duplicate vote prevention

teropa · Sep 10, 2015 · 3371786 · 3371786 · mark-stephenson- · May 15, 2018
1 parent 80b1cd6
commit 3371786
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Showing 4 changed files with 68 additions and 15 deletions.
diff --git a/src/core.js b/src/core.js
@@ -34,14 +34,29 @@ export function next(state) {
   }
 }
 
-export function vote(voteState, entry) {
+function removePreviousVote(voteState, voter) {
+  const previousVote = voteState.getIn(['votes', voter]);
+  if (previousVote) {
+    return voteState.updateIn(['tally', previousVote], t => t - 1)
+                    .removeIn(['votes', voter]);
+  } else {
+    return voteState;
+  }
+}
+
+function addVote(voteState, entry, voter) {
   if (voteState.get('pair').includes(entry)) {
-    return voteState.updateIn(
-      ['tally', entry],
-      0,
-      tally => tally + 1
-    );
+    return voteState.updateIn(['tally', entry], 0, t => t + 1)
+                    .setIn(['votes', voter], entry);
   } else {
     return voteState;
   }
 }
+
+export function vote(voteState, entry, voter) {
+  return addVote(
+    removePreviousVote(voteState, voter),
+    entry,
+    voter
+  );
+}
diff --git a/src/reducer.js b/src/reducer.js
@@ -8,7 +8,7 @@ export default function reducer(state = INITIAL_STATE, action) {
     return next(state);
   case 'VOTE':
     return state.update('vote',
-                        voteState => vote(voteState, action.entry));
+                        voteState => vote(voteState, action.entry, action.clientId));
   }
   return state;
 }
diff --git a/test/core_spec.js b/test/core_spec.js
@@ -120,13 +120,16 @@ describe('application logic', () => {
         vote(Map({
           round: 1,
           pair: List.of('Trainspotting', '28 Days Later')
-        }), 'Trainspotting')
+        }), 'Trainspotting', 'voter1')
       ).to.equal(
         Map({
           round: 1,
           pair: List.of('Trainspotting', '28 Days Later'),
           tally: Map({
             'Trainspotting': 1
+          }),
+          votes: Map({
+            voter1: 'Trainspotting'
           })
         })
       );
@@ -140,15 +143,47 @@ describe('application logic', () => {
           tally: Map({
             'Trainspotting': 3,
             '28 Days Later': 2
-          })
-        }), 'Trainspotting')
+          }),
+          votes: Map()
+        }), 'Trainspotting', 'voter1')
       ).to.equal(
         Map({
           round: 1,
           pair: List.of('Trainspotting', '28 Days Later'),
           tally: Map({
             'Trainspotting': 4,
             '28 Days Later': 2
+          }),
+          votes: Map({
+            voter1: 'Trainspotting'
+          })
+        })
+      );
+    });
+
+    it('nullifies previous vote for the same voter', () => {
+      expect(
+        vote(Map({
+          round: 1,
+          pair: List.of('Trainspotting', '28 Days Later'),
+          tally: Map({
+            'Trainspotting': 3,
+            '28 Days Later': 2
+          }),
+          votes: Map({
+            voter1: '28 Days Later'
+          })
+        }), 'Trainspotting', 'voter1')
+      ).to.equal(
+        Map({
+          round: 1,
+          pair: List.of('Trainspotting', '28 Days Later'),
+          tally: Map({
+            'Trainspotting': 4,
+            '28 Days Later': 1
+          }),
+          votes: Map({
+            voter1: 'Trainspotting'
           })
         })
       );

diff --git a/test/reducer_spec.js b/test/reducer_spec.js
@@ -39,14 +39,17 @@ describe('reducer', () => {
       },
       entries: []
     });
-    const action = {type: 'VOTE', entry: 'Trainspotting'};
+    const action = {type: 'VOTE', entry: 'Trainspotting', clientId: 'voter1'};
     const nextState = reducer(initialState, action);
 
     expect(nextState).to.equal(fromJS({
       vote: {
         round: 1,
         pair: ['Trainspotting', '28 Days Later'],
-        tally: {Trainspotting: 1}
+        tally: {Trainspotting: 1},
+        votes: {
+          voter1: 'Trainspotting'
+        }
       },
       entries: []
     }));
@@ -64,9 +67,9 @@ describe('reducer', () => {
     const actions = [
       {type: 'SET_ENTRIES', entries: ['Trainspotting', '28 Days Later']},
       {type: 'NEXT'},
-      {type: 'VOTE', entry: 'Trainspotting'},
-      {type: 'VOTE', entry: '28 Days Later'},
-      {type: 'VOTE', entry: 'Trainspotting'},
+      {type: 'VOTE', entry: 'Trainspotting', clientId: 'voter1'},
+      {type: 'VOTE', entry: '28 Days Later', clientId: 'voter2'},
+      {type: 'VOTE', entry: 'Trainspotting', clientId: 'voter3'},
       {type: 'NEXT'}
     ];
     const finalState = actions.reduce(reducer, Map());