Music/MusicTests/ScannerServiceTests.swift

import Testing
import Foundation
@testable import Music

struct ScannerServiceTests {
    // Creates a temp directory with audio and non-audio files, verifies only audio files are discovered.
    // 1. Creates a unique temporary directory.
    // 2. Creates files with audio extensions (mp3, m4a, flac, wav, aiff) and non-audio extensions (txt, png, json).
    // 3. Creates a subdirectory with a nested mp3 file to test recursive discovery.
    // 4. Calls ScannerService.discoverAudioFiles and checks that exactly 6 audio files are found.
    // 5. Verifies all discovered files have audio-only extensions.
    // 6. Cleans up the temp directory.
    @Test func discoverAudioFiles() throws {
        let tmpDir = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString)
        try FileManager.default.createDirectory(at: tmpDir, withIntermediateDirectories: true)
        defer { try? FileManager.default.removeItem(at: tmpDir) }

        let audioFiles = ["song.mp3", "track.m4a", "audio.flac", "sound.wav", "music.aiff"]
        let nonAudioFiles = ["readme.txt", "image.png", "data.json"]

        for name in audioFiles + nonAudioFiles {
            FileManager.default.createFile(atPath: tmpDir.appendingPathComponent(name).path, contents: Data())
        }

        let subDir = tmpDir.appendingPathComponent("subfolder")
        try FileManager.default.createDirectory(at: subDir, withIntermediateDirectories: true)
        FileManager.default.createFile(atPath: subDir.appendingPathComponent("nested.mp3").path, contents: Data())

        let discovered = ScannerService.discoverAudioFiles(in: tmpDir)
        #expect(discovered.count == 6)

        let extensions = Set(discovered.map { $0.pathExtension.lowercased() })
        #expect(extensions.isSubset(of: ["mp3", "m4a", "flac", "wav", "aiff", "aac", "alac"]))
    }

    // Verifies resolveBitrate uses the OS estimate when it is positive.
    // 1. Passes a positive estimatedDataRate in bits/sec (320450).
    // 2. Expects it rounded to kbps (320450/1000 = 320.45, which rounds to 320), ignoring size/duration.
    @Test func resolveBitrateUsesEstimateWhenPositive() {
        let kbps = ScannerService.resolveBitrate(estimatedDataRate: 320_450,
                                                 fileSizeBytes: 5_000_000,
                                                 durationSeconds: 200)
        #expect(kbps == 320)
    }

    // Verifies the size/duration fallback when the OS estimate is 0 (the AVFoundation bug).
    // 1. Passes estimatedDataRate 0 with a real file size and duration.
    // 2. Expects 230_358_479 * 8 / 7198.54 s / 1000 -> ~256.0 -> 256 kbps (matches ffprobe).
    @Test func resolveBitrateFallsBackToSizeAndDuration() {
        let kbps = ScannerService.resolveBitrate(estimatedDataRate: 0,
                                                 fileSizeBytes: 230_358_479,
                                                 durationSeconds: 7198.5371428571425)
        #expect(kbps == 256)
    }

    // Verifies nil (never 0) when the estimate is 0 and duration is unusable.
    // 1. Zero duration cannot yield a value -> nil.
    // 2. A NaN duration (CMTimeGetSeconds can return NaN) is also nil, not 0.
    @Test func resolveBitrateReturnsNilWhenNoDuration() {
        #expect(ScannerService.resolveBitrate(estimatedDataRate: 0,
                                              fileSizeBytes: 230_358_479,
                                              durationSeconds: 0) == nil)
        #expect(ScannerService.resolveBitrate(estimatedDataRate: 0,
                                              fileSizeBytes: 230_358_479,
                                              durationSeconds: .nan) == nil)
    }

    // Verifies nil when the estimate is 0 and there is no file size.
    // 1. Missing fileSizeBytes with estimate 0 -> nil (never 0).
    @Test func resolveBitrateReturnsNilWhenNoFileSize() {
        #expect(ScannerService.resolveBitrate(estimatedDataRate: 0,
                                              fileSizeBytes: nil,
                                              durationSeconds: 200) == nil)
    }

    // Verifies the core invariant: no input combination ever yields 0.
    // 1. All-zero inputs return nil so the UI renders "—" instead of "0 kbps".
    @Test func resolveBitrateNeverReturnsZero() {
        #expect(ScannerService.resolveBitrate(estimatedDataRate: 0,
                                              fileSizeBytes: 0,
                                              durationSeconds: 0) == nil)
    }

    // Verifies the fallback never returns 0 for sub-kbps inputs (corrupt/truncated file).
    // 1. Estimate 0, a 1-byte file with a 1-hour duration -> 8/3600/1000 ≈ 0 kbps.
    // 2. Must return nil (never 0), upholding the "—" display invariant.
    @Test func resolveBitrateFallbackBelowOneKbpsReturnsNil() {
        #expect(ScannerService.resolveBitrate(estimatedDataRate: 0,
                                              fileSizeBytes: 1,
                                              durationSeconds: 3600) == nil)
    }

    // Verifies the estimate branch never returns 0 for a sub-kbps estimate.
    // 1. A tiny positive estimate (400 bits/s -> 0.4 kbps) rounds to 0.
    // 2. With no size/duration to fall back on, the result must be nil, not 0.
    @Test func resolveBitrateSubKbpsEstimateReturnsNil() {
        #expect(ScannerService.resolveBitrate(estimatedDataRate: 400,
                                              fileSizeBytes: nil,
                                              durationSeconds: nil) == nil)
    }

    // Verifies a (non-physical) negative estimate falls through to the formula.
    // 1. estimatedDataRate -1 fails the `> 0` guard.
    // 2. Falls back to size/duration -> 256 kbps, never a negative kbps.
    @Test func resolveBitrateNegativeEstimateFallsBackToFormula() {
        #expect(ScannerService.resolveBitrate(estimatedDataRate: -1,
                                              fileSizeBytes: 230_358_479,
                                              durationSeconds: 7198.5371428571425) == 256)
    }
}