/**
 * Gravatar URL helper using SHA-256 (Gravatar migrated from MD5 to SHA-256).
 */

function sha256Sync(input: string): string {
  // Use a synchronous SHA-256 implementation for Gravatar hashing.
  // SubtleCrypto is async-only, so we use a minimal pure-JS SHA-256.
  const K = [
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
  ];

  function rotr(x: number, n: number) { return (x >>> n) | (x << (32 - n)); }
  function ch(x: number, y: number, z: number) { return (x & y) ^ (~x & z); }
  function maj(x: number, y: number, z: number) { return (x & y) ^ (x & z) ^ (y & z); }
  function sigma0(x: number) { return rotr(x, 2) ^ rotr(x, 13) ^ rotr(x, 22); }
  function sigma1(x: number) { return rotr(x, 6) ^ rotr(x, 11) ^ rotr(x, 25); }
  function gamma0(x: number) { return rotr(x, 7) ^ rotr(x, 18) ^ (x >>> 3); }
  function gamma1(x: number) { return rotr(x, 17) ^ rotr(x, 19) ^ (x >>> 10); }

  const bytes = new TextEncoder().encode(input);
  const bitLen = bytes.length * 8;

  // Padding
  const padLen = ((bytes.length + 8 >> 6) + 1) << 6;
  const padded = new Uint8Array(padLen);
  padded.set(bytes);
  padded[bytes.length] = 0x80;
  const view = new DataView(padded.buffer);
  view.setUint32(padLen - 4, bitLen, false);

  let h0 = 0x6a09e667, h1 = 0xbb67ae85, h2 = 0x3c6ef372, h3 = 0xa54ff53a;
  let h4 = 0x510e527f, h5 = 0x9b05688c, h6 = 0x1f83d9ab, h7 = 0x5be0cd19;

  const w = new Int32Array(64);

  for (let offset = 0; offset < padLen; offset += 64) {
    const block = new DataView(padded.buffer, offset, 64);
    for (let i = 0; i < 16; i++) w[i] = block.getInt32(i * 4, false);
    for (let i = 16; i < 64; i++) w[i] = (gamma1(w[i - 2]) + w[i - 7] + gamma0(w[i - 15]) + w[i - 16]) | 0;

    let a = h0, b = h1, c = h2, d = h3, e = h4, f = h5, g = h6, h = h7;

    for (let i = 0; i < 64; i++) {
      const t1 = (h + sigma1(e) + ch(e, f, g) + K[i] + w[i]) | 0;
      const t2 = (sigma0(a) + maj(a, b, c)) | 0;
      h = g; g = f; f = e; e = (d + t1) | 0;
      d = c; c = b; b = a; a = (t1 + t2) | 0;
    }

    h0 = (h0 + a) | 0; h1 = (h1 + b) | 0; h2 = (h2 + c) | 0; h3 = (h3 + d) | 0;
    h4 = (h4 + e) | 0; h5 = (h5 + f) | 0; h6 = (h6 + g) | 0; h7 = (h7 + h) | 0;
  }

  const hex = (n: number) => (n >>> 0).toString(16).padStart(8, '0');
  return hex(h0) + hex(h1) + hex(h2) + hex(h3) + hex(h4) + hex(h5) + hex(h6) + hex(h7);
}

/**
 * Generate a Gravatar URL from an email address.
 * Uses SHA-256 (Gravatar's current API).
 * @param email - The user's email
 * @param size - Image size in pixels (default 32)
 * @returns Gravatar URL with 'retro' fallback for unregistered emails
 */
export function gravatarUrl(email: string, size = 32): string {
  const hash = sha256Sync(email.trim().toLowerCase());
  return `https://www.gravatar.com/avatar/${hash}?s=${size}&d=retro`;
}

/**
 * Generate initials from a pseudo (for avatar fallback).
 * @returns 1-2 uppercase letters
 */
export function initialsFromPseudo(pseudo: string): string {
  const parts = pseudo.trim().split(/\s+/);
  if (parts.length >= 2) return (parts[0][0] + parts[1][0]).toUpperCase();
  return pseudo.slice(0, 2).toUpperCase();
}
