/**
 * Perceptual hash (pHash) for image dedup using Sharp.
 * Average hashing: resize to 32x32 grayscale, compute mean, create 1024-bit hash.
 */

const sharp = require('sharp');

async function imageToPHash(buffer) {
  // Resize to 32x32 grayscale
  const { data, info } = await sharp(buffer)
    .resize(32, 32, { fit: 'fill' })
    .greyscale()
    .raw()
    .toBuffer({ resolveWithObject: true });

  // Compute average pixel value
  let sum = 0;
  for (let i = 0; i < data.length; i++) {
    sum += data[i];
  }
  const avg = sum / data.length;

  // Create hash: 1 if pixel > avg, 0 otherwise
  let hash = '';
  for (let i = 0; i < data.length; i++) {
    hash += data[i] > avg ? '1' : '0';
  }
  return hash;
}

function hammingDistance(hash1, hash2) {
  if (hash1.length !== hash2.length) return Infinity;
  let dist = 0;
  for (let i = 0; i < hash1.length; i++) {
    if (hash1[i] !== hash2[i]) dist++;
  }
  return dist;
}

function isSimilar(hash1, hash2, threshold = 150) {
  return hammingDistance(hash1, hash2) <= threshold;
}

module.exports = { imageToPHash, hammingDistance, isSimilar };