/**
 * Raster (bit-image) receipt bytes. ESC/POS text mode can't render Devanagari
 * or Malayalam (09-UX §5.3), so non-Latin receipts print as a 1-bit raster via
 * GS v 0. This module is the pure part — thresholding pixels and packing bits;
 * the canvas that draws the glyphs lives in the app (apps/pos/src/raster.ts),
 * because canvas is a browser API and byte-packing must stay testable.
 */
const GS = 0x1d

/** 1 bit per pixel, row-major; `bits[y*width + x]` is 1 for a printed (black) dot. */
export interface Bitmap {
  width: number
  height: number
  bits: Uint8Array
}

/**
 * Pack one pixel row (0/1 values) into bytes, most-significant bit = leftmost
 * pixel, padded with zeros to a whole byte. 9 pixels → 2 bytes.
 */
export function packRasterRow(row: ArrayLike<number>): number[] {
  const bytes = new Array<number>(Math.ceil(row.length / 8)).fill(0)
  for (let i = 0; i < row.length; i++) {
    if (row[i]) bytes[i >> 3]! |= 0x80 >> (i & 7)
  }
  return bytes
}

/**
 * Threshold RGBA pixel data (canvas `ImageData.data`) into a 1-bpp bitmap.
 * A dot prints when it is opaque and darker than `threshold` (Rec.601 luma).
 */
export function bitonalFromRGBA(
  data: ArrayLike<number>, width: number, height: number, threshold = 128,
): Bitmap {
  const bits = new Uint8Array(width * height)
  for (let i = 0; i < width * height; i++) {
    const r = data[i * 4]!, g = data[i * 4 + 1]!, b = data[i * 4 + 2]!, a = data[i * 4 + 3]!
    const luma = 0.299 * r + 0.587 * g + 0.114 * b
    bits[i] = a >= 128 && luma < threshold ? 1 : 0
  }
  return { width, height, bits }
}

/** GS v 0 raster bit-image command for a bitmap (m=0, normal density). */
export function rasterToEscPos(bmp: Bitmap): Uint8Array {
  const bytesPerRow = Math.ceil(bmp.width / 8)
  const out: number[] = [GS, 0x76, 0x30, 0, bytesPerRow & 0xff, (bytesPerRow >> 8) & 0xff, bmp.height & 0xff, (bmp.height >> 8) & 0xff]
  for (let y = 0; y < bmp.height; y++) {
    const row = bmp.bits.subarray(y * bmp.width, (y + 1) * bmp.width)
    out.push(...packRasterRow(row))
  }
  return Uint8Array.from(out)
}