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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_bitseq_from_selection(self, selection_start: int, selection_width: int):
 """ get start and end index of bit sequence from selected samples :rtype: tuple[int,int,int,int] :return: start_message index, start index, end message index, end index """

        start_message, start_index, end_message, end_index = -1, -1, -1, -1
        if not self.messages or not self.messages[0].bit_sample_pos:
            return start_message, start_index, end_message, end_index

        if selection_start + selection_width < self.messages[0].bit_sample_pos[0]:
            return start_message, start_index, end_message, end_index

        for i, msg in enumerate(self.messages):
            msg_sample_pos = msg.bit_sample_pos
            if msg_sample_pos[-2] < selection_start:
                continue
            elif start_message == -1:
                start_message = i
                for j, sample_pos in enumerate(msg_sample_pos):
                    if sample_pos < selection_start:
                        continue
                    elif start_index == -1:
                        start_index = j
                        if msg_sample_pos[-1] - selection_start < selection_width:
                            break
                    elif sample_pos - selection_start > selection_width:
                        return start_message, start_index, i, j
            elif msg_sample_pos[-1] - selection_start < selection_width:
                continue
            else:
                for j, sample_pos in enumerate(msg_sample_pos):
                    if sample_pos - selection_start > selection_width:
                        return start_message, start_index, i, j

        last_message = len(self.messages) - 1
        last_index = len(self.messages[-1].plain_bits) + 1
        return start_message, start_index, last_message, last_index