mixboard/Sources/Export/DAWProjectExporter.swift

import Foundation

/// Exports a playlist in the DAWproject open exchange format.
/// DAWproject is an open standard for DAW session interchange developed by
/// Bitwig and PreSonus. It's supported by Bitwig Studio, Studio One, REAPER, and others.
///
/// A .dawproject file is a ZIP archive containing:
///   - project.xml  (session metadata, tracks, clips, markers)
///   - metadata.xml (basic project info)
///   - Audio Files/  (referenced audio files)
struct DAWProjectExporter: DAWExporter {
    static let formatID = "dawproject"
    static let formatName = "DAWproject"
    static let fileExtension = "dawproject"

    static func export(playlist: Playlist, to url: URL, options: ExportOptions) throws {
        let entries = playlist.sortedEntries
        let sampleRate = options.targetSampleRate ?? 44100

        // DAWproject is a ZIP, but for simplicity we'll write the XML and provide
        // instructions for bundling. For a complete implementation, use ZIPFoundation.
        // Here we export the project.xml which is the core of the format.

        let xmlURL = url.deletingPathExtension().appendingPathExtension("dawproject.xml")

        let projectXML = buildProjectXML(
            playlist: playlist,
            entries: entries,
            sampleRate: sampleRate,
            options: options
        )

        let metadataXML = buildMetadataXML(playlist: playlist)

        // Write project XML
        try projectXML.write(to: xmlURL, atomically: true, encoding: .utf8)

        // Write metadata alongside
        let metadataURL = url.deletingLastPathComponent()
            .appendingPathComponent("metadata.xml")
        try metadataXML.write(to: metadataURL, atomically: true, encoding: .utf8)
    }

    // MARK: - Project XML

    private static func buildProjectXML(
        playlist: Playlist,
        entries: [PlaylistEntry],
        sampleRate: Double,
        options: ExportOptions
    ) -> String {
        var xml = """
        <?xml version="1.0" encoding="UTF-8"?>
        <Project version="1.0">
            <Application name="MixBoard" version="1.0" />
            <Transport>
                <Tempo max="200" min="60" value="\(playlist.targetBPM ?? 120)" />
                <TimeSignature denominator="4" numerator="4" />
            </Transport>
            <Structure>
                <Track contentType="audio" name="\(escapeXML(playlist.name))" color="#4A90D9">
                    <Channel role="regular" audioChannels="2">
                        <Volume max="2" min="0" value="1" />
                        <Pan max="1" min="-1" value="0" />
                    </Channel>
                </Track>
            </Structure>
            <Arrangement>
                <Lanes>
                    <Lanes track="0">

        """

        var timelinePosition: TimeInterval = 0

        for (index, entry) in entries.enumerated() {
            guard let track = entry.track,
                  let fileURL = options.effectiveFileURL(for: track) else { continue }

            let clipStart = timelinePosition
            let startOffset = entry.startOffset
            let clipDuration = entry.effectiveDuration
            let relativePath = "\(options.audioFilesRelativePath)/\(fileURL.lastPathComponent)"

            // Apply crossfade overlap
            if index > 0 {
                timelinePosition -= entry.crossfadeDuration
            }

            xml += """
                            <Clip time="\(clipStart)" duration="\(clipDuration)" name="\(escapeXML(track.title))">
                                <Audio>
                                    <File path="\(escapeXML(relativePath))" />
                                    <Playback offset="\(startOffset)" duration="\(clipDuration)" />
                                </Audio>

            """

            // Gain adjustment
            if entry.gainAdjustment != 0 {
                xml += """
                                <Gain value="\(entry.gainAdjustment)" />

                """
            }

            // Crossfades
            if options.includeCrossfades {
                if entry.crossfadeDuration > 0 {
                    xml += """
                                <FadeIn duration="\(entry.crossfadeDuration)" curve="linear" />

                    """
                }
                if index + 1 < entries.count, entries[index + 1].crossfadeDuration > 0 {
                    xml += """
                                <FadeOut duration="\(entries[index + 1].crossfadeDuration)" curve="linear" />

                    """
                }
            }

            xml += """
                            </Clip>

            """

            timelinePosition = clipStart + clipDuration
        }

        xml += """
                    </Lanes>
                </Lanes>
            </Arrangement>

        """

        // Markers
        if options.includeCuePoints {
            xml += "    <Markers>\n"
            var markerTimeline: TimeInterval = 0

            for (index, entry) in entries.enumerated() {
                guard let track = entry.track else { continue }
                if index > 0 {
                    markerTimeline -= entry.crossfadeDuration
                }

                for cuePoint in track.cuePoints.sorted() {
                    let markerTime = markerTimeline + cuePoint.timestamp - entry.startOffset
                    let name = cuePoint.name.isEmpty ? cuePoint.type.rawValue : cuePoint.name
                    xml += """
                    <Marker time="\(markerTime)" name="\(escapeXML(name))" color="\(cuePoint.color)" />

                    """
                }

                markerTimeline += entry.effectiveDuration
            }

            xml += "    </Markers>\n"
        }

        xml += """
        </Project>
        """

        return xml
    }

    // MARK: - Metadata XML

    private static func buildMetadataXML(playlist: Playlist) -> String {
        """
        <?xml version="1.0" encoding="UTF-8"?>
        <MetaData>
            <Title>\(escapeXML(playlist.name))</Title>
            <Artist></Artist>
            <Comment>Exported from MixBoard</Comment>
            <CreatedAt>\(ISO8601DateFormatter().string(from: Date()))</CreatedAt>
        </MetaData>
        """
    }

    private static func escapeXML(_ string: String) -> String {
        string
            .replacingOccurrences(of: "&", with: "&amp;")
            .replacingOccurrences(of: "<", with: "&lt;")
            .replacingOccurrences(of: ">", with: "&gt;")
            .replacingOccurrences(of: "\"", with: "&quot;")
    }
}