Improve stability of thumbnail url generation

Sources/NextcloudFileProviderKit/Metadata/ItemMetadata.swift

@@ -162,15 +162,18 @@
         guard hasPreview else {
             return nil
         }
-
-        let urlBase = urlBase.urlEncoded!
-        // Leave the leading slash in webdavUrl
-        let webdavUrl = urlBase + Account.webDavFilesUrlSuffix + user
-        let serverFileRelativeUrl =
-            serverUrl.replacingOccurrences(of: webdavUrl, with: "") + "/" + fileName
-
-        let urlString =
-            "\(urlBase)/index.php/core/preview.png?file=\(serverFileRelativeUrl)&x=\(size.width)&y=\(size.height)&a=1&mode=cover"
-        return URL(string: urlString)
+        guard #available(macOS 13.0, iOS 16.0, visionOS 1.0, *) else {
+            return URL(
+                string: "\(urlBase.urlEncoded ?? "")/index.php/core/preview?fileId=\(fileId)&x=\(size.width)&y=\(size.height)&a=true"
+            )
+        }
+        return URL(string: urlBase.urlEncoded ?? "")?
+            .appending(components: "index.php", "core", "preview")
+            .appending(queryItems: [
+                .init(name: "fileId", value: fileId),
+                .init(name: "x", value: "\(size.width)"),
+                .init(name: "y", value: "\(size.height)"),
+                .init(name: "a", value: "true")
+            ])
     }
 }

Tests/NextcloudFileProviderKitTests/ItemMetadataTests.swift

@@ -0,0 +1,23 @@
+//
+//  ItemMetadataTests.swift
+//  NextcloudFileProviderKit
+//
+//  Created by Claudio Cambra on 23/5/25.
+//
+
+import Foundation
+import Testing
+@testable import NextcloudFileProviderKit
+
+struct ItemMetadataTests {
+    @Test func thumbnailUrlCorrect() {
+        let account =
+            Account(user: "user", id: "id", serverUrl: "https://examplecloud.com", password: "bla")
+        var item = SendableItemMetadata(ocId: "ec-test", fileName: "test.txt", account: account)
+        item.fileId = "test"
+        item.hasPreview = true
+        let expectedUrl = URL(string: "https://examplecloud.com/index.php/core/preview?fileId=test&x=250.0&y=250.0&a=true")
+        #expect(expectedUrl != nil)
+        #expect(item.thumbnailUrl(size: .init(width: 250, height: 250)) == expectedUrl)
+    }
+}