import SwiftUI
import AppKit


enum DJPasteboardPayload {
    static func song(_ pasteboard: NSPasteboard) -> SongDragReference? {
        guard let text = pasteboard.string(forType:.string),text.hasPrefix("KJMix.song.v1:"),
              let data = Data(base64Encoded:String(text.dropFirst("KJMix.song.v1:".count))) else { return nil }
        return try? JSONDecoder().decode(SongDragReference.self,from:data)
    }
    static func files(_ pasteboard: NSPasteboard) -> [URL] {
        (pasteboard.readObjects(forClasses:[NSURL.self],options:[.urlReadingFileURLsOnly:true]) as? [URL] ?? []).filter(\.isFileURL)
    }
}

struct DJLibraryDragTitle: NSViewRepresentable {
    let title: String
    let reference: SongDragReference
    let fontSize: Double
    let select: () -> Void
    var doubleClick: (() -> Void)? = nil
    var selectAll: (() -> Void)? = nil
    func makeNSView(context: Context) -> DJLibraryDragView { DJLibraryDragView() }
    func updateNSView(_ view: DJLibraryDragView,context: Context) {
        let redraw = view.title != title || view.fontSize != fontSize
        view.title = title;view.reference = reference;view.fontSize = fontSize;view.select = select;view.doubleClick = doubleClick;view.selectAllTracks = selectAll
        if redraw {
            view.toolTip = "Double-click to load alternating decks, or drag \(title) to either deck";view.setAccessibilityLabel(title);view.needsDisplay = true
        }
    }
    func sizeThatFits(_ proposal: ProposedViewSize,nsView: DJLibraryDragView,context: Context) -> CGSize? { .init(width:proposal.width ?? 240,height:24) }
}

final class DJLibraryDragView: NSView {
    var title = ""
    var reference: SongDragReference?
    var fontSize: Double = 11
    var select: (() -> Void)?
    var doubleClick: (() -> Void)?
    var selectAllTracks: (() -> Void)?
    override var acceptsFirstResponder: Bool { true }
    @objc override func selectAll(_ sender: Any?) { selectAllTracks?() }
    private var armed = false
    private var dragging = false
    override init(frame: NSRect) { super.init(frame:frame);setAccessibilityElement(true);setAccessibilityRole(.staticText) }
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }
    override func acceptsFirstMouse(for event: NSEvent?) -> Bool { true }
    override func draw(_ dirtyRect: NSRect) {
        let paragraph = NSMutableParagraphStyle();paragraph.lineBreakMode = .byTruncatingTail
        let font = NSFont.systemFont(ofSize:fontSize,weight:.medium)
        let rect = NSRect(x:0,y:(bounds.height-ceil(font.ascender-font.descender))/2,width:bounds.width,height:ceil(font.ascender-font.descender)+2)
        (title as NSString).draw(in:rect,withAttributes:[.font:font,.foregroundColor:NSColor.white,.paragraphStyle:paragraph])
    }
    override func mouseDown(with event: NSEvent) { window?.makeFirstResponder(self);armed = true;dragging = false }
    override func mouseDragged(with event: NSEvent) {
        guard armed else { return }
        dragging = true
        NSCursor.closedHand.set()
        for target in DJNativeDropView.targets.allObjects where target.window === window {
            let inside = !target.isHiddenOrHasHiddenAncestor && target.bounds.contains(target.convert(event.locationInWindow,from:nil))
            target.layer?.borderWidth = inside ? 2 : 0
            target.layer?.borderColor = target.tint.cgColor
        }
    }
    override func mouseUp(with event: NSEvent) {
        defer {
            armed = false;dragging = false;NSCursor.arrow.set()
            for target in DJNativeDropView.targets.allObjects { target.layer?.borderWidth = 0 }
        }
        guard dragging,let reference,let window else { select?();if armed,event.clickCount == 2 { doubleClick?() };return }
        for target in DJNativeDropView.targets.allObjects where target.window === window && !target.isHiddenOrHasHiddenAncestor {
            if target.bounds.contains(target.convert(event.locationInWindow,from:nil)),target.validSong?(reference) == true {
                let receive = target.acceptSong
                DispatchQueue.main.async { receive?(reference) }
                break
            }
        }
    }

