import base64
import os
import select
import sys
import termios
import tty
from dataclasses import dataclass
from pathlib import Path

from engine import runtime, typist
from engine.state import State
from supervisor import SCREEN, SCREEN_SHAPE


DETACH = b"\x1d"
SHOWN_BACK = 65536


@dataclass(frozen=True)
class ScreenPart:
    data: str
    at: int
    rows: int
    cols: int

    @classmethod
    def blank(cls, rows: int, cols: int) -> "ScreenPart":
        return cls("", 0, rows, cols)


def screen_since(root: Path, terminal: str, since: int) -> ScreenPart:
    screen = runtime.session_file(root, terminal, SCREEN)
    shape = {"rows": 40, "cols": 120, **State(runtime.session_file(root, terminal, SCREEN_SHAPE)).all()}
    if not screen.is_file():
        return ScreenPart.blank(int(shape["rows"]), int(shape["cols"]))
    size = screen.stat().st_size
    at = max(0, size - SHOWN_BACK) if since < 0 or since > size else since
    with screen.open("rb") as shown:
        shown.seek(at)
        fresh = shown.read(size - at)
    return ScreenPart(base64.b64encode(fresh).decode(), at + len(fresh), int(shape["rows"]), int(shape["cols"]))


def attach(root: Path, session: str) -> str:
    screen = runtime.session_file(root, session, SCREEN)
    if not screen.is_file():
        return f"journal: no session {session} to attach to"
    at = max(0, screen.stat().st_size - SHOWN_BACK)
    saved = termios.tcgetattr(sys.stdin.fileno())
    tty.setraw(sys.stdin.fileno())
    try:
        while True:
            with screen.open("rb") as shown:
                shown.seek(at)
                fresh = shown.read()
            at += len(fresh)
            os.write(sys.stdout.fileno(), fresh)
            ready, _, _ = select.select([sys.stdin.fileno()], [], [], 0.2)
            if ready:
                keys = os.read(sys.stdin.fileno(), 4096)
                if not keys or DETACH in keys:
                    break
                typist.send(root, session, keys)
    finally:
        termios.tcsetattr(sys.stdin.fileno(), termios.TCSADRAIN, saved)
    return f"\njournal: left session {session}; it runs on"