// This plugin mutates the `files` map of metalsmith
// at build time to only keep what was updated
// We consider any update in layouts/ to trigger an update on every html file
// Otherwise, if it's an asset or a file with no layout then we compare
// the file's last modification time to the process start time

const path = require('path');
const async = require('async');
const chokidar = require('chokidar');

let lastRunTime = false;
let layoutChange = true;
let cssChange = true;
const layoutFiles = path.join(__dirname, '../../src/layouts/**/*');
const cssFiles = path.join(__dirname, '../../src/stylesheets/**/*');
const CSSEntryPoints = ['stylesheets/index.css', 'stylesheets/header.css'];

const hasChanged = file =>
  file.stats && file.stats.ctime && file.stats.mtime
    ? Date.parse(file.stats.ctime) > lastRunTime ||
      Date.parse(file.stats.mtime) > lastRunTime
    : true;

module.exports = function onlyChanged(files, metalsmith, cb) {
  if (lastRunTime === false) {
    chokidar
      .watch(layoutFiles, { ignoreInitial: true })
      .on('all', () => {
        layoutChange = true;
      })
      .on('error', err => {
        throw err;
      });

    chokidar
      .watch(cssFiles, { ignoreInitial: true })
      .on('all', () => {
        cssChange = true;
      })
      .on('error', err => {
        throw err;
      });

    lastRunTime = Date.now();
    layoutChange = false;
    cssChange = false;
    cb(null);
    return;
  }

  async.parallel(
    Object.entries(files).map(([name, file]) => done => {
      if (!file.stats) {
        done(null); // keep file, we do not know
        return;
      }

      if (!file.layout) {
        const cssEntryPointNeedsUpdate =
          CSSEntryPoints.indexOf(name) !== -1 && cssChange === true;

        if (!hasChanged(file) && !cssEntryPointNeedsUpdate) {
          // file has no layout and was not updated, remove file
          // from files to process
          // eslint-disable-next-line no-param-reassign
          delete files[name];
        }

        done(null);
        return;
      }

      if (/\.html$/.test(name) && layoutChange === true) {
        done(null); // html page need rebuild, some layout files changed
        return;
      }

      if (!hasChanged(file)) {
        // eslint-disable-next-line no-param-reassign
        delete files[name]; // file was not updated, layouts were not updated
      }

      done(null);
    }),
    err => {
      if (!err) {
        lastRunTime = Date.now();
        layoutChange = false;
        cssChange = false;
        console.log(`[metalsmith]: onlyChanged | ${Object.keys(files)}`); // eslint-disable-line no-console
      }
      cb(err);
    }
  );
};