ccn/Packages/Persistence/Sources/Public/Methods/Probe.swift

import HummingbirdFluent
import SQLKit

/// A readiness probe reporting whether the database behind a `Fluent` service is reachable.
///
/// Built once around the application's `Fluent` service and called as a function whenever a fresh answer is needed — typically from a readiness endpoint:
/// `let ready = await probe()`.
public struct Probe: Sendable {

    // MARK: Properties

    /// The `Fluent` service whose default database is probed.
    private let fluent: Fluent

    // MARK: Initializers

    /// Creates a probe for the default database of the given `Fluent` service.
    /// - Parameter fluent: the `Fluent` service whose default database is probed.
    public init(
        fluent: Fluent
    ) {
        self.fluent = fluent
    }

    // MARK: Methods

    /// Reports whether the database behind the `Fluent` service is reachable.
    ///
    /// Runs a trivial `SELECT 1` against the default database — the cheapest statement both the MySQL/MariaDB and SQLite backends understand — so
    /// a readiness check does not depend on any particular schema or model. Any failure (connection refused, authentication error, pool exhausted) is
    /// reported as not reachable rather than thrown, so callers can map it straight onto a readiness response. A default database that is not an SQL
    /// database is likewise reported as not reachable.
    /// - Returns: `true` when the database answers the probe, `false` otherwise.
    public func callAsFunction() async -> Bool {
        guard let database = fluent.db() as? any SQLDatabase else {
            return false
        }
        
        do {
            try await database.raw("SELECT 1").run()
            
            return true
        } catch {
            return false
        }

    }
}