// src/lib/pdf/compress.ts — from tinytinytools.com
// Served verbatim from the working tree. Method: https://tinytinytools.com/guides
import { PDFDocument } from 'pdf-lib';
import { openRenderDocument, type RenderAdapters } from './render';

export const COMPRESSOR_DPIS = Object.freeze([72, 96, 150] as const);

/**
 * The three presets the UI offers, ordered least to most aggressive.
 *
 * `detail` states the DPI and JPEG quality the preset actually applies rather than a
 * predicted size reduction. Reduction depends on the source — page count, dimensions,
 * how much of the page is photographic, and how well the original was already
 * compressed — so a "~60-80% smaller" badge would be a number we cannot stand behind.
 * The settings are verifiable; a forecast is not.
 */
export const COMPRESSION_LEVELS = Object.freeze([
  {
    id: 'low',
    label: 'Low',
    summary: 'Best quality, largest file',
    detail: '150 DPI · quality 90',
    dpi: 150,
    quality: 90,
  },
  {
    id: 'recommended',
    label: 'Recommended',
    summary: 'Balanced size and legibility',
    detail: '96 DPI · quality 75',
    dpi: 96,
    quality: 75,
  },
  {
    id: 'high',
    label: 'High',
    summary: 'Smallest file, softest detail',
    detail: '72 DPI · quality 50',
    dpi: 72,
    quality: 50,
  },
] as const);

export type CompressionLevel = (typeof COMPRESSION_LEVELS)[number];
export type CompressionLevelId = CompressionLevel['id'];

export const DEFAULT_COMPRESSION_LEVEL_ID: CompressionLevelId = 'recommended';

/** Resolve a level id to its DPI/quality pair, falling back to the default preset. */
export function resolveCompressionLevel(id: unknown): CompressionLevel {
  return (
    COMPRESSION_LEVELS.find(level => level.id === id)
    ?? COMPRESSION_LEVELS.find(level => level.id === DEFAULT_COMPRESSION_LEVEL_ID)!
  );
}

export async function compressPdfBytes(
  bytes: Uint8Array,
  options: { dpi: number; quality: number },
  renderAdapters?: RenderAdapters,
  onProgress?: (pageNumber: number, pageCount: number) => void,
): Promise<Uint8Array> {
  if (!(COMPRESSOR_DPIS as readonly number[]).includes(options.dpi)) {
    throw new Error('Choose a DPI preset.');
  }
  if (!Number.isFinite(options.quality) || options.quality < 40 || options.quality > 95) {
    throw new Error('Choose a quality between 40 and 95.');
  }

  const renderDoc = await openRenderDocument(bytes, renderAdapters);
  try {
    const out = await PDFDocument.create();
    for (const pageInfo of renderDoc.pages) {
      onProgress?.(pageInfo.pageNumber, renderDoc.pageCount);
      const image = await renderDoc.renderPage(pageInfo.pageNumber, {
        scale: options.dpi / 72,
        format: 'jpeg',
        quality: options.quality,
      });
      const embedded = await out.embedJpg(new Uint8Array(await image.blob.arrayBuffer()));
      const page = out.addPage([pageInfo.widthPt, pageInfo.heightPt]);
      page.drawImage(embedded, { x: 0, y: 0, width: pageInfo.widthPt, height: pageInfo.heightPt });
    }
    return out.save();
  } finally {
    await renderDoc.destroy();
  }
}