import XCTest

@testable import Transui

final class MP3EncoderTests: XCTestCase {
  func testExtractsSupportedPCMDataFromWAV() throws {
    let samples = Data([0x01, 0x02, 0x03, 0x04])
    let wav = makeWAV(samples: samples)

    XCTAssertEqual(try MP3Encoder.pcmData(fromWAV: wav), samples)
  }

  func testRejectsWrongSampleRate() {
    XCTAssertThrowsError(try MP3Encoder.pcmData(fromWAV: makeWAV(sampleRate: 44_100)))
  }

  private func makeWAV(sampleRate: UInt32 = 16_000, samples: Data = Data([0, 0])) -> Data {
    var data = Data("RIFF".utf8)
    append(UInt32(36 + samples.count), to: &data)
    data.append(Data("WAVEfmt ".utf8))
    append(UInt32(16), to: &data)
    append(UInt16(1), to: &data)
    append(UInt16(1), to: &data)
    append(sampleRate, to: &data)
    append(sampleRate * 2, to: &data)
    append(UInt16(2), to: &data)
    append(UInt16(16), to: &data)
    data.append(Data("data".utf8))
    append(UInt32(samples.count), to: &data)
    data.append(samples)
    return data
  }

  private func append(_ value: UInt16, to data: inout Data) {
    data.append(UInt8(value & 0xff))
    data.append(UInt8(value >> 8))
  }

  private func append(_ value: UInt32, to data: inout Data) {
    data.append(UInt8(value & 0xff))
    data.append(UInt8((value >> 8) & 0xff))
    data.append(UInt8((value >> 16) & 0xff))
    data.append(UInt8((value >> 24) & 0xff))
  }
}