Musubi/Packages/MusubiKit/Tests/AudioMatrixTests/DSPTests.swift

import CAudioRing
import Foundation
import Testing
@testable import AudioMatrix
import MusubiCore

@Suite struct RingTests {
    @Test func writesAndReadsAcrossWrap() throws {
        let ring = try #require(musubi_ring_create(8, 2))
        defer { musubi_ring_destroy(ring) }
        var input: [Float] = (0..<12).map(Float.init) // 6 frames
        var output = [Float](repeating: 0, count: 12)

        #expect(musubi_ring_write(ring, &input, 6) == 6)
        #expect(musubi_ring_read(ring, &output, 4) == 4)
        #expect(Array(output[0..<8]) == (0..<8).map(Float.init))
        // Wraps around the end of the buffer.
        #expect(musubi_ring_write(ring, &input, 6) == 6)
        #expect(musubi_ring_available(ring) == 8)
        #expect(musubi_ring_read(ring, &output, 6) == 6)
        #expect(Array(output[0..<4]) == [8, 9, 10, 11])
        #expect(Array(output[4..<12]) == (0..<8).map(Float.init))
    }

    @Test func dropsWhatDoesNotFit() throws {
        let ring = try #require(musubi_ring_create(4, 1))
        defer { musubi_ring_destroy(ring) }
        var input: [Float] = [1, 2, 3, 4, 5, 6]
        #expect(musubi_ring_write(ring, &input, 6) == 4)
        #expect(musubi_ring_skip(ring, 3) == 3)
        #expect(musubi_ring_available(ring) == 1)
    }
}

@Suite struct ResamplerTests {
    @Test func unitStepPassesSignalThroughWithDelay() {
        var resampler = Resampler()
        let frames = 64
        let input: [Float] = (0..<frames).flatMap { [Float($0), -Float($0)] }
        var output = [Float](repeating: 0, count: frames * 2)

        #expect(resampler.inputFramesNeeded(outputFrames: frames, step: 1) == frames)
        input.withUnsafeBufferPointer { resampler.process(input: $0.baseAddress!, output: &output, outputFrames: frames, step: 1) }
        // Three frames of latency from the 4-point interpolation history.
        for frame in 3..<frames {
            #expect(output[frame * 2] == Float(frame - 3))
            #expect(output[frame * 2 + 1] == -Float(frame - 3))
        }
    }

    @Test func convertsRateAndKeepsFrequency() {
        // 1 kHz at 44.1 kHz in, 48 kHz out.
        let step = 44_100.0 / 48_000.0
        var resampler = Resampler()
        let outFrames = 4800
        let inFrames = resampler.inputFramesNeeded(outputFrames: outFrames, step: step)
        #expect(abs(inFrames - 4410) <= 1)

        let input: [Float] = (0..<inFrames).flatMap { i -> [Float] in
            let v = Float(sin(2 * Double.pi * 1000 * Double(i) / 44_100))
            return [v, v]
        }
        var output = [Float](repeating: 0, count: outFrames * 2)
        input.withUnsafeBufferPointer { resampler.process(input: $0.baseAddress!, output: &output, outputFrames: outFrames, step: step) }

        // Compare against an ideal 1 kHz sine at 48 kHz (skipping the start-up latency).
        let latency = 3.0 / step
        var maxError: Float = 0
        for i in 100..<outFrames {
            let expected = Float(sin(2 * Double.pi * 1000 * (Double(i) - latency) / 48_000))
            maxError = max(maxError, abs(output[i * 2] - expected))
        }
        #expect(maxError < 0.01)
    }
}

@Suite struct DriftControllerTests {
    @Test func primesBeforePlaying() {
        var drift = DriftController(sourceRate: 48_000, outputRate: 48_000, targetLatency: 0.02) // 960 frames
        #expect(drift.update(available: 500, needed: 512) == .fill)
        #expect(drift.update(available: 960, needed: 512) == .play(step: 1))
    }

    @Test func trimsBacklogAfterPrimingWithoutCountingOverrun() {
        var drift = DriftController(sourceRate: 48_000, outputRate: 48_000) // target 960
        #expect(drift.update(available: 6700, needed: 512) == .skip(frames: 5740, step: 1))
        #expect(drift.overruns == 0)
        #expect(drift.update(available: 960, needed: 512) == .play(step: 1))
    }

    @Test func countsUnderrunAndRefills() {
        var drift = DriftController(sourceRate: 48_000, outputRate: 48_000)
        _ = drift.update(available: 1000, needed: 512)
        #expect(drift.update(available: 100, needed: 512) == .fill)
        #expect(drift.underruns == 1)
        #expect(drift.update(available: 600, needed: 512) == .fill) // still priming
    }

    @Test func skipsOnOverrun() {
        var drift = DriftController(sourceRate: 48_000, outputRate: 48_000)
        _ = drift.update(available: 1000, needed: 512)
        #expect(drift.update(available: 5000, needed: 512) == .skip(frames: 4040, step: 1))
        #expect(drift.overruns == 1)
    }

    /// Sender clock 200 ppm fast: the fill level must stay bounded without under- or overruns.
    @Test func followsClockDrift() {
        let outputRate = 48_000.0, sourceRate = 48_000.0 * 1.0002
        var drift = DriftController(sourceRate: 48_000, outputRate: outputRate)
        let block = 512
        var fill = 960.0
        var produced = 0.0
        for _ in 0..<(60 * 94) { // ~60 s of 512-frame cycles
            produced += sourceRate * Double(block) / outputRate
            let whole = produced.rounded(.down)
            fill += whole
            produced -= whole
            var resampler = Resampler()
            switch drift.update(available: Int(fill), needed: block + 4) {
            case .play(let step):
                fill -= Double(resampler.inputFramesNeeded(outputFrames: block, step: step))
            case .fill:
                break
            case .skip(let frames, let step):
                fill -= Double(frames) + Double(resampler.inputFramesNeeded(outputFrames: block, step: step))
            }
        }
        #expect(drift.underruns == 0)
        #expect(drift.overruns == 0)
        #expect(fill > 400 && fill < 2000)
        #expect(drift.correction > 0)
    }
}

@Suite struct LevelTests {
    @Test func convertsDecibels() {
        #expect(Level.gain(fromDB: 0) == 1)
        #expect(abs(Level.gain(fromDB: -6) - 0.501) < 0.001)
        #expect(Level.gain(fromDB: -60) == 0)
        #expect(Level.db(fromGain: 0) == Level.floorDB)
        #expect(abs(Level.db(fromGain: 0.5) + 6.02) < 0.01)
    }

    @Test func selectsChannels() {
        #expect(ChannelSelection.left.sample(left: 1, right: 0) == 1)
        #expect(ChannelSelection.right.sample(left: 1, right: 0) == 0)
        #expect(ChannelSelection.mono.sample(left: 1, right: 0) == 0.5)
    }
}