voice-cat/clients/apple/Sources/VoiceCatCore/Callbacks.swift

// C callbacks use an unretained `user` context. Client destruction joins callback threads,
// and transient event pointers are copied before the callback returns.

import VoiceCatC
import Foundation

/// Internal: builds the `vc_callbacks` struct wired to VoiceCatClient's C function pointers.
/// The `user` context is an Unmanaged-passUnretained pointer to the client — resolved back
/// to the client inside `onEvent`/`onLevel` below.
internal enum Callbacks {
    /// The `on_event` C function pointer. Non-capturing @convention(c) closure — resolves
    /// the VoiceCatClient from `user` and enqueues a safe copy of the event.
    static let onEvent: @convention(c) (
        UnsafeMutableRawPointer?, UnsafePointer<vc_event>?
    ) -> Void = { user, ev in
        guard let user, let ev else { return }
        let client = Unmanaged<VoiceCatClient>.fromOpaque(user).takeUnretainedValue()
        // Copy the event (including text) to a Swift value NOW — the raw vc_event is
        // invalid after this callback returns.
        client.enqueueEvent(VoiceCatEvent.from(ev.pointee))
    }

    /// The `on_level` C function pointer. Coalesces to "latest sample per stream_id"
    /// (intermediate values are visually irrelevant — same as C#'s ConcurrentDictionary).
    static let onLevel: @convention(c) (
        UnsafeMutableRawPointer?, UInt32, Float
    ) -> Void = { user, streamId, rms in
        guard let user else { return }
        let client = Unmanaged<VoiceCatClient>.fromOpaque(user).takeUnretainedValue()
        client.enqueueLevel(streamId, rms)
    }

    /// Construct the vc_callbacks struct for a given client.
    static func make(user: UnsafeMutableRawPointer) -> vc_callbacks {
        vc_callbacks(on_event: onEvent, on_level: onLevel, user: user)
    }
}