"""Request body-size measurement and a leak-free 413 handler.

Werkzeug enforces the byte ceiling itself from ``app.config['MAX_CONTENT_LENGTH']`` (lazily, when
the body is read), so this module only adds the two things around it: a passive ``before_request``
that records the observed ``Content-Length`` of every request carrying a body, and a 413 handler
that renders a fixed message so the configured limit never reaches the client. The measurement is
what lets the limit be right-sized from real traffic, which APM cannot otherwise observe.
"""

from flask import Flask, Response, request
from owsresponse import response
from owsresponse.adaptors.flask import flaskify
from werkzeug.exceptions import RequestEntityTooLarge

from core.config import Config
from core.hardening import observability as obs


def setup_body_limit(app: Flask, config: type[Config]) -> None:
    """Install body-size measurement and the generic 413 handler on ``app``.

    The ceiling itself comes from ``MAX_CONTENT_LENGTH`` in the app config; this only observes and
    renders. Both are always on (no enable flag).
    """

    @app.before_request
    def _measure_body() -> None:
        size = request.content_length
        if size:
            obs.request_body_bytes(size, request.endpoint or '')

    @app.errorhandler(RequestEntityTooLarge)
    def _body_too_large(_e: RequestEntityTooLarge) -> Response:
        obs.body_too_large()
        return flaskify(
            response.create_error_response(
                message='request body too large',
                status=413,
                code='error',
            )
        )