(function(){
  'use strict';
  const $ = id => document.getElementById(id);
  const form = $('paint-form');
  if (!form || !window.SCT) return;

  function updateMode(){
    const mode = $('project-type').value;
    const roomLabel = $('room-count-label');
    roomLabel.textContent = mode === 'exterior' ? 'Number of identical wall sections' : 'Number of identical rooms';
    $('ceiling-wrap').hidden = mode === 'exterior';
    if (mode === 'exterior') $('include-ceiling').checked = false;
  }

  function calculate(event){
    if (event) event.preventDefault();
    SCT.showError($('paint-error'), '');

    const length = SCT.positive($('length').value);
    const width = SCT.positive($('width').value);
    const height = SCT.positive($('height').value);
    const rooms = Math.max(1, SCT.integer($('rooms').value, 1));
    const coats = Math.max(1, SCT.integer($('coats').value, 1));
    const doors = SCT.integer($('doors').value);
    const windows = SCT.integer($('windows').value);
    const coverage = SCT.positive($('coverage').value, 350);
    const waste = SCT.positive($('waste').value);
    const price = SCT.positive($('price').value);
    const includeCeiling = $('include-ceiling').checked;
    const includePrimer = $('include-primer').checked;
    const primerCoverage = SCT.positive($('primer-coverage').value, 300);
    const primerPrice = SCT.positive($('primer-price').value);

    if (!length || !width || !height || !coverage){
      SCT.showError($('paint-error'), 'Enter positive room dimensions and paint coverage.');
      return;
    }

    const wallAreaSingle = 2 * (length + width) * height;
    const openingAreaSingle = (doors * 20) + (windows * 15);
    const wallPaintableSingle = Math.max(0, wallAreaSingle - openingAreaSingle);
    const ceilingAreaSingle = includeCeiling ? length * width : 0;
    const baseArea = (wallPaintableSingle + ceilingAreaSingle) * rooms;
    const coatedArea = baseArea * coats;
    const adjustedArea = coatedArea * (1 + waste / 100);
    const exactGallons = adjustedArea / coverage;
    const gallonsToBuy = Math.ceil(exactGallons);

    const primerArea = includePrimer ? baseArea * (1 + waste / 100) : 0;
    const exactPrimerGallons = includePrimer && primerCoverage ? primerArea / primerCoverage : 0;
    const primerGallonsToBuy = Math.ceil(exactPrimerGallons);
    const paintCost = gallonsToBuy * price;
    const primerCost = primerGallonsToBuy * primerPrice;
    const totalCost = paintCost + primerCost;

    const wholeGallons = Math.floor(exactGallons);
    const remainderQuarts = Math.ceil((exactGallons - wholeGallons) * 4);
    const shoppingPaint = gallonsToBuy <= 1
      ? SCT.plural(gallonsToBuy, 'gallon')
      : `${SCT.plural(gallonsToBuy, 'gallon')} of finish paint`;

    SCT.setText('paint-main-result', SCT.plural(gallonsToBuy, 'gallon'));
    SCT.setText('exact-paint', `${SCT.format(exactGallons, 2)} gal`);
    SCT.setText('paint-area', `${SCT.format(adjustedArea, 0)} ft²`);
    SCT.setText('primer-result', includePrimer ? SCT.plural(primerGallonsToBuy, 'gallon') : 'Not included');
    SCT.setText('paint-cost', price ? SCT.money(paintCost) : '—');
    SCT.setText('primer-cost', includePrimer && primerPrice ? SCT.money(primerCost) : '—');
    SCT.setText('total-cost', (price || primerPrice) ? SCT.money(totalCost) : '—');
    SCT.setText('base-area', `${SCT.format(baseArea, 0)} ft²`);
    SCT.setText('coated-area', `${SCT.format(coatedArea, 0)} ft²`);
    SCT.setText('waste-result', `${SCT.format(waste, 0)}%`);
    SCT.setText('coverage-result', `${SCT.format(coverage, 0)} ft²/gal`);
    SCT.setText('shopping-list', includePrimer
      ? `Buy ${shoppingPaint} and ${SCT.plural(primerGallonsToBuy, 'gallon')} of primer.`
      : `Buy ${shoppingPaint}.`);
    SCT.setText('quart-option', exactGallons < 1
      ? `Small project option: about ${Math.max(1, remainderQuarts)} quart${remainderQuarts === 1 ? '' : 's'} before rounding to full gallons.`
      : `Calculated use before purchase rounding: ${wholeGallons} gallon${wholeGallons === 1 ? '' : 's'}${remainderQuarts ? ` plus about ${remainderQuarts} quart${remainderQuarts === 1 ? '' : 's'}` : ''}.`);
    $('paint-results').removeAttribute('hidden');
  }

  function loadExample(){
    const values = {
      'project-type':'interior','length':'14','width':'12','height':'8','rooms':'2','coats':'2',
      'doors':'1','windows':'2','coverage':'350','waste':'10','price':'39.99',
      'primer-coverage':'300','primer-price':'29.99'
    };
    Object.entries(values).forEach(([id,value]) => { $(id).value = value; });
    $('include-ceiling').checked = true;
    $('include-primer').checked = true;
    updateMode();
    calculate();
  }

  form.addEventListener('submit', calculate);
  $('project-type').addEventListener('change', updateMode);
  $('example-btn').addEventListener('click', loadExample);
  $('reset-btn').addEventListener('click', () => SCT.reset(form, () => { updateMode(); calculate(); }));
  $('print-btn').addEventListener('click', SCT.print);
  updateMode();
  calculate();
})();