#
# Copyright (C) 2021 GNS3 Technologies Inc.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
Reads the configuration file and store the settings for the server.
"""

import sys
import os
import shutil
import secrets
import configparser

from enum import Enum
from pydantic import ValidationError
from .schemas import ServerConfig
from .version import __version_info__
from .utils.file_watcher import FileWatcher

import logging

log = logging.getLogger(__name__)


class ConfigConflictError(Exception):
    """
    Raised when a configuration option is set in a configuration file that
    takes precedence over the main configuration file.
    """


# List options written back to the configuration file as semicolon-separated
# values; every other list option is comma-separated (must match the field
# validators splitting them in gns3server.schemas.config).
LIST_OPTION_SEPARATORS = {"additional_images_paths": ";"}


class Config:
    """
    Configuration file management using configparser.

    :param files: Array of configuration files (optional)
    :param profile: Profile settings (default use standard config file)
    """

    def __init__(self, files=None, profile=None):

        self._settings = None
        self._files = files
        self._profile = profile

        if files and len(files):
            if not os.access(files[0], os.R_OK) or not os.path.isfile(files[0]):
                raise SystemExit(f"Unable to read configuration file: {files[0]}")
            directory_name = os.path.dirname(files[0])
            if not directory_name or directory_name == "":
                files[0] = os.path.dirname(os.path.abspath(files[0])) + os.path.sep + files[0]
            self._main_config_file = files[0]
        else:
            self._main_config_file = None

        # Monitor configuration files for changes
        self._watched_files = {}
        self._watch_callback = []

        appname = "GNS3"
        version = f"{__version_info__[0]}.{__version_info__[1]}"

        # On UNIX-like platforms, the configuration file location can be one of the following:
        # 1: $HOME/.config/GNS3/gns3_server.conf
        # 2: $HOME/.config/GNS3.conf
        # 3: /etc/xdg/GNS3/gns3_server.conf
        # 4: /etc/xdg/GNS3.conf
        # 5: gns3_server.conf in the current working directory

        home = os.path.expanduser("~")
        server_filename = "gns3_server.conf"

        if self._profile:
            legacy_user_dir = os.path.join(home, ".config", appname, "profiles", self._profile)
            versioned_user_dir = os.path.join(home, ".config", appname, version, "profiles", self._profile)
        else:
            legacy_user_dir = os.path.join(home, ".config", appname)
            versioned_user_dir = os.path.join(home, ".config", appname, version)

        if self._files is None and not hasattr(sys, "_called_from_test"):
            self._files = [
                os.path.join(os.getcwd(), server_filename),
                os.path.join(versioned_user_dir, server_filename),
                os.path.join(home, ".config", appname + ".conf"),
                os.path.join("/etc/gns3", server_filename),
                os.path.join("/etc/xdg", appname, server_filename),
                os.path.join("/etc/xdg", appname + ".conf"),
            ]

        if self._files is None:
            self._files = []

        if self._main_config_file is None:

            if not os.path.exists(versioned_user_dir):
                # Try to migrate the configuration files and database from the previous version if it exists
                previous_version = f"{__version_info__[0]}.{int(__version_info__[1]) - 1}"
                if self._profile:
                    previous_versioned_user_dir = os.path.join(home, ".config", appname, previous_version, "profiles", self._profile)
                else:
                    previous_versioned_user_dir = os.path.join(home, ".config", appname, previous_version)
                if os.path.exists(previous_versioned_user_dir):
                    try:
                        shutil.copytree(previous_versioned_user_dir, versioned_user_dir, symlinks=True, ignore_dangling_symlinks=True)
                        log.info(f"Migrated configuration files and database from '{previous_versioned_user_dir}' to '{versioned_user_dir}'")
                    except OSError as e:
                        log.error(f"Cannot migrate old config files and database from '{previous_versioned_user_dir}: {e}")

            os.makedirs(versioned_user_dir, exist_ok=True)
            try:
                # migrate the server config file
                old_server_config = os.path.join(legacy_user_dir, server_filename)
                new_server_config = os.path.join(versioned_user_dir, server_filename)
                if not os.path.exists(new_server_config) and os.path.exists(old_server_config):
                    shutil.copyfile(old_server_config, new_server_config)
            except OSError as e:
                log.error(f"Cannot migrate old config files: {e}")

            self._main_config_file = os.path.join(versioned_user_dir, server_filename)
            for file in self._files:
                if os.path.exists(file):
                    self._main_config_file = file
                    break

        self.clear()
        self._watch_config_file()

