"""Shared validation for PostgreSQL schema names."""

from __future__ import annotations

import re

# Lowercase-only on purpose. The schema is created *quoted*
# (``CREATE SCHEMA IF NOT EXISTS "<schema>"``, case-preserved) but pinned via an
# *unquoted* ``search_path`` token, which PostgreSQL folds to lowercase. Allowing
# uppercase here would let the two diverge so tables silently land in ``public``.
# No anchors: validation uses ``re.fullmatch`` so the whole value must match.
# A ``$``-anchored ``re.match`` would accept a trailing newline (``"deerflow\n"``):
# Python's ``$`` matches just before a single trailing ``\n``, which then
# creates a *quoted* schema literally named ``deerflow\n`` while the *unquoted*
# ``search_path`` folds to ``deerflow`` and misses it, silently landing tables
# in ``public``.
POSTGRES_SCHEMA_PATTERN = r"[a-z_][a-z0-9_]{0,62}"
_POSTGRES_SCHEMA_RE = re.compile(POSTGRES_SCHEMA_PATTERN)


def validate_postgres_schema(value: str) -> str:
    """Validate the v1 plain-identifier PostgreSQL schema contract."""
    if value == "":
        return value
    if not _POSTGRES_SCHEMA_RE.fullmatch(value):
        raise ValueError(f"postgres_schema must be a plain lowercase PostgreSQL identifier matching {POSTGRES_SCHEMA_PATTERN}; got {value!r}. Mixed-case and quoted identifiers are not supported.")
    return value