:wave: NFT allows creating token cross-sharing between DAO and DAO.

Using :wave: NFT instead of swapping DAO tokens directly allows token owners to choose whether to continue an unwilling friendship, reducing the psychological hurdle for token cross-sharing.


## Normal flow
1. Requestor sends `wave`, Escrow mints a new :wave: NFT and hold it until the responder answers the request.
2. Responder sends `handshake`, receive the requestor's :wave: NFT from Escrow, and Escrow mints a new :wave: NFT, sends it to the requestor.
https://www.figma.com/file/xU8UfY7V4ndP119KPxPLhH/Friendships?type=whiteboard&node-id=0%3A1&t=r7RNdhpxYGfmnyKg-1

## When the responder denies the friend request
1. Requestor sends `wave`, Escrow mints a new :wave: NFT and hold it until the responder answers the request.
2. Responder sends `deny`, Escrow burns the requestor's :wave: NFT, and withdraws all staking rewards, sends (refunds) the rewards to the requstor.
https://www.figma.com/file/xU8UfY7V4ndP119KPxPLhH/Friendships?type=whiteboard&node-id=0%3A1&t=r7RNdhpxYGfmnyKg-1

## UIs

// Still in progress...

## Proposed major interfaces

/* @dev Send a new :wave: as a friendship request.
 * @param _to Property address of the recipient.
 * @param _from Property address of the requestor.
 * @param _amount Amount of the requestor's token to offer.
 * @param _duration Duration sec for locking the requestor's token as a friendship.
 * @param _payload Reserved unused argument.
 * @return Created :wave: NFT ID.
 */
function wave(
    address _to,
    address _from,
    uint256 _amount,
    uint256 _duration,
    bytes32 _paylod,
) external returns(uint256);

/* @dev Create a friendship. \
 * The caller must be the author of the `_to` Property. (More flexible option??)
 * @param _wave :wave: NFT ID to respond.
 * @param _amount Amount of the responder's token to provide.
 * @param _duration Duration sec for locking the responder's token as a friendship.
 * @param _payload Reserved unused argument.
 * @return Created :wave: NFT ID.
 */
function handshake(
    uint256 _wave,
    uint256 _amount,
    uint256 _duration,
    bytes32 _paylod,
) external returns(uint256);

/* @dev Deny the requested :wave: 👋 \
 * Burn the pending :wave: NFT and release/send the locked Property to the :wave: minter, and withdraw/send all staking rewards to the requestor.
 * The caller must be the author of the `_to` Property. (More flexible option??)
 * @param _wave :wave: NFT ID to close.
 * @return Success or failure.
 */
function deny(uint256 _wave) external returns(bool);

/* @dev Burn :wave: NFT. \
 * Release/send the locked Property to the :wave: minter, and withdraw/send all staking rewards to the friend.
 * The caller must be the :wave: minter, and the given duration must have elapsed.
 * @param _wave :wave: NFT ID to close.
 * @return Success or failure.
 */
function bye(uint256 _wave) external returns(bool);

/* @dev Withdraw all staking rewards from the :wave: and send it to its current owner.
 * @param _wave :wave: NFT ID.
 * @return Success or failure.
 */
function earn(uint256 _wave) external returns(bool);

// Returns the :wave: NFT URI.
function tokenURI(uint256 _id) view returns(string memory);