# Specification

Perennial's intent system has a light footprint onchain. It uses a few modules ot extend the standard `update()` functionality of the markets. 

## Intent Structure

Intents take the form of an EIP-712 signed message. Below is the structure of an intent order:

```json
{
  "amount":            // The size and direction of the order being opened by the taker
                       //       - Positive opens long / Negative opens short
                       //       - The maker will open the opposite side of the order
                       //       - To close, open an order in the opposite direction
  "price":             // The price to execute the order at
  "fee":               // The solver fee, a percentage of the substractive interface fee
  "originator":        // The referral address of the originator of the order (ex. the interface)
  "solver":            // The referral address of the solver of the order (ex. the router)   
  "collateralization": // The minimium collateralization ratio that must be maintained after the order is executed
  "common": {
    "account": // The target account of the message (usually the account on behalf of which the action is being performed)
    "signer":  // EOA signing the message (usually either the account or a delegate of the account)
    "domain":  // ensures the message is unique to a particular protocol version, chain, and verifier
    "nonce":   // per-sender nonce which is automatically cancelled upon validation
    "group":   // per-sender nonce which must be manually cancelled with a GroupCancellation message
    "expiry":  // prevents this message from having the intended effect after a specified timestamp
  }
}
```

## Market - Update()

These signed Intents submitted by a **Maker** to the intent specific `update()` function on each market instance. 

```solidity
/// @notice Updates both the long and short positions of an intent order
/// @dev - One side is specified in the signed intent, while the sender is assumed to be the counterparty
///      - The sender is charged the settlement fee
/// @param account The account that is filling this intent (maker)
/// @param intent The intent that is being filled
/// @param signature The signature of the intent that is being filled
function update(address account, Intent calldata intent, bytes memory signature) external nonReentrant whenNotPaused {
    if (intent.fee.gt(UFixed6Lib.ONE)) revert MarketInvalidIntentFeeError();

    verifier.verifyIntent(intent, signature);

    _updateIntent(
        account,
        address(0),
        intent.amount.mul(Fixed6Lib.NEG_ONE),
        intent.price,
        address(0),
        address(0),
        UFixed6Lib.ZERO,
        UFixed6Lib.ZERO,
        true,
        false
    ); // account
    _updateIntent(
        intent.common.account,
        intent.common.signer,
        intent.amount,
        intent.price,
        intent.originator,
        intent.solver,
        intent.fee,
        intent.collateralization,
        false,
        true
    ); // signer
}
```

See the file [here](https://github.com/equilibria-xyz/perennial-v2/blob/v2.3/packages/perennial/contracts/Market.sol#L144)

## Intent Verifier

Key to operation of the intent system is the intent verifier. This contract checks the validity of the intent, the signature, and if the signer is approved as a signer on the account.

You can learn more about this module [here](https://github.com/equilibria-xyz/perennial-v2/tree/v2.3/packages/perennial-verifier)

## Other Modules

* [Trigger Orders](https://github.com/equilibria-xyz/perennial-v2/blob/v2.3/packages/perennial-order/README.md) - A specification for trigger based orders in Perennial
* [Collateral Accounts](https://github.com/equilibria-xyz/perennial-v2/tree/v2.3/packages/perennial-account) -  A collateral management system that enables 1-click-trading