### Engine Connection Protocol

Source: https://github.com/ryanfrancesconi/spfk-au-host/blob/main/README.md

Provides an example implementation of the AudioEngineConnection protocol, which allows custom AVAudioEngine integration.

```swift
// Implement AudioEngineConnection to provide your own AVAudioEngine
struct MyEngine: AudioEngineConnection {
    let engine: AVAudioEngine

    func connectAndAttach(
        _ node1: AVAudioNode, to node2: AVAudioNode, format: AVAudioFormat?)
    async throws {
        engine.attach(node1)
        engine.attach(node2)
        engine.connect(node1, to: node2, format: format)
    }
}
```

--------------------------------

### Effects Chain

Source: https://github.com/ryanfrancesconi/spfk-au-host/blob/main/README.md

Demonstrates how to create an AudioUnitChain, update its IO, insert effects by AudioComponentDescription, and connect the chain.

```swift
import SPFKAUHost

// Create a chain with a delegate that provides engine connection
let chain = AudioUnitChain(delegate: myEngine)
try await chain.updateIO(input: playerNode, output: mixerNode)

// Insert effects by AudioComponentDescription
try await chain.insertAudioUnit(componentDescription: reverbDesc, at: 0)
try await chain.insertAudioUnit(componentDescription: delayDesc, at: 1)
try await chain.connect()
```

--------------------------------

### Host Musical Context

Source: https://github.com/ryanfrancesconi/spfk-au-host/blob/main/README.md

Demonstrates how to set and update the musical context (tempo, time signature) for Audio Units.

```swift
let hostState = HostAUState()
hostState.musicalContext.currentTempo = 120
hostState.musicalContext.timeSignatureNumerator = 4
hostState.musicalContext.timeSignatureDenominator = 4

// Provide to Audio Units via their blocks
await chainData.update(hostAUState: hostState)

// Mutations are reflected live — no need to reassign blocks
hostState.musicalContext.currentTempo = 140
```

--------------------------------

### Manufacturer Collection for Menus

Source: https://github.com/ryanfrancesconi/spfk-au-host/blob/main/README.md

Shows how to create and iterate through a collection of Audio Units grouped by manufacturer, useful for populating menus.

```swift
let groups = AudioUnitManufacturerCollection.createGroup(
    from: availableComponents
)

for manufacturer in groups {
    print(manufacturer.name)  // "Apple", "FabFilter", etc.
    for component in manufacturer.components {
        print("  \(component.name)")  // "AUDelay", "Pro-Q 3", etc.
    }
}
```

--------------------------------

### Bypass and Reorder

Source: https://github.com/ryanfrancesconi/spfk-au-host/blob/main/README.md

Shows how to bypass individual effects or the entire chain, and how to reorder effects within the chain.

```swift
// Bypass a single effect
try await chain.bypassEffect(at: 0, state: true, reconnect: true)

// Bypass entire chain
try await chain.bypassEffects(state: true)

// Move effect from slot 0 to slot 2
try await chain.moveEffect(from: 0, to: 2)
```

--------------------------------

### Component Cache

Source: https://github.com/ryanfrancesconi/spfk-au-host/blob/main/README.md

Illustrates the usage of AudioUnitCacheManager for loading, updating, and validating cached Audio Components.

```swift
let cacheManager = AudioUnitCacheManager(cachesDirectory: cachesURL)
cacheManager.update(delegate: self)
cacheManager.update(cacheURL: nil) // uses default

// Load cached components or create fresh cache
try await cacheManager.load()

if cacheManager.validationIsNeeded {
    try await cacheManager.createCache()
}
```

--------------------------------

### Architecture Diagram

Source: https://github.com/ryanfrancesconi/spfk-au-host/blob/main/README.md

A hierarchical breakdown of the SPFKAUHost project structure, detailing its components and their responsibilities.

```text
SPFKAUHost
  |-- AudioUnitChain                Actor-based effects chain manager
  |   |-- AudioUnitChain+Connect    Connection, bypass, move, remove operations
  |   |-- AudioUnitChain+Insert     Insert, load chain description, AU instantiation
  |   |-- AudioUnitChain+Instantiate  Out-of-process/in-process effect and instrument creation
  |   |-- AudioUnitChainData        Actor holding the effects slot array and state
  |   |-- AudioUnitChainDelegate    Protocol combining AudioEngineConnection + AudioUnitAvailability
  |   |-- AudioUnitChainEvent       Events: insert, remove, bypass, move, connection error
  |   |-- AudioUnitDescription      AVAudioUnit wrapper with independent bypass flag
  |
  |-- AudioUnitCacheManager         Actor managing AU cache lifecycle
  |   |-- +Cache                    XML cache read/write/parse/remove
  |   |-- +Validation               System component discovery and validation pipeline
  |   |-- AudioUnitCacheEvent       Events: caching started, updated, loaded, validating
  |   |-- AudioUnitCacheObservation  NotificationCenter observer for component changes
  |   |-- ComponentCollection       Filtered views: passed, failed, unavailable effects
  |   |-- SystemComponentsResponse  Validation results container
  |   |-- Validation/
  |       |-- AudioUnitValidator    Multi-strategy validator (API, async, external auval)
  |       |-- ComponentValidationResult  Per-component validation state and metadata
  |
  |-- Definitions
  |   |-- AudioUnitManufacturerCollection  Manufacturer-grouped component hierarchy
  |   |-- AudioUnitPresets           Factory and user preset loading and full state I/O
  |   |-- AudioUnitStateNotifier    Parameter change notification via AudioToolbox
  |   |-- HostAUState               Musical context + transport state block provider
  |   |-- HostMusicalContext         Tempo, time signature, beat position
  |   |-- HostTransportState         Transport flags, sample position, cycle boundaries
  |   |-- S_AVAudioUnitComponent     Sendable copy of AVAudioUnitComponent properties
  |
  |-- Protocols
  |   |-- AudioEngineConnection      Node attach/connect abstraction
  |   |-- AudioEngineNode            Input/output node, bypass, detach, format access
  |   |-- AudioUnitAvailability      Available components and manufacturer collections
  |
  |-- Tests
      |-- TestAudioUnitContent       Mock delegate for unit testing without AVAudioEngine
```

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