feat: add HLSManifestGenerator with TDD tests

MusicShared/Sources/MusicShared/HLSManifestGenerator.swift

@@ -0,0 +1,42 @@
+import Foundation
+
+public enum HLSManifestGenerator: Sendable {
+    public struct TimeRange: Equatable, Sendable {
+        public var start: Double
+        public var duration: Double
+    }
+
+    public static func manifest(trackId: Int64, duration: Double, segmentDuration: Double) -> String {
+        let count = segmentCount(duration: duration, segmentDuration: segmentDuration)
+        let targetDuration = Int(segmentDuration.rounded(.up))
+
+        var lines: [String] = [
+            "#EXTM3U",
+            "#EXT-X-VERSION:3",
+            "#EXT-X-TARGETDURATION:\(targetDuration)",
+            "#EXT-X-MEDIA-SEQUENCE:0",
+        ]
+
+        for i in 0..<count {
+            let range = segmentTimeRange(index: i, trackDuration: duration, segmentDuration: segmentDuration)
+            lines.append(String(format: "#EXTINF:%.3f,", range.duration))
+            lines.append("segments/\(i).mp3")
+        }
+
+        lines.append("#EXT-X-ENDLIST")
+        lines.append("")
+        return lines.joined(separator: "\n")
+    }
+
+    public static func segmentCount(duration: Double, segmentDuration: Double) -> Int {
+        guard duration > 0, segmentDuration > 0 else { return 0 }
+        return Int((duration / segmentDuration).rounded(.up))
+    }
+
+    public static func segmentTimeRange(index: Int, trackDuration: Double, segmentDuration: Double) -> TimeRange {
+        let start = Double(index) * segmentDuration
+        let remaining = trackDuration - start
+        let duration = min(segmentDuration, remaining)
+        return TimeRange(start: start, duration: duration)
+    }
+}

MusicShared/Tests/MusicSharedTests/HLSManifestGeneratorTests.swift

@@ -0,0 +1,78 @@
+import Testing
+@testable import MusicShared
+
+struct HLSManifestGeneratorTests {
+    // Generates a manifest for a 16-second track with 6s segments.
+    // Expects 3 segments: 6s, 6s, 4s (remainder).
+    @Test func generatesCorrectManifestForTypicalTrack() {
+        let manifest = HLSManifestGenerator.manifest(
+            trackId: 42,
+            duration: 16.0,
+            segmentDuration: 6.0
+        )
+
+        #expect(manifest.contains("#EXTM3U"))
+        #expect(manifest.contains("#EXT-X-VERSION:3"))
+        #expect(manifest.contains("#EXT-X-TARGETDURATION:6"))
+        #expect(manifest.contains("#EXT-X-MEDIA-SEQUENCE:0"))
+        #expect(manifest.contains("#EXTINF:6.000,"))
+        #expect(manifest.contains("#EXTINF:4.000,"))
+        #expect(manifest.contains("segments/0.mp3"))
+        #expect(manifest.contains("segments/1.mp3"))
+        #expect(manifest.contains("segments/2.mp3"))
+        #expect(!manifest.contains("segments/3.mp3"))
+        #expect(manifest.contains("#EXT-X-ENDLIST"))
+    }
+
+    // A track whose duration is an exact multiple of the segment duration.
+    // Expects no short final segment.
+    @Test func exactMultipleOfSegmentDuration() {
+        let manifest = HLSManifestGenerator.manifest(
+            trackId: 1,
+            duration: 12.0,
+            segmentDuration: 6.0
+        )
+
+        let segmentCount = manifest.components(separatedBy: "#EXTINF:6.000,").count - 1
+        #expect(segmentCount == 2)
+        #expect(!manifest.contains("segments/2.mp3"))
+    }
+
+    // A very short track (shorter than one segment).
+    // Expects a single segment with the track's full duration.
+    @Test func veryShortTrack() {
+        let manifest = HLSManifestGenerator.manifest(
+            trackId: 7,
+            duration: 2.5,
+            segmentDuration: 6.0
+        )
+
+        #expect(manifest.contains("#EXTINF:2.500,"))
+        #expect(manifest.contains("segments/0.mp3"))
+        #expect(!manifest.contains("segments/1.mp3"))
+    }
+
+    // Segment count helper returns the correct number of segments.
+    @Test func segmentCountCalculation() {
+        #expect(HLSManifestGenerator.segmentCount(duration: 16.0, segmentDuration: 6.0) == 3)
+        #expect(HLSManifestGenerator.segmentCount(duration: 12.0, segmentDuration: 6.0) == 2)
+        #expect(HLSManifestGenerator.segmentCount(duration: 2.5, segmentDuration: 6.0) == 1)
+        #expect(HLSManifestGenerator.segmentCount(duration: 6.0, segmentDuration: 6.0) == 1)
+    }
+
+    // Time range for a given segment index returns correct start and duration.
+    @Test func segmentTimeRange() {
+        // Track: 16s, segment: 6s → segments at 0-6, 6-12, 12-16
+        let range0 = HLSManifestGenerator.segmentTimeRange(
+            index: 0, trackDuration: 16.0, segmentDuration: 6.0
+        )
+        #expect(range0.start == 0.0)
+        #expect(range0.duration == 6.0)
+
+        let range2 = HLSManifestGenerator.segmentTimeRange(
+            index: 2, trackDuration: 16.0, segmentDuration: 6.0
+        )
+        #expect(range2.start == 12.0)
+        #expect(range2.duration == 4.0)
+    }
+}