}

struct DJDeckDropZone<Content: View>: NSViewRepresentable {
    let system: DJSystem
    let letter: String
    let content: Content
    init(system: DJSystem,letter: String,@ViewBuilder content: () -> Content) { self.system = system;self.letter = letter;self.content = content() }
    func makeNSView(context: Context) -> DJNativeDropView {
        let view = DJNativeDropView();updateNSView(view,context:context);return view
    }
    func updateNSView(_ view: DJNativeDropView,context: Context) {
        view.host.rootView = AnyView(content.environment(\.colorScheme,context.environment.colorScheme))
        view.tint = letter == "A" ? .systemCyan : .systemOrange
        view.acceptSong = { [weak system] reference in
            guard let system,reference.library == system.dragSession,let song = system.songs.first(where:{$0.id == reference.song}) else { return }
            if letter == "Queue" { system.automix.enqueue([song]) } else { system.load(song,into:letter) }
        }
        view.acceptFiles = letter == "Queue" ? nil : { [weak system] urls in system?.requestFileLoad(urls,into:letter) }
        view.validSong = { [weak system] reference in reference.library == system?.dragSession }
    }
    func sizeThatFits(_ proposal: ProposedViewSize,nsView: DJNativeDropView,context: Context) -> CGSize? {
        .init(width:proposal.width ?? nsView.host.fittingSize.width,height:proposal.height ?? nsView.host.fittingSize.height)
    }
}

final class DJNativeDropView: NSView {
    static let targets = NSHashTable<DJNativeDropView>.weakObjects()
    let host = DJDropHostingView(rootView:AnyView(EmptyView()))
    var tint = NSColor.systemCyan
    var acceptSong: ((SongDragReference) -> Void)?
    var acceptFiles: (([URL]) -> Void)?
    var validSong: ((SongDragReference) -> Bool)?
    override init(frame: NSRect) {
        super.init(frame:frame);Self.targets.add(self);registerForDraggedTypes([.string,.fileURL]);wantsLayer = true
        host.dropTarget = self;host.registerForDraggedTypes([.string,.fileURL])
        host.translatesAutoresizingMaskIntoConstraints = false;addSubview(host)
        NSLayoutConstraint.activate([host.leadingAnchor.constraint(equalTo:leadingAnchor),host.trailingAnchor.constraint(equalTo:trailingAnchor),host.topAnchor.constraint(equalTo:topAnchor),host.bottomAnchor.constraint(equalTo:bottomAnchor)])
    }
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }
    private func accepts(_ pasteboard: NSPasteboard) -> Bool {
        if let song = DJPasteboardPayload.song(pasteboard) { return validSong?(song) == true }
        return !DJPasteboardPayload.files(pasteboard).isEmpty
    }
    override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
        let allowed = accepts(sender.draggingPasteboard)
        layer?.borderWidth = allowed ? 2 : 0;layer?.borderColor = tint.cgColor
        return allowed ? .copy : []
    }
    override func draggingUpdated(_ sender: NSDraggingInfo) -> NSDragOperation { accepts(sender.draggingPasteboard) ? .copy : [] }
    override func draggingExited(_ sender: NSDraggingInfo?) { layer?.borderWidth = 0 }
    override func prepareForDragOperation(_ sender: NSDraggingInfo) -> Bool { accepts(sender.draggingPasteboard) }
    override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
        layer?.borderWidth = 0
        if let song = DJPasteboardPayload.song(sender.draggingPasteboard),validSong?(song) == true {
            let receive = acceptSong
            // Finish the native dragging session before a load rebuilds any SwiftUI rows.
            DispatchQueue.main.async { receive?(song) };return true
        }
        let files = DJPasteboardPayload.files(sender.draggingPasteboard)
        guard !files.isEmpty else { return false }
        let receive = acceptFiles;DispatchQueue.main.async { receive?(files) };return true
    }
    override func concludeDragOperation(_ sender: NSDraggingInfo?) { layer?.borderWidth = 0 }
}

// NSHostingView participates in AppKit drag destination lookup itself. Forward
// its callbacks so embedded SwiftUI content cannot shadow the deck destination.
final class DJDropHostingView: NSHostingView<AnyView> {
    weak var dropTarget: DJNativeDropView?
    override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation { dropTarget?.draggingEntered(sender) ?? [] }
    override func draggingUpdated(_ sender: NSDraggingInfo) -> NSDragOperation { dropTarget?.draggingUpdated(sender) ?? [] }
    override func draggingExited(_ sender: NSDraggingInfo?) { dropTarget?.draggingExited(sender) }
    override func prepareForDragOperation(_ sender: NSDraggingInfo) -> Bool { dropTarget?.prepareForDragOperation(sender) ?? false }
    override func performDragOperation(_ sender: NSDraggingInfo) -> Bool { dropTarget?.performDragOperation(sender) ?? false }
    override func concludeDragOperation(_ sender: NSDraggingInfo?) { dropTarget?.concludeDragOperation(sender) }
}