import abc
from copy import deepcopy
import logging
import os
import yaml

from typing import Any, Dict, Iterator, List, MutableMapping, Optional, Tuple, Type, Union

from ..collections import CaseInsensitiveDict, CaseInsensitiveSet
from ..exceptions import PatroniException
from ..utils import parse_bool, parse_int, parse_real

logger = logging.getLogger(__name__)


class _Transformable(abc.ABC):

    def __init__(self, version_from: int, version_till: Optional[int] = None) -> None:
        self.__version_from = version_from
        self.__version_till = version_till

    @classmethod
    def get_subclasses(cls) -> Iterator[Type['_Transformable']]:
        """Recursively get all subclasses of :class:`_Transformable`.

        :yields: each subclass of :class:`_Transformable`.
        """
        for subclass in cls.__subclasses__():
            yield from subclass.get_subclasses()
            yield subclass

    @property
    def version_from(self) -> int:
        return self.__version_from

    @property
    def version_till(self) -> Optional[int]:
        return self.__version_till

    @abc.abstractmethod
    def transform(self, name: str, value: Any) -> Optional[Any]:
        """Verify that provided value is valid.

        :param name: GUC's name
        :param value: GUC's value
        :returns: the value (sometimes clamped) or ``None`` if the value isn't valid
        """


class Bool(_Transformable):

    def transform(self, name: str, value: Any) -> Optional[Any]:
        if parse_bool(value) is not None:
            return value
        logger.warning('Removing bool parameter=%s from the config due to the invalid value=%s', name, value)


class Number(_Transformable):

    def __init__(self, *, version_from: int, version_till: Optional[int] = None, min_val: Union[int, float],
                 max_val: Union[int, float], unit: Optional[str] = None) -> None:
        super(Number, self).__init__(version_from, version_till)
        self.__min_val = min_val
        self.__max_val = max_val
        self.__unit = unit

    @property
    def min_val(self) -> Union[int, float]:
        return self.__min_val

    @property
    def max_val(self) -> Union[int, float]:
        return self.__max_val

    @property
    def unit(self) -> Optional[str]:
        return self.__unit

    @staticmethod
    @abc.abstractmethod
    def parse(value: Any, unit: Optional[str]) -> Optional[Any]:
        """Convert provided value to unit."""

    def transform(self, name: str, value: Any) -> Union[int, float, None]:
        num_value = self.parse(value, self.unit)
        if num_value is not None:
            if num_value < self.min_val:
                logger.warning('Value=%s of parameter=%s is too low, increasing to %s%s',
                               value, name, self.min_val, self.unit or '')
                return self.min_val
            if num_value > self.max_val:
                logger.warning('Value=%s of parameter=%s is too big, decreasing to %s%s',
                               value, name, self.max_val, self.unit or '')
                return self.max_val
            return value
        logger.warning('Removing %s parameter=%s from the config due to the invalid value=%s',
                       self.__class__.__name__.lower(), name, value)


class Integer(Number):

    @staticmethod
    def parse(value: Any, unit: Optional[str]) -> Optional[int]:
        return parse_int(value, unit)


class Real(Number):

    @staticmethod
    def parse(value: Any, unit: Optional[str]) -> Optional[float]:
        return parse_real(value, unit)


class Enum(_Transformable):

    def __init__(self, *, version_from: int, version_till: Optional[int] = None,
                 possible_values: Tuple[str, ...]) -> None:
        super(Enum, self).__init__(version_from, version_till)
        self.__possible_values = possible_values

    @property
    def possible_values(self) -> Tuple[str, ...]:
        return self.__possible_values

    def transform(self, name: str, value: Optional[Any]) -> Optional[Any]:
        if str(value).lower() in self.possible_values:
            return value
        logger.warning('Removing enum parameter=%s from the config due to the invalid value=%s', name, value)


class EnumBool(Enum):

    def transform(self, name: str, value: Optional[Any]) -> Optional[Any]:
        if parse_bool(value) is not None:
            return value
        return super(EnumBool, self).transform(name, value)


class String(_Transformable):

    def transform(self, name: str, value: Optional[Any]) -> Optional[Any]:
        return value


# Format:
#  key  - parameter name
#  value - variable length tuple of `_Transformable` objects. Each object in the tuple represents a different
#          validation of the GUC across postgres versions. If a GUC validation has never changed over time, then it will
#          have a single object in the tuple. For example, `password_encryption` used to be a boolean GUC up to Postgres
#          10, at which point it started being an enum. In that case the value of `password_encryption` would be a tuple
#          of 2 `_Transformable` objects (`Bool` and `Enum`, respectively), each one reprensenting a different
#          validation rule.
parameters = CaseInsensitiveDict()
recovery_parameters = CaseInsensitiveDict()


class ValidatorFactoryNoType(PatroniException):
    """Raised when a validator spec misses a type."""


class ValidatorFactoryInvalidType(PatroniException):
    """Raised when a validator spec contains an invalid type."""


class ValidatorFactoryInvalidSpec(PatroniException):
    """Raised when a validator spec contains an invalid set of attributes."""


class ValidatorFactory:
    """Factory class used to build Patroni validator objects based on the given specs."""

