Kata

Vowel harmony is a phenomenon in some languages. It means that "A vowel or vowels in a word are changed to sound the same (thus "in harmony.")" (wikipedia). This kata is based on vowel harmony in Hungarian.

Task:

Your goal is to create a function dative() (Dative() in C#) which returns the valid form of a valid Hungarian word w in dative case i. e. append the correct suffix nek or nak to the word w based on vowel harmony rules.

Vowel Harmony Rules (simplified)

When the last vowel in the word is

1. a front vowel (e, é, i, í, ö, ő, ü, ű) the suffix is -nek
2. a back vowel (a, á, o, ó, u, ú) the suffix is -nak

Examples:

dative("ablak") == "ablaknak"
dative("szék") == "széknek"
dative("otthon") == "otthonnak"

dative("ablak") == "ablaknak"
dative("szék") == "széknek"
dative("otthon") == "otthonnak"

dative("ablak"); // "ablaknak"
dative("szék"); // "széknek"
dative("otthon"); // "otthonnak"

dative "ablak"   -- "ablaknak"
dative "szék"    -- "széknek"
dative "otthon"  -- "otthonnak"

Kata.dative("ablak") == "ablaknak"
Kata.dative("szék") == "széknek"
Kata.dative("otthon") == "otthonnak"

Kata.Dative("ablak") == "ablaknak"
Kata.Dative("szék") == "széknek"
Kata.Dative("otthon") == "otthonnak"

Kata.dative("ablak") == "ablaknak"
Kata.dative("szék") == "széknek"
Kata.dative("otthon") == "otthonnak"

Kata.dative("ablak") == "ablaknak"
Kata.dative("szék") == "széknek"
Kata.dative("otthon") == "otthonnak"

Dative("ablak") ==> "ablaknak", nil
Dative("szék") ==> "széknek", nil
Dative("otthon") ==> "otthonnak", nil

dative("ablak") // "ablaknak"
dative("szék") // "széknek"
dative("otthon") // "otthonnak"

Preconditions:

1. To keep it simple: All words end with a consonant :)
2. All strings are unicode strings.
3. There are no grammatical exceptions in the tests.