"""Per-assembly playback progress, persisted so playback can resume exactly
where the user left off, across app restarts and reboots."""
import datetime
import json
import os

XDG_STATE_HOME = os.environ.get("XDG_STATE_HOME", os.path.expanduser("~/.local/state"))
STATE_DIR = os.path.join(XDG_STATE_HOME, "assembly-player")
STATE_PATH = os.path.join(STATE_DIR, "state.json")


def _now():
    return datetime.datetime.now().astimezone().isoformat(timespec="seconds")


def load_all():
    if not os.path.exists(STATE_PATH):
        return {}
    try:
        with open(STATE_PATH, "r", encoding="utf-8") as f:
            return json.load(f)
    except (json.JSONDecodeError, OSError):
        return {}


def save_all(data):
    os.makedirs(STATE_DIR, exist_ok=True)
    tmp_path = STATE_PATH + ".tmp"
    with open(tmp_path, "w", encoding="utf-8") as f:
        json.dump(data, f, indent=2, ensure_ascii=False)
    os.replace(tmp_path, STATE_PATH)


def _blank_entry():
    return {"sessions": [], "current": None, "position": 0.0, "completed": [], "updated": _now()}


class AssemblyState:
    """Convenience wrapper around the state entry for a single assembly code."""

    def __init__(self, code):
        self.code = code
        self._all = load_all()
        self._entry = self._all.setdefault(code, _blank_entry())

    def set_sessions(self, ordered_titles):
        self._entry["sessions"] = ordered_titles
        self._persist()

    def update_progress(self, title, position):
        self._entry["current"] = title
        self._entry["position"] = position
        self._entry["updated"] = _now()
        self._persist()

    def mark_completed(self, title):
        if title not in self._entry["completed"]:
            self._entry["completed"].append(title)
        if self._entry.get("current") == title:
            self._entry["current"] = None
            self._entry["position"] = 0.0
        self._persist()

    def resume_target(self):
        """Return (title, position) to resume at, or (None, 0) if nothing to resume."""
        current = self._entry.get("current")
        sessions = self._entry.get("sessions") or []
        completed = set(self._entry.get("completed") or [])

        if current and current not in completed:
            return current, self._entry.get("position", 0.0)

        for title in sessions:
            if title not in completed:
                return title, 0.0

        return None, 0.0

    def _persist(self):
        self._all[self.code] = self._entry
        save_all(self._all)