const fs = require('fs')
const parse = require('csv-parse')
const stringify = require('csv-stringify')

const parklandInput = fs.createReadStream('./data/media_01_parkland_shooting.csv')
const averageInput = fs.createReadStream('./data/media_02_average_of_seven_shootings.csv')
const parklandParser = parse()
const averageParser = parse()
const stringifier = stringify()
const output = fs.createWriteStream('./data/media.csv')

let finishCount = 0
let parkland = [], average = []
function finish() {
  finishCount += 1
  console.log(finishCount)
  if (finishCount < 2) { return }
  console.log('finishing')
  let a, b, nn
  for (let n = 0; n < 12 * 8; n += 1) {
    nn = n / 8
    a = find(nn, parkland)
    b = find(nn, average)
    stringifier.write([n, a, b])
  }
  stringifier.end()
}

/*
  Given the sequence A of pairs (i,j) describing coordinates and an offset n,
  find i where A[i][0] <= n and n < A[i+1][0]
  and use these to interpolate the value of A(n) -> j or whatever you call it.
*/
function find(n, a) {
  let head, tail, dist
  for (let i = 1, len = a.length; i < len; i++) {
    if (a[i][0] > n) {
      head = a[i-1]
      tail = a[i]
      dist = (n - head[0]) / (tail[0] - head[0])
      console.log(n, head, tail)
      return lerp(dist, head[1], tail[1])
    }
  }
}
function lerp(n, a, b) {
  return (b-a) * n + a
}

parklandInput.on('readable', function() {
  let buf
  while ((buf = parklandInput.read()) !== null) {
    parklandParser.write(buf)
  }
})
parklandInput.on('error', function(err){
  console.error('parklandInput error', err.message)
})
parklandInput.on('finish', function(){
  parklandParser.end()
})

averageInput.on('readable', function() {
  let buf
  while ((buf = averageInput.read()) !== null) {
    averageParser.write(buf)
  }
})
averageInput.on('error', function(err){
  console.error('averageInput error', err.message)
})
averageInput.on('finish', function(){
    console.log('enddd')
  averageParser.end()
})

parklandParser.on('readable', function(){
  let row
  while (row = parklandParser.read()) {
    parkland.push(row.map(n => parseFloat(n)))
  }
  // console.log('p', parkland.length)
  if (parkland.length == 108) finish()
})
parklandParser.on('error', function(err){
  console.error('parklandParser error', err.message)
})
parklandParser.on('end', function(){
  finish()
})

averageParser.on('readable', function(){
  let row
  while (row = averageParser.read()) {
    average.push(row.map(n => parseFloat(n)))
  }
  if (average.length == 89) finish()
})
averageParser.on('error', function(err){
  console.error('averageParser error', err.message)
})
averageParser.on('end', function(){
  finish()
})

stringifier.on('readable', function(){
  let row
  while (row = stringifier.read()){
    output.write(row)
  }
})
stringifier.on('error', function(err){
  console.error('stringifier error', err.message)
})
stringifier.on('finish', function(){
  output.end()
})