Keyboard: scroll up/down with vim bindings

App/Browser View/BrowserViewController+Keyboard.swift

@@ -7,6 +7,51 @@
 
 import Foundation
 
+@objc
+protocol VIMBindings
+{
+    func scrollDownPressed(_ sender: Any?)
+    func scrollUpPressed(_ sender: Any?)
+}
+
+extension BrowserViewController: VIMBindings
+{
+    static let keyboardScrollAmount: CGFloat = 33.0
+    
+    override var keyCommands: [UIKeyCommand]? {
+        get {
+            [
+                UIKeyCommand(input: "j", modifierFlags: [], action: #selector(VIMBindings.scrollDownPressed)),
+                UIKeyCommand(input: "k", modifierFlags: [], action: #selector(VIMBindings.scrollUpPressed)),
+            ]
+        }
+    }
+    
+    override func canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool {
+        if action == #selector(VIMBindings.scrollDownPressed) || action == #selector(VIMBindings.scrollUpPressed) {
+            return webView._currentContentView().isFocusingElement == false
+        }
+        
+        return super.canPerformAction(action, withSender: sender)
+    }
+    
+    func scrollDownPressed(_ sender: Any?) {
+        var offset = webView.scrollView.contentOffset
+        offset.y += Self.keyboardScrollAmount
+        offset.y = min(offset.y, webView.scrollView.contentSize.height - webView.scrollView.bounds.height)
+        
+        webView.scrollView.setContentOffset(offset, animated: false)
+    }
+    
+    func scrollUpPressed(_ sender: Any?) {
+        var offset = webView.scrollView.contentOffset
+        offset.y -= Self.keyboardScrollAmount
+        offset.y = max(offset.y, webView.scrollView.contentInset.top)
+        
+        webView.scrollView.setContentOffset(offset, animated: false)
+    }
+}
+
 extension BrowserViewController: ShortcutResponder
 {
     internal func updateCommandKeyState(forPresses presses: Set<UIPress>) {