DTwitter.sol

pragma solidity ^0.4.24;

contract DTwitter {
    /**
     * User
     *
     * Struct holding the profile deatils of the user.
     */
    struct User {
        uint creationDate;      // date user was created
        string username;        // username of the user
        string description;     // user profile description
        address owner;          // address of the account who created the user
        string picture;         // IFPS hash of the user's profile picture
        string[] tweets;        // array that holds the user's tweets
    }

    /**
     * users
     *
     * Maps the keccak256 hash of a username to the deatils of the user
     *
     * {bytes32} [KEY] the keccak256 hash of the username
     * {User} the User struct containing the deatils of the user
     */
    mapping (bytes32 => User) public users;

    
    /**
     * owners
     *
     * Maps the address of the owner account to the username hash of the 
     * owned user. This is needed so we can retrieve an account from the
     * current address
     *
     * {address} [KEY] the address of the owner who owns the user
     * {bytes32} the keccak256 hash of the username
     */
    mapping (address => bytes32) public owners;

    /**
     * NewTweet
     *
     * Event to be emitted once a tweet is stored in the contract
     * {bytes32} _from - keccak256-hashed username of user who posted the tweet.
     *                          This field is indexed so it can be filtered.
     * {string} tweet - the tweet contents
     */
    event NewTweet(
        bytes32 indexed _from,
        string tweet,
        uint time
    );

    /**
     * createAccount
     *
     * Creates a user account, storing the user (and user details) in the contract.
     * Additionally, a mapping is created between the owner who created the user
     * (msg.sender) and the keccak256-hash of the username
     * {string} username - the username of the user
     * {string} description - the user profile description
     */
    function createAccount(string username, string description) public {
        // ensure a null or empty string wasn't passed in
        require(bytes(username).length > 0);

        // generate the username hash using keccak
        bytes32 usernameHash = keccak256(abi.encodePacked(username));

        // reject if username already registered
        require(users[usernameHash].creationDate == 0);

        // reject if sending adddress already created a user
        require(owners[msg.sender] == 0);

        // add a user to the users mapping and populate details 
        // (creationDate, owner, username, description)
        users[usernameHash].creationDate = now;
        users[usernameHash].owner = msg.sender;
        users[usernameHash].username = username;
        users[usernameHash].description = description;
        // add entry to our owners mapping so we can retrieve
        // user by their address
        owners[msg.sender] = usernameHash;
    }

    /**
     * editAccount
     *
     * Edits the deteails of a user's profile.
     * {bytes32} usernameHash - the keccak256-hashed username of the user to edit
     * {string} description (optional) - the updated user profile description
     * {string} pictureHash (optional) - the IFPS hash of the user's updated profile picture
     */
    function editAccount(bytes32 usernameHash, string description, string pictureHash) public {
        // ensure the user exists and that the creator of the user is the
        // sender of the transaction
        require(users[usernameHash].owner == msg.sender);

        // update the description (could be empty)
        users[usernameHash].description = description;
        // only update the user's picture if the hash passed in is
        if (bytes(pictureHash).length > 0) {
        users[usernameHash].picture = pictureHash;
        }
        // not empty or null (essentially disallows deletions)
    }

    /**
     * userExists
     *
     * Validates whether or not a user has an account in the user mapping
     * {bytes32} usernameHash - the keccak256-hashed username of the user to validate
     * {bool} - returns true if the hashed username exists in the user mapping, false otherwise
     */
    function userExists(bytes32 usernameHash) public view returns (bool) {
        // must check a property... bc solidity!
        return users[usernameHash].creationDate != 0;
    }

    /**
     * tweet
     *
     * Adds a tweet to the user's tweets and emits an event notifying listeners
     * that a tweet happened. Assumes the user sending the transaction is the tweeter.
     * {string} content - the tweet content
     */
    function tweet(string content) public {
        // ensure the sender has an account
        require(owners[msg.sender].length > 0);

        // get the username hash of the sender's account
        bytes32 usernameHash = owners[msg.sender];

        // get our user
        User storage user = users[usernameHash];
        // get our new tweet index
        uint tweetIndex = user.tweets.length++;
        // update the user's tweets at the tweet index
        user.tweets[tweetIndex] = content;
        // emit the tweet event and notify the listeners
        emit NewTweet(usernameHash, content, now);
    }

}