from . import parser
from . block import Block
from typing import NamedTuple

class Patch(NamedTuple):
    """
    Patch represents chunk of chat data
    which is fetched by asyncdl.download_patch._fetch().
    """
    chats : list = []
    continuation : str = None
    first : int = None
    last : int = None

def fill(block:Block, patch:Patch):
    block_end = block.end
    if patch.last < block_end or block.is_last:
        set_patch(block, patch)
        return
    for line in reversed(patch.chats):
        line_offset = parser.get_offset(line)
        if line_offset < block_end:
            break
        patch.chats.pop()
    set_patch(block, patch._replace(
        continuation = None,
        last = line_offset
        )
    )
    block.remaining=0
    block.done=True


def split(parent_block:Block, child_block:Block, patch:Patch):
    parent_block.during_split = False
    if patch.first <= parent_block.last:
        ''' When patch overlaps with parent_block,
        discard this block. '''
        child_block.continuation = None
        ''' Leave child_block.during_split == True 
         to exclude from during_split sequence. '''
        return    
    child_block.during_split = False
    child_block.first = patch.first
    parent_block.end = patch.first
    fill(child_block, patch)
    

def set_patch(block:Block, patch:Patch):
    block.continuation = patch.continuation
    block.chat_data.extend(patch.chats)
    block.last = patch.last
    block.remaining = block.end-block.last