import { checkHttpStatus, parseJSON } from './utils'; const MAX_GAS_FAST = 250; interface RawGasEstimates { safeLow: number; standard: number; fast: number; fastest: number; block_time: number; blockNum: number; } export interface GasEstimates { safeLow: number; standard: number; fast: number; fastest: number; time: number; chainId: number; isDefault: boolean; } export function fetchGasEstimates(): Promise { return fetch('https://dev.blockscale.net/api/gasexpress.json', { mode: 'cors' }) .then(checkHttpStatus) .then(parseJSON) .then((res: object) => { // Make sure it looks like a raw gas estimate, and it has valid values const keys = ['safeLow', 'standard', 'fast', 'fastest']; keys.forEach(key => { if (typeof res[key] !== 'number') { throw new Error( `Gas estimate API has invalid shape: Expected numeric key '${key}' in response, got '${ res[key] }' instead` ); } }); // Make sure the estimate isn't totally crazy const estimateRes = res as RawGasEstimates; if (estimateRes.fast > MAX_GAS_FAST) { throw new Error( `Gas estimate response estimate too high: Max fast is ${MAX_GAS_FAST}, was given ${ estimateRes.fast }` ); } if ( estimateRes.safeLow > estimateRes.standard || estimateRes.standard > estimateRes.fast || estimateRes.fast > estimateRes.fastest ) { throw new Error( `Gas esimates are in illogical order: should be safeLow < standard < fast < fastest, received ${ estimateRes.safeLow } < ${estimateRes.standard} < ${estimateRes.fast} < ${estimateRes.fastest}` ); } return estimateRes; }) .then((res: RawGasEstimates) => ({ ...res, time: Date.now(), chainId: 1, isDefault: false })); }