Solidity exercise: multi-signed contract

MultiSignedContract.sol

pragma solidity ^0.4.18;

/**
 * All authorities must approved each defined action
 * */
contract MultiSignedContract {
    
    address owner;
    address[] authorities;
    mapping (string => address[]) internal actions;
    
    function MultiSignedContract() public {
        owner = msg.sender;
        authorities.push(owner);
    }
   
    function addAuthority(address user) public {
        require(msg.sender == owner);
        
        bool alreadyExists = false;
        for(uint i = 0; i < authorities.length; i++) {
            if(authorities[i] == user) {
                alreadyExists = true;
            }
        }
        
        if(!alreadyExists) {
            authorities.push(user);
        }
    }
    
    function addAction(string actionName) public returns(bool) {
        require(msg.sender == owner);
        
        if(actions[actionName].length == 0) {
            actions[actionName].push(msg.sender);
            return true;
        }
        return false;
    }
    
    event Approved(string actionName);
    
    function approveAction(string actionName) public returns(int){
        
        // check action exists
        if(actions[actionName].length == 0) {
            return 0;
        }
        
        // sign
        if(!userAlreadySigned(actionName, msg.sender)) {
            actions[actionName].push(msg.sender);
            return 1;
        }
        
        // emmit event if all authorities already signed
        if(actionIsApproved(actionName)) {
            Approved(actionName);
            return 2;
        }
    }
    
    function userAlreadySigned(string actionName, address user) public view returns(bool) {
        
        for(uint i = 0; i < actions[actionName].length; i++) {
            if(actions[actionName][i] == user) {
                return true;
            }
        }
        return false;
    }
    
    function actionIsApproved(string actionName) public view returns(bool) {
        
        if(authorities.length == 0) {
            return false;
        }
        
        uint i = 0;
        bool approved = true;
        
        do {
           approved = approved && userAlreadySigned(actionName, authorities[i]);
           i++;
        } while( approved && i < authorities.length);
        
        return approved;
    }
}