# SPDX-FileCopyrightText: 2023 Egor Guslyancev <electromagneticcyclone@disroot.org>
#
# SPDX-License-Identifier: AGPL-3.0-or-later

"The module provides DB backends."

import pickle as p
from os import path


class PrototypeDB:
    "Prototype for database classes."

    def __init__(self, dbfile: str):
        pass

    def save(self, dbfo: str = None):
        "Export database to the file."
        raise AssertionError("Unimplemented method")

    def load(self, dbfi: str = None):
        "Import database from the file."
        raise AssertionError("Unimplemented method")

    def write(self, field: str, value: any, data=None):
        "Write `value` to the database's `field`. `data` argument is not used. Returns new db."
        raise AssertionError("Unimplemented method")

    def read(self, field: str, default: any = None, data=None) -> any:
        "Read `field` from the database. `default` argument returned when where's no such a field."
        raise AssertionError("Unimplemented method")

    def pop(self, field: str) -> any:
        "Remove `field` from the database."
        raise AssertionError("Unimplemented method")


class PickleDB(PrototypeDB):
    "Database that uses pickle as a backend."
    __db = {}
    __dbfile = ""

    def __init__(self, dbfile: str):
        self.__dbfile = dbfile
        self.load()

    def save(self, dbfo: str = None):
        "Export database to the file."
        if dbfo is None:
            dbfo = self.__dbfile
        with open(dbfo, "wb") as fo:
            p.dump(self.__db, fo)

    def load(self, dbfi: str = None):
        "Import database from the file."
        if dbfi is None:
            dbfi = self.__dbfile
        if not path.exists(dbfi):
            self.save()
            return
        with open(dbfi, "rb") as fi:
            self.__db = p.load(fi)

    def write(self, field: str, value: any, data=None):
        "Write `value` to the database's `field`. `data` argument is not used. Returns new db."
        head = False
        if data is None:
            data = self.__db
            head = True
        field = field.split(".")
        if len(field) == 1:
            data[field[0]] = value
        else:
            if (field[0] not in data) or (data[field[0]] is None):
                data[field[0]] = {}
            if not isinstance(data[field[0]], dict):
                raise ValueError("Поле не является группой.")
            data[field[0]] = self.write(".".join(field[1:]), value, data[field[0]])
        self.save()
        if head:
            self.__db = data
        return data

    def read(self, field: str, default: any = None, data=None) -> any:
        "Read `field` from the database. `default` argument returned when where's no such a field."
        if data is None:
            data = self.__db
        if field == "":
            return data
        field = field.split(".")
        if field[0] not in data:
            return default
        if len(field) == 1:
            return data[field[0]]
        return self.read(".".join(field[1:]), default, data[field[0]])

    def pop(self, field: str) -> any:
        "Remove `field` from the database."
        ret = self.read(field)
        field = field.split(".")
        val = self.read(".".join(field[:-1]))
        if not isinstance(val, dict):
            return None
        val.pop(field[-1])
        self.write(".".join(field[:-1]), val)
        return ret