const { chromium } = require('playwright');
const fs = require('fs');

/**
 * Extract contrast ratios for all visible text elements on a page.
 * Writes JSON report with violations where contrast < threshold.
 *
 * Usage:
 *   node extract-contrast.js https://example.com [--threshold 4.5] [--output contrast-report.json]
 */

function luminance(r, g, b) {
  const a = [r, g, b].map(v => {
    v /= 255;
    return v <= 0.03928 ? v / 12.92 : Math.pow((v + 0.055) / 1.055, 2.4);
  });
  return a[0] * 0.2126 + a[1] * 0.7152 + a[2] * 0.0722;
}

function hexToRgb(hex) {
  const m = hex.replace('#', '').match(/^([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})$/i);
  if (!m) return null;
  return { r: parseInt(m[1], 16), g: parseInt(m[2], 16), b: parseInt(m[3], 16) };
}

function parseRgb(rgb) {
  const m = rgb.match(/rgba?\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*(?:,\s*([\d.]+)\s*)?\)/);
  if (!m) return null;
  return { r: +m[1], g: +m[2], b: +m[3], a: m[4] !== undefined ? parseFloat(m[4]) : 1 };
}

function colorToRgb(str) {
  if (!str || str === 'transparent' || str === 'rgba(0, 0, 0, 0)') return null;
  if (str.startsWith('#')) return hexToRgb(str);
  return parseRgb(str);
}

function contrastRatio(c1, c2) {
  if (!c1 || !c2) return null;
  const l1 = luminance(c1.r, c1.g, c1.b) + 0.05;
  const l2 = luminance(c2.r, c2.g, c2.b) + 0.05;
  return l1 > l2 ? l1 / l2 : l2 / l1;
}

function getEffectiveBackground(el) {
  while (el && el !== document.documentElement) {
    const style = window.getComputedStyle(el);
    const bg = style.backgroundColor;
    if (bg && bg !== 'rgba(0, 0, 0, 0)' && bg !== 'transparent') {
      return bg;
    }
    el = el.parentElement;
  }
  return 'rgb(255, 255, 255)';
}

async function extractContrast(url, threshold = 4.5) {
  const browser = await chromium.launch({ headless: true });
  const page = await browser.newPage();
  await page.goto(url, { waitUntil: 'networkidle' });

  const issues = await page.evaluate(({ threshold }) => {
    function luminance(r, g, b) {
      const a = [r, g, b].map(v => {
        v /= 255;
        return v <= 0.03928 ? v / 12.92 : Math.pow((v + 0.055) / 1.055, 2.4);
      });
      return a[0] * 0.2126 + a[1] * 0.7152 + a[2] * 0.0722;
    }
    function parseColor(str) {
      if (!str || str === 'transparent') return null;
      if (str.startsWith('#')) {
        const m = str.replace('#', '').match(/^([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})$/i);
        return m ? { r: parseInt(m[1], 16), g: parseInt(m[2], 16), b: parseInt(m[3], 16) } : null;
      }
      const m = str.match(/rgba?\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*(?:,\s*([\d.]+)\s*)?\)/);
      return m ? { r: +m[1], g: +m[2], b: +m[3] } : null;
    }
    function contrast(c1, c2) {
      if (!c1 || !c2) return 0;
      const l1 = luminance(c1.r, c1.g, c1.b) + 0.05;
      const l2 = luminance(c2.r, c2.g, c2.b) + 0.05;
      return l1 > l2 ? l1 / l2 : l2 / l1;
    }

    const results = [];
    const walker = document.createTreeWalker(document.body, NodeFilter.SHOW_TEXT);
    let node;
    const seen = new Set();
    while ((node = walker.nextNode())) {
      const el = node.parentElement;
      if (!el || !el.getBoundingClientRect) continue;
      const rect = el.getBoundingClientRect();
      if (rect.width === 0 || rect.height === 0) continue;
      const text = node.textContent.trim();
      if (!text || text.length < 2) continue;

      let bg = window.getComputedStyle(el).backgroundColor;
      if (!bg || bg === 'rgba(0, 0, 0, 0)' || bg === 'transparent') {
        let p = el.parentElement;
        while (p) {
          const s = window.getComputedStyle(p);
          if (s.backgroundColor && s.backgroundColor !== 'rgba(0, 0, 0, 0)' && s.backgroundColor !== 'transparent') {
            bg = s.backgroundColor;
            break;
          }
          p = p.parentElement;
        }
        if (!bg) bg = 'rgb(255, 255, 255)';
      }

      const style = window.getComputedStyle(el);
      const color = style.color;
      const colorRgb = parseColor(color);
      const bgRgb = parseColor(bg);
      const ratio = contrast(colorRgb, bgRgb);
      if (ratio < threshold) {
        const key = el.tagName + (el.className ? '.' + el.className.split(/\s+/).join('.') : '') + '::' + color + '::' + bg;
        if (seen.has(key)) continue;
        seen.add(key);
        results.push({
          tagName: el.tagName,
          className: el.className || '',
          id: el.id || '',
          selector: el.tagName.toLowerCase() + (el.id ? '#' + el.id : '') + (el.className ? '.' + el.className.split(/\s+/).join('.') : ''),
          color,
          backgroundColor: bg,
          ratio: Math.round(ratio * 100) / 100,
          textLength: text.length,
          textPreview: text.slice(0, 80).replace(/\s+/g, ' '),
          fontSize: style.fontSize,
          fontWeight: style.fontWeight,
          isInvisible: ratio <= 1.2,
        });
      }
    }
    return results;
  }, { threshold });

  await browser.close();

  const report = {
    url,
    threshold,
    totalViolations: issues.length,
    invisibleCount: issues.filter(i => i.isInvisible).length,
    issues: issues.sort((a, b) => a.ratio - b.ratio),
  };

  return report;
}

async function main() {
  const url = process.argv[2];
  if (!url) {
    console.error('Usage: node extract-contrast.js <url> [--threshold 4.5] [--output report.json]');
    process.exit(1);
  }
  const threshold = (process.argv.indexOf('--threshold') >= 0 ? parseFloat(process.argv[process.argv.indexOf('--threshold') + 1]) : null) || 4.5;
  const outputIdx = process.argv.indexOf('--output');
  const output = outputIdx >= 0 ? process.argv[outputIdx + 1] : null;

  const report = await extractContrast(url, threshold);
  const json = JSON.stringify(report, null, 2);

  if (output) {
    fs.writeFileSync(output, json);
    console.log(`Report written to ${output}`);
  } else {
    console.log(json);
  }
}

main().catch(e => {
  console.error(e);
  process.exit(1);
});