OneCAD-Draft/crates/dwg-thumbnailer/macos/ThumbnailProvider.swift

// macOS QuickLook thumbnail extension for DWG files.
//
// Calls the Rust core (`dwg_thumbnail_png`, linked from libdwg_thumbnailer.a)
// to extract the embedded preview as PNG, then hands it to QuickLook.
//
// Add this file to a "Thumbnail Extension" target, expose the C ABI through a
// bridging header that #includes `dwg_thumbnailer.h`, and link the static lib
// (see README). QLSupportedContentTypes must list the DWG UTI (com.autodesk.dwg).

import QuickLookThumbnailing
import CoreGraphics
import ImageIO
import Foundation

final class ThumbnailProvider: QLThumbnailProvider {
    override func provideThumbnail(
        for request: QLFileThumbnailRequest,
        _ handler: @escaping (QLThumbnailReply?, Error?) -> Void
    ) {
        let maxDim = UInt32(max(request.maximumSize.width, request.maximumSize.height))

        var ptr: UnsafeMutablePointer<UInt8>? = nil
        var len: Int = 0
        let ok = request.fileURL.path.withCString { cpath in
            dwg_thumbnail_png(cpath, maxDim, &ptr, &len)
        }
        guard ok, let p = ptr, len > 0 else {
            handler(nil, nil) // no preview → QuickLook falls back
            return
        }
        let data = Data(bytes: p, count: len)
        dwg_thumbnail_free(p, len)

        guard
            let src = CGImageSourceCreateWithData(data as CFData, nil),
            let cg = CGImageSourceCreateImageAtIndex(src, 0, nil)
        else {
            handler(nil, nil)
            return
        }

        // Fit and center the embedded bitmap in the requested thumbnail.
        let maxSize = request.maximumSize
        let nativeSize = CGSize(width: cg.width, height: cg.height)
        let scale = min(maxSize.width / nativeSize.width, maxSize.height / nativeSize.height)
        let drawSize = CGSize(width: nativeSize.width * scale, height: nativeSize.height * scale)
        let origin = CGPoint(x: (maxSize.width - drawSize.width) / 2, y: (maxSize.height - drawSize.height) / 2)

        let reply = QLThumbnailReply(contextSize: maxSize) { (ctx: CGContext) -> Bool in
            ctx.draw(cg, in: CGRect(origin: origin, size: drawSize))
            return true
        }
        handler(reply, nil)
    }
}