import discord.message
import re


async def parse(message, commandIndex, trigger=None, script=None, cmdIndex=None,
                argsStart=None, argsEnd=None):
    """
    Reads user messages looking for valid command triggers (!COMMAND).
    When found the associated command is called from 'commandIndex'.

    :param message: Message from which the command will be parsed.
    :type message: discord.message.Message
    :param commandIndex: Index of command/function pairs that
        determine which command will be run for each !COMMAND keyword.
        eg. {'!hello': func_hello}
    :type commandIndex: dict
    :return: Awaited result of the executed command.
    """

    # Sterilizes user input
    assert isinstance(message, discord.message.Message), (
        'Invalid type for args \'message\':'
        f' Expected <class \'discord.message.Message\'>'
        f' got {type(message)}'
    )
    assert isinstance(commandIndex, dict), (
        'Invalid type for args \'commandIndex\':'
        f' Expected {type({})}'
        f' got {type(commandIndex)}'
    )

    # Updates non-required args
    if trigger is None: trigger = lambda x: x.content.startswith('!')
    if script is None: script = r'"(.*?)"|(\S+)'
    if cmdIndex is None: cmdIndex = 0
    if argsStart is None: argsStart = 1
    if argsEnd is None: argsEnd = -1

    # Trigger condition
    if trigger(message):

        # Using regex script given through 'script', the message is
        # decomposed into a list of strings which will be given as
        # args to desired command.
        raw = [
            ''.join(x)
            for x in re.findall(script, message.content)
        ]

        # 'raw' must contain data by this point to avoid index errors
        # later on.
        assert raw, 'Not enough items in \'raw\': Minimum 1'

        # Gathers the command, and all args from 'raw' using
        # 'cmdIndex', 'argsStart', and 'argsEnd'.
        command, args = raw[cmdIndex], raw[argsStart:argsEnd]

        # Begins the awaited execution of the associated command
        # located in 'commandIndex'.
        if command in commandIndex:
            return await commandIndex[command](message, args)