/**
 * Generates the PWA icon set (pure Node, no image dependencies):
 *   public/icons/icon-192.png          (manifest, "any")
 *   public/icons/icon-512.png          (manifest, "any")
 *   public/icons/icon-maskable-512.png (manifest, "maskable" – content in safe zone)
 *   public/icons/apple-touch-icon.png  (iOS home screen, 180px)
 *
 * Run: node scripts/generate-icons.mjs
 */
import fs from 'node:fs'
import path from 'node:path'
import zlib from 'node:zlib'
import { fileURLToPath } from 'node:url'

const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..')
const OUT = path.join(ROOT, 'public', 'icons')

// ---------------------------------------------------------------- tiny canvas
/** analytic-coverage rasterizer: supersample 4x4 point samples per pixel */
function render(size, shapes, background) {
  const px = new Uint8Array(size * size * 4)
  const S = 4 // supersampling factor
  for (let y = 0; y < size; y++) {
    for (let x = 0; x < size; x++) {
      let r = 0
      let g = 0
      let b = 0
      let covered = 0
      for (let sy = 0; sy < S; sy++) {
        for (let sx = 0; sx < S; sx++) {
          const fx = x + (sx + 0.5) / S
          const fy = y + (sy + 0.5) / S
          const hit = topmost(shapes, fx, fy)
          const bg = background(fx, fy)
          const c = hit ?? bg
          r += c[0]
          g += c[1]
          b += c[2]
          if (hit) covered++
        }
      }
      const n = S * S
      const i = (y * size + x) * 4
      px[i] = Math.round(r / n)
      px[i + 1] = Math.round(g / n)
      px[i + 2] = Math.round(b / n)
      px[i + 3] = 255
    }
  }
  return px
}

function topmost(shapes, x, y) {
  for (let i = shapes.length - 1; i >= 0; i--) {
    if (shapes[i].hit(x, y)) return shapes[i].color
  }
  return null
}

function rect(x1, y1, x2, y2, color) {
  return { hit: (x, y) => x >= x1 && x < x2 && y >= y1 && y < y2, color }
}

function circle(cx, cy, r, color) {
  return { hit: (x, y) => (x - cx) ** 2 + (y - cy) ** 2 < r * r, color }
}

// ---------------------------------------------------------------- design
// coordinates in a 512x512 design space; `s` scales the motif into the
// maskable safe zone, everything stays centered
function towerShapes(s = 1) {
  const t = (v) => 256 + (v - 256) * s
  const gold = [245, 197, 66]
  const goldDark = [217, 169, 46]
  const goldDeep = [196, 148, 32]
  const dark = [23, 18, 10]
  return [
    rect(t(168), t(396), t(344), t(432), goldDeep), // plinth
    rect(t(186), t(196), t(326), t(400), gold), // tower body
    rect(t(186), t(196), t(210), t(400), goldDark), // body shading (left)
    rect(t(186), t(166), t(218), t(198), gold), // merlon 1
    rect(t(237), t(166), t(269), t(198), gold), // merlon 2
    rect(t(288), t(166), t(320), t(198), gold), // merlon 3
    circle(t(256), t(338), t(20) - t(0), dark), // door arch
    rect(t(236), t(338), t(276), t(400), dark), // door
    rect(t(247), t(238), t(265), t(292), dark), // window slit
  ]
}

/** vertical gradient background matching the game theme */
function bg(x, y) {
  const k = y / 511
  const top = [30, 42, 61]
  const bottom = [14, 19, 26]
  return [
    Math.round(top[0] + (bottom[0] - top[0]) * k),
    Math.round(top[1] + (bottom[1] - top[1]) * k),
    Math.round(top[2] + (bottom[2] - top[2]) * k),
  ]
}

// ---------------------------------------------------------------- PNG encoder
const CRC_TABLE = (() => {
  const table = new Int32Array(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
  }
  return table
})()

function crc32(buf) {
  let c = -1
  for (let i = 0; i < buf.length; i++) c = CRC_TABLE[(c ^ buf[i]) & 0xff] ^ (c >>> 8)
  return (c ^ -1) >>> 0
}

function chunk(type, data) {
  const out = Buffer.alloc(12 + data.length)
  out.writeUInt32BE(data.length, 0)
  out.write(type, 4, 'ascii')
  data.copy(out, 8)
  out.writeUInt32BE(crc32(out.subarray(4, 8 + data.length)), 8 + data.length)
  return out
}

function encodePng(size, rgba) {
  const ihdr = Buffer.alloc(13)
  ihdr.writeUInt32BE(size, 0)
  ihdr.writeUInt32BE(size, 4)
  ihdr[8] = 8 // bit depth
  ihdr[9] = 6 // color type RGBA
  const raw = Buffer.alloc(size * (size * 4 + 1))
  for (let y = 0; y < size; y++) {
    raw[y * (size * 4 + 1)] = 0 // filter: none
    Buffer.from(rgba.buffer, y * size * 4, size * 4).copy(raw, y * (size * 4 + 1) + 1)
  }
  return Buffer.concat([
    Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]),
    chunk('IHDR', ihdr),
    chunk('IDAT', zlib.deflateSync(raw, { level: 9 })),
    chunk('IEND', Buffer.alloc(0)),
  ])
}

// ---------------------------------------------------------------- generate
fs.mkdirSync(OUT, { recursive: true })

const targets = [
  { file: 'icon-192.png', size: 192, maskable: false },
  { file: 'icon-512.png', size: 512, maskable: false },
  { file: 'icon-maskable-512.png', size: 512, maskable: true },
  { file: 'apple-touch-icon.png', size: 180, maskable: false },
]

for (const { file, size, maskable } of targets) {
  const k = size / 512 // design space -> pixel space
  const shapes = towerShapes(maskable ? 0.66 : 0.92).map((sh) => {
    // scale design coordinates into pixel space by wrapping the hit test
    const hit = sh.hit
    return { hit: (x, y) => hit(x / k, y / k), color: sh.color }
  })
  const background = (x, y) => bg(x / k, y / k)
  const px = render(size, shapes, background)
  fs.writeFileSync(path.join(OUT, file), encodePng(size, px))
  console.log(`erstellt: public/icons/${file} (${size}x${size}${maskable ? ', maskable' : ''})`)
}