import os
import hashlib
import asyncio

class password():
    """
    This class represents password in the system, it is also used to hash
    password, to protect it agains attacks.

    Methods
    -------
    get_salt_length() : int
        Return size in bytes of salt for passwords.

    get_algorithm() : str
        Return name of algorithm used to hash password.

    async comare(password: str) : bool
        Check that password given as parameter is same as hashed password
        stored by password object which that function run on.

    result() : str
        Get hashed result password, to store it in database.

    async from_plain_text(password: str) : password
        It create new password object from given plain password. It get 
        random salt, and create new hash.

    async from_hash(hashed: str) : password
        It create new password object from already hashed password, it is
        usefull to compare password with plain text password.
    """

    def __init__(self, hashed: str) -> None:
        """
        It create new password from hashed content, it would not being 
        called outside this class.

        Parameters
        ----------
        hashed : str
            Already hashed password
        """

        self.__hash = hashed

    @staticmethod
    def get_salt_length() -> int:
        """
        It return salt length for the password in the bytes. To add
        salt to password it must be string, and it is converted to hex 
        values. That mean, size of string salt is twice of salt lenght
        in bytes.

        Returns
        -------
        int
            Lenght of the passwords salt.
        """

        return 12

    @staticmethod
    def get_algorithm() -> str:
        """
        That return name of the algorithm which would be used to hash 
        password.

        Returns
        -------
        str
            Name of the password which would be used to hash password.
        """

        return "sha512"

    @staticmethod
    def get_iterations() -> int:
        """
        That return count of the iterations of the algorithm. 

        Returns
        -------
        int
            Count of the iterations of the algorithm.
        """

        return 50000

    @staticmethod
    async def __generate_hash(
        content: str, 
        salt: str,
        iterations: int
    ) -> str:
        """
        That function generate hash of the password from the password
        and its salt. That function is async, because hashing algorithm
        take a lot of time. 

        Parameters
        ----------
        content : str
            Plain password.

        salt : str
            Salt to use with password.

        iterations : int
            Count of iterations for hashing algorithm.

        Returns 
        -------
        str
            Hashed password.
        """

        content = content.encode("UTF-8")
        salt = salt.encode("UTF-8")

        hashed = await asyncio.to_thread(
            hashlib.pbkdf2_hmac,
            password.get_algorithm(),
            content,
            salt,
            iterations
        )

        hashed = hashed.hex()
        salt = salt.decode("UTF-8")
        iterations = str(iterations)

        return hashed + ":" + salt + ":" + iterations
    
    def __get_salt(self) -> str:
        """
        That function return salt used to hash password from that hash.
        It could raise error, when hash is not correct.

        Raises
        ------
        RuntimeError
            When salt syntax is not correct.

        Returns
        -------
        str
            Salt of the hash.
        """

        try:
            _, salt, _ = self.__hash.split(":")
            return salt

        except:
            raise RuntimeError("Hash is incorrect.")

    def __get_own_iterations(self) -> int:
        """
        That return count of iterations stored in the hash. It is required, 
        to make old passwords work after change of the password iterations 
        in the app.

        Raises
        ------
        RuntimeError
            When hash syntax is not correct.

        Returns
        -------
        int
            Count of iterations from hash.
        """

        try:
            _, _, iterations = self.__hash.split(":")
            return int(iterations)

        except:
            raise RuntimeError("Hash is incorrect.")

    async def compare(self, target: str) -> bool:
        """
        That function compare given plain text password with already 
        hashed password. It is async, because it must calculate hash of
        the given plain text with hashed password salt, to compare result
        hashes.

        Parameters
        ----------
        str
            Plain text to compare hashed password with.

        Returns
        -------
        bool
            True when passwords are same, False when not.
        """

        salt = self.__get_salt()
        iterations = self.__get_own_iterations()

        hashed_target = await self.__generate_hash(
            target, 
            salt,
            iterations
        )

        return self.__hash == hashed_target
    
    def result(self) -> str:
        """
        It return hash of the password.

        Returns
        -------
        str
            Hash of the password.
        """

        return self.__hash

    def __repr__(self) -> str:
        """
        It return part of the password hash, to make it readable while 
        debugging.

        Returns
        -------
        str
            Part of the hashed password.
        """

        return "Password: \"" + self.__hash[0:20] + "\"." 

    def __str__(self) -> str:
        """
        Return password hash.

        Returns
        -------
        str
            Password hash.
        """

        return self.__hash

    async def from_plain_text(content: str) -> object:
        """
        It create new hashed password from plain text. It is async, 
        because hashing process take a lot of time.

        Parameters
        ----------
        content : str
            Plain text password to make hash from.

        Returns
        -------
        password
            New password object with that password as hash.
        """

        salt = os.urandom(password.get_salt_length())
        salt = salt.hex()
        iterations = password.get_iterations()

        hashed = await password.__generate_hash(
            content, 
            salt, 
            iterations
        )

        return password(hashed)

    async def from_hash(hashed: str) -> object:
        """
        It create new password object from already hashed password content
        It is async, to make it similar to from_plain_text.

        Parameters
        ----------
        hashed : str
            Already hashed password.

        Returns
        -------
        password
            New password object from given hash.
        """

        return password(hashed)