add a hook for getting the USDC price of any currency

src/utils/useUSDCPrice.ts

@@ -0,0 +1,66 @@
+import { ChainId, Currency, currencyEquals, JSBI, Price, WETH } from '@uniswap/sdk'
+import { useMemo } from 'react'
+import { USDC } from '../constants'
+import { PairState, usePairs } from '../data/Reserves'
+import { useActiveWeb3React } from '../hooks'
+import { wrappedCurrency } from './wrappedCurrency'
+
+/**
+ * Returns the price in USDC of the input currency
+ * @param currency currency to compute the USDC price of
+ */
+export default function useUSDCPrice(currency?: Currency): Price | undefined {
+  const { chainId } = useActiveWeb3React()
+  const wrapped = wrappedCurrency(currency, chainId)
+  const tokenPairs: [Currency | undefined, Currency | undefined][] = useMemo(
+    () => [
+      [
+        chainId && wrapped && currencyEquals(WETH[chainId], wrapped) ? undefined : currency,
+        chainId ? WETH[chainId] : undefined
+      ],
+      [wrapped?.equals(USDC) ? undefined : wrapped, chainId === ChainId.MAINNET ? USDC : undefined],
+      [chainId ? WETH[chainId] : undefined, chainId === ChainId.MAINNET ? USDC : undefined]
+    ],
+    [chainId, currency, wrapped]
+  )
+  const [[ethPairState, ethPair], [usdcPairState, usdcPair], [usdcEthPairState, usdcEthPair]] = usePairs(tokenPairs)
+
+  return useMemo(() => {
+    if (!currency || !wrapped || !chainId) {
+      return
+    }
+    // handle weth/eth
+    if (wrapped.equals(WETH[chainId])) {
+      if (usdcPair) {
+        const price = usdcPair.priceOf(WETH[chainId])
+        return new Price(currency, USDC, price.denominator, price.numerator)
+      } else {
+        return undefined
+      }
+    }
+    // handle usdc
+    if (wrapped.equals(USDC)) {
+      return new Price(USDC, USDC, '1', '1')
+    }
+
+    const ethPairETHAmount = ethPair?.reserveOf(WETH[chainId])
+    const ethPairETHUSDCValue: JSBI =
+      ethPairETHAmount && usdcEthPair ? usdcEthPair.priceOf(WETH[chainId]).quote(ethPairETHAmount).raw : JSBI.BigInt(0)
+
+    // all other tokens
+    // first try the usdc pair
+    if (usdcPairState === PairState.EXISTS && usdcPair && usdcPair.reserveOf(USDC).greaterThan(ethPairETHUSDCValue)) {
+      const price = usdcPair.priceOf(wrapped)
+      return new Price(currency, USDC, price.denominator, price.numerator)
+    }
+    if (ethPairState === PairState.EXISTS && ethPair && usdcEthPairState === PairState.EXISTS && usdcEthPair) {
+      if (usdcEthPair.reserveOf(USDC).greaterThan('0') && ethPair.reserveOf(WETH[chainId]).greaterThan('0')) {
+        const ethUsdcPrice = usdcEthPair.priceOf(USDC)
+        const currencyEthPrice = ethPair.priceOf(WETH[chainId])
+        const usdcPrice = ethUsdcPrice.multiply(currencyEthPrice).invert()
+        return new Price(currency, USDC, usdcPrice.denominator, usdcPrice.numerator)
+      }
+    }
+    return
+  }, [chainId, currency, ethPair, ethPairState, usdcEthPair, usdcEthPairState, usdcPair, usdcPairState, wrapped])
+}