import os

import peewee

DATABASE_FILE = "mre_concise_cursor_bug.sqlite"
SERVICE_NAME = "example_feed_service"

db = peewee.SqliteDatabase(DATABASE_FILE)


class BaseModel(peewee.Model):
    class Meta:
        database = db


class SubscriptionState(BaseModel):
    """Mirrors the SubscriptionState model from the application."""

    service = peewee.CharField(unique=True)
    cursor = peewee.BigIntegerField()

    def __str__(self):
        return f"<SubscriptionState service='{self.service}', cursor={self.cursor}>"


# --- Firehose Client Simulation ---
class SimulatedFirehoseClient:
    def __init__(self, cursor_param=None):
        self.effective_start_point = (
            "LATEST (HEAD)" if cursor_param is None else cursor_param
        )
        print(f"  FirehoseClient: Will request from {self.effective_start_point}")


# --- Application Logic Simulation ---
def run_firehose_initialization_simulation(step_name):
    print(f"\\n--- {step_name} ---")

    initial_db_state = SubscriptionState.get_or_none(
        SubscriptionState.service == SERVICE_NAME
    )
    print(f"  App: DB state before client init: {initial_db_state}")

    client_init_cursor = initial_db_state.cursor if initial_db_state else None
    client = SimulatedFirehoseClient(cursor_param=client_init_cursor)

    # HERE IS THE (POTENTIAL) PROBLEM
    if initial_db_state is None:
        print(
            f"  App: No DB state, creating SubscriptionState(service='{SERVICE_NAME}', cursor=0)"
        )
        SubscriptionState.create(service=SERVICE_NAME, cursor=0)

    final_db_state = SubscriptionState.get_or_none(
        SubscriptionState.service == SERVICE_NAME
    )
    print(f"  App: DB state after client init & potential create: {final_db_state}")
    print(
        f"  Outcome: Client targets '{client.effective_start_point}', DB stores cursor '{final_db_state.cursor if final_db_state else None}'"
    )
    return (
        client.effective_start_point,
        final_db_state.cursor if final_db_state else None,
    )


def demonstrate_bug():
    print("MRE: Concise Firehose Cursor Bug Demonstration")
    print(
        "Illustrates premature `cursor=0` write vs. client's actual firehose start point.\\n"
    )

    if os.path.exists(DATABASE_FILE):
        os.remove(DATABASE_FILE)
    db.connect()
    db.create_tables([SubscriptionState])

    try:
        s1_client_target, s1_db_cursor = run_firehose_initialization_simulation(
            "Step 1: First App Run (Empty DB)"
        )
        s2_client_target, s2_db_cursor = run_firehose_initialization_simulation(
            "Step 2: App Restart (Reads DB from Step 1)"
        )

        print("\\n--- Bug Analysis ---")
        bug_is_present = (
            s1_client_target == "LATEST (HEAD)"
            and s1_db_cursor == 0
            and s2_client_target == 0
            and s2_db_cursor == 0
        )
        if bug_is_present:
            print("  Result: Bug Confirmed.")
            print(
                f"    - First run: Client aims for '{s1_client_target}', but DB is set to '{s1_db_cursor}'."
            )
            print(
                f"    - Restart: Client incorrectly aims for '{s2_client_target}' due to DB state."
            )
            print(
                "    - Implication: App would try to process all history from cursor 0."
            )
        else:
            print("  Result: Bug pattern not matched. Please review output.")

    finally:
        if not db.is_closed():
            db.close()
        if os.path.exists(DATABASE_FILE):
            os.remove(DATABASE_FILE)
            print(f"\\n(Cleaned up {DATABASE_FILE})")


if __name__ == "__main__":
    demonstrate_bug()