Calculate the median price of a token on Uniswap V2
Submitted by:
moonthoon
This function calculates the median price of a token that is on Uniswap V2. It works by sampling up to 4 prices over a given time period then chooses the median value
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
// Max sample size is 4 due to 5 http request limit
const SAMPLE_SIZE = 4
// The number of decimals the price in USD is formatted to
const DECIMALS = 18
// A block buffer to take into consideration the synchronization of the subgraph
const GRAPH_BLOCK_BUFFER = 50
const AVG_SECONDS_PER_BLOCK = 12
// Token address
const token = args[0].toLowerCase();
// Pair address
const pair = args[1]
// Period in seconds
const period = args[2]
const blockRange = period / AVG_SECONDS_PER_BLOCK
if (!secrets.rpc) {
throw Error("\"rpc\" environment variable not set")
}
const blockNumberResponse = await Functions.makeHttpRequest({
url: secrets.rpc,
method: "POST",
headers: {
"Accept": "application/json",
"Content-Type": "application/json",
},
data: JSON.stringify({
jsonrpc: "2.0",
method: "eth_blockNumber",
params: [],
id: "1",
}),
})
if (blockNumberResponse.error) {
throw Error("Unable to fetch current block number")
}
const blockNumber = parseInt(blockNumberResponse.data.result, 16) - GRAPH_BLOCK_BUFFER
const fetchPrice = (blockNumber) => Functions.makeHttpRequest({
url: "https://api.thegraph.com/subgraphs/name/uniswap/uniswap-v2",
method: "POST",
data: {
query: `{
pair(id: "${pair}", block: {number: ${blockNumber}}) {
token0 {
id
}
token1 {
id
}
reserve0
reserve1
reserveUSD
}
}`,
},
})
const stringToBigInt = (str) => {
const splitStr = str.split(".")
const decimals = splitStr[1].slice(0, DECIMALS).padEnd(DECIMALS, "0")
return BigInt(`${splitStr[0]}${decimals}`)
}
const getPrice = async (blockNumber) => {
const {
error,
data: {
errors,
data,
},
} = await fetchPrice(blockNumber)
if (error.error || errors) {
throw Error("Unable to fetch price from subgraph")
}
const { pair: { token0: { id: token0 }, token1: { id: token1 }, reserve0, reserve1, reserveUSD } } = data
const token0LC = token0.toLowerCase()
const token1LC = token1.toLowerCase()
if (token0LC !== token && token1LC !== token) {
throw Error("Token not found as part of the pair")
}
const tokenReserveInUSD = stringToBigInt(reserveUSD) / 2n
const tokenReserve = stringToBigInt(token0LC === token ? reserve0 : reserve1)
return BigInt(10 ** DECIMALS) * tokenReserveInUSD / tokenReserve
}
const pickRandomBlock = () => {
return blockNumber - Math.round(Math.random() * blockRange)
}
let prices = []
for (let i = 0; i < SAMPLE_SIZE; i++) {
const price = await getPrice(pickRandomBlock())
prices.push(price)
}
const midpoint = SAMPLE_SIZE % 2 === 0 ? SAMPLE_SIZE / 2 : (SAMPLE_SIZE + 1) / 2
const median = prices[midpoint]
return Functions.encodeUint256(median)