# Copyright (C) 2018 Avatao.com Innovative Learning Kft.
# All Rights Reserved. See LICENSE file for details.

from os.path import dirname
from re import findall
from re import compile as compileregex
from abc import ABC, abstractmethod

from watchdog.events import PatternMatchingEventHandler

from tfw.mixins import CallbackMixin, ObserverMixin
from tfw.decorators import RateLimiter


class CallbackEventHandler(PatternMatchingEventHandler, ABC):
    def __init__(self, files, *callbacks):
        super().__init__(files)
        self.callbacks = callbacks

    @RateLimiter(rate_per_second=2)
    def on_modified(self, event):
        for callback in self.callbacks:
            callback()


class HistoryMonitor(CallbackMixin, ObserverMixin, ABC):
    """
    Abstract class capable of monitoring and parsing a history file such as
    bash HISTFILEs. Monitoring means detecting when the file was changed and
    notifying subscribers about new content in the file.

    This is useful for monitoring CLI sessions.

    To specify a custom HistoryMonitor inherit from this class and override the
    command pattern property and optionally the sanitize_command method.
    See examples below.
    """
    def __init__(self, histfile):
        self.histfile = histfile
        self._history = []
        self._last_length = len(self._history)
        self.observer.schedule(
            CallbackEventHandler(
                [self.histfile],
                self._fetch_history,
                self._invoke_callbacks
            ),
            dirname(self.histfile)
        )

    @property
    def history(self):
        return self._history

    def _fetch_history(self):
        self._last_length = len(self._history)
        with open(self.histfile, 'r') as ifile:
            pattern = compileregex(self.command_pattern)
            data = ifile.read()
            self._history = [
                self.sanitize_command(command)
                for command in findall(pattern, data)
            ]

    @property
    @abstractmethod
    def command_pattern(self):
        raise NotImplementedError

    def sanitize_command(self, command):
        # pylint: disable=no-self-use
        return command

    def _invoke_callbacks(self):
        if self._last_length < len(self._history):
            self._execute_callbacks(self.history)


class BashMonitor(HistoryMonitor):
    """
    HistoryMonitor for monitoring bash CLI sessions.
    This requires the following to be set in bash
    (note that this is done automatically by TFW):
    PROMPT_COMMAND="history -a"
    shopt -s cmdhist
    shopt -s histappend
    unset HISTCONTROL
    """
    @property
    def command_pattern(self):
        return r'.+'

    def sanitize_command(self, command):
        return command.strip()


class GDBMonitor(HistoryMonitor):
    """
    HistoryMonitor to monitor GDB sessions.
    For this to work "set trace-commands on" must be set in GDB.
    """
    @property
    def command_pattern(self):
        return r'(?<=\n)\+(.+)\n'