    @property
    def settings(self) -> ServerConfig:
        """
        Return the settings.
        """

        return self._settings

    def listen_for_config_changes(self, callback):
        """
        Call the callback when the configuration file change
        """
        self._watch_callback.append(callback)

    @property
    def profile(self):
        """
        Settings profile
        """
        return self._profile

    @property
    def config_dir(self):
        """
        Return the directory where the configuration file is located.
        """

        return os.path.dirname(self._main_config_file)

    @property
    def controller_vars(self):
        """
        Return the controller variables file path.
        """

        controller_vars_filename = "gns3_controller.vars"
        return os.path.join(self.config_dir, controller_vars_filename)

    @property
    def server_config(self):
        """
        Return the server configuration file path.
        """

        server_config_filename = "gns3_server.conf"
        return os.path.join(self.config_dir, server_config_filename)

    def clear(self):
        """
        Restart with a clean config
        """

        self.read_config()

    def _watch_config_file(self):
        """
        Add config files to be monitored for changes.
        """

        for file in self._files:
            if os.path.exists(file):
                self._watched_files[file] = FileWatcher(file, self._config_file_change)

    def _config_file_change(self, file_path):
        """
        Callback when a config file has been updated.
        """

        log.info(f"'{file_path}' has been updated, reloading the config...")
        self.reload_and_notify()

    def reload_and_notify(self):
        """
        Reload the configuration files and notify registered listeners.
        """

        self.read_config()
        for callback in self._watch_callback:
            callback()

    def reload(self):
        """
        Reload configuration
        """

        self.read_config()

    @staticmethod
    def _stringify_option(option: str, value) -> str:
        """
        Serialize a settings value to its INI string representation.
        """

        if isinstance(value, bool):
            return str(value)
        if isinstance(value, Enum):
            return str(value.value)
        if isinstance(value, list):
            return LIST_OPTION_SEPARATORS.get(option, ",").join(value)
        return str(value)

    def update_config(self, changes: dict) -> list:
        """
        Apply setting changes to the main configuration file (read-modify-write).

        Only the submitted options are set or removed, preserving any unknown
        options present in the file. The merged configuration is validated
        before anything is written to disk, so an invalid change leaves the
        file untouched (a file that fails validation would permanently kill
        the FileWatcher polling loop when it gets reloaded).

        :param changes: mapping of section name to {option: value}; a value of
            None removes the option from the file, restoring its default
        :returns: sorted list of changed options as "Section.option" strings

        :raises pydantic.ValidationError: the merged settings are invalid
        :raises ConfigConflictError: an option is set in a configuration file
            that takes precedence over the main configuration file
        :raises OSError: the configuration file could not be written
        """

        if not changes:
            return []

        main_config_file = self._main_config_file
        existing_files = [file for file in self._files if os.path.isfile(file)]

        # per-file parsers to find which file wins for an option
        # (later files take precedence, mirroring read_config)
        per_file_parsers = []
        for file in existing_files:
            parser = configparser.ConfigParser(interpolation=None)
            parser.read(file, encoding="utf-8")
            per_file_parsers.append(parser)

        # view of what gets written: the main configuration file only
        write_parser = configparser.ConfigParser(interpolation=None)
        if os.path.isfile(main_config_file):
            write_parser.read(main_config_file, encoding="utf-8")

