function hashSeed(seed: string): number {
  let h = 2166136261 >>> 0;
  for (let i = 0; i < seed.length; i += 1) {
    h ^= seed.charCodeAt(i);
    h = Math.imul(h, 16777619) >>> 0;
  }
  return h >>> 0;
}

function mulberry32(seed: number): () => number {
  let t = seed >>> 0;
  return () => {
    t += 0x6d2b79f5;
    let x = Math.imul(t ^ (t >>> 15), t | 1);
    x ^= x + Math.imul(x ^ (x >>> 7), x | 61);
    return ((x ^ (x >>> 14)) >>> 0) / 4294967296;
  };
}

const SKIN_PALETTE = ["#f6d3b3", "#e6be95", "#d7a980", "#f8dec6", "#c99264"];
const HAIR_PALETTE = ["#2f1b12", "#4a2f1d", "#6d4c41", "#212121", "#4e342e", "#1b5e20"];
const ACCENT_PALETTE = ["#7cb342", "#00b0d6", "#ffb300", "#8d6e63", "#ab47bc", "#ef5350"];

export function buildAvatarSeed(...parts: Array<string | number | null | undefined>): string {
  const cleaned = parts
    .map((part) => String(part ?? "").trim())
    .filter((part) => part.length > 0);
  return cleaned.length > 0 ? cleaned.join("|") : "guest|pixel";
}

export function generatePixelAvatarDataUri(seedInput: string, pixelSize = 10): string {
  const seed = buildAvatarSeed(seedInput);
  const rng = mulberry32(hashSeed(seed));
  const skin = SKIN_PALETTE[Math.floor(rng() * SKIN_PALETTE.length)] ?? SKIN_PALETTE[0];
  const hair = HAIR_PALETTE[Math.floor(rng() * HAIR_PALETTE.length)] ?? HAIR_PALETTE[0];
  const accent = ACCENT_PALETTE[Math.floor(rng() * ACCENT_PALETTE.length)] ?? ACCENT_PALETTE[0];
  const bg = rng() > 0.5 ? "#1f1f1f" : "#2b2b2b";
  const border = rng() > 0.5 ? "#000000" : "#3e2723";

  const width = 8 * pixelSize;
  const height = 8 * pixelSize;
  const rects: string[] = [
    `<rect width="${width}" height="${height}" fill="${bg}"/>`,
    `<rect x="0" y="0" width="${width}" height="${pixelSize}" fill="${accent}" opacity="0.4"/>`,
  ];

  for (let y = 0; y < 8; y += 1) {
    for (let x = 0; x < 4; x += 1) {
      const fillFace = y >= 1 && y <= 6 && x >= 1;
      const threshold = fillFace ? 0.2 : 0.52;
      if (rng() < threshold) continue;

      const color = y <= 1 ? hair : y >= 6 ? accent : skin;
      const leftX = x * pixelSize;
      const rightX = (7 - x) * pixelSize;
      const yPos = y * pixelSize;
      rects.push(`<rect x="${leftX}" y="${yPos}" width="${pixelSize}" height="${pixelSize}" fill="${color}"/>`);
      if (rightX !== leftX) {
        rects.push(`<rect x="${rightX}" y="${yPos}" width="${pixelSize}" height="${pixelSize}" fill="${color}"/>`);
      }
    }
  }

  const eyeY = 3 * pixelSize;
  rects.push(`<rect x="${2 * pixelSize}" y="${eyeY}" width="${pixelSize}" height="${pixelSize}" fill="#111"/>`);
  rects.push(`<rect x="${5 * pixelSize}" y="${eyeY}" width="${pixelSize}" height="${pixelSize}" fill="#111"/>`);

  const mouthY = 5 * pixelSize;
  rects.push(`<rect x="${3 * pixelSize}" y="${mouthY}" width="${2 * pixelSize}" height="${pixelSize}" fill="${hair}" opacity="0.8"/>`);
  rects.push(`<rect x="${0}" y="${0}" width="${width}" height="${height}" fill="none" stroke="${border}" stroke-width="${Math.max(2, Math.floor(pixelSize / 4))}"/>`);

  const svg = `<svg xmlns="http://www.w3.org/2000/svg" width="${width}" height="${height}" viewBox="0 0 ${width} ${height}" shape-rendering="crispEdges">${rects.join("")}</svg>`;
  return `data:image/svg+xml;utf8,${encodeURIComponent(svg)}`;
}