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"""Config providers that work with files"""
import json
import logging
import os
import pwd
from abc import abstractmethod
from contextlib import suppress
from textwrap import dedent
from typing import Mapping, Optional, Protocol

import yaml

from defence360agent.utils import atomic_rewrite

logger = logging.getLogger(__name__)

# Don't read config if its file is larger than this.
_MAX_CONFIG_SIZE = 1 << 20  # 1MiB


class IConfigProvider(Protocol):
    @abstractmethod
    def read_config_file(
        self, force_read: bool = False, ignore_errors: bool = True
    ):
        raise NotImplementedError

    @abstractmethod
    def write_config_file(self, config: Mapping) -> None:
        raise NotImplementedError

    @abstractmethod
    def modified_since(self, timestamp: Optional[float]) -> bool:
        raise NotImplementedError


class ConfigError(Exception):
    pass


class JsonMessage:
    """Pretty-print given *obj* as JSON.

    To be used for logging. Example:

      logging.info("object: %s", JsonMessage(obj))

    """

    def __init__(self, obj):
        self._obj = obj

    def __str__(self):
        return json.dumps(self._obj, sort_keys=True)


def diff_section(prev_section: Optional[dict], section: Optional[dict]):
    """Return difference between config sections."""
    prev_section = prev_section or {}
    section = section or {}
    removed_settings = prev_section.keys() - section.keys()
    added_settings = section.keys() - prev_section.keys()
    return {
        "-": {v: prev_section[v] for v in removed_settings},
        "+": {v: section[v] for v in added_settings},
        # modified settings
        "?": {
            v: (prev_section[v], section[v])
            for v in (prev_section.keys() & section.keys())
            if prev_section[v] != section[v]
        },
    }


def diff_config(prev_conf: dict, conf: dict):
    """Compare *prev_conf* with the current *conf*."""
    removed_sections = prev_conf.keys() - conf.keys()
    yield {section: prev_conf[section] for section in removed_sections}
    added_sections = conf.keys() - prev_conf.keys()
    yield {section: conf[section] for section in added_sections}
    # changed sections
    yield {
        section: diff_section(prev_conf[section], conf[section])
        for section in (prev_conf.keys() & conf.keys())
        if prev_conf[section] != conf[section]
    }


def exclude_equals(*, main_conf: dict, base_conf: dict) -> dict:
    """
    Return dict derived from *main_conf* excluding parts
    that are equal in *base_conf*.
    For example,
    >>> base_conf = {
        "SECTION1": {"OPTION1": "default", "OPTION2": "default"},
        "SECTION2": {"OPTION1": "default"}
    }
    >>> main_conf = {
        "SECTION1": {"OPTION1": "value", "OPTION2": "default"},
        "SECTION2": {"OPTION1": "default"}
    }
    >>>
    >>> exclude_equals(main_conf=main_conf, base_conf=base_conf)
    {'SECTION1': {'OPTION1': 'value'}}
    >>>
    """
    _, added, changed = diff_config(base_conf, main_conf)
    result = {}
    for section, value in main_conf.items():
        if section in added.keys():
            result[section] = value
        if section in changed.keys():
            result.setdefault(section, {}).update(changed[section]["+"])
            result.setdefault(section, {}).update(
                {k: v[1] for k, v in changed[section]["?"].items()}
            )
    return result


class ConfigReader:
    """
    ConfigFile file for settings page.
    Location config file is PATH
    """

    def __init__(self, path, disclaimer="", permissions=None):
        self.path = path
        self.disclaimer = disclaimer
        self.permissions = permissions

    def __repr__(self):
        return "<{classname}({path})>".format(
            classname=self.__class__.__qualname__, path=self.path
        )

    def __str__(self):
        return f"ConfigReader at {self.path}"

    def read_config_file(
        self, force_read: bool = False, ignore_errors: bool = True
    ) -> dict:
        """Read config file into memory.

