mempool/backend/src/api/fee-api.ts

const config = require('../../mempool-config.json');
import { MempoolBlock } from '../interfaces';
import projectedBlocks from './mempool-blocks';

class FeeApi {
  constructor() { }

  defaultFee = config.LIQUID ? 0.1 : 1;

  public getRecommendedFee() {
    const pBlocks = projectedBlocks.getMempoolBlocks();

    if (!pBlocks.length) {
      return {
        'fastestFee': this.defaultFee,
        'halfHourFee': this.defaultFee,
        'hourFee': this.defaultFee,
      };
    }

    const firstMedianFee = this.optimizeMedianFee(pBlocks[0]);
    const secondMedianFee = pBlocks[1] ? this.optimizeMedianFee(pBlocks[1], firstMedianFee) : this.defaultFee;
    const thirdMedianFee = pBlocks[2] ? this.optimizeMedianFee(pBlocks[2], secondMedianFee) : this.defaultFee;

    return {
      'fastestFee': firstMedianFee,
      'halfHourFee': secondMedianFee,
      'hourFee': thirdMedianFee,
    };
  }

  private optimizeMedianFee(pBlock: MempoolBlock, previousFee?: number): number {
    const useFee = previousFee ? (pBlock.medianFee + previousFee / 2) : pBlock.medianFee;
    if (pBlock.blockVSize <= 500000) {
      return this.defaultFee;
    }
    if (pBlock.blockVSize <= 950000) {
      const multiplier = (pBlock.blockVSize - 500000) / 500000;
      return Math.max(Math.round(useFee * multiplier), this.defaultFee);
    }
    return Math.round(useFee);
  }
}

export default new FeeApi();