Wav.swift

import Foundation

fileprivate typealias WavByte = UInt8
fileprivate typealias WavInt = UInt32
fileprivate typealias WavShort = UInt16

fileprivate struct WavConstants {
	static let RIFF = [WavByte]("RIFF".utf8)
	static let WAVE = [WavByte]("WAVE".utf8)
	static let fmt = [WavByte]("fmt ".utf8)
	static let data = [WavByte]("data".utf8)
	static let rawSampleRate = 48000
	static let sampleRate = WavInt(rawSampleRate).byteArray
	static let rawBitsPerSample = 16
	static let bitsPerSample = WavShort(rawBitsPerSample).byteArray
	static let rawChannels = 2
	static let channels = WavShort(rawChannels).byteArray
}

struct Wav {

	private static let headerLength = 44
	private static let intSize = MemoryLayout<WavInt>.size
	private static let shortSize = MemoryLayout<WavShort>.size
	func createWav(_ data: Data) -> Data {
		var header = Data(capacity: Wav.headerLength)

		header.append(WavConstants.RIFF, count: Wav.intSize) // Big 0...3
		header.append(WavInt(data.count + Wav.headerLength - 8).byteArray, count: Wav.intSize) // Little 4...7 Filesize
		header.append(WavConstants.WAVE, count: Wav.intSize) // Big 8...11
		header.append(WavConstants.fmt, count: Wav.intSize) // Big 12...15
		header.append(WavInt(16).byteArray, count: Wav.intSize) // Little 16...19 Length of above data
		header.append(WavShort(1).byteArray, count: Wav.shortSize) // Little 20...21 Pcm format
		header.append(WavConstants.channels, count: Wav.shortSize) // Little 22..23
		header.append(WavConstants.sampleRate, count: Wav.intSize) // Little 24...27
		header.append(WavInt((WavConstants.rawSampleRate * WavConstants.rawBitsPerSample * WavConstants.rawChannels)/8).byteArray, count: Wav.intSize) // Little 28...31
		header.append(WavShort(WavConstants.rawBitsPerSample * WavConstants.rawChannels / 8).byteArray, count: Wav.shortSize) // Little 32...33
		header.append(WavConstants.bitsPerSample, count: Wav.shortSize) // Little 34...35
		header.append(WavConstants.data, count: Wav.intSize) // Big 36...39
		header.append(WavInt(max(0, data.count - Wav.headerLength)).byteArray, count: Wav.intSize) // Little 40...43
		header.append(data)
		return header
	}
}

fileprivate extension UInt32 {
	var byteArray: [WavByte] {
		// Little Endian
		return [
			WavByte(self & 0xff),
			WavByte((self >> 8) & 0xff),
			WavByte((self >> 16) & 0xff),
			WavByte((self >> 32) & 0xff)
		]
	}
}

fileprivate extension UInt16 {
	var byteArray: [WavByte] {
		// Little endian
		return [
			WavByte(self & 0xff),
			WavByte((self >> 8) & 0xff)
		]
	}
}