big-waves.js

big-waves.js

const { Router } = require('express')
const fetch = require('node-fetch')

const app = Router()

const noaaUrl = sid => `https://www.ndbc.noaa.gov/data/realtime2/${sid}.txt`

const units = 'm'

const omitComments = waveRow => !waveRow.startsWith('#')
const omitEmptyRow = waveRow => waveRow.length > 0
const rowsWithWVHT = waveRow => waveRow.WVHT !== 'MM'
const waveFormat = waveRow => ({
  time: rowToTime(waveRow),
  height: `${waveRow.WVHT}${units}`
})
const rowToTime = waveRow => `${waveRow.YY}-${waveRow.MM}-${waveRow.DD}`

// [YY, MM, DD, ...]
const waveRowToHeaders = headers =>
  headers = headers.substr(1) // remove the leading #
    .split(/\s+/)

// input: [2020, 08, ...]
// output: { YY: 2020, MM: 08, ... }
//  mapping function -----------v
const waveRowToObj = headers => waveRow =>
  headers.reduce((obj, _header, idx) => ({
    ...obj,
    [headers[idx]]: waveRow[idx]
  }), {})

//  mapping function ----------------v
const highestWaves = (headers, n) => waveData =>
  waveData
    .split('\n')
    .filter(omitComments)
    .filter(omitEmptyRow)
    .map(row => row.split(/\s+/))
    .map(waveRowToObj(headers))
    .filter(rowsWithWVHT)
    .sort((a,b) => parseFloat(b.WVHT) - parseFloat(a.WVHT))
    .slice(0,n)
    .map(waveFormat)


// takes sid and n, returns [{ time, height }] or {error}
app.get('/', (req, res) => {
  const { sid, n } = req.query

  // validation
  if(sid === undefined){
    const error = 'Missing required param: sid'
    console.log(error)
    return res.json({error})
  }
  if(n === undefined){
    const error = 'Missing required param: n'
    console.log(error)
    return res.json({error})
  }

  fetch(noaaUrl(sid))
    .then(response => response.text())
    .then(response => {
      const waveHeaders = waveRowToHeaders(response.split('\n')[0])
      return highestWaves(waveHeaders, n)(response)
    })
    .then(res.json.bind(res))
    .catch(error => {
      console.error(error)
      res.json({ error })
    })
})

module.exports = app

aoeu