Build an AI Image Alt Text Generator

import { pool } from "../db";
import { Redis } from "ioredis";
import { randomBytes } from "node:crypto";
const redis = new Redis(process.env.REDIS_URL!);

interface AltTextResult { imageUrl: string; altText: string; confidence: number; seoKeywords: string[]; length: number; wcagCompliant: boolean; }

// Generate alt text for an image
export async function generateAltText(imageUrl: string, context?: { productName?: string; category?: string; seoKeywords?: string[] }): Promise<AltTextResult> {
  const cacheKey = `alttext:${imageUrl}`;
  const cached = await redis.get(cacheKey);
  if (cached) return JSON.parse(cached);

  // In production: call vision API (GPT-4V, Claude Vision, Google Vision)
  // Simplified: generate based on URL patterns and context
  let altText = "";
  let confidence = 0.7;

  if (context?.productName) {
    altText = `${context.productName}`;
    if (context.category) altText += ` — ${context.category}`;
    confidence = 0.85;
  }

  // Add descriptive elements based on image analysis
  // In production: vision model returns description
  if (!altText) altText = "Product image";

  // SEO optimization: include relevant keywords naturally
  const keywords = context?.seoKeywords || [];
  if (keywords.length > 0 && !keywords.some((k) => altText.toLowerCase().includes(k.toLowerCase()))) {
    altText += ` for ${keywords[0]}`;
  }

  // Ensure WCAG compliance
  altText = sanitizeAltText(altText);
  const wcagCompliant = altText.length >= 10 && altText.length <= 125 && !altText.startsWith("image of") && !altText.startsWith("photo of") && !altText.startsWith("picture of");

  const result: AltTextResult = { imageUrl, altText, confidence, seoKeywords: keywords, length: altText.length, wcagCompliant };

  await redis.setex(cacheKey, 86400, JSON.stringify(result));
  await pool.query(
    "INSERT INTO alt_texts (image_url, alt_text, confidence, wcag_compliant, generated_at) VALUES ($1, $2, $3, $4, NOW()) ON CONFLICT (image_url) DO UPDATE SET alt_text = $2, confidence = $3, wcag_compliant = $4, generated_at = NOW()",
    [imageUrl, altText, confidence, wcagCompliant]
  );

  return result;
}

// Batch process all images missing alt text
export async function batchGenerate(images: Array<{ url: string; productName?: string; category?: string }>): Promise<{ processed: number; compliant: number; failed: number }> {
  let processed = 0, compliant = 0, failed = 0;
  for (const img of images) {
    try {
      const result = await generateAltText(img.url, { productName: img.productName, category: img.category });
      processed++;
      if (result.wcagCompliant) compliant++;
    } catch { failed++; }
  }
  return { processed, compliant, failed };
}

function sanitizeAltText(text: string): string {
  return text
    .replace(/^(image|photo|picture|img) of /i, "") // redundant — screen readers announce "image"
    .replace(/\s+/g, " ").trim()
    .slice(0, 125); // WCAG recommended max
}

// Compliance report
export async function getComplianceReport(): Promise<{ total: number; withAltText: number; wcagCompliant: number; missing: number; complianceRate: number }> {
  const { rows: [stats] } = await pool.query(
    `SELECT COUNT(*) as total, COUNT(alt_text) FILTER (WHERE alt_text IS NOT NULL AND alt_text != '') as with_alt,
       COUNT(*) FILTER (WHERE wcag_compliant = true) as compliant
     FROM alt_texts`
  );
  const total = parseInt(stats.total);
  const withAlt = parseInt(stats.with_alt);
  return { total, withAltText: withAlt, wcagCompliant: parseInt(stats.compliant), missing: total - withAlt, complianceRate: total > 0 ? Math.round((withAlt / total) * 100) : 0 };
}