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, token: String? = nil) -> 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",
        ]

        let tokenQuery = token.map { "?token=\($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\(tokenQuery)")
        }

        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)
    }
}