const AVATAR_PALETTES = [
  ["#1f2937", "#3b82f6"],
  ["#0f172a", "#22c55e"],
  ["#172554", "#06b6d4"],
  ["#3f1d2e", "#ec4899"],
  ["#1f2937", "#f59e0b"],
  ["#111827", "#a855f7"],
  ["#052e16", "#14b8a6"],
  ["#3f3f46", "#e11d48"],
] as const;

export function getInitials(name?: string): string {
  return (name || "User")
    .split(/\s+/)
    .filter(Boolean)
    .slice(0, 2)
    .map((part) => part[0]?.toUpperCase() || "")
    .join("") || "U";
}

function hashSeed(seed: string): number {
  let hash = 0;
  for (let i = 0; i < seed.length; i += 1) {
    hash = (hash * 31 + seed.charCodeAt(i)) >>> 0;
  }
  return hash;
}

export function generateAvatarDataUrl(seed: string, name?: string, paletteOffset = 0): string {
  const safeSeed = seed || "default";
  const hash = hashSeed(safeSeed);
  const paletteIndex = (hash + paletteOffset) % AVATAR_PALETTES.length;
  const palette = AVATAR_PALETTES[paletteIndex];
  const initials = getInitials(name);

  const svg = `
<svg xmlns="http://www.w3.org/2000/svg" width="128" height="128" viewBox="0 0 128 128">
  <defs>
    <linearGradient id="g" x1="0" y1="0" x2="1" y2="1">
      <stop offset="0%" stop-color="${palette[0]}"/>
      <stop offset="100%" stop-color="${palette[1]}"/>
    </linearGradient>
  </defs>
  <rect width="128" height="128" fill="url(#g)"/>
  <circle cx="64" cy="64" r="52" fill="rgba(255,255,255,0.12)"/>
  <text x="64" y="78" text-anchor="middle" font-family="Arial, sans-serif" font-size="44" font-weight="700" fill="white">${initials}</text>
</svg>`;

  return `data:image/svg+xml;utf8,${encodeURIComponent(svg)}`;
}

export function buildAvatarPresets(seed: string, name?: string, count = 6): string[] {
  const urls: string[] = [];
  for (let i = 0; i < count; i += 1) {
    urls.push(generateAvatarDataUrl(`${seed}:${i}`, name, i));
  }
  return urls;
}