Library Example

contracts/core/Pool.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity 0.6.12;
+pragma experimental ABIEncoderV2;
+
+import './Position.sol';
+
+contract Pool {
+    using Position for mapping(bytes32 => Position.Info);
+    using Position for Position.Info;
+
+    mapping (bytes32 => Position.Info) public positions;
+
+    function getPosition(
+        address account,
+        address collateralToken,
+        uint256 marketId,
+        bool isLong
+    ) external view returns (Position.Info memory) {
+        return positions.get(account, collateralToken, marketId, isLong);
+    }
+
+    function increasePosition(
+        address account,
+        address collateralToken,
+        uint256 marketId,
+        bool isLong,
+        uint256 sizeDelta,
+        uint256 collateralDelta
+    ) external {
+        Position.Info storage position = positions.get(account, collateralToken, marketId, isLong);
+        position.increase(sizeDelta, collateralDelta);
+    }
+}

contracts/core/Position.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity 0.6.12;
+
+library Position {
+    struct Info {
+        uint256 size;
+        uint256 collateralAmount;
+        uint256 averagePrice;
+        uint256 entryFundingRate;
+        uint256 reserveAmount;
+        uint256 updatedAt;
+    }
+
+    function get(
+        mapping(bytes32 => Info) storage self,
+        address account,
+        address collateralToken,
+        uint256 marketId,
+        bool isLong
+    ) internal view returns (Position.Info storage) {
+         return self[keccak256(abi.encodePacked(account, collateralToken, marketId, isLong))];
+    }
+
+    function increase(
+        Info storage self,
+        uint256 sizeDelta,
+        uint256 collateralDelta
+    ) internal {
+        Info memory _self = self;
+        self.size = _self.size + sizeDelta;
+        self.collateralAmount = _self.collateralAmount + collateralDelta;
+        self.averagePrice = _self.averagePrice + 1;
+        self.entryFundingRate = _self.entryFundingRate + 2;
+        self.reserveAmount = _self.reserveAmount + 3;
+        self.updatedAt = block.timestamp;
+    }
+}

test/core/Pool.js

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+const { expect, use } = require("chai")
+const { solidity } = require("ethereum-waffle")
+const { deployContract } = require("../shared/fixtures")
+const { expandDecimals, getBlockTime, increaseTime, mineBlock, reportGasUsed } = require("../shared/utilities")
+const { toChainlinkPrice } = require("../shared/chainlink")
+const { toUsd, toNormalizedPrice } = require("../shared/units")
+const { initVault, getBnbConfig, getBtcConfig, getDaiConfig, validateVaultBalance } = require("./Vault/helpers")
+
+use(solidity)
+
+const USD_PRECISION = expandDecimals(1, 30)
+
+describe("Pool", function () {
+  const provider = waffle.provider
+  const [wallet, user0, user1, user2, user3] = provider.getWallets()
+  let eth
+  let pool
+
+  beforeEach(async () => {
+    eth = await deployContract("Token", [])
+    pool = await deployContract("Pool", [])
+  })
+
+  it("increasePosition", async () => {
+    await pool.increasePosition(user0.address, eth.address, 17, true, 1000, 200)
+    let position = await pool.getPosition(user0.address, eth.address, 17, true)
+    console.log("position",
+      position.size.toString(),
+      position.collateralAmount.toString(),
+      position.averagePrice.toString(),
+      position.entryFundingRate.toString(),
+      position.reserveAmount.toString(),
+      position.updatedAt.toString()
+    )
+
+    await pool.increasePosition(user0.address, eth.address, 17, true, 500, 100)
+
+    position = await pool.getPosition(user0.address, eth.address, 17, true)
+    console.log("position",
+      position.size.toString(),
+      position.collateralAmount.toString(),
+      position.averagePrice.toString(),
+      position.entryFundingRate.toString(),
+      position.reserveAmount.toString(),
+      position.updatedAt.toString()
+    )
+  })
+})