Give mixed selections something to do

A Drag of different kinds showed an empty wheel, because the catalog only
answers for a single category. Filee's answer is a mixed profile, so add
Zip (one archive, flat names) and Merge (non-PDFs are converted to PDF
first); a multi-file drag of one kind gets Zip too.

Sources/Konverter/Core/Tools.swift

@@ -20,7 +20,7 @@ enum ToolID: String, CaseIterable, Identifiable, Codable {
     // Subtitles
     case shiftSubtitle
     // Archives
-    case extractArchive, listArchive
+    case extractArchive, listArchive, createArchive
     // Media metadata
     case mediaInfo
 
@@ -65,6 +65,7 @@ enum ToolID: String, CaseIterable, Identifiable, Codable {
         case .shiftSubtitle: return "Shift Time"
         case .extractArchive: return "Extract"
         case .listArchive: return "List Contents"
+        case .createArchive: return "Zip"
         case .mediaInfo: return "Info"
         }
     }
@@ -100,6 +101,7 @@ enum ToolID: String, CaseIterable, Identifiable, Codable {
         case .shiftSubtitle: return "clock.arrow.circlepath"
         case .extractArchive: return "archivebox"
         case .listArchive: return "list.bullet.rectangle"
+        case .createArchive: return "doc.zipper"
         }
     }
 
@@ -122,7 +124,7 @@ enum ToolID: String, CaseIterable, Identifiable, Codable {
             return .spreadsheet
         case .shiftSubtitle:
             return .subtitle
-        case .extractArchive, .listArchive:
+        case .extractArchive, .listArchive, .createArchive:
             return .archive
         case .mediaInfo:
             return .video
@@ -131,7 +133,10 @@ enum ToolID: String, CaseIterable, Identifiable, Codable {
 
     /// Tools that only make sense for a multi-file selection.
     var requiresMultipleFiles: Bool {
-        self == .mergePDF || self == .imagesToPDF || self == .collageImages
+        switch self {
+        case .mergePDF, .imagesToPDF, .collageImages, .createArchive: return true
+        default: return false
+        }
     }
 
     var minimumFileCount: Int { requiresMultipleFiles ? 2 : 1 }
@@ -151,6 +156,26 @@ enum ToolID: String, CaseIterable, Identifiable, Codable {
     static func tools(for category: FileCategory) -> [ToolID] {
         allCases.filter { $0.category == category }
     }
+
+    /// Tools that accept a drag of mixed kinds. When a selection cannot become
+    /// one format, there is still something useful to do with it: Filee calls
+    /// this a mixed profile, and it is why its donut is never empty.
+    static func combineTools(for urls: [URL]) -> [ToolID] {
+        guard urls.count >= 2 else { return [] }
+        var tools: [ToolID] = []
+        if urls.allSatisfy(canBecomePDF) { tools.append(.mergePDF) }
+        tools.append(.createArchive)
+        return tools
+    }
+
+    /// Kinds that `Converter` knows how to turn into a PDF, which is what
+    /// ``mergePDF`` needs from anything that is not a PDF already.
+    static func canBecomePDF(_ url: URL) -> Bool {
+        switch FileKind.category(of: url) {
+        case .image, .pdf, .document, .slides, .spreadsheet, .ebook: return true
+        default: return false
+        }
+    }
 }
 
 /// One editable field in a tool's options form.
@@ -256,6 +281,8 @@ extension ToolID {
             ]
         case .shiftSubtitle:
             return [ToolField("offset", "Shift by", .decimal(min: -600, max: 600), default: "1", unit: "s")]
+        case .createArchive:
+            return [ToolField("name", "Archive name", .text, default: "Archive", help: "Saved beside the first file")]
         case .listArchive, .extractArchive, .wordCount, .mediaInfo, .readQR, .stripMetadata,
              .grayscaleImage, .normalizeAudio, .extractPDFText, .documentToPDF, .sheetsToCSV,
              .muteVideo, .mergePDF, .imagesToPDF: