WIP: iOS Keyboard Shortcut for Emacs

UITextView+EmacsKeyboardShortcut.swift

//
//  UITextView+Ext.swift
//  BTKeyboardInputTest
//
//  Created by Shingo Fukuyama on 10/10/16.
//  Copyright © 2016 Shingo Fukuyama. All rights reserved.
//

import UIKit

extension UITextView {
    
    func ext_caretTo(position: Int) {
        guard self.isFirstResponder else { return }
        if let newPosition = self.ext_position(fromInt: position) {
            self.ext_caretTo(textPosition: newPosition)
        }
    }
    
    func ext_caretTo(textPosition position: UITextPosition) {
        guard self.isFirstResponder else { return }
        self.selectedTextRange = self.textRange(from: position, to: position)
    }
    
    func ext_caretPosition() -> Int {
        if let selectedTextRange = self.selectedTextRange {
            let caretPosition = self.ext_beginningOffset(textPosition: selectedTextRange.start)
            return caretPosition
        }
        return 0
    }
    
    func ext_selectAll() {
        self.selectedTextRange = self.textRange(from: self.beginningOfDocument, to: self.endOfDocument)
    }
    
    func ext_beginningOffset(textPosition: UITextPosition) -> Int {
        return self.offset(from: self.beginningOfDocument, to: textPosition)
    }
    
    func ext_position(fromInt: Int) -> UITextPosition? {
        return self.position(from: self.beginningOfDocument, in: UITextLayoutDirection.right, offset: fromInt)
    }
    
    func ext_select(from: Int, to: Int) {
        if let start = self.ext_position(fromInt: from),
            let end = self.ext_position(fromInt: to) {
            self.selectedTextRange = self.textRange(from: start, to: end)
        }
    }
    
    func ext_caretForward() {
        guard self.isFirstResponder else { return }
        guard let range = self.selectedTextRange else { return }
        if let pos = self.position(from: range.start, offset: 1) {
            self.ext_caretTo(textPosition: pos)
        }
    }
    
    func ext_caretBackward() {
        guard self.isFirstResponder else { return }
        guard let range = self.selectedTextRange else { return }
        if let pos = self.position(from: range.start, offset: -1) {
            self.ext_caretTo(textPosition: pos)
        }
    }
    
    func ext_caretUpward() {
        guard let range = self.selectedTextRange else { return }
        guard let lineHeight = self.font?.lineHeight else { return }
        var caret = self.firstRect(for: range)
        // At the end of the last line of the document
        if caret.origin.y == CGFloat.infinity {
            guard let rangeTo = self.position(from: range.start, offset: -1) else { return }
            guard let newRange = self.textRange(from: range.start, to: rangeTo) else { return }
            caret = self.firstRect(for: newRange)
            caret.origin.y += lineHeight
        }
        caret.origin.y = max(caret.origin.y - lineHeight, 0)
        caret.size.width = 1
        if let pos = self.closestPosition(to: caret.origin) {
            self.selectedTextRange = self.textRange(from: pos, to: pos)
        }
    }
    
    func ext_caretDownward() {
        guard let range = self.selectedTextRange else { return }
        guard let lineHeight = self.font?.lineHeight else { return }
        var caret = self.firstRect(for: range)
        // At the end of the last line of the document
        if caret.origin.y == CGFloat.infinity {
            return
        }
        caret.origin.y = max(caret.origin.y + lineHeight, 0)
        caret.size.width = 1
        if let pos = self.closestPosition(to: caret.origin) {
            self.selectedTextRange = self.textRange(from: pos, to: pos)
        }
    }
    
    func ext_setupKeyboardShortcuts(controller: UIViewController) {
        
        let cf = UIKeyCommand(input: "f", modifierFlags: .control, action: #selector(ext_caretForward))
        let cb = UIKeyCommand(input: "b", modifierFlags: .control, action: #selector(ext_caretBackward))
        let cp = UIKeyCommand(input: "p", modifierFlags: .control, action: #selector(ext_caretUpward))
        let cn = UIKeyCommand(input: "n", modifierFlags: .control, action: #selector(ext_caretDownward))
        controller.addKeyCommand(cf)
        controller.addKeyCommand(cb)
        controller.addKeyCommand(cp)
        controller.addKeyCommand(cn)
        
        let clf = UIKeyCommand(input: "f", modifierFlags: .alphaShift, action: #selector(ext_caretForward))
        let clb = UIKeyCommand(input: "b", modifierFlags: .alphaShift, action: #selector(ext_caretBackward))
        let clp = UIKeyCommand(input: "p", modifierFlags: .alphaShift, action: #selector(ext_caretUpward))
        let cln = UIKeyCommand(input: "n", modifierFlags: .alphaShift, action: #selector(ext_caretDownward))
        controller.addKeyCommand(clf)
        controller.addKeyCommand(clb)
        controller.addKeyCommand(clp)
        controller.addKeyCommand(cln)
        
        // Command+Space cannot override the default one
        //let sSPC = UIKeyCommand(input: " ", modifierFlags: .command, action: #selector())
        //controller.addKeyCommand(sSPC)
    }

}