"""As-of harness (§6.6 look-ahead guard).

Every scorer reads the `visible_claims` TEMP VIEW, never `claims` directly: at nomination time only
claims dated <= as_of are visible, so the backtest can't reward noticing what already happened. The
view also resolves merged canonical topics (topics.status='merged') to a stable `topic_id`.
"""
from __future__ import annotations

import sqlite3


class Scorer:
    """Context manager that binds a run to an as_of date and exposes `visible_claims`.

    mode='backtest' enforces strict as-of discipline; 'forward' is the live pilot. as_of is a
    controlled ISO date (YYYY-MM-DD) — safe to inline into the view DDL (views can't take params)."""

    def __init__(self, conn: sqlite3.Connection, as_of: str, *, mode: str = "backtest") -> None:
        self.conn = conn
        self.as_of = as_of
        self.mode = mode

    def __enter__(self) -> "Scorer":
        self.conn.executescript(
            f"""
            DROP VIEW IF EXISTS visible_claims;
            CREATE TEMP VIEW visible_claims AS
            SELECT c.*,
              COALESCE((SELECT t.merged_into FROM topics t
                        WHERE t.topic_canonical = c.topic_canonical AND t.status='merged'),
                       c.topic_canonical) AS topic_id
            FROM claims c
            JOIN documents d ON d.doc_id = c.doc_id
            WHERE c.date IS NOT NULL AND c.date <= '{self.as_of}';
            """
        )
        return self

    def __exit__(self, *exc) -> None:
        self.conn.execute("DROP VIEW IF EXISTS visible_claims")

    def count_visible(self) -> int:
        return self.conn.execute("SELECT COUNT(*) FROM visible_claims").fetchone()[0]