signal-bot/signal_bot/art_command.py

# Copyright (c) 2026 Krzysztof Rudnicki. MIT licence.
"""The !sztuka command: one work of art, and what it is.

A near-copy of !pułapka, deliberately: same committed pool of Commons page
ids, same single imageinfo request, same live-fetched caption, same absence
of a cache. What ``traps_command`` says about each of those holds here.

The one thing that is new is the skew. The pool is two lists rather than one,
and ``POLISH_SHARE`` per cent of posts come from the Polish one **whatever
the two sizes are** -- the pool is chosen before the work is. That is worth
saying out loud because the other reading is defensible and this is not it:
if the Polish pool holds two thousand works and the world pool twenty
thousand, an individual Polish work is drawn about ten times as often as an
individual foreign one. Skewing the output is the entire point; a merged pool
weighted by size would produce a command that is 90% foreign and technically
correct.

Nothing is cached, for the reason ``traps_command`` gives: a uniform draw
from tens of thousands warms a cache essentially never, so the disk would
fill with pictures nobody asks for twice.
"""

from __future__ import annotations

import json
import secrets
from base64 import b64encode
from pathlib import Path
from typing import TYPE_CHECKING, Final

from signal_bot.animals import load_aliases
from signal_bot.commons import caption_for, imageinfo_params, page_of
from signal_bot.endpoints import THUMB_WIDTH

if TYPE_CHECKING:
    from collections.abc import Callable, Sequence

    from signal_bot.context import CommandContext
    from signal_bot.decorators import Decorator
    from signal_bot.http_client import ImageFetcher
    from signal_bot.registry import CommandRegistry, Handler

COMMAND_NAME: Final = "art"
DESCRIPTION: Final = "losowe dzieło sztuki"
ART_FILE: Final = Path(__file__).with_name("art.json")

# Per cent of posts drawn from the Polish pool.
POLISH_SHARE: Final = 60
PER_CENT: Final = 100


def load_art(path: Path = ART_FILE) -> tuple[tuple[int, ...], tuple[int, ...]]:
    """Read both pools.

    The file holds Commons page ids -- bare integers -- and that is checked
    here rather than assumed, for the reason ``traps_command.load_traps``
    gives. It matters more for art than for traps: a Commons painting
    filename is very often literally somebody's name, so a pool of filenames
    would be a list of names committed to a public repository.

    Args:
        path: Where to read the pools from. Defaults to the shipped file.

    Returns:
        The Polish pool and the world pool.

    Raises:
        ValueError: If either pool is empty or holds anything but integers.
    """
    document = json.loads(path.read_text(encoding="utf-8"))
    pools: list[tuple[int, ...]] = []
    for name in ("polish", "world"):
        pool = document[name]
        if not pool or not all(isinstance(page, int) for page in pool):
            msg = f"{path} must hold a non-empty list of Commons page ids under {name!r}"
            raise ValueError(msg)
        pools.append(tuple(pool))
    return pools[0], pools[1]


def random_art(
    polish: Sequence[int],
    world: Sequence[int],
    randbelow: Callable[[int], int] = secrets.randbelow,
) -> int:
    """Return one page id, skewed towards the Polish pool.

    secrets rather than random for the reason animals.paged_url gives: the
    choice is not security-sensitive, but ruff's ALL rule set flags `random`
    and this repository forbids the noqa that would silence it.

    ``randbelow`` is a parameter because ``secrets.randbelow`` cannot be
    seeded, and a test that asserted the 60/40 split by taking real draws
    would either flake or need thousands of iterations. Injecting it lets the
    test name the branch it means.
    """
    pool = polish if randbelow(PER_CENT) < POLISH_SHARE else world
    return pool[randbelow(len(pool))]


def art_handler(
    fetcher: ImageFetcher,
    api_url: str,
    pools: tuple[Sequence[int], Sequence[int]] | None = None,
) -> Handler:
    """Build the handler that posts one random work of art."""
    polish, world = load_art() if pools is None else (tuple(pools[0]), tuple(pools[1]))

    async def handler(ctx: CommandContext) -> None:
        # One request, because the caption and the picture have to describe
        # the same file; two would be a chance for them to disagree.
        document = await fetcher.fetch_json(
            api_url,
            imageinfo_params(THUMB_WIDTH, page_id=random_art(polish, world), describe=True),
        )
        page = page_of(document)
        image = await fetcher.fetch_image(str(page["imageinfo"][0]["thumburl"]))
        await ctx.reply_image(b64encode(image).decode("ascii"), caption_for(page))

    return handler


def register_art_command(
    registry: CommandRegistry,
    fetcher: ImageFetcher,
    api_url: str,
    *,
    decorate: Decorator | None = None,
    aliases: dict[str, list[str]] | None = None,
    pools: tuple[Sequence[int], Sequence[int]] | None = None,
) -> None:
    """Register !sztuka under every trigger aliases.json gives it."""
    table = load_aliases() if aliases is None else aliases
    handler = art_handler(fetcher, api_url, pools)
    if decorate is not None:
        handler = decorate(handler)
    registry.register(COMMAND_NAME, table[COMMAND_NAME], handler, DESCRIPTION)