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hello.sol

pragma solidity >=0.4.22 <0.6.0;

contract HelloWorld {
    
    string greeting = "Hello world";
    address last_updater;
    
    mapping (address => string[]) public greetings_map;
    
    event HelloEvent(string);
    
    function hello() public returns (string memory) {
        emit HelloEvent(greeting);
        return (greeting);
    }
    
    function updateMessage(string memory _greeting) public {
        greetings_map[msg.sender].push(_greeting);
        greeting = _greeting;
        last_updater = msg.sender;
    }

    function getMessage(address user, uint i) public view returns(string memory) {
        string[] memory greetings = greetings_map[user];
        if (i >= greetings.length) {
            return "";
        }
        return greetings[i];
    }
    
    function latestMessage() public view returns (string memory, address) {
        return (greeting, last_updater);
    }
}