    TYPES: Dict[str, Type[_Transformable]] = {cls.__name__: cls for cls in _Transformable.get_subclasses()}

    def __new__(cls, validator: Dict[str, Any]) -> _Transformable:
        """Parse a given Postgres GUC *validator* into the corresponding Patroni validator object.

        :param validator: a validator spec for a given parameter. It usually comes from a parsed YAML file.

        :returns: the Patroni validator object that corresponds to the specification found in *validator*.

        :raises :class:`ValidatorFactoryNoType`: if *validator* contains no ``type`` key.
        :raises :class:`ValidatorFactoryInvalidType`: if ``type`` key from *validator* contains an invalid value.
        :raises :class:`ValidatorFactoryInvalidSpec`: if *validator* contains an invalid set of attributes for the
            given ``type``.

        :Example:

            If a given validator was defined as follows in the YAML file:

            ```yaml
            - type: String
            version_from: 90300
            version_till: null
            ```

            Then this method would receive *validator* as:

            ```python
            {
                'type': 'String',
                'version_from': 90300,
                'version_till': None
            }
            ```

            And this method would return a :class:`String`:

            ```python
            String(90300, None)
            ```
        """
        validator = deepcopy(validator)
        try:
            type_ = validator.pop('type')
        except KeyError as exc:
            raise ValidatorFactoryNoType('Validator contains no type.') from exc

        if type_ not in cls.TYPES:
            raise ValidatorFactoryInvalidType(f'Unexpected validator type: `{type_}`.')

        for key, value in validator.items():
            # :func:`_transform_parameter_value` expects :class:`tuple` instead of :class:`list`
            if isinstance(value, list):
                tmp_value: List[Any] = value
                validator[key] = tuple(tmp_value)

        try:
            return cls.TYPES[type_](**validator)
        except Exception as exc:
            raise ValidatorFactoryInvalidSpec(
                f'Failed to parse `{type_}` validator (`{validator}`): `{str(exc)}`.') from exc


def _get_postgres_guc_validators(config: Dict[str, Any], parameter: str) -> Tuple[_Transformable, ...]:
    """Get all validators of *parameter* from *config*.

    Loop over all validators specs of *parameter* and return them parsed as Patroni validators.

    :param config: Python object corresponding to an YAML file, with values of either ``parameters`` or
        ``recovery_parameters`` key.
    :param parameter: name of the parameter found under *config* which validators should be parsed and returned.

    :rtype: yields any exception that is faced while parsing a validator spec into a Patroni validator object.
    """
    validators: List[_Transformable] = []
    for validator_spec in config.get(parameter, []):
        try:
            validator = ValidatorFactory(validator_spec)
            validators.append(validator)
        except (ValidatorFactoryNoType, ValidatorFactoryInvalidType, ValidatorFactoryInvalidSpec) as exc:
            logger.warning('Faced an issue while parsing a validator for parameter `%s`: `%r`', parameter, exc)

    return tuple(validators)


class InvalidGucValidatorsFile(PatroniException):
    """Raised when reading or parsing of a YAML file faces an issue."""


def _read_postgres_gucs_validators_file(file: str) -> Dict[str, Any]:
    """Read an YAML file and return the corresponding Python object.

    :param file: path to the file to be read. It is expected to be encoded with ``UTF-8``, and to be a YAML document.

    :returns: the YAML content parsed into a Python object. If any issue is faced while reading/parsing the file, then
        return ``None``.

    :raises :class:`InvalidGucValidatorsFile`: if faces an issue while reading or parsing *file*.
    """
    try:
        with open(file, encoding='UTF-8') as stream:
            return yaml.safe_load(stream)
    except Exception as exc:
        raise InvalidGucValidatorsFile(
            f'Unexpected issue while reading parameters file `{file}`: `{str(exc)}`.') from exc


def _load_postgres_gucs_validators() -> None:
    """Load all Postgres GUC validators from YAML files.

