Event Design

// Define events FIRST, then build the contract around them
interface IVaultEvents {
    event Deposited(address indexed user, address indexed token, uint256 amount, uint256 shares);
    event Withdrawn(address indexed user, address indexed token, uint256 amount, uint256 shares);
    event FeeCollected(address indexed collector, uint256 amount);
    event StrategyUpdated(address indexed oldStrategy, address indexed newStrategy);
    event EmergencyShutdown(address indexed triggeredBy, uint256 timestamp);
}

// GOOD: key actors indexed for filtering, amounts in data for reading
event Transfer(address indexed from, address indexed to, uint256 amount);

// GOOD: token indexed for per-token queries
event Swap(
    address indexed sender,
    address indexed tokenIn,
    address indexed tokenOut,
    uint256 amountIn,
    uint256 amountOut,
    uint256 fee
);

// BAD: indexing a string hashes it — you can't read the original value from the topic
event NameChanged(string indexed name); // topic = keccak256(name), not the string

// GOOD: specific, past tense
event LiquidityAdded(address indexed provider, uint256 amount0, uint256 amount1, uint256 liquidity);
event PositionLiquidated(address indexed owner, address indexed liquidator, uint256 debt, uint256 collateral);
event OracleUpdated(address indexed oldOracle, address indexed newOracle);

// BAD: vague
event Updated(uint256 value);
event Action(address user, uint256 amount);

// Subgraph entity: Position
// Maps to events: PositionOpened, PositionClosed, PositionModified
event PositionOpened(
    uint256 indexed positionId,
    address indexed owner,
    address indexed market,
    bool isLong,
    uint256 size,
    uint256 collateral,
    uint256 entryPrice
);

event PositionClosed(
    uint256 indexed positionId,
    address indexed owner,
    uint256 exitPrice,
    int256 pnl,
    uint256 fee
);

// Include all fields the subgraph handler needs — avoid requiring
// additional contract reads in the handler (those are slow and expensive)

// subgraph handler — events should contain all data needed
export function handlePositionOpened(event: PositionOpened): void {
  let position = new Position(event.params.positionId.toString());
  position.owner = event.params.owner;
  position.market = event.params.market;
  position.isLong = event.params.isLong;
  position.size = event.params.size;
  position.collateral = event.params.collateral;
  position.entryPrice = event.params.entryPrice;
  position.openedAt = event.block.timestamp;
  position.openTxHash = event.transaction.hash;
  position.save();
}

// Saves ~375 gas (one fewer topic), but indexers can't filter by event name
event Transfer(address indexed from, address indexed to, uint256 indexed tokenId, uint256 amount) anonymous;

// A governance proposal should log everything needed for a governance dashboard
event ProposalCreated(
    uint256 indexed proposalId,
    address indexed proposer,
    address[] targets,
    uint256[] values,
    bytes[] calldatas,
    string description,
    uint256 startBlock,
    uint256 endBlock
);

event VoteCast(
    uint256 indexed proposalId,
    address indexed voter,
    uint8 support,      // 0=against, 1=for, 2=abstain
    uint256 weight,
    string reason
);