potential split between CLI and core library

Sources/AudioTeeCore/Core/AudioBuffer.swift

@@ -0,0 +1,105 @@
+import CoreAudio
+import Foundation
+
+public class AudioBuffer {
+  private var buffer: [UInt8]
+  private var writeIndex: Int = 0
+  private var readIndex: Int = 0
+  private var availableBytes: Int = 0
+  private let maxBufferSize: Int
+
+  private let bytesPerChunk: Int
+  private let chunkDuration: Double
+
+  public init(format: AudioStreamBasicDescription, chunkDuration: Double = 0.2) {
+
+    // Pre-calculate chunk parameters
+    let bytesPerFrame = Int(format.mBytesPerFrame)
+    let samplesPerChunk = Int(format.mSampleRate * chunkDuration)
+    self.bytesPerChunk = samplesPerChunk * bytesPerFrame
+    self.chunkDuration = Double(samplesPerChunk) / format.mSampleRate
+
+    // Calculate max buffer size to hold ~10 seconds of audio, way more than the maximum we allow
+    let bytesPerSecond = Int(format.mSampleRate) * bytesPerFrame
+    self.maxBufferSize = bytesPerSecond * 10
+
+    // Pre-allocated ring buffer
+    self.buffer = Array(repeating: 0, count: maxBufferSize)
+  }
+
+  public func append(_ data: Data) {
+    guard availableBytes + data.count <= maxBufferSize else {
+      Logger.error(
+        "Audio buffer overflow",
+        context: [
+          "requested": String(data.count),
+          "available": String(maxBufferSize - availableBytes),
+        ])
+      return
+    }
+
+    data.withUnsafeBytes { bytes in
+      let sourceBytes = bytes.bindMemory(to: UInt8.self)
+      let dataSize = sourceBytes.count
+
+      // Check if we can copy in one block (no wrap-around)
+      if writeIndex + dataSize <= maxBufferSize {
+        // only one write needed
+        buffer.replaceSubrange(writeIndex..<writeIndex + dataSize, with: sourceBytes)
+        writeIndex = (writeIndex + dataSize) % maxBufferSize
+      } else {
+        // two writes needed due to wrap-around
+        let firstChunkSize = maxBufferSize - writeIndex
+        let secondChunkSize = dataSize - firstChunkSize
+
+        buffer.replaceSubrange(writeIndex..<maxBufferSize, with: sourceBytes.prefix(firstChunkSize))
+        buffer.replaceSubrange(0..<secondChunkSize, with: sourceBytes.suffix(secondChunkSize))
+
+        writeIndex = secondChunkSize
+      }
+    }
+
+    availableBytes += data.count
+  }
+
+  public func processChunks() -> [AudioPacket] {
+    var packets: [AudioPacket] = []
+
+    while let packet = nextChunk() {
+      packets.append(packet)
+    }
+
+    return packets
+  }
+
+  private func nextChunk() -> AudioPacket? {
+    // Check if we have enough data for a complete chunk
+    guard availableBytes >= bytesPerChunk else { return nil }
+
+    var chunkData = Data(capacity: bytesPerChunk)
+
+    // Check if we can copy in one block (no wrap-around)
+    if readIndex + bytesPerChunk <= maxBufferSize {
+      // one copy needed
+      chunkData.append(contentsOf: buffer[readIndex..<readIndex + bytesPerChunk])
+      readIndex = (readIndex + bytesPerChunk) % maxBufferSize
+    } else {
+      // two copies needed due to wrap-around
+      let firstChunkSize = maxBufferSize - readIndex
+      let secondChunkSize = bytesPerChunk - firstChunkSize
+
+      chunkData.append(contentsOf: buffer[readIndex..<maxBufferSize])
+      chunkData.append(contentsOf: buffer[0..<secondChunkSize])
+
+      readIndex = secondChunkSize
+    }
+
+    availableBytes -= bytesPerChunk
+
+    return AudioPacket(
+      timestamp: Date(),
+      duration: chunkDuration,
+      data: chunkData
+    )
+  }
+}