const csv = require('fast-csv')
const fs = require('fs')

let records = []

/**
 * Parse CSV file and call processor functions on every line.
 */
function start (dataFile) {
  csv
    .parseFile(dataFile, {
      delimiter: ';'
    })
    .on("data", function (data) {
      if (data[0] !== 'Bereich') processInput(...data)
    })
    .on("end", createHTML)
}

/**
 * Generate one object for every line in the CSV file and push
 * it to the records array.
 */
function processInput (section, chair, category, audience, abbreviation,
                       topic, description, deadline, link) {
  records.push({
    section, chair, category, audience, abbreviation, topic, description, deadline, link
  })
}

/**
 * Generate HTML from the records array.
 * The resulting markup is written to ./result.txt.
 */
function createHTML() {
  let resultString = ''
  const recordsBySection = groupBy(records, x => x.section)

  Array.from(['Informatik', 'Angewandte Informatik', 'Wirtschaftsinformatik'])
    .forEach(function (section) {
      if (recordsBySection.has(section)) {
        resultString += `<h1>${section}</h1>\n`

        let recordsByChair = groupBy(recordsBySection.get(section), x => x.chair)
        let chairs = [...recordsByChair.keys()].sort()
        chairs.forEach(function (chair) {
          resultString += `<h3>${chair}</h3>\n`

          let recordsByCategory = groupBy(recordsByChair.get(chair), x => x.category)
          let categories = [...recordsByCategory.keys()].sort()
          categories.forEach(function (category) {

            recordsByCategory.get(category).forEach(function (cur) {
              resultString += `<div style="border: 1px solid lightgray; box-shadow: 0px 2px 4px rgba(0,0,0,0.3); padding: 1rem; margin-bottom: 1rem;"><h5>${category}`
              resultString += cur.abbreviation ? ` ${cur.abbreviation}` : ''
              resultString += `: ${cur.topic} (${cur.audience})</h5>\n`
              resultString += `<p><strong>Kurzbeschreibung:</strong> ${cur.description}</p>\n`
              resultString += `<p><strong>Anmeldefrist</strong>: ${cur.deadline}</p>\n`
              resultString += `<p><strong>Weitere Informationen und Anmeldung:</strong> `
              resultString += cur.link.startsWith('http') ? `<br/><a href="${cur.link}">${cur.link}</a>` : cur.link
              resultString += `</p></div>\n`
            })
          })
        })
      }
  })

  fs.writeFileSync('result.txt', resultString)
  console.log(`Successfully parsed ${process.argv[2]}.`)
}

if (process.argv[2]) {
  start(process.argv[2])
} else {
  console.error("Missing argument. You have to pass the name of the data file.")
}

/**
 * Group an array of records by a given key.
 * Taken from the answer to this question:
 * https: //stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-an-array-of-objects#38327540
 */
function groupBy(list, keyGetter) {
  const map = new Map();
  list.forEach((item) => {
    const key = keyGetter(item);
    const collection = map.get(key);
    if (!collection) {
      map.set(key, [item]);
    } else {
      collection.push(item);
    }
  });
  return map;
}