// One-off dev-time script — generates the app's PWA icon PNGs with zero
// dependencies (no ImageMagick/PIL/canvas available in this environment).
// Run once (`node scripts/generate-icons.js`), commit the output under
// public/icons/ like any other static asset. Not required at runtime.

const fs = require('node:fs');
const path = require('node:path');
const zlib = require('node:zlib');

const OUT_DIR = path.join(__dirname, '..', 'public', 'icons');

// App's own --school blue (public/css/shared.css)
const BG = [74, 144, 217];
const WHITE = [255, 255, 255];

function distToSegment(px, py, x1, y1, x2, y2) {
  const dx = x2 - x1;
  const dy = y2 - y1;
  const lengthSq = dx * dx + dy * dy;
  let t = lengthSq === 0 ? 0 : ((px - x1) * dx + (py - y1) * dy) / lengthSq;
  t = Math.max(0, Math.min(1, t));
  const cx = x1 + t * dx;
  const cy = y1 + t * dy;
  return Math.hypot(px - cx, py - cy);
}

// Rounded-rect coverage (0..1) for anti-aliased corners; `radius` in px.
function roundedRectCoverage(x, y, w, h, radius) {
  const inCoreX = x >= radius && x <= w - radius;
  const inCoreY = y >= radius && y <= h - radius;
  if (inCoreX || inCoreY) return 1;

  const cx = x < radius ? radius : w - radius;
  const cy = y < radius ? radius : h - radius;
  const dist = Math.hypot(x - cx, y - cy);
  if (dist <= radius - 0.5) return 1;
  if (dist >= radius + 0.5) return 0;
  return radius + 0.5 - dist; // 1px anti-aliased band
}

function mix(a, b, t) {
  return a + (b - a) * t;
}

// Checkmark path, proportional to icon size.
function checkmarkCoverage(x, y, size, strokeHalfWidth) {
  const p1 = [size * 0.27, size * 0.53];
  const p2 = [size * 0.43, size * 0.68];
  const p3 = [size * 0.74, size * 0.32];
  const d = Math.min(
    distToSegment(x, y, p1[0], p1[1], p2[0], p2[1]),
    distToSegment(x, y, p2[0], p2[1], p3[0], p3[1])
  );
  if (d <= strokeHalfWidth - 0.5) return 1;
  if (d >= strokeHalfWidth + 0.5) return 0;
  return strokeHalfWidth + 0.5 - d;
}

function renderIcon({ size, cornerRadiusRatio, glyphStrokeRatio }) {
  const buf = Buffer.alloc(size * size * 4);
  const radius = size * cornerRadiusRatio;
  const strokeHalfWidth = size * glyphStrokeRatio;

  for (let y = 0; y < size; y++) {
    for (let x = 0; x < size; x++) {
      const bgCoverage = cornerRadiusRatio > 0 ? roundedRectCoverage(x + 0.5, y + 0.5, size, size, radius) : 1;
      const glyphCoverage = checkmarkCoverage(x + 0.5, y + 0.5, size, strokeHalfWidth);

      // Composite: background (with its own edge coverage against
      // transparent) under the white glyph stroke.
      let r = mix(0, BG[0], bgCoverage);
      let g = mix(0, BG[1], bgCoverage);
      let b = mix(0, BG[2], bgCoverage);
      let a = mix(0, 255, bgCoverage);

      r = mix(r, WHITE[0], glyphCoverage);
      g = mix(g, WHITE[1], glyphCoverage);
      b = mix(b, WHITE[2], glyphCoverage);
      a = mix(a, 255, glyphCoverage);

      const idx = (y * size + x) * 4;
      buf[idx] = Math.round(r);
      buf[idx + 1] = Math.round(g);
      buf[idx + 2] = Math.round(b);
      buf[idx + 3] = Math.round(a);
    }
  }

  return buf;
}

function crc32(buf) {
  return zlib.crc32(buf);
}

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

function encodePng(rgbaBuf, width, height) {
  const signature = Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]);

  const ihdrData = Buffer.alloc(13);
  ihdrData.writeUInt32BE(width, 0);
  ihdrData.writeUInt32BE(height, 4);
  ihdrData[8] = 8; // bit depth
  ihdrData[9] = 6; // color type: truecolor + alpha
  ihdrData[10] = 0; // compression
  ihdrData[11] = 0; // filter
  ihdrData[12] = 0; // interlace
  const ihdr = chunk('IHDR', ihdrData);

  const stride = width * 4;
  const raw = Buffer.alloc((stride + 1) * height);
  for (let y = 0; y < height; y++) {
    raw[y * (stride + 1)] = 0; // filter type: None
    rgbaBuf.copy(raw, y * (stride + 1) + 1, y * stride, y * stride + stride);
  }
  const idat = chunk('IDAT', zlib.deflateSync(raw));

  const iend = chunk('IEND', Buffer.alloc(0));

  return Buffer.concat([signature, ihdr, idat, iend]);
}

function writeIcon(filename, { size, cornerRadiusRatio, glyphStrokeRatio }) {
  const rgba = renderIcon({ size, cornerRadiusRatio, glyphStrokeRatio });
  const png = encodePng(rgba, size, size);
  fs.mkdirSync(OUT_DIR, { recursive: true });
  fs.writeFileSync(path.join(OUT_DIR, filename), png);
  console.log(`wrote ${filename} (${png.length} bytes)`);
}

writeIcon('icon-192.png', { size: 192, cornerRadiusRatio: 0.18, glyphStrokeRatio: 0.045 });
writeIcon('icon-512.png', { size: 512, cornerRadiusRatio: 0.18, glyphStrokeRatio: 0.045 });
writeIcon('apple-touch-icon-180.png', { size: 180, cornerRadiusRatio: 0.18, glyphStrokeRatio: 0.045 });
// Maskable: background fills edge-to-edge (no rounding — the OS applies its
// own mask), glyph confined within the inner ~80% "safe zone" is handled
// implicitly here since the checkmark path itself is well within that area.
writeIcon('icon-maskable-512.png', { size: 512, cornerRadiusRatio: 0, glyphStrokeRatio: 0.038 });