memind/vision-image-thumb.mjs

import sharp from 'sharp';

export const VISION_THUMB_MAX_SIDE = 1280;
export const VISION_THUMB_MAX_BYTES = 600 * 1024;
export const VISION_THUMB_JPEG_QUALITY = 78;

/**
 * Build a smaller JPEG buffer for vision-model analysis only.
 * Page generation still uses the full public standard image elsewhere.
 */
export async function buildVisionThumbnailBuffer(
  buffer,
  mimeType = 'image/jpeg',
  {
    maxSide = VISION_THUMB_MAX_SIDE,
    maxBytes = VISION_THUMB_MAX_BYTES,
    quality = VISION_THUMB_JPEG_QUALITY,
  } = {},
) {
  if (!Buffer.isBuffer(buffer) || buffer.length === 0) {
    throw new Error('vision thumb: empty buffer');
  }

  const metadata = await sharp(buffer, { sequentialRead: true }).metadata();
  const width = Number(metadata.width ?? 0);
  const height = Number(metadata.height ?? 0);
  if (!width || !height) {
    throw new Error('vision thumb: invalid dimensions');
  }

  const longest = Math.max(width, height);
  const resizeWidth = longest > maxSide ? Math.max(1, Math.round((width * maxSide) / longest)) : null;
  const resizeHeight = longest > maxSide ? Math.max(1, Math.round((height * maxSide) / longest)) : null;

  let pipeline = sharp(buffer, { sequentialRead: true }).rotate();
  if (resizeWidth && resizeHeight) {
    pipeline = pipeline.resize({
      width: resizeWidth,
      height: resizeHeight,
      fit: 'inside',
      withoutEnlargement: true,
    });
  }

  let nextQuality = quality;
  let candidate = await pipeline
    .flatten({ background: '#ffffff' })
    .jpeg({ quality: nextQuality, mozjpeg: true })
    .toBuffer();

  while (candidate.length > maxBytes && nextQuality > 52) {
    nextQuality = Math.max(52, nextQuality - 8);
    candidate = await sharp(buffer, { sequentialRead: true })
      .rotate()
      .resize({
        width: resizeWidth ?? width,
        height: resizeHeight ?? height,
        fit: 'inside',
        withoutEnlargement: true,
      })
      .flatten({ background: '#ffffff' })
      .jpeg({ quality: nextQuality, mozjpeg: true })
      .toBuffer();
  }

  return candidate;
}

export const visionThumbInternals = {
  VISION_THUMB_MAX_SIDE,
  VISION_THUMB_MAX_BYTES,
  VISION_THUMB_JPEG_QUALITY,
};