from enum import Enum
from typing import List


TODO_FILE_NAME = "TODO.md"

TODO_LINE_START_COMPLETED = "- [x] "
TODO_LINE_START_UNCOMPLETED = "- [ ] "


class PrevItemState(Enum):
    COMPLETED = 0
    UNCOMPLETED = 1
    UNDETERMINED = 2


def main():
    with open(TODO_FILE_NAME) as todo_file:
        todo_lines = todo_file.readlines()

    completed: List[str] = []
    uncompleted: List[str] = []

    prev_item_state = PrevItemState.UNDETERMINED

    for [index, line] in enumerate(todo_lines):
        if len(line) == 0:
            continue

        if line.startswith(TODO_LINE_START_COMPLETED):
            completed.append(line)
            prev_item_state = PrevItemState.COMPLETED
        elif line.startswith(TODO_LINE_START_UNCOMPLETED):
            uncompleted.append(line)
            prev_item_state = PrevItemState.UNCOMPLETED
        elif line[0].isspace():
            if prev_item_state == PrevItemState.COMPLETED:
                completed.append(line)
            elif prev_item_state == PrevItemState.UNCOMPLETED:
                uncompleted.append(line)
            elif prev_item_state == PrevItemState.UNDETERMINED:
                print(
                    f"Error: todo line {index + 1} starts with whitespace but there is "
                    "no previous item"
                )
                exit(1)
        else:
            print(f"Error: todo line {index + 1} does not have correct syntax")
            exit(1)

    with open(TODO_FILE_NAME, "w") as todo_file:
        todo_file.writelines(uncompleted)
        todo_file.writelines(completed)


if __name__ == "__main__":
    main()