        # view of what the server will load: all configuration files merged
        merged_parser = configparser.ConfigParser(interpolation=None)
        merged_parser.read(existing_files, encoding="utf-8")

        changed = []
        for section, options in changes.items():
            for option, value in options.items():
                winner = None
                for file, parser in zip(reversed(existing_files), reversed(per_file_parsers)):
                    if parser.has_option(section, option):
                        winner = file
                        break
                if winner is not None and winner != main_config_file:
                    raise ConfigConflictError(
                        f"'{section}.{option}' is set in '{winner}' which takes precedence "
                        f"over the main configuration file '{main_config_file}'"
                    )
                if value is None:
                    # explicit null: remove the option to restore its default
                    if write_parser.has_option(section, option):
                        write_parser.remove_option(section, option)
                    if merged_parser.has_option(section, option):
                        merged_parser.remove_option(section, option)
                else:
                    option_value = self._stringify_option(option, value)
                    if not write_parser.has_section(section):
                        write_parser.add_section(section)
                    write_parser.set(section, option, option_value)
                    if not merged_parser.has_section(section):
                        merged_parser.add_section(section)
                    merged_parser.set(section, option, option_value)
                changed.append(f"{section}.{option}")

        # validate the merged settings before touching the file on disk
        ServerConfig(**merged_parser._sections)

        directory_name = os.path.dirname(main_config_file)
        if directory_name:
            os.makedirs(directory_name, exist_ok=True)
        tmp_file = main_config_file + ".tmp"
        fd = os.open(tmp_file, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
        with os.fdopen(fd, "w", encoding="utf-8") as f:
            write_parser.write(f)
        os.replace(tmp_file, main_config_file)

        self.reload_and_notify()
        return sorted(changed)

    def get_config_files(self):
        """
        Return the config files in use.
        """

        return self._watched_files

    def _load_jwt_secret_key(self):
        """
        Load the JWT secret key.
        """

        jwt_secret_key_path = os.path.join(self._settings.Server.secrets_dir, "gns3_jwt_secret_key")
        if not os.path.exists(jwt_secret_key_path):
            log.info(f"No JWT secret key configured, generating one in '{jwt_secret_key_path}'...")
            try:
                with open(jwt_secret_key_path, "w+", encoding="utf-8") as fd:
                    fd.write(secrets.token_hex(32))
            except OSError as e:
                log.error(f"Could not create JWT secret key file '{jwt_secret_key_path}': {e}")
        try:
            with open(jwt_secret_key_path, encoding="utf-8") as fd:
                jwt_secret_key_content = fd.read()
                self._settings.Controller.jwt_secret_key = jwt_secret_key_content
        except OSError as e:
            log.error(f"Could not read JWT secret key file '{jwt_secret_key_path}': {e}")

    def _load_encryption_key(self):
        """
        Load the encryption key for sensitive data (API keys, etc.).
        """
        from .utils.encryption import init_encryption

        try:
            init_encryption(self._settings.Server.secrets_dir)
        except Exception as e:
            log.error(f"Could not initialize encryption: {e}")

    def _load_secret_files(self):
        """
        Load the secret files.
        """

        if not self._settings.Server.secrets_dir:
            self._settings.Server.secrets_dir = os.path.dirname(self.server_config)

        self._load_jwt_secret_key()
        self._load_encryption_key()

    def read_config(self):
        """
        Read the configuration files and validate the settings.
        """

        config = configparser.ConfigParser(interpolation=None)
        try:
            parsed_files = config.read(self._files, encoding="utf-8")
        except configparser.Error as e:
            log.error("Can't parse configuration file: %s", str(e))
            return
        if not parsed_files:
            log.warning("No configuration file could be found or read")
            self._settings = ServerConfig()
            # Still load secret files even without a config file
            self._load_secret_files()
            return

        for file in parsed_files:
            log.info(f"Configuration file '{file}' loaded")
            self._watched_files[file] = os.stat(file).st_mtime

        try:
            self._settings = ServerConfig(**config._sections)
        except ValidationError as e:
            log.critical(f"Could not validate configuration file settings: {e}")
            raise

        self._load_secret_files()

    @staticmethod
    def instance(*args, **kwargs):
        """
        Singleton to return only one instance of Config.

        :returns: instance of Config
        """

        if not hasattr(Config, "_instance") or Config._instance is None:
            Config._instance = Config(*args, **kwargs)
        return Config._instance

    @staticmethod
    def reset():
        """
        Reset singleton
        """

        Config._instance = None