NMKeyConverter.h

//
//  NMKeyConverter.h
//  NMKit
//
//  Created by Nicholas Moore on 23/12/2011.
//  Copyright (c) 2011 __MyCompanyName__. All rights reserved.
//

#import <Foundation/Foundation.h>
#include <Carbon/Carbon.h>

@interface NMKeyConverter : NSObject

@property (readonly) TISInputSourceRef sourceRef;
@property (readonly) NSString *keyboardLayoutName;
@property (readonly) NSString *inputSourceId;

+ (NMKeyConverter *)currentKeyConverter;
+ (NMKeyConverter *)qwertyKeyConverter;
- (id)initWithInputSourceRef:(TISInputSourceRef) sourceRef;

- (NSString *)charForKeyCode:(CGKeyCode)keyCode;
- (NSNumber *)keyCodeForChar:(NSString *)character commandDown:(BOOL)commandDown;
    
@end

NMKeyConverter.m

//
//  NMKeyConverter.m
//  NMKit
//
//  Created by Nicholas Moore on 23/12/2011.
//  Copyright (c) 2011 __MyCompanyName__. All rights reserved.
//

#import "NMKeyConverter.h"
#import "NMRegexUtils.h"

@interface NMKeyConverter ()
@property TISInputSourceRef sourceRef;
@property NSString *keyboardLayoutName;
@property NSData *keyboardLayoutData;
@property NSString *inputSourceId;
@property NSDictionary *charToKeyCode;

@end

@implementation NMKeyConverter

+ (NMKeyConverter *)currentKeyConverter
{
    static NMKeyConverter *currentKeyConverter=nil;
    
    // get the current input source
    const TISInputSourceRef sourceRef = TISCopyCurrentASCIICapableKeyboardLayoutInputSource();
    if (sourceRef) {
        if (!currentKeyConverter) {
            currentKeyConverter=[[NMKeyConverter alloc] initWithInputSourceRef:sourceRef];
        }
        else if ([currentKeyConverter sourceRef] != sourceRef) {
            currentKeyConverter=[[NMKeyConverter alloc] initWithInputSourceRef:sourceRef];
        }
        CFRelease(sourceRef);
    }
    
    return currentKeyConverter;
}

// get a stable QWERTY layout for when input source is Dvorak - QWERTY ⌘
// https://stackoverflow.com/questions/28184241/tis-services-selecting-czech
+ (NMKeyConverter *)qwertyKeyConverter
{
    static NMKeyConverter *qwertyKeyConverter=nil;
    
    if (!qwertyKeyConverter) {
        NSDictionary* properties = @{ (__bridge NSString*)kTISPropertyInputSourceID: @"com.apple.keylayout.ABC" };
        NSArray* sources = CFBridgingRelease(TISCreateInputSourceList((__bridge CFDictionaryRef)properties, NO));
        TISInputSourceRef sourceRef = (__bridge TISInputSourceRef)sources.firstObject;
        if (sourceRef) {
            qwertyKeyConverter=[[NMKeyConverter alloc] initWithInputSourceRef:sourceRef];
        }
    }
    
    return qwertyKeyConverter;
}


- (id)initWithInputSourceRef:(TISInputSourceRef) sourceRef
{
    self=[super init];
    if (self)
    {
        if (!sourceRef) {
            NMLogError(@"No keyboard input source.");
            return nil;
        }

        if (sourceRef) {
            CFRetain(sourceRef);
        }
        self.sourceRef=sourceRef;
        self.keyboardLayoutName=(__bridge NSString*)TISGetInputSourceProperty(_sourceRef, kTISPropertyLocalizedName);
        self.inputSourceId=(__bridge NSString*)TISGetInputSourceProperty(_sourceRef, kTISPropertyInputSourceID);
        self.keyboardLayoutData=(__bridge NSData*)TISGetInputSourceProperty(_sourceRef, kTISPropertyUnicodeKeyLayoutData);
        if (!self.keyboardLayoutData) {
            NMLogError(@"No keyboard layout data. Name: %@", _keyboardLayoutName);
            return nil;
        }
        
        // now build the lookup dictionary
        const int KEYCODE_COUNT=128;
        _charToKeyCode=[NSMutableDictionary dictionaryWithCapacity:KEYCODE_COUNT];
        for (int i=0; i<KEYCODE_COUNT; i++) {
            NSString *c=[self charForKeyCode:i];
            if (c) {
                ((NSMutableDictionary *)_charToKeyCode)[c] = @(i);
            }
        }
        NMLogFine(@"Created KeyConverter with ID %@ and layout name %@", self.inputSourceId, self.keyboardLayoutName);

    }

    return self;
}

- (void)dealloc
{
    if (_sourceRef) {
        CFRelease(_sourceRef);
    }
}

- (NSString *)charForKeyCode:(CGKeyCode)keyCode
{
    NSString *result=nil;
    
    const int MAX_STRING_LENGTH=4;
    UniChar unicodeString[MAX_STRING_LENGTH];
    UniCharCount actualStringLength=0;
    UInt32 deadKeyState=0;
    
    UCKeyTranslate((UCKeyboardLayout *)[_keyboardLayoutData bytes], 
                   keyCode, 
                   kUCKeyActionDisplay, 
                   0, 
                   LMGetKbdType(), 
                   kUCKeyTranslateNoDeadKeysBit, 
                   &deadKeyState, 
                   MAX_STRING_LENGTH, 
                   &actualStringLength, 
                   unicodeString);
    
    if (actualStringLength==1) {
        result=[[NSString stringWithCharacters:unicodeString length:1] uppercaseString];          
    }

    return result;
}

- (NSNumber *)keyCodeForChar:(NSString *)character commandDown:(BOOL)commandDown
{
    if (commandDown&&[self.inputSourceId isEqualToString:@"com.apple.keylayout.DVORAK-QWERTYCMD"]) {
        return [[NMKeyConverter qwertyKeyConverter] keyCodeForChar:character commandDown:NO];
    }    
    return _charToKeyCode[character];
}

@end