Implements attachment previewing

kordophone2/Transcript/TranscriptDisplayItems.swift

@@ -0,0 +1,61 @@
+//
+//  TranscriptDisplayItems.swift
+//  kordophone2
+//
+//  Created by James Magahern on 8/24/25.
+//
+
+import Foundation
+import SwiftUI
+
+extension TranscriptView.ViewModel
+{
+    internal func rebuildDisplayItems(animated: Bool = false) {
+        var displayItems: [DisplayItem] = []
+        var lastDate: Date = .distantPast
+        
+        let client = XPCClient()
+        let dateAnnotationTimeInterval: TimeInterval = 60 * 60 * 30 // 30m
+        for message in messages {
+            if message.date.timeIntervalSince(lastDate) > dateAnnotationTimeInterval {
+                lastDate = message.date
+                displayItems.append(.date(message.date))
+            }
+            
+            for attachment in message.attachments {
+                displayItems.append(.attachment(attachment))
+                
+                if !attachment.isPreviewDownloaded {
+                    Task.detached {
+                        try await client.downloadAttachment(attachmentId: attachment.id, preview: true)
+                    }
+                }
+            }
+            
+            displayItems.append(.message(message))
+        }
+        
+        let animation: Animation? = animated ? .default : nil
+        withAnimation(animation) {
+            self.displayItems = displayItems
+        }
+    }
+}
+
+enum DisplayItem: Identifiable
+{
+    case message(Display.Message)
+    case attachment(Display.ImageAttachment)
+    case date(Date)
+    
+    var id: String {
+        switch self {
+        case .message(let message):
+            message.id
+        case .attachment(let attachment):
+            attachment.id
+        case .date(let date):
+            date.description
+        }
+    }
+}