    Recursively walk through ``available_parameters`` directory and load validators of each found YAML file into
    ``parameters`` and/or ``recovery_parameters`` variables.

    Walk through directories in top-down fashion and for each of them:
        * Sort files by name;
        * Load validators from YAML files that were found.

    Any problem faced while reading or parsing files will be logged as a ``WARNING`` by the child function, and the
    corresponding file or validator will be ignored.

    By default Patroni only ships the file ``0_postgres.yml``, which contains Community Postgres GUCs validators, but
    that behavior can be extended. For example: if a vendor wants to add GUC validators to Patroni for covering a custom
    Postgres build, then they can create their custom YAML files under ``available_parameters`` directory.

    Each YAML file may contain either or both of these root attributes, here called sections:
        * ``parameters``: general GUCs that would be written to ``postgresql.conf``;
        * ``recovery_parameters``: recovery related GUCs that would be written to ``recovery.conf`` (Patroni later
            writes them to ``postgresql.conf`` if running PG 12 and above).

    Then, each of these sections, if specified, may contain one or more attributes with the following structure:
        * key: the name of a GUC;
        * value: a list of validators. Each item in the list must contain a ``type`` attribute, which must be one among:
            * ``Bool``; or
            * ``Integer``; or
            * ``Real``; or
            * ``Enum``; or
            * ``EnumBool``; or
            * ``String``.

            Besides the ``type`` attribute, it should also contain all the required attributes as per the corresponding
            class in this module.

    .. seealso::
        * :class:`Bool`;
        * :class:`Integer`;
        * :class:`Real`;
        * :class:`Enum`;
        * :class:`EnumBool`;
        * :class:`String`.

    :Example:

        This is a sample content for an YAML file based on Postgres GUCs, showing each of the supported types and
        sections:

        ```yaml
        parameters:
          archive_command:
          - type: String
            version_from: 90300
            version_till: null
          archive_mode:
          - type: Bool
            version_from: 90300
            version_till: 90500
          - type: EnumBool
            version_from: 90500
            version_till: null
            possible_values:
            - always
          archive_timeout:
          - type: Integer
            version_from: 90300
            version_till: null
            min_val: 0
            max_val: 1073741823
            unit: s
          autovacuum_vacuum_cost_delay:
          - type: Integer
            version_from: 90300
            version_till: 120000
            min_val: -1
            max_val: 100
            unit: ms
          - type: Real
            version_from: 120000
            version_till: null
            min_val: -1
            max_val: 100
            unit: ms
          client_min_messages:
          - type: Enum
            version_from: 90300
            version_till: null
            possible_values:
            - debug5
            - debug4
            - debug3
            - debug2
            - debug1
            - log
            - notice
            - warning
            - error
        recovery_parameters:
          archive_cleanup_command:
          - type: String
            version_from: 90300
            version_till: null
        ```
    """
    conf_dir = os.path.join(
        os.path.dirname(os.path.abspath(__file__)),
        'available_parameters',
    )
    yaml_files: List[str] = []

    for root, _, files in os.walk(conf_dir):
        for file in sorted(files):
            full_path = os.path.join(root, file)
            if file.lower().endswith(('.yml', '.yaml')):
                yaml_files.append(full_path)
            else:
                logger.info('Ignored a non-YAML file found under `available_parameters` directory: `%s`.', full_path)

    for file in yaml_files:
        try:
            config: Dict[str, Any] = _read_postgres_gucs_validators_file(file)
        except InvalidGucValidatorsFile as exc:
            logger.warning(str(exc))
            continue

        logger.debug(f'Parsing validators from file `{file}`.')

        mapping = {
            'parameters': parameters,
            'recovery_parameters': recovery_parameters,
        }

        for section in ['parameters', 'recovery_parameters']:
            section_var = mapping[section]

            config_section = config.get(section, {})
            for parameter in config_section.keys():
                section_var[parameter] = _get_postgres_guc_validators(config_section, parameter)


_load_postgres_gucs_validators()


def _transform_parameter_value(validators: MutableMapping[str, Tuple[_Transformable, ...]],
                               version: int, name: str, value: Any,
                               available_gucs: CaseInsensitiveSet) -> Optional[Any]:
    """Validate *value* of GUC *name* for Postgres *version* using defined *validators* and *available_gucs*.

    :param validators: a dictionary of all GUCs across all Postgres versions. Each key is the name of a Postgres GUC,
        and the corresponding value is a variable length tuple of :class:`_Transformable`. Each item is a validation
        rule for the GUC for a given range of Postgres versions. Should either contain recovery GUCs or general GUCs,
        not both.
    :param version: Postgres version to validate the GUC against.
    :param name: name of the Postgres GUC.
    :param value: value of the Postgres GUC.
    :param available_gucs: a set of all GUCs available in Postgres *version*. Each item is the name of a Postgres
        GUC. Used for a couple purposes:
        * Disallow writing GUCs to ``postgresql.conf`` (or ``recovery.conf``) that does not exist in Postgres *version*;
        * Avoid ignoring GUC *name* if it does not have a validator in *validators*, but is a valid GUC in Postgres
            *version*.

    :returns: the return value may be one among:
        * *value* transformed to the expected format for GUC *name* in Postgres *version*, if *name* is present in
            *available_gucs* and has a validator in *validators* for the corresponding Postgres *version*; or
        * The own *value* if *name* is present in *available_gucs* but not in *validators*; or
        * ``None`` if *name* is not present in *available_gucs*.
    """
    if name in available_gucs:
        for validator in validators.get(name, ()) or ():
            if version >= validator.version_from and\
                    (validator.version_till is None or version < validator.version_till):
                return validator.transform(name, value)
        # Ideally we should have a validator in *validators*. However, if none is available, we will not discard a
        # setting that exists in Postgres *version*, but rather allow the value with no validation.
        return value
    logger.warning('Removing unexpected parameter=%s value=%s from the config', name, value)


def transform_postgresql_parameter_value(version: int, name: str, value: Any,
                                         available_gucs: CaseInsensitiveSet) -> Optional[Any]:
    """Validate *value* of GUC *name* for Postgres *version* using ``parameters`` and *available_gucs*.

    :param version: Postgres version to validate the GUC against.
    :param name: name of the Postgres GUC.
    :param value: value of the Postgres GUC.
    :param available_gucs: a set of all GUCs available in Postgres *version*. Each item is the name of a Postgres
        GUC. Used for a couple purposes:
        * Disallow writing GUCs to ``postgresql.conf`` that does not exist in Postgres *version*;
        * Avoid ignoring GUC *name* if it does not have a validator in ``parameters``, but is a valid GUC in Postgres
            *version*.

    :returns: The return value may be one among
        * The original *value* if *name* seems to be an extension GUC (contains a period '.'); or
        * ``None`` if **name** is a recovery GUC; or
        * *value* transformed to the expected format for GUC *name* in Postgres *version* using validators defined in
            ``parameters``. Can also return ``None``. See :func:`_transform_parameter_value`.
    """
    if '.' in name and name not in parameters:
        # likely an extension GUC, so just return as it is. Otherwise, if `name` is in `parameters`, it's likely a
        # namespaced GUC from a custom Postgres build, so we treat that over the usual validation means.
        return value
    if name in recovery_parameters:
        return None
    return _transform_parameter_value(parameters, version, name, value, available_gucs)


def transform_recovery_parameter_value(version: int, name: str, value: Any,
                                       available_gucs: CaseInsensitiveSet) -> Optional[Any]:
    """Validate *value* of GUC *name* for Postgres *version* using ``recovery_parameters`` and *available_gucs*.

    :param version: Postgres version to validate the recovery GUC against.
    :param name: name of the Postgres recovery GUC.
    :param value: value of the Postgres recovery GUC.
    :param available_gucs: a set of all GUCs available in Postgres *version*. Each item is the name of a Postgres
        GUC. Used for a couple purposes:
        * Disallow writing GUCs to ``recovery.conf`` (or ``postgresql.conf`` depending on *version*), that does not
        exist in Postgres *version*;
        * Avoid ignoring recovery GUC *name* if it does not have a validator in ``recovery_parameters``, but is a valid
            GUC in Postgres *version*.

    :returns: *value* transformed to the expected format for recovery GUC *name* in Postgres *version* using validators
        defined in ``recovery_parameters``. It can also return ``None``. See :func:`_transform_parameter_value`.
    """
    # Recovery settings are not present in ``postgres --describe-config`` output of Postgres <= 11. In that case we
    # just pass down the list of settings defined in Patroni validators so :func:`_transform_parameter_value` will not
    # discard the recovery GUCs when running Postgres <= 11.
    # NOTE: At the moment this change was done Postgres 11 was almost EOL, and had been likely extensively used with
    # Patroni, so we should be able to rely solely on Patroni validators as the source of truth.
    return _transform_parameter_value(
        recovery_parameters, version, name, value,
        available_gucs if version >= 120000 else CaseInsensitiveSet(recovery_parameters.keys()))
