#
#   load_parsers.py
#   
#   Search for and load files which parse logs for particular services
#

import imp
import importlib
import os
import glob
import pkgutil
import inspect
from pathlib import Path
from sys import path
from typing import NamedTuple

parser_dir = "/usr/share/logparse/"
main_module = "__init__"
default_parsers = ["cron_journald", "httpd", "mem", "postfix", "smbd", "sshd_journald", "sudo", "sysinfo", "temperature", "zfs"]
deprecated_parsers = ["sshd", "cron"]

import logging
logger = logging.getLogger(__name__)

class Parser():
    """
    Base class that every parser should inherit
    """
    def __init__(self, name=None, path=None, info=None):
        self.name = str(name) if name else None
        self.path = Path(path) if path else None
        self.info = dict(info) if info else None
        self.logger = logging.getLogger(__name__)

    def load(self):
        logger.debug("Loading parser {0} from {1}".format(self.name, str(self.path) if self.path != None else "defaults"))
        return importlib.import_module(self.name)

    def parse_log(self, **args):
        """
        Every parser should provide the parse_log method which is executed at
        runtime to analyse logs.
        """
        raise NotImplementedError("Failed to find an entry point for parser " + self.name)

class ParserLoader:
    """
    This class searches for parsers in the main logparse package and
    optionally in another external package (default /usr/share/logparse).
    """

    def __init__(self, pkg):
        """
        Initiate search for parsers
        """
        self.pkg = pkg 
        self.parsers= []
        self.reload()


    def reload(self):
        """
        Reset parsers list and iterate through package modules
        """
        self.parsers= []
        self.seen_paths = []
        logger.debug("Looking for parsers in package {0}".format(str(self.pkg)))
        self.walk_package(self.pkg)

    def walk_package(self, package):
        """
        Check package and subdirectories for loadable modules
        """

        imported_package = __import__(package, fromlist=["null"]) # fromlist must be non-empty to load target module rather than parent package

        for _, parser_name, ispkg in pkgutil.iter_modules(imported_package.__path__, imported_package.__name__ + '.'):
            if not ispkg:
                parser_module = __import__(parser_name, fromlist=["null"])
                clsmembers = inspect.getmembers(parser_module, inspect.isclass)
                for (_, c) in clsmembers:
                    # Ignore the base Parser class
                    if issubclass(c, Parser) & (c is not Parser):
                        logger.debug("Found parser {0}.{1}".format(c.__module__, c.__name__))
                        self.parsers.append(c())


        # Recurse subpackages

        all_current_paths = []
        if isinstance(imported_package.__path__, str):
            all_current_paths.append(imported_package.__path__)
        else:
            all_current_paths.extend([x for x in imported_package.__path__])

        for pkg_path in all_current_paths:
            if pkg_path not in self.seen_paths:
                self.seen_paths.append(pkg_path)

                # Get subdirectories of package
                child_pkgs = [p for p in os.listdir(pkg_path) if os.path.isdir(os.path.join(pkg_path, p))]

                # Walk through each subdirectory
                for child_pkg in child_pkgs:
                    self.walk_package(package + '.' + child_pkg)

def findall():
    logger.debug("Searching for parsers in {0}".format(parser_dir))
    path.append(os.path.abspath(parser_dir))
    parsers = []
    parser_candidates = os.listdir(parser_dir)
    for parser_name in parser_candidates:
        location = os.path.join(parser_dir, parser_name)
        if not os.path.isdir(location) or not main_module + '.py' in os.listdir(location):
            logger.warning("Rejecting parser {0} due to invalid structure".format(location))
            continue
        info = imp.find_module(main_module, [location])
        parser_obj = Parser(parser_name, location, info)
        parsers.append(parser_obj)
        logger.debug("Added parser {0}".format(parser_obj.name))
    return parsers

def search(name):
    logger.debug("Searching for parser {0}".format(name))
    if name in default_parsers:
        logger.debug("Found parser {0} in default modules".format(name))
        return Parser('.'.join(__name__.split('.')[:-1] + [name]))
    elif name in deprecated_parsers:
        logger.debug("Found parser {0} in deprecated modules".format(name))
        return Parser('.'.join(__name__.split('.')[:-1] + [name]))
    else:
        return None

def load(parser):
    logger.debug("Loading parser {0} from {1}".format(parser.name, parser.path if parser.path != None else "defaults"))
    return importlib.import_module(parser.name)