"""Raw sample pruning per spec §3.4, ST-5.

Raw samples are pruned opportunistically to 14 days.
Hour observations and day aggregates are retained indefinitely.
"""
import sqlite3
from datetime import datetime, timedelta, timezone

# Spec §3.4: Raw-sample retention
RAW_SAMPLE_RETENTION_DAYS = 14


def prune_old_samples(
    conn: sqlite3.Connection,
    now: datetime,
    retention_days: int = RAW_SAMPLE_RETENTION_DAYS,
) -> int:
    """Remove raw samples older than retention_days.

    Args:
        conn: Connection to the observation store.
        now: Current UTC time.
        retention_days: Number of days to retain (default 14).

    Returns:
        Number of samples removed.
    """
    cutoff = (now - timedelta(days=retention_days)).isoformat()
    cursor = conn.execute("DELETE FROM samples WHERE ts < ?", (cutoff,))
    conn.commit()
    return cursor.rowcount