add static methods to exchange...

... for calculating liquidity-related values

exchange address -> Token

src/constants.ts

@@ -27,10 +27,14 @@ export enum TradeType {
 // exports for internal consumption
 export const ZERO = JSBI.BigInt(0)
 export const ONE = JSBI.BigInt(1)
+export const TWO = JSBI.BigInt(2)
+export const THREE = JSBI.BigInt(3)
+export const FIVE = JSBI.BigInt(5)
 export const TEN = JSBI.BigInt(10)
 export const _100 = JSBI.BigInt(100)
 export const _997 = JSBI.BigInt(997)
 export const _1000 = JSBI.BigInt(1000)
+export const MINIMUM_LIQUIDITY = _1000
 
 export enum SolidityType {
   uint8 = 'uint8',

src/entities/exchange.ts

@@ -6,16 +6,18 @@ import { getNetwork } from '@ethersproject/networks'
 import { getDefaultProvider } from '@ethersproject/providers'
 import { Contract } from '@ethersproject/contracts'
 
-import { FACTORY_ADDRESS, INIT_CODE_HASH, ZERO, ONE, _997, _1000 } from '../constants'
+import { BigintIsh } from '../types'
+import { FACTORY_ADDRESS, INIT_CODE_HASH, ZERO, ONE, FIVE, _997, _1000, MINIMUM_LIQUIDITY } from '../constants'
 import ERC20 from '../abis/ERC20.json'
+import { sqrt, parseBigintIsh } from '../utils'
 import { InsufficientReservesError, InsufficientInputAmountError } from '../errors'
 import { Token } from './token'
 import { TokenAmount } from './fractions/tokenAmount'
 
 let CACHE: { [token0Address: string]: { [token1Address: string]: string } } = {}
 
 export class Exchange {
-  public readonly address: string
+  public readonly liquidityToken: Token
   private readonly tokenAmounts: [TokenAmount, TokenAmount]
 
   static getAddress(tokenA: Token, tokenB: Token): string {
@@ -55,7 +57,13 @@ export class Exchange {
     const tokenAmounts = tokenAmountA.token.sortsBefore(tokenAmountB.token) // does safety checks
       ? [tokenAmountA, tokenAmountB]
       : [tokenAmountB, tokenAmountA]
-    this.address = Exchange.getAddress(tokenAmounts[0].token, tokenAmounts[1].token)
+    this.liquidityToken = new Token(
+      tokenAmounts[0].token.chainId,
+      Exchange.getAddress(tokenAmounts[0].token, tokenAmounts[1].token),
+      18,
+      'UNI-V2',
+      'Uniswap V2'
+    )
     this.tokenAmounts = tokenAmounts as [TokenAmount, TokenAmount]
   }
 
