Find the corresponding repo for a WhosOnFirst ID

wof-finding-aid.ts

/**
 * download the ccmap file (updated every time the data updates):
 *
 * curl -OL https://data.geocode.earth/wof/dist/meta/whosonfirst-data-admin.ccmap.gz
 *
 *
 * convert ccmap file to typescript (save stdout to `whosonfirst-data-admin.ccmap.ts`):
 *
 * import fs from 'node:fs'
 * const data = fs.readFileSync('whosonfirst-data-admin.ccmap.gz', 'base64')
 * process.stdout.write(`export default "${data}"`)
 *
**/

import pako from 'pako'
import ccmap from './whosonfirst-data-admin.ccmap'

// find is a slow-yet-memory-efficient method of
// finding the wofid in the delta compressed map
export const find = (wofid: number) => {
  const gdata = Uint8Array.from(atob(ccmap), c => c.charCodeAt(0))
  const data = new TextDecoder().decode(pako.ungzip(gdata))

  let o = 0
  let prev = 0

  while (o < data.length) {
    const cc = data.substring(o, o+2); o += 2
    let delta = data.substring(o, o+1); o += 1

    while (true) {
      const next = data.substring(o, o+1)
      if (isNaN(parseInt(next))) break
      delta += next; o += 1
    }

    prev = (prev + parseInt(delta))
    if (prev === wofid) return cc
  }

  return null
}