"""
Mutable session state and the dataset registry.

All Bokeh callbacks share state through:
  - _S  : per-session scalar flags (active dataset index, render token, etc.)
  - _all_datasets : list of dataset dicts loaded at startup
  - active_ds()   : returns the currently selected dataset dict

Panels read dataset data via active_ds()['key'] rather than through
module-level aliases, making data-flow explicit.
"""

from __future__ import annotations


class _S:
    """Mutable scalars shared by all callbacks. No global statements needed."""
    active: int = 0          # index into _all_datasets
    render_token: int = 0    # bump on each feature selection; stale renders bail out
    search_filter = None     # None or set of feature indices matching current name search
    color_by: str = "Log Frequency"
    hf_push = None           # active Bokeh timeout handle for debounced HuggingFace push
    gallery_page: int = 0    # current page in the MEI thumbnail gallery


_all_datasets: list[dict] = []


def active_ds() -> dict:
    """Return the currently selected dataset dict."""
    return _all_datasets[_S.active]


def display_name(feat: int) -> str:
    """Label to show in tables: manual name takes priority over auto-interp."""
    ds = active_ds()
    manual = ds['feature_names'].get(feat)
    if manual:
        return manual
    auto = ds['auto_interp_names'].get(feat)
    return f"[auto] {auto}" if auto else ""