.load(json_file, cls=JsonLoader)
    return simstat_object