@@ -120,4 +128,65 @@ export class Exchange {
     )
     return [inputAmount, new Exchange(inputReserve.add(inputAmount), outputReserve.subtract(outputAmount))]
   }
+
+  getLiquidityMinted(totalSupply: TokenAmount, tokenAmountA: TokenAmount, tokenAmountB: TokenAmount): TokenAmount {
+    invariant(totalSupply.token.equals(this.liquidityToken), 'LIQUIDITY')
+    const tokenAmounts = tokenAmountA.token.sortsBefore(tokenAmountB.token) // does safety checks
+      ? [tokenAmountA, tokenAmountB]
+      : [tokenAmountB, tokenAmountA]
+    invariant(tokenAmounts[0].token.equals(this.token0) && tokenAmounts[1].token.equals(this.token1), 'TOKEN')
+
+    let liquidity: JSBI
+    if (JSBI.equal(totalSupply.raw, ZERO)) {
+      liquidity = JSBI.subtract(sqrt(JSBI.multiply(tokenAmounts[0].raw, tokenAmounts[1].raw)), MINIMUM_LIQUIDITY)
+    } else {
+      const amount0 = JSBI.divide(JSBI.multiply(tokenAmounts[0].raw, totalSupply.raw), this.reserve0.raw)
+      const amount1 = JSBI.divide(JSBI.multiply(tokenAmounts[1].raw, totalSupply.raw), this.reserve1.raw)
+      liquidity = JSBI.lessThanOrEqual(amount0, amount1) ? amount0 : amount1
+    }
+    if (!JSBI.greaterThan(liquidity, ZERO)) {
+      throw new InsufficientInputAmountError()
+    }
+    return new TokenAmount(this.liquidityToken, liquidity)
+  }
+
+  getLiquidityValue(
+    token: Token,
+    totalSupply: TokenAmount,
+    liquidity: TokenAmount,
+    feeOn: boolean = false,
+    kLast?: BigintIsh
+  ): TokenAmount {
+    invariant(token.equals(this.token0) || token.equals(this.token1), 'TOKEN')
+    invariant(totalSupply.token.equals(this.liquidityToken), 'TOTAL_SUPPLY')
+    invariant(liquidity.token.equals(this.liquidityToken), 'LIQUIDITY')
+    invariant(JSBI.lessThanOrEqual(liquidity.raw, totalSupply.raw), 'LIQUIDITY')
+
+    let totalSupplyAdjusted: TokenAmount
+    if (!feeOn) {
+      totalSupplyAdjusted = totalSupply
+    } else {
+      invariant(!!kLast, 'K_LAST')
+      const kLastParsed = parseBigintIsh(kLast as any)
+      if (!JSBI.equal(kLastParsed, ZERO)) {
+        const rootK = sqrt(JSBI.multiply(this.reserve0.raw, this.reserve1.raw))
+        const rootKLast = sqrt(kLastParsed)
+        if (JSBI.greaterThan(rootK, rootKLast)) {
+          const numerator = JSBI.multiply(totalSupply.raw, JSBI.subtract(rootK, rootKLast))
+          const denominator = JSBI.add(JSBI.multiply(rootK, FIVE), rootKLast)
+          const feeLiquidity = JSBI.divide(numerator, denominator)
+          totalSupplyAdjusted = totalSupply.add(new TokenAmount(this.liquidityToken, feeLiquidity))
+        } else {
+          totalSupplyAdjusted = totalSupply
+        }
+      } else {
+        totalSupplyAdjusted = totalSupply
+      }
+    }
+
+    return new TokenAmount(
+      token,
+      JSBI.divide(JSBI.multiply(liquidity.raw, this.reserveOf(token).raw), totalSupplyAdjusted.raw)
+    )
+  }
 }

src/utils.ts

@@ -4,7 +4,7 @@ import JSBI from 'jsbi'
 import { getAddress } from '@ethersproject/address'
 
 import { BigintIsh } from './types'
-import { ZERO, SolidityType, SOLIDITY_TYPE_MAXIMA } from './constants'
+import { ZERO, ONE, TWO, THREE, SolidityType, SOLIDITY_TYPE_MAXIMA } from './constants'
 
 export function validateSolidityTypeInstance(value: JSBI, solidityType: SolidityType): void {
   invariant(JSBI.greaterThanOrEqual(value, ZERO), `${value} is not a ${solidityType}.`)
@@ -29,3 +29,21 @@ export function parseBigintIsh(bigintIsh: BigintIsh): JSBI {
     ? JSBI.BigInt(bigintIsh.toString())
     : JSBI.BigInt(bigintIsh)
 }
+
+// mock the on-chain sqrt function
+export function sqrt(y: JSBI): JSBI {
+  validateSolidityTypeInstance(y, SolidityType.uint256)
+  let z: JSBI = ZERO
+  let x: JSBI
+  if (JSBI.greaterThan(y, THREE)) {
+    z = y
+    x = JSBI.add(JSBI.divide(y, TWO), ONE)
+    while (JSBI.lessThan(x, z)) {
+      z = x
+      x = JSBI.divide(JSBI.add(JSBI.divide(y, x), x), TWO)
+    }
+  } else if (JSBI.notEqual(y, ZERO)) {
+    z = ONE
+  }
+  return z
+}

test/data.test.ts

@@ -14,6 +14,6 @@ describe('data', () => {
   it('Exchange', async () => {
     const token = new Token(ChainId.RINKEBY, '0xc7AD46e0b8a400Bb3C915120d284AafbA8fc4735', 18) // DAI
     const exchange = await Exchange.fetchData(WETH[ChainId.RINKEBY], token)
-    expect(exchange.address).toEqual('0xC0568fA2FC63123B7352c506076DFa5623D62Db5')
+    expect(exchange.liquidityToken.address).toEqual('0xC0568fA2FC63123B7352c506076DFa5623D62Db5')
   })
 })

