ownable

pragma solidity ^0.4.21;

contract Ownable {
    address public owner;
    
    event OwnerChanged(address oldOwner, address newOwner);
    
    function Ownable() {
        owner = msg.sender;
    }
    
    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }
    
    function changeOwner(address _newOwner) external onlyOwner {
        address oldOwner = owner;
        owner = _newOwner;
        OwnerChanged(oldOwner, _newOwner);
    }
}

contract Greeting is Ownable {
    struct GreetingItem {
        string greeting;
        address greeter;
    }
    
    modifier hasNotGreetYet() {
        require(greetingsMap[msg.sender].greeter == address(0));
        _;
    }
    
    mapping(address => GreetingItem) greetingsMap;
    
    uint count;
    address lastGreeterAddress;
    address owner;
    
    event NewGreetingCreated(address newGreeter, string newGreeting);
    
    function Greeting() public {
    
    }
    
    function greet(string _greeting) hasNotGreetYet onlyOwner public {
        count += 1;
        GreetingItem memory greetingItem = GreetingItem(_greeting, msg.sender);
        greetingsMap[msg.sender] = greetingItem;
        lastGreeterAddress = msg.sender;
        NewGreetingCreated(msg.sender, _greeting);
    }
    
    function getGreeting() public constant returns (string lastGreeting, address lastGreeter, uint lastCount) {
        GreetingItem storage greetingItem = greetingsMap[lastGreeterAddress];
        return (greetingItem.greeting, greetingItem.greeter, count);
    }
}