add getOceanNeeded

package-lock.json

@@ -2786,6 +2786,11 @@
       "integrity": "sha1-9lNNFRSCabIDUue+4m9QH5oZEpA=",
       "dev": true
     },
+    "decimal.js": {
+      "version": "10.2.0",
+      "resolved": "https://registry.npmjs.org/decimal.js/-/decimal.js-10.2.0.tgz",
+      "integrity": "sha512-vDPw+rDgn3bZe1+F/pyEwb1oMG2XTlRVgAa6B4KccTEpYgF8w6eQllVbQcfIJnZyvzFtFpxnpGtx8dd7DJp/Rw=="
+    },
     "decode-uri-component": {
       "version": "0.2.0",
       "resolved": "https://registry.npmjs.org/decode-uri-component/-/decode-uri-component-0.2.0.tgz",

package.json

@@ -40,6 +40,7 @@
     "@ethereum-navigator/navigator": "^0.5.0",
     "@oceanprotocol/contracts": "^0.3.1",
     "bignumber.js": "^9.0.0",
+    "decimal.js": "^10.2.0",
     "fs": "0.0.1-security",
     "node-fetch": "^2.6.0",
     "save-file": "^2.3.1",

src/balancer/OceanPool.ts

@@ -330,4 +330,41 @@ export class OceanPool extends Pool {
         }
         return result
     }
+
+    public async getOceanNeeded(
+        account: string,
+        poolAddress: string,
+        dtRequired: string
+    ): Promise<string> {
+        await this.getDTAddress(account, poolAddress)
+        const tokenBalanceIn = await this.getReserve(
+            account,
+            poolAddress,
+            this.oceanAddress
+        )
+        const tokenWeightIn = await this.getDenormalizedWeight(
+            account,
+            poolAddress,
+            this.oceanAddress
+        )
+        const tokenBalanceOut = await this.getReserve(
+            account,
+            poolAddress,
+            this.dtAddress
+        )
+        const tokenWeightOut = await this.getDenormalizedWeight(
+            account,
+            poolAddress,
+            this.dtAddress
+        )
+        const swapFee = await this.getSwapFee(account, poolAddress)
+        return super.calcInGivenOut(
+            tokenBalanceIn,
+            tokenWeightIn,
+            tokenBalanceOut,
+            tokenWeightOut,
+            dtRequired,
+            swapFee
+        )
+    }
 }

src/balancer/balancerlib.ts

@@ -1,9 +1,10 @@
 // import * as jsonFactoryABI from './artifacts/SFactory.json'
 // import * as jsonPoolABI from './artifacts/SPool.json'
-
 import * as jsonFactoryABI from '@oceanprotocol/contracts/artifacts/development/SFactory.json'
 import * as jsonPoolABI from '@oceanprotocol/contracts/artifacts/development/SPool.json'
 
+const Decimal = require('decimal.js')
+
 /**
  * Provides a interface to Balancer BPool & BFactory
  
@@ -857,4 +858,22 @@ export class Pool extends PoolFactory {
         }
         return price
     }
+
+    public async calcInGivenOut(
+        tokenBalanceIn,
+        tokenWeightIn,
+        tokenBalanceOut,
+        tokenWeightOut,
+        tokenAmountOut,
+        swapFee
+    ) {
+        const weightRatio = Decimal(tokenWeightOut).div(Decimal(tokenWeightIn))
+        const diff = Decimal(tokenBalanceOut).minus(tokenAmountOut)
+        const y = Decimal(tokenBalanceOut).div(diff)
+        const foo = y.pow(weightRatio).minus(Decimal(1))
+        const tokenAmountIn = Decimal(tokenBalanceIn)
+            .times(foo)
+            .div(Decimal(1).minus(Decimal(swapFee)))
+        return tokenAmountIn
+    }
 }

test/unit/balancer/Balancer.test.ts

@@ -133,13 +133,18 @@ describe('Balancer flow', () => {
             const currentDtReserve = await Pool.getDTReserve(alice, alicePoolAddress)
             assert(currentDtReserve > 0)
         })
-        it('Get dtToken pool reserve ', async () => {
+        it('Get Ocean pool reserve ', async () => {
             const currentOceanReserve = await Pool.getOceanReserve(
                 alice,
                 alicePoolAddress
             )
             assert(currentOceanReserve > 0)
         })
+        it('Get amount of Ocean needed to buy 1 dtToken', async () => {
+            const requiredOcean = await Pool.getOceanNeeded(alice, alicePoolAddress, '1')
+            assert(requiredOcean > 0)
+        })
+
         it('Bob should search for pools with this DT', async () => {
             const pools = await Pool.searchPoolforDT(bob, tokenAddress)
             assert(pools.length > 0)