new tests

DBSyn/DiagramLogic.swift

@@ -0,0 +1,25 @@
+import Foundation
+import CoreGraphics
+
+/// Pure schema-diagram operations shared by the UI and XCTest suite.
+enum DiagramLogic {
+    static func selectedObjects(_ requested: Set<String>, available: [String]) -> Set<String> {
+        requested.intersection(Set(available))
+    }
+
+    static func arrangedPositions(_ names: [String]) -> [String: CGPoint] {
+        let countPerRow = max(1, Int(ceil(sqrt(Double(max(1, names.count))))))
+        var positions: [String: CGPoint] = [:]
+        for (index, name) in names.enumerated() {
+            positions[name] = CGPoint(x: CGFloat(index % countPerRow) * 290 + 30,
+                                      y: CGFloat(index / countPerRow) * 300 + 30)
+        }
+        return positions
+    }
+
+    static func translatedPosition(_ origin: CGPoint, translation: CGSize, zoom: CGFloat) -> CGPoint {
+        let scale = max(zoom, 0.1)
+        return CGPoint(x: origin.x + translation.width / scale,
+                       y: origin.y + translation.height / scale)
+    }
+}