/**
 * This script exists only to periodically generate a
 * 'popularities.json' file from a Glean page view CSV export.
 *
 * Generally, only the core MDN Web Docs team needs to run this. The output
 * file gets added to our npm package so it's easily available to everyone.
 */
import fs from "node:fs";

import * as csv from "@fast-csv/parse";

const CURRENT_URL = "https://popularities.mdn.mozilla.net/current.csv";

async function fetchPopularities() {
  // eslint-disable-next-line n/no-unsupported-features/node-builtins
  const response = await fetch(CURRENT_URL);
  const csv = await response.text();
  return csv;
}

interface PopularitiesResult {
  rowCount: number;
  popularities: { [uri: string]: number };
  pageviews: [string, number][];
}

export async function runMakePopularitiesFile({
  outfile,
  maxUris,
}: {
  outfile: string;
  maxUris: number;
}): Promise<PopularitiesResult> {
  const pageviews: [string, number][] = [];
  let biggestCount = null;
  const raw = await fetchPopularities();
  return new Promise((resolve, reject) => {
    csv
      .parseString(raw, {
        headers: true,
      })
      .on("error", (error) => console.error(error))
      .on("data", (row) => {
        const uri = row.Page;
        const count = parseInt(row.Pageviews);

        if (
          uri.includes("/docs/") &&
          !uri.includes("$") &&
          !uri.includes("?")
        ) {
          if (biggestCount === null) {
            // First row!
            biggestCount = count;
          }
          // The pageviews CSV file is always sorted by biggest to last.
          // And the floating point number we record as the URI's "popularity"
          // just needs to be relative.
          // By computing it as a ratio between the biggest you get decent
          // looking floating point numbers that aren't affected by the
          // date range in the CSV export.
          pageviews.push([uri, count / biggestCount]);
        }
      })
      .on("end", (rowCount: number) => {
        if (!pageviews.length) {
          return reject(new Error("No pageviews found!"));
        }
        const popularities: { [uri: string]: number } = {};
        pageviews.slice(0, maxUris).forEach(([uri, popularity]) => {
          popularities[uri] = parseFloat(popularity.toFixed(5));
        });
        fs.writeFileSync(
          outfile,
          JSON.stringify(
            { popularities: popularities, date: new Date().toISOString() },
            null,
            2
          )
        );
        resolve({ rowCount, popularities, pageviews });
      });
  });
}