import logging
import os

from pathlib import Path, PureWindowsPath
from pydantic import BaseModel
from time import strftime, localtime
from typing import Union

import pandas as pd

from ..conf import defaults
from .models import Model

logger = logging.getLogger(__name__)


class CsvTable(object):
    def __init__(self, fpath: Path):
        self.path = fpath
        self.empty = True

    def append(self, coords: dict, data: pd.DataFrame) -> bool:
        assert isinstance(data, pd.DataFrame)
        for c in reversed(coords.keys()):
            data.insert(0, c, coords[c])
        if self.empty:
            data.to_csv(self.path, index=False, mode='w', header=True)
        else:
            data.to_csv(self.path, index=False, mode='a', header=False)
        self.empty = False
        return True

class _Session(object):
    """
    Singleton class for a server session that persists data between API calls
    """

    log_format = '%(asctime)s - %(levelname)s - %(message)s'

    def __init__(self, root: str = None):
        self.models = {} # model_id : model object
        self.paths = self.make_paths(root)

        self.logfile = self.paths['logs'] / f'session.log'
        logging.basicConfig(filename=self.logfile, level=logging.INFO, force=True, format=self.log_format)

        self.log_info('Initialized session')
        self.tables = {}

    def write_to_table(self, name: str, coords: dict, data: pd.DataFrame):
        """
        Write data to a named data table, initializing if it does not yet exist.
        :param name: name of the table to persist through session
        :param coords: dictionary of coordinates to associate with all rows in this method call
        :param data: DataFrame containing data
        :return: True if successful
        """
        try:
            if name in self.tables.keys():
                table = self.tables.get(name)
            else:
                table = CsvTable(self.paths['tables'] / (name + '.csv'))
                self.tables[name] = table
        except Exception:
            raise CouldNotCreateTable(f'Unable to create table named {name}')

        try:
            table.append(coords, data)
            return True
        except Exception:
            raise CouldNotAppendToTable(f'Unable to append data to table named {name}')

    def get_paths(self):
        return self.paths

    def set_data_directory(self, key: str, path: str):
        if not key in self.paths.keys():
            raise InvalidPathError(f'No such path {key}')
        if not Path(path).exists():
            raise InvalidPathError(f'Could not find {path}')
        self.paths[key] = Path(path)

    @staticmethod
    def make_paths(root: str = None) -> dict:
        """
        Set paths where images, logs, etc. are located in this session
        :param root: absolute path to top-level directory
        :return: dictionary of session paths
        """
        if root is None:
            root_path = Path(defaults.root)
        else:
            root_path = Path(root)
        sid = _Session.create_session_id(root_path)
        paths = {'root': root_path}
        for pk in ['inbound_images', 'outbound_images', 'logs', 'tables']:
            pa = root_path / sid / defaults.subdirectories[pk]
            paths[pk] = pa
            try:
                pa.mkdir(parents=True, exist_ok=True)
            except Exception:
                raise CouldNotCreateDirectory(f'Could not create directory: {pa}')
        return paths

    @staticmethod
    def create_session_id(look_where: Path) -> str:
        """
        Autogenerate a session ID by incrementing from a list of log files.
        """
        yyyymmdd = strftime('%Y%m%d', localtime())
        idx = 0
        while os.path.exists(look_where / f'{yyyymmdd}-{idx:04d}'):
            idx += 1
        return f'{yyyymmdd}-{idx:04d}'

    def get_log_data(self) -> list:
        log = []
        with open(self.logfile, 'r') as fh:
            for line in fh:
                k = ['datatime', 'level', 'message']
                v = line.strip().split(' - ')[0:3]
                log.insert(0, dict(zip(k, v)))
        return log

    def log_info(self, msg):
        logger.info(msg)

    def log_warning(self, msg):
        logger.warning(msg)

    def log_error(self, msg):
        logger.error(msg)

    def load_model(self, ModelClass: Model, params: Union[BaseModel, None] = None) -> dict:
        """
        Load an instance of a given model class and attach to this session's model registry
        :param ModelClass: subclass of Model
        :param params: optional parameters that are passed to the model's construct
        :return: model_id of loaded model
        """
        mi = ModelClass(params=params)
        assert mi.loaded, f'Error loading instance of {ModelClass.__name__}'
        ii = 0

        def mid(i):
            return f'{ModelClass.__name__}_{i:02d}'

        while mid(ii) in self.models.keys():
            ii += 1

        key = mid(ii)
        self.models[key] = {
            'object': mi,
            'params': getattr(mi, 'params', None)
        }
        self.log_info(f'Loaded model {key}')
        return key

    def describe_loaded_models(self) -> dict:
        return {
            k: {
                'class': self.models[k]['object'].__class__.__name__,
                'params': self.models[k]['params'],
            }
            for k in self.models.keys()
        }

    def find_param_in_loaded_models(self, key: str, value: str, is_path=False) -> str:
        """
        Returns model_id of first model where key and value match with .params field, or None
        :param is_path: uses platform-independent path comparison if True
        """

        models = self.describe_loaded_models()
        for mid, det in models.items():
            if is_path:
                if PureWindowsPath(det.get('params').get(key)).as_posix() == Path(value).as_posix():
                    return mid
            else:
                if det.get('params').get(key) == value:
                    return mid
        return None

    def restart(self, **kwargs):
        self.__init__(**kwargs)


# create singleton instance
session = _Session()


class Error(Exception):
    pass

class InferenceRecordError(Error):
    pass

class CouldNotInstantiateModelError(Error):
    pass

class CouldNotCreateDirectory(Error):
    pass

class CouldNotCreateTable(Error):
    pass

class CouldNotAppendToTable(Error):
    pass

class InvalidPathError(Error):
    pass