fees.js

const { getMempoolClient } = require('./utils/mempool')

const FEE_PREF = process.env.FEE_PREFERENCE || 'medium'
if (FEE_PREF !== 'high' && FEE_PREF !== 'medium' && FEE_PREF !== 'low') {
    throw new Error('FEE_PREFERENCE must be one of: high, medium, low')
}

if (process.env.MIN_FEE_BUFFER && process.env.MIN_FEE_BUFFER_PERCENT) {
    throw new Error('MIN_FEE_BUFFER and MIN_FEE_BUFFER_PERCENT cannot both be set')
}
let MIN_FEE_BUFFER_PERCENT
if (process.env.MIN_FEE_BUFFER_PERCENT) {
    MIN_FEE_BUFFER_PERCENT = parseFloat(process.env.MIN_FEE_BUFFER_PERCENT)
    if (MIN_FEE_BUFFER_PERCENT < 1 || MIN_FEE_BUFFER_PERCENT > 2) {
        console.log('MIN_FEE_BUFFER_PERCENT must be between 1.00 and 2.00')
    }
}
const MIN_FEE_BUFFER = parseFloat(process.env.MIN_FEE_BUFFER || 3)
const NEXT_BLOCK_FEE_SLOT = parseInt(process.env.NEXT_BLOCK_FEE_SLOT || 0)

// Get fee rate from mempool.space
async function get_fee_rate() {
    if (process.env.AUTO_RBF) {
        return get_min_next_block_fee_rate()
    }
    const { data } = await getMempoolClient()
        .get(`/api/v1/fees/recommended`)
        .catch((err) => {
            console.error(err)
            return { data: {} }
        })
    if (FEE_PREF === 'high') return data.fastestFee
    if (FEE_PREF === 'medium') return data.halfHourFee
    if (FEE_PREF === 'low') return data.hourFee
    throw new Error('FEE_PREFERENCE must be one of: high, medium, low')
}

async function get_min_next_block_fee_rate() {
    const { data } = await getMempoolClient()
        .get(`/api/v1/fees/mempool-blocks`)
        .catch((err) => {
            console.error(err)
            return {}
        })
    if (!data) {
        throw new Error('Could not get mempool blocks')
    }
    if (MIN_FEE_BUFFER_PERCENT) {
        const min_fee_buffer_percent = parseFloat(process.env.MIN_FEE_BUFFER_PERCENT)
        return Math.ceil(data[0].feeRange[NEXT_BLOCK_FEE_SLOT] * min_fee_buffer_percent * 10) / 10
    }
    // We add 3 right now because we want to be sure we get into the next block.
    return Math.ceil((data[0].feeRange[NEXT_BLOCK_FEE_SLOT] + MIN_FEE_BUFFER) * 10) / 10
}

module.exports = {
    get_fee_rate,
    get_min_next_block_fee_rate,
}