"""Single relay, synthetic delivery; local SQL effects only."""


def place_order(db, order_id, amount, checkpoint=lambda stage: None):
    db.execute("BEGIN IMMEDIATE")
    try:
        db.execute("INSERT INTO orders VALUES (?, ?)", (order_id, amount))
        changed = db.execute(
            "UPDATE wallet SET balance = balance - ? WHERE id = 'demo' AND balance >= ?",
            (amount, amount),
        ).rowcount
        if changed != 1:
            raise ValueError("insufficient balance")
        checkpoint("before_outbox")
        db.execute("INSERT INTO outbox(event_id, order_id, amount) VALUES (?, ?, ?)",
                   ("order-created:" + order_id, order_id, amount))
        db.execute("COMMIT")
    except BaseException:
        if db.in_transaction:
            db.execute("ROLLBACK")
        raise


def relay_once(db, send, checkpoint=lambda stage: None):
    row = db.execute(
        "SELECT event_id, order_id, amount FROM outbox WHERE sent = 0 ORDER BY rowid LIMIT 1"
    ).fetchone()
    if row is None:
        return False
    event = dict(zip(("event_id", "order_id", "amount"), row))
    send(event)
    checkpoint("after_send")
    db.execute("UPDATE outbox SET sent = 1 WHERE event_id = ?", (event["event_id"],))
    return True


def consume(db, event, checkpoint=lambda stage: None):
    if (not isinstance(event, dict) or set(event) != {"event_id", "order_id", "amount"}
            or any(not isinstance(event[key], str) or not 1 <= len(event[key]) <= 200
                   for key in ("event_id", "order_id"))
            or type(event["amount"]) is not int or not 1 <= event["amount"] <= 1_000_000):
        raise ValueError("invalid event")
    db.execute("BEGIN IMMEDIATE")
    try:
        inserted = db.execute(
            "INSERT INTO processed VALUES (?, ?, ?) ON CONFLICT(event_id) DO NOTHING",
            (event["event_id"], event["order_id"], event["amount"]),
        ).rowcount
        if inserted == 0:
            previous = db.execute(
                "SELECT order_id, amount FROM processed WHERE event_id = ?",
                (event["event_id"],),
            ).fetchone()
            if previous != (event["order_id"], event["amount"]):
                raise ValueError("event ID reused with different payload")
            db.execute("COMMIT")
            return False
        checkpoint("after_dedup")
        db.execute("INSERT INTO notifications(order_id, amount) VALUES (?, ?)",
                   (event["order_id"], event["amount"]))
        db.execute("COMMIT")
        return True
    except BaseException:
        if db.in_transaction:
            db.execute("ROLLBACK")
        raise