        Raises ConfigError.
        """
        try:
            if os.path.getsize(self.path) > _MAX_CONFIG_SIZE:
                raise ConfigError("Config file is too large")
            filename = self.path
            with open(filename, "r") as config_file:
                logger.info("Reading config file %s", filename)
                text = config_file.read()
        except UnicodeDecodeError as e:
            raise ConfigError("Unable to decode config file") from e
        except FileNotFoundError:
            return {}
        return self.load_config_body(text)

    def load_config_body(self, text: str) -> dict:
        try:
            config = yaml.safe_load(text)
        except yaml.YAMLError as e:
            raise ConfigError(
                f"Imunify360 config is not valid YAML document ({e})"
            ) from e

        if config is None:
            return {}

        if not isinstance(config, dict):
            raise ConfigError(
                "Imunify360 config is invalid or empty"
                ": path={!r}, text={!r}".format(self.path, text)
            )

        return config

    def _pre_write(self):
        pass

    def _post_write(self):
        pass

    def write_config_file(self, config) -> str:
        self._pre_write()
        config_text = ""
        if self.disclaimer:
            config_text += dedent(self.disclaimer)
            config_text += "\n"
        config_text += yaml.dump(config, default_flow_style=False)
        atomic_rewrite(
            self.path, config_text, backup=False, permissions=self.permissions
        )
        self._post_write()
        return config_text

    def modified_since(self, timestamp: Optional[float]) -> bool:
        return True


class CachedConfigReader(ConfigReader):
    def __init__(self, path, disclaimer="", permissions=None):
        super().__init__(path, disclaimer)
        self.mtime: Optional[float] = None
        self.size: Optional[float] = None
        self._config = {}
        self.permissions = permissions

    def __str__(self):
        return (
            "{classname} <'{path}', modified at {mtime}, {size} bytes>".format(
                classname=self.__class__.__qualname__,
                path=self.path,
                mtime=self.mtime,
                size=self.size,
            )
        )

    def read_config_file(
        self, force_read: bool = False, ignore_errors: bool = True
    ):
        """Update config if config file is modified"""
        if self.modified_since(self.mtime) or force_read:
            prev_config = self._config
            try:
                self._config = super().read_config_file()
            except ConfigError as error:
                if not ignore_errors:
                    raise
                logger.exception(
                    "Intentionally ignoring known config error: %s", error
                )

                logger.warning(
                    "%s is invalid, using previous settings: %s",
                    self,
                    JsonMessage(self._config),
                )
            else:
                if self.mtime is not None:  # don't log on startup
                    diffs = list(diff_config(prev_config, self._config))
                    if any(diffs):
                        # content has changed, log it
                        logger.info(
                            "%s modified: removed=%s, added=%s, changed=%s",
                            self,
                            *map(JsonMessage, diffs),
                        )

            try:
                stat = os.stat(self.path)
                self.mtime = stat.st_mtime
                self.size = stat.st_size
            except FileNotFoundError:
                self.mtime = 0.0
                self.size = 0.0

        return self._config

    def modified_since(self, timestamp: Optional[float]) -> bool:
        """Whether the config has updated since *timestamp*.

        (as defined by its last modification time and size)
        :param timestamp: None means that the file has never been read before
        """
        # On startup consider timestamp to be None
        if timestamp is None:
            timestamp = 0.0
        try:
            stat = os.stat(self.path)
        except FileNotFoundError:
            st_mtime, st_size = 0.0, 0.0
        else:
            st_mtime, st_size = stat.st_mtime, stat.st_size
        return st_mtime > timestamp or st_size != self.size


class WriteOnlyConfigReader(CachedConfigReader):
    def read_config_file(self, *_, **__):
        return self._config

    def write_config_file(self, config):
        config_text = super().write_config_file(config)
        self._config = self.load_config_body(config_text)
        return config_text


class UserConfigReader(CachedConfigReader):
    def __init__(self, path, username):
        super().__init__(path)
        self.username = username

    def __str__(self):
        return f"Config of user {self.username}"

    def _pre_write(self):
        confdir = os.path.dirname(self.path)
        with suppress(FileExistsError):
            os.mkdir(os.path.dirname(self.path))
        os.chown(confdir, 0, pwd.getpwnam(self.username).pw_gid)
        os.chmod(confdir, 0o750)

    def _post_write(self):
        os.chown(self.path, 0, pwd.getpwnam(self.username).pw_gid)
        os.chmod(self.path, 0o640)