1  pragma solidity ^0.5.0;
 2  
 3  contract DReddit {
 4  
 5    enum Ballot { NONE, UPVOTE, DOWNVOTE }
 6  
 7    struct Post {
 8      uint creationDate;   
 9      bytes description;   
10      address owner;
11      uint upvotes;
12      uint downvotes;
13      mapping(address => Ballot) voters;
14    }
15  
16    Post [] public posts;
17  
18    event NewPost(
19      uint indexed postId,
20      address owner,
21      bytes description
22    );
23  
24    event NewVote(
25      uint indexed postId,
26      address owner,
27      uint8 vote
28    );
29  
30    function createPost(bytes memory _description) public {
31      uint postId = posts.length++;
32  
33      posts[postId] = Post({
34        creationDate: block.timestamp,
35        description: _description,
36        owner: msg.sender,
37        upvotes: 0,
38        downvotes: 0
39      });
40  
41      emit NewPost(postId, msg.sender, _description);
42    }
43  
44    function vote(uint _postId, uint8 _vote) public {
45      Post storage post = posts[_postId];
46  
47      require(post.creationDate != 0, "Post does not exist");
48      require(post.voters[msg.sender] == Ballot.NONE, "You already voted on this post");
49  
50      Ballot ballot = Ballot(_vote);
51  
52      if (ballot == Ballot.UPVOTE) {
53          post.upvotes++;
54      } else {
55          post.downvotes++;
56      }
57  
58      post.voters[msg.sender] = ballot;
59      emit NewVote(_postId, msg.sender, _vote);
60    }
61  
62    function canVote(uint _postId) public view returns (bool) {
63      if (_postId > posts.length - 1) return false;
64      Post storage post = posts[_postId];
65      return (post.voters[msg.sender] == Ballot.NONE);
66    }
67  
68    function getVote(uint _postId) public view returns (uint8) {
69      Post storage post = posts[_postId];
70      return uint8(post.voters[msg.sender]);
71    }
72  
73    function numPosts() public view returns (uint) {
74      return posts.length;
75    }
76  }
77