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HelloYou.sol

pragma solidity ^0.4.18;

// import './SomeContract.sol';

contract HelloYou {
  event Hello(address you);
  
  function sayHello() public {
    address _person = msg.sender;
    
    Hello(_person);
  }
}

Todo.sol

pragma solidity ^0.4.18;

import './TodoBank.sol';
import './TodoStorage.sol';

// @title  Todo
// @author Luke Hedger
contract Todo {
  /*
   * @notice todoBank state variable to store reference to TodoBank contract
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#state-variables
   */
  TodoBank todoBank;

  /*
   * @notice todoStorage state variable to store reference to TodoStorage
   *         contract
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#state-variables
   */
  TodoStorage todoStorage;

  /*
   * @notice TodoAdded event
   * @param {bytes32} todoId
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#events
   */
  event TodoAdded(bytes32 todoId);

  /*
   * @notice Todo contract constructor function - called when creating the
   *         contract. Will instantiate the TodoBank and TodoStorage contracts
   *         at the provided addresses.
   * @param {address} _todoBank    Address of the deployed TodoBank contract
   * @param {address} _todoStorage Address of the deployed TodoStorage contract
   * @see http://solidity.readthedocs.io/en/develop/contracts.html#creating-contracts
   */
  function Todo(address _todoBank, address _todoStorage) public {
    todoBank = TodoBank(_todoBank);

    todoStorage = TodoStorage(_todoStorage);
  }

  /*
   * @notice Method to add a new todo for message sender
   * @param {bytes32} _todoId Swarm hash of todo metadata
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#functions
   */
  function addTodo(bytes32 _todoId) public payable {
    /*
     * @notice Compute `_userId` from hash of `msg.sender` address
     */
    bytes32 _userId = keccak256(msg.sender);

    /*
     * @notice Call the `setTodo` method on the TodoStorage contract
     */
    todoStorage.setTodo(_todoId, _userId);

    /*
     * @notice Call the `setTodoDeposit` method on the TodoBank contract.
     *         `msg.value` sent in transaction is used as the deposit amount.
     */
    todoBank.setTodoDeposit(_todoId, msg.value);

    /*
     * @notice Trigger the `TodoAdded` event
     */
    TodoAdded(_todoId);
  }

  /*
   * @notice Method to get a user's todo by index from the array of todos stored
   * @param  {uint}    _index Index of required todo
   * @return {bytes32} todoId
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#functions
   */
  function getTodo(uint _index) public view returns (bytes32) {
    /*
     * @notice Compute `_userId` from hash of `msg.sender` address
     */
    bytes32 _userId = keccak256(msg.sender);

    /*
     * @notice Call the `getTodoByIndex` method on the TodoStorage contract
     */
    return todoStorage.getTodoByIndex(_index, _userId);
  }

  /*
   * @notice Method to get a user's todo by index from the array of todos stored
   * @return {uint} todoCount
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#functions
   */
  function getTodoCount() public view returns (uint) {
    /*
     * @notice Compute `_userId` from hash of `msg.sender` address
     */
    bytes32 _userId = keccak256(msg.sender);

    /*
     * @notice Call the `getTodoCount` method on the TodoStorage contract.
     */
    return todoStorage.getTodoCount(_userId);
  }
}

TodoBank.sol

pragma solidity ^0.4.18;

// @title  TodoBank
// @author Luke Hedger
contract TodoBank {
  /*
   * @notice Store todo deposit in TodoVault as a mapping of `bytes32` to `uint`
   * @see http://solidity.readthedocs.io/en/develop/types.html#mappings
   */
  mapping(bytes32 => uint) TodoVault;

  /*
   * @notice Get a todo deposit value from the vault
   * @param {bytes32} _todoId
   * @return {uint}   todoDeposit
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#functions
   */
  function getTodoDeposit(bytes32 _todoId) public view returns (uint) {
    /*
     * @notice Get deposit from vault by todoId
     */
    return TodoVault[_todoId];
  }

  /*
   * @notice Set a todo deposit value to the vault
   * @param {bytes32} _todoId
   * @param {uint}    _deposit
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#functions
   */
  function setTodoDeposit(bytes32 _todoId, uint _deposit) public {
    /*
     * @notice Set deposit to vault by todoId
     */
    TodoVault[_todoId] = _deposit;
  }
}

TodoStorage.sol

pragma solidity ^0.4.18;

// @title  TodoStorage
// @author Luke Hedger
contract TodoStorage {
  /*
   * @notice Store todos in TodoStore as a mapping of `bytes32` to `bytes32[]`
   * @see http://solidity.readthedocs.io/en/develop/types.html#mappings
   */
  mapping(bytes32 => bytes32[]) TodoStore;

  /*
   * @notice Get todo by index
   * @param  {uint}    _index
   * @param  {bytes32} _user
   * @return {bytes32} todo
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#functions
   */
  function getTodoByIndex(uint _index, bytes32 _user) public view returns (bytes32) {
    /*
     * @notice Get todo from store by userId and index
     */
    return TodoStore[_user][_index];
  }

  /*
   * @notice Get number of todos for a user
   * @param  {bytes32} _user
   * @return {uint}    todoCount
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#functions
   */
  function getTodoCount(bytes32 _user) public view returns (uint) {
    /*
     * @notice Get length of todo array from store by userId
     */
    return TodoStore[_user].length;
  }

  /*
   * @notice Set a todo to the store
   * @param {bytes32} _todoId
   * @param {bytes32} _user
   * @see https://solidity.readthedocs.io/en/develop/structure-of-a-contract.html#functions
   */
  function setTodo(bytes32 _todoId, bytes32 _user) public {
    /*
     * @notice Push todo to store by userId
     */
    TodoStore[_user].push(_todoId);
  }
}