import math
import os
from logging import exception
from typing import Optional


class Int2IntMapLike():
    """
    A file used to map byte numbers of the filter view to byte numbers in the original file.
    Each line contains the two integers separated by a comma.
    The first column is sorted ascending. This allows us to do binary searches.
    The file uses 4kb blocks. That means we add fill bytes (newlines) if a line would cross a 4kb block boundary.
    """
    blocksize = 4096

    def __init__(self, file):
        self._file = file
        self._handle = open(file, "w+t")

    def close(self):
        if not self._handle.closed:
            self._handle.close()

    def reset(self):
        self._handle.truncate(0)

    def add(self, start: int, length: int, val: int):
        line = "%d,%d,%d\n" % (start, length, val)
        length = len(line)
        offset = self._handle.tell()
        if offset % self.blocksize + length > self.blocksize:
            fill_bytes = self.blocksize - offset % self.blocksize
            self._handle.write("\n" * fill_bytes)
        self._handle.write(line)

    def find(self, key: int) -> Optional[int]:
        size = os.stat(self._file).st_size
        if size == 0:
            return None
        total_blocks = math.ceil(size / self.blocksize)
        step = math.ceil(total_blocks / 2)
        offset = (step - 1) * self.blocksize
        while step >= 1:
            self._handle.seek(offset)
            block = self._handle.read(self.blocksize)
            lines = block.split("\n")
            is_before = None
            for line in lines:
                if len(line) == 0:
                    continue
                token = line.split(",")
                start = int(token[0])
                length = int(token[1])
                val = int(token[2])

                if key >= start and key - start < length:
                    return val
                tmp = key < start
                if is_before != None and tmp != is_before:
                    return None
                is_before = tmp

            if step == 1:
                return None

            step = math.ceil(step / 2)
            if is_before:
                offset = offset - step * self.blocksize
            else:
                offset = offset + step * self.blocksize