/**
 * cli:scaffold-pwa — png.ts
 *
 * Deterministic solid-color PNG encoder — node:zlib deflateSync + a hand-rolled
 * CRC32 table, zero third-party dependencies. Emits valid 8-bit truecolor RGB
 * PNGs (color type 2, no interlace, filter None on every scanline).
 *
 * Used for the placeholder launcher icons (pwa-192/pwa-512/pwa-512-maskable/
 * apple-touch-icon): a solid fill trivially satisfies the maskable safe zone,
 * and byte-determinism keeps re-runs diff-clean until the client ships real
 * artwork (the files are emitted skip-if-exists — dev-owned once replaced).
 */
import { deflateSync } from 'node:zlib'

/** PNG signature: 89 50 4E 47 0D 0A 1A 0A. */
export const PNG_SIGNATURE = Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a])

const CRC_TABLE = (() => {
  const table = new Uint32Array(256)
  for (let n = 0; n < 256; n++) {
    let c = n
    for (let k = 0; k < 8; k++) {
      c = c & 1 ? 0xedb88320 ^ (c >>> 1) : c >>> 1
    }
    table[n] = c >>> 0
  }
  return table
})()

function crc32(buf: Buffer): number {
  let crc = 0xffffffff
  for (let i = 0; i < buf.length; i++) {
    crc = CRC_TABLE[(crc ^ buf[i]) & 0xff] ^ (crc >>> 8)
  }
  return (crc ^ 0xffffffff) >>> 0
}

function chunk(type: string, data: Buffer): Buffer {
  const len = Buffer.alloc(4)
  len.writeUInt32BE(data.length, 0)
  const typeBuf = Buffer.from(type, 'ascii')
  const crcBuf = Buffer.alloc(4)
  crcBuf.writeUInt32BE(crc32(Buffer.concat([typeBuf, data])), 0)
  return Buffer.concat([len, typeBuf, data, crcBuf])
}

/** Parse '#rrggbb' → [r, g, b]. Throws on any other shape. */
export function parseHexColor(rgbHex: string): [number, number, number] {
  const m = /^#([0-9a-fA-F]{6})$/.exec(rgbHex)
  if (!m) {
    throw new Error(`parseHexColor: expected '#rrggbb', got '${rgbHex}'`)
  }
  const v = parseInt(m[1], 16)
  return [(v >> 16) & 0xff, (v >> 8) & 0xff, v & 0xff]
}

/**
 * Encode a width×height solid-color PNG (8-bit RGB, no alpha, no interlace).
 * Deterministic: same inputs → byte-identical output.
 */
export function encodePng(width: number, height: number, rgbHex: string): Buffer {
  if (!Number.isInteger(width) || !Number.isInteger(height) || width <= 0 || height <= 0) {
    throw new Error(`encodePng: invalid dimensions ${width}x${height}`)
  }
  const [r, g, b] = parseHexColor(rgbHex)

  const ihdr = Buffer.alloc(13)
  ihdr.writeUInt32BE(width, 0)
  ihdr.writeUInt32BE(height, 4)
  ihdr[8] = 8 // bit depth
  ihdr[9] = 2 // color type 2 = truecolor RGB
  ihdr[10] = 0 // compression: deflate
  ihdr[11] = 0 // filter method 0
  ihdr[12] = 0 // no interlace

  // Raw image data: per scanline, 1 filter byte (0 = None) + width*3 RGB bytes.
  const stride = 1 + width * 3
  const raw = Buffer.alloc(height * stride)
  for (let y = 0; y < height; y++) {
    const row = y * stride
    raw[row] = 0
    for (let x = 0; x < width; x++) {
      const px = row + 1 + x * 3
      raw[px] = r
      raw[px + 1] = g
      raw[px + 2] = b
    }
  }
  const idat = deflateSync(raw, { level: 9 })

  return Buffer.concat([
    PNG_SIGNATURE,
    chunk('IHDR', ihdr),
    chunk('IDAT', idat),
    chunk('IEND', Buffer.alloc(0)),
  ])
}