recognize.ts

/**
 * This file was originally written by winderica
 */
import sharp from "sharp";

// https://github.com/winderica/DailyReport/blob/4ab18c3850e60ba3074db4f2fcb76695c0335ab8/assets/digits.png
const digitsStr = `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`;

const transpose = (data: Buffer, width: number) => {
  return [...new Array(width).keys()].map((i) =>
    [...data].filter((_, j) => j % width === i)
  );
};

const match = (pixels: number[][], digits: number[][]) => {
  const scores = [...new Array(10)].map(() => 0);
  for (let i = 0; i < 180; i++) {
    for (let j = 0; j < 20; j++) {
      if (pixels[i % 18][j] === digits[i][j]) {
        scores[~~(i / 18)]++;
      }
    }
  }
  return scores.indexOf(Math.max(...scores));
};

export const recognize = async (ab: ArrayBuffer) => {
  const buffer = new Uint8Array(ab);
  const data = await sharp(buffer, { page: 1 })
    .extract({ left: 0, top: 19, width: 87, height: 20 })
    .toColourspace("b-w")
    .threshold(254)
    .raw()
    .toBuffer();
  const digitsImage = Buffer.from(digitsStr, "base64");
  const digits = transpose(
    await sharp(digitsImage).toColourspace("b-w").raw().toBuffer(),
    180
  );
  const pixels = [[...new Array(20)].map(() => 255), ...transpose(data, 87)];
  return [...new Array(4).keys()]
    .map((i) => match(pixels.slice(i * 22, i * 22 + 18), digits))
    .join("");
};