//
//  CastV2PlatformReader.swift
//  OpenCastSwift Mac
//
//  Created by Miles Hollingsworth on 4/22/18
//  Copyright © 2018 Miles Hollingsworth. All rights reserved.
//

let maxBufferLength = 8192

import Foundation

class CastV2PlatformReader {
  let stream: InputStream
  var readPosition = 0
  var buffer = Data(capacity: maxBufferLength)

  init(stream: InputStream) {
    self.stream = stream
  }

  func readStream() {
    objc_sync_enter(self)
    defer { objc_sync_exit(self) }

    var totalBytesRead = 0
    let bufferSize = 32

    while stream.hasBytesAvailable {
      var bytes = [UInt8](repeating: 0, count: bufferSize)

      let bytesRead = stream.read(&bytes, maxLength: bufferSize)

      if bytesRead < 0 { continue }

      buffer.append(Data(bytes: &bytes, count: bytesRead))

      totalBytesRead += bytesRead
    }
  }

  func nextMessage() -> Data? {
    objc_sync_enter(self)
    defer { objc_sync_exit(self) }

    let headerSize = MemoryLayout<UInt32>.size
    guard buffer.count - readPosition >= headerSize else { return nil }
    let header = buffer.withUnsafeBytes({ (pointer: UnsafePointer<Int8>) -> UInt32 in
      return pointer.advanced(by: self.readPosition).withMemoryRebound(to: UInt32.self, capacity: 1, { $0.pointee })
    })

    let payloadSize = Int(CFSwapInt32BigToHost(header))

    readPosition += headerSize

    guard buffer.count >= readPosition + payloadSize, buffer.count - readPosition >= payloadSize, payloadSize >= 0 else {
      // Message hasn't arrived
      readPosition -= headerSize
      return nil
    }

    let payload = buffer.withUnsafeBytes({ (pointer: UnsafePointer<Int8>) -> Data in
      return Data(bytes: pointer.advanced(by: self.readPosition), count: payloadSize)
    })
    readPosition += payloadSize

    resetBufferIfNeeded()

    return payload
  }

  private func resetBufferIfNeeded() {
    guard buffer.count >= maxBufferLength else { return }

    if readPosition == buffer.count {
      buffer = Data(capacity: maxBufferLength)
    } else {
      buffer = buffer.advanced(by: readPosition)
    }

    readPosition = 0
  }
}