MNG-19 Create rankingService.js (#33)

* Create rankingService.js

* MNG-19 Update rankingService.js

some small changes and:
- removed print to html function
- created update from localStorage function

src/service/rankingService.js

@@ -0,0 +1,49 @@
+export const rankingService = (mode, user) => {
+  const PokemonApiRanking = checkLocalStorage(); //update from localStorage
+  let currentMode; //path to scores array for current mode
+  switch(mode) {
+    case WHO_IS_THAT_POKEMON:
+      currentMode = PokemonApiRanking.mode1.scores;
+    break;
+    case WHAT_DOES_THIS_POKEMON_LOOK_LIKE:
+      currentMode = PokemonApiRanking.mode2.scores;
+    break;
+    case GUESS_THE_TYPE:
+      currentMode = PokemonApiRanking.mode3.scores;
+    break;
+    default:
+      throw new Error('Wrong game mode!');
+  }
+  currentMode.push(user);
+  currentMode.sort( (a,b) => {
+    const scoreCompare = b.score - a.score;
+    if(scoreCompare != 0) { // compare scores
+      return scoreCompare;
+    } else { // scores are the same => compare times
+      return b.timeInSeconds - a.timeInSeconds;
+    }
+   } );
+  if(currentMode.length > 3) {
+    currentMode.pop();
+  }
+
+  localStorage.setItem('PokemonApiRanking', JSON.stringify(PokemonApiRanking)); //save in localStorage
+}
+
+const checkLocalStorage = () => {
+  const PokemonApiRanking = JSON.parse(localStorage.getItem('PokemonApiRanking')) || {
+    mode1: {
+      name : "Whos that pokemon?",
+      scores : []
+    },
+    mode2: {
+      name : "What it looks like?",
+      scores : []
+    },
+    mode3: {
+      name : "Guess the type!",
+      scores : []
+    }
+  }
+  return PokemonApiRanking;
+}