test/miscellaneous.test.ts

@@ -0,0 +1,106 @@
+import { ChainId, Token, TokenAmount, Exchange, InsufficientInputAmountError } from '../src'
+
+describe('miscellaneous', () => {
+  it('getLiquidityMinted:0', async () => {
+    const tokenA = new Token(ChainId.RINKEBY, '0x0000000000000000000000000000000000000001', 18)
+    const tokenB = new Token(ChainId.RINKEBY, '0x0000000000000000000000000000000000000002', 18)
+    const exchange = new Exchange(new TokenAmount(tokenA, '0'), new TokenAmount(tokenB, '0'))
+
+    expect(() => {
+      exchange.getLiquidityMinted(
+        new TokenAmount(exchange.liquidityToken, '0'),
+        new TokenAmount(tokenA, '1000'),
+        new TokenAmount(tokenB, '1000')
+      )
+    }).toThrow(InsufficientInputAmountError)
+
+    expect(() => {
+      exchange.getLiquidityMinted(
+        new TokenAmount(exchange.liquidityToken, '0'),
+        new TokenAmount(tokenA, '1000000'),
+        new TokenAmount(tokenB, '1')
+      )
+    }).toThrow(InsufficientInputAmountError)
+
+    const liquidity = exchange.getLiquidityMinted(
+      new TokenAmount(exchange.liquidityToken, '0'),
+      new TokenAmount(tokenA, '1001'),
+      new TokenAmount(tokenB, '1001')
+    )
+
+    expect(liquidity.raw.toString()).toEqual('1')
+  })
+
+  it('getLiquidityMinted:!0', async () => {
+    const tokenA = new Token(ChainId.RINKEBY, '0x0000000000000000000000000000000000000001', 18)
+    const tokenB = new Token(ChainId.RINKEBY, '0x0000000000000000000000000000000000000002', 18)
+    const exchange = new Exchange(new TokenAmount(tokenA, '10000'), new TokenAmount(tokenB, '10000'))
+
+    expect(
+      exchange
+        .getLiquidityMinted(
+          new TokenAmount(exchange.liquidityToken, '10000'),
+          new TokenAmount(tokenA, '2000'),
+          new TokenAmount(tokenB, '2000')
+        )
+        .raw.toString()
+    ).toEqual('2000')
+  })
+
+  it('getLiquidityValue:!feeOn', async () => {
+    const tokenA = new Token(ChainId.RINKEBY, '0x0000000000000000000000000000000000000001', 18)
+    const tokenB = new Token(ChainId.RINKEBY, '0x0000000000000000000000000000000000000002', 18)
+    const exchange = new Exchange(new TokenAmount(tokenA, '1000'), new TokenAmount(tokenB, '1000'))
+
+    {
+      const liquidityValue = exchange.getLiquidityValue(
+        tokenA,
+        new TokenAmount(exchange.liquidityToken, '1000'),
+        new TokenAmount(exchange.liquidityToken, '1000'),
+        false
+      )
+      expect(liquidityValue.token.equals(tokenA)).toBe(true)
+      expect(liquidityValue.raw.toString()).toBe('1000')
+    }
+
+    // 500
+    {
+      const liquidityValue = exchange.getLiquidityValue(
+        tokenA,
+        new TokenAmount(exchange.liquidityToken, '1000'),
+        new TokenAmount(exchange.liquidityToken, '500'),
+        false
+      )
+      expect(liquidityValue.token.equals(tokenA)).toBe(true)
+      expect(liquidityValue.raw.toString()).toBe('500')
+    }
+
+    // tokenB
+    {
+      const liquidityValue = exchange.getLiquidityValue(
+        tokenB,
+        new TokenAmount(exchange.liquidityToken, '1000'),
+        new TokenAmount(exchange.liquidityToken, '1000'),
+        false
+      )
+      expect(liquidityValue.token.equals(tokenB)).toBe(true)
+      expect(liquidityValue.raw.toString()).toBe('1000')
+    }
+  })
+
+  it('getLiquidityValue:feeOn', async () => {
+    const tokenA = new Token(ChainId.RINKEBY, '0x0000000000000000000000000000000000000001', 18)
+    const tokenB = new Token(ChainId.RINKEBY, '0x0000000000000000000000000000000000000002', 18)
+    const exchange = new Exchange(new TokenAmount(tokenA, '1000'), new TokenAmount(tokenB, '1000'))
+
+    const liquidityValue = exchange.getLiquidityValue(
+      tokenA,
+      new TokenAmount(exchange.liquidityToken, '500'),
+      new TokenAmount(exchange.liquidityToken, '500'),
+      true,
+      '250000' // 500 ** 2
+    )
+    expect(liquidityValue.token.equals(tokenA)).toBe(true)
+    expect(liquidityValue.raw.toString()).toBe('917') // ceiling(1000 - (500 * (1 / 6)))
+  })
+})