108 lines
2.6 KiB
Solidity
108 lines
2.6 KiB
Solidity
pragma solidity ^0.5.0;
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// @notice Contract to create posts
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contract DReddit {
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enum Ballot { NONE, UPVOTE, DOWNVOTE }
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struct Post {
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uint creationDate;
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string description;
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address owner;
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uint upvotes;
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uint downvotes;
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mapping(address => Ballot) voters;
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}
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Post[] public posts;
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event NewPost (
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uint indexed postId,
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address owner,
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string description
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);
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event Vote(
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uint indexed postId,
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address voter,
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uint8 vote
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);
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// @notice Number of posts created
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// @return Num of posts
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function numPosts()
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public
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view
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returns(uint)
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{
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return posts.length;
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}
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// @notice Create Post
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// @param _ipfsHash IPFS hash of the content of the post
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function create(string memory _ipfsHash) public
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{
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require(bytes(_ipfsHash).length > 0, "IPFS hash is required");
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posts.push(Post({
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creationDate: now,
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description: _ipfsHash,
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owner: msg.sender,
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upvotes: 0,
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downvotes: 0
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}));
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emit NewPost(posts.length - 1, msg.sender, _ipfsHash);
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}
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// @notice Vote on a post
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// @param _postId Id of the post to up/downvote
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// @param _vote Vote selection: 0 -> none, 1 -> upvote, 2 -> downvote
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function vote(uint _postId, uint8 _vote)
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public
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{
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Post storage p = posts[_postId];
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require(p.creationDate != 0, 'Post does not exist.');
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require(p.voters[msg.sender] == Ballot.NONE, 'You already voted on this post.');
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Ballot b = Ballot(_vote);
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require(b != Ballot.NONE, 'Invalid vote');
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if (b == Ballot.UPVOTE) {
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p.upvotes++;
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} else {
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p.downvotes++;
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}
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p.voters[msg.sender] = b;
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emit Vote(_postId, msg.sender, _vote);
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}
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// @notice Determine if the sender can vote on a post
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// @param _postId Id of the post
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// @return bool that indicates if the sender can vote or not
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function canVote(uint _postId)
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public
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view
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returns (bool)
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{
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if (_postId > posts.length - 1) return false;
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Post storage p = posts[_postId];
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return (p.voters[msg.sender] == Ballot.NONE);
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}
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// @notice Obtain vote for specific post
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// @param _postId Id of the post
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// @return uint that represents the vote: 0 -> none, 1 -> upvote, 2 -> downvote
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function getVote(uint _postId)
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public
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view
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returns (uint8)
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{
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Post storage p = posts[_postId];
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return uint8(p.voters[msg.sender]);
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}
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}
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