"""Keep a full page of device identities visible within the inline response budget."""

import json
from typing import Any


def compact_scada_catalog(output: dict[str, Any], budget: int) -> dict[str, Any] | None:
    """Project attributes, never rows; full task evidence is persisted before this step."""
    rows = output.get("data")
    if output.get("source") != "list_scada_devices" or not isinstance(rows, list):
        return None
    if not all(isinstance(row, dict) and "device_id" in row for row in rows):
        return None
    fields = ("device_id", "device_type", "measurement_unit")
    preview = {
        **output,
        "data": [{key: row[key] for key in fields if key in row} for row in rows],
        "truncated": True,
        "data_gaps": [
            *output.get("data_gaps", []),
            "All devices in this page are listed with IDs, types and units; "
            "other attributes are omitted. Use get_scada_device for model mapping, "
            "coordinates and other device details. Use page.has_more to check for more devices.",
        ],
    }
    if len(json.dumps(preview, ensure_ascii=False).encode()) > budget:
        return None
    return preview