const SHORT_EDGE = 768
const LONG_EDGE = 1344

export const ASPECT_PRESETS: Record<string, { width: number; height: number }> = {
  '16:9': { width: 1344, height: 768 },
  '9:16': { width: 768, height: 1344 },
  '1:1': { width: 1024, height: 1024 }
}

export function snap32(value: number) {
  return Math.max(32, Math.round(value / 32) * 32)
}

/** Fit the source still to H3's native 768 short-edge canvas, 32px grid, 1344 long-edge cap. */
export function autoResolution(srcWidth: number, srcHeight: number) {
  const ratio = srcWidth / Math.max(srcHeight, 1)
  let width: number
  let height: number
  if (ratio >= 1) {
    height = SHORT_EDGE
    width = Math.min(LONG_EDGE, height * ratio)
  } else {
    width = SHORT_EDGE
    height = Math.min(LONG_EDGE, width / ratio)
  }
  width = snap32(width)
  height = snap32(height)
  if (width > LONG_EDGE) width = LONG_EDGE
  if (height > LONG_EDGE) height = LONG_EDGE
  return { width: Math.max(32, width), height: Math.max(32, height) }
}

export function imageDimensions(buf: Buffer) {
  if (buf.length < 24) return null
  if (buf[0] === 0x89 && buf[1] === 0x50 && buf[2] === 0x4e && buf[3] === 0x47) {
    return { width: buf.readUInt32BE(16), height: buf.readUInt32BE(20) }
  }
  if (buf[0] === 0x47 && buf[1] === 0x49 && buf[2] === 0x46) {
    return { width: buf.readUInt16LE(6), height: buf.readUInt16LE(8) }
  }
  if (buf[0] === 0x42 && buf[1] === 0x4d && buf.length >= 26) {
    return { width: buf.readInt32LE(18), height: Math.abs(buf.readInt32LE(22)) }
  }
  if (buf.toString('ascii', 0, 4) === 'RIFF' && buf.toString('ascii', 8, 12) === 'WEBP') {
    return webpSize(buf)
  }
  if (buf[0] === 0xff && buf[1] === 0xd8) {
    return jpegSize(buf)
  }
  return null
}

function webpSize(buf: Buffer) {
  const kind = buf.toString('ascii', 12, 16)
  if (kind === 'VP8X' && buf.length >= 30) {
    const width = 1 + buf[24] + (buf[25] << 8) + (buf[26] << 16)
    const height = 1 + buf[27] + (buf[28] << 8) + (buf[29] << 16)
    return { width, height }
  }
  if (kind === 'VP8 ' && buf.length >= 30) {
    return { width: buf.readUInt16LE(26) & 0x3fff, height: buf.readUInt16LE(28) & 0x3fff }
  }
  if (kind === 'VP8L' && buf.length >= 25) {
    const bits = buf.readUInt32LE(21)
    return { width: (bits & 0x3fff) + 1, height: ((bits >> 14) & 0x3fff) + 1 }
  }
  return null
}

function jpegSize(buf: Buffer) {
  let offset = 2
  while (offset + 9 < buf.length) {
    if (buf[offset] !== 0xff) return null
    const marker = buf[offset + 1]
    if (marker === 0xd8 || marker === 0xd9) {
      offset += 2
      continue
    }
    const length = buf.readUInt16BE(offset + 2)
    if (marker >= 0xc0 && marker <= 0xc3) {
      return { width: buf.readUInt16BE(offset + 7), height: buf.readUInt16BE(offset + 5) }
    }
    offset += 2 + length
  }
  return null
}

export function resolveOutputSize(aspect: string | undefined, image: Buffer, fallbackWidth?: number, fallbackHeight?: number) {
  if (aspect && ASPECT_PRESETS[aspect]) {
    return ASPECT_PRESETS[aspect]
  }
  const fromFields = Number(fallbackWidth) && Number(fallbackHeight)
    ? { width: snap32(Number(fallbackWidth)), height: snap32(Number(fallbackHeight)) }
    : null
  const size = imageDimensions(image)
  if (size?.width && size?.height) {
    return autoResolution(size.width, size.height)
  }
  return fromFields || ASPECT_PRESETS['16:9']
}