import { deflateSync } from 'zlib'
import { nativeImage, type NativeImage } from 'electron'

// CRC32 table polynomial used by PNG.
function crc32(buf: Buffer): number {
  let crc = 0xffffffff
  for (const b of buf) {
    crc ^= b
    for (let i = 0; i < 8; i++) crc = crc & 1 ? (crc >>> 1) ^ 0xedb88320 : crc >>> 1
  }
  return (crc ^ 0xffffffff) >>> 0
}

function pngChunk(type: string, data: Buffer): Buffer {
  const t = Buffer.from(type, 'ascii')
  const len = Buffer.alloc(4)
  len.writeUInt32BE(data.length)
  const crc = Buffer.alloc(4)
  crc.writeUInt32BE(crc32(Buffer.concat([t, data])))
  return Buffer.concat([len, t, data, crc])
}

/**
 * Build a 16×16 RGBA PNG containing a solid-colour filled circle. Used for the
 * Windows taskbar overlay badge. No external deps — pure Node.js (Buffer + zlib).
 */
function makeDotPng(r: number, g: number, b: number): NativeImage {
  const W = 16,
    H = 16
  const px = Buffer.alloc(W * H * 4, 0) // transparent bg
  const cx = W / 2,
    cy = H / 2,
    rad = W / 2 - 1.5

  for (let y = 0; y < H; y++) {
    for (let x = 0; x < W; x++) {
      const dx = x + 0.5 - cx,
        dy = y + 0.5 - cy
      if (dx * dx + dy * dy <= rad * rad) {
        const i = (y * W + x) * 4
        px[i] = r
        px[i + 1] = g
        px[i + 2] = b
        px[i + 3] = 255
      }
    }
  }

  // PNG: IHDR (8-bit RGBA, no interlace), filter-0 rows, deflated IDAT, IEND.
  const ihdr = Buffer.alloc(13)
  ihdr.writeUInt32BE(W, 0)
  ihdr.writeUInt32BE(H, 4)
  ihdr[8] = 8 // bit depth
  ihdr[9] = 6 // colour type: RGBA

  const rows = Buffer.alloc(H * (1 + W * 4))
  for (let y = 0; y < H; y++) {
    rows[y * (1 + W * 4)] = 0 // filter type: None
    px.copy(rows, y * (1 + W * 4) + 1, y * W * 4, (y + 1) * W * 4)
  }

  const sig = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10])
  const png = Buffer.concat([
    sig,
    pngChunk('IHDR', ihdr),
    pngChunk('IDAT', deflateSync(rows)),
    pngChunk('IEND', Buffer.alloc(0))
  ])
  return nativeImage.createFromBuffer(png)
}

// Lazy-initialised singletons — created on first use so this module is safe to
// import before the app is ready (nativeImage.createFromBuffer is fine post-ready).
let activeBadge: NativeImage | null = null
let errorBadge: NativeImage | null = null

/** Green dot badge for the taskbar overlay — shown when downloads are active. */
export function getActiveBadge(): NativeImage {
  if (!activeBadge) activeBadge = makeDotPng(58, 185, 108) // #3ab96c
  return activeBadge
}

/** Red dot badge for the taskbar overlay — shown when a download has errored. */
export function getErrorBadge(): NativeImage {
  if (!errorBadge) errorBadge = makeDotPng(217, 48, 37) // #d93025
  return errorBadge
}