A short script to center the foremost window on screen

center-window.swift

#!/usr/bin/env swift

import AppKit

// Function to get the frontmost window
func getFrontmostWindow() -> AXUIElement? {
    guard let app = NSWorkspace.shared.frontmostApplication else {
        return nil
    }
    let appElement = AXUIElementCreateApplication(app.processIdentifier)
    var value: CFTypeRef?
    let result = AXUIElementCopyAttributeValue(appElement, kAXFocusedWindowAttribute as CFString, &value)
    return result == .success ? (value as! AXUIElement) : nil
}

// Function to get the monitor where the window is located
func getMonitorForWindow(_ window: AXUIElement) -> NSScreen? {
    var windowFrame = CGRect.zero
    var value: CFTypeRef?
    if AXUIElementCopyAttributeValue(window, kAXPositionAttribute as CFString, &value) == .success,
       AXValueGetValue(value as! AXValue, .cgPoint, &windowFrame.origin) {
        if AXUIElementCopyAttributeValue(window, kAXSizeAttribute as CFString, &value) == .success,
           AXValueGetValue(value as! AXValue, .cgSize, &windowFrame.size) {
            return NSScreen.screens.first(where: { $0.frame.intersects(windowFrame) })
        }
    }
    return nil
}

// Function to set window position
func setWindowPosition(_ window: AXUIElement, position: CGPoint) {
    var mutablePosition = position
    if let positionValue = AXValueCreate(AXValueType.cgPoint, &mutablePosition) {
        AXUIElementSetAttributeValue(window, kAXPositionAttribute as CFString, positionValue)
    }
}

// Function to get window size
func getWindowSize(_ window: AXUIElement) -> CGSize? {
    var value: CFTypeRef?
    if AXUIElementCopyAttributeValue(window, kAXSizeAttribute as CFString, &value) == .success {
        var windowSize = CGSize.zero
        if AXValueGetValue(value as! AXValue, .cgSize, &windowSize) {
            return windowSize
        }
    }
    return nil
}

// Main execution
if let window = getFrontmostWindow(), let windowSize = getWindowSize(window) {
    if let screen = getMonitorForWindow(window) ?? NSScreen.main {
        let screenFrame = screen.visibleFrame
        let newX = screenFrame.origin.x + (screenFrame.width - windowSize.width) / 2
        let newY = screenFrame.origin.y + (screenFrame.height - windowSize.height) / 2
        setWindowPosition(window, position: CGPoint(x: newX, y: newY))
    }
}