[FEATURE] Escrow contract

[YoshihitoAso]

1. Is your feature request related to a problem? Please describe.

• I'd like to add a simple contract for escrowing tokens.

2. Describe the solution you'd like

• The specifications are as follows

Specifications

State

• balances（コントラクト入庫残高）

  // account => token => amount
  mapping(address => mapping(address => uint256)) private balances;

• commitments（エスクロー中数量：拘束数量）

  // account => token => amount
  mapping(address => mapping(address => uint256)) private commitments;

• latest escrow id（直近エスクローID）

  uint256 public latestEscrowId

Methods

• token fallback

  /// @param _from アカウントアドレス：残高を保有するアドレス
  /// @param _value デポジット数量
  function tokenFallback(address _from, uint _value, bytes memory /*_data*/) public

• withdraw

  /// @param _token トークンアドレス
  /// @return 処理結果
  function withdraw(address _token)

• create escrow

  /// @param _token トークンアドレス
  /// @param _recipient トークン受領者
  /// @param _amount 数量
  /// @param _agent エスクローエージェント
  /// @param _data イベント出力用の任意のデータ
  function createEscrow(
  address _token,
  address _recipient,
  uint256 _amount,
  address _agent,
  string memory _data
  )

• cancel escrow

  /// @param _escrowId エスクローID
  function cancelEscrow(uint256 _escrowId)

• finish escrow

  /// @param _escrowId エスクローID
  function finishEscrow(uint256 _escrowId)

Events

• escrow created

  event EscrowCreated(
  uint256 indexed escrowId,
  address indexed token,
  address sender,
  address recipient,
  uint256 amount,
  address agent,
  string data
  );

• escrow canceled

  event EscrowCanceled(
  uint256 indexed escrowId,
  address indexed token,
  address sender,
  address recipient,
  uint256 amount,
  address agent
  );

• escrow finished

  event EscrowFinished(
  uint256 indexed escrowId,
  address indexed token,
  address sender,
  address recipient,
  uint256 amount,
  address agent
  );

• withdrawn

  event Withdrawn(
  address indexed token,
  address indexed account
  );