from typing import List
from million.model.hole import Hole
from million.model.message import Message
from million.model.sequence import Sequence


def compute_sequences(messages: List[Message], accepted_max: int = 1_000_000) -> List[Sequence]:
    sequences: List[Sequence] = []
    current_sequence = Sequence(
        start=messages[0].get_counted_value(),
        start_message=messages[0],
        end=messages[0].get_counted_value(),
        end_message=messages[0]
    )
    for i in range(1, len(messages)):
        message = messages[i]
        message_value = message.get_counted_value()
        if message_value > accepted_max:
            continue
        if message_value - current_sequence.end == 1:
            current_sequence.end = message_value
            current_sequence.end_message = message
        else:
            sequences.append(current_sequence)
            current_sequence = Sequence(
                start=message_value,
                start_message=message,
                end=message_value,
                end_message=message
            )

    # order the sequences by start
    sequences.sort(key=lambda s: s.start)

    merged_sequences: List[Sequence] = []
    current_sequence = sequences[0]
    for i in range(1, len(sequences)):
        sequence = sequences[i]
        sequence_start_is_in_current_sequence = current_sequence.start <= sequence.start and current_sequence.end >= sequence.start
        sequence_end_is_further = sequence.end > current_sequence.end
        sequence_start_is_current_end_or_next = sequence.start == current_sequence.end + 1

        if sequence_start_is_in_current_sequence or sequence_start_is_current_end_or_next:
            if sequence_end_is_further:
                current_sequence.end = sequence.end
                current_sequence.end_message = sequence.end_message
        else:
            merged_sequences.append(current_sequence)
            current_sequence = sequence

    # Having merged the sequences once, any sequence having start = end can be removed
    return [s for s in merged_sequences if s.start != s.end]


def find_holes(messages: List[Message], accepted_max: int = 1_000_000) -> List[Hole]:
    """
    Find the holes in the conversation
    """
    merged_sequences = compute_sequences(messages, accepted_max)
    holes = []
    for i in range(1, len(merged_sequences)):
        previous_sequence = merged_sequences[i - 1]
        sequence = merged_sequences[i]
        if sequence.start - previous_sequence.end > 1:
            holes.append(Hole(
                start=previous_sequence.end,
                end=sequence.start,
                start_message=previous_sequence.end_message,
                end_message=sequence.start_message
            ))
    return holes