/**
 * Pure-JS SHA-256 (no native module / no expo-crypto dependency).
 * EAS 빌드 안전: 추가 네이티브 모듈 불필요.
 * PIN 평문 저장 금지 — 이 해시 결과만 SecureStore에 저장한다.
 */

function rrot(x: number, n: number): number {
  return (x >>> n) | (x << (32 - n))
}

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 toBytes(str: string): number[] {
  const utf8: number[] = []
  for (let i = 0; i < str.length; i++) {
    let c = str.charCodeAt(i)
    if (c < 0x80) utf8.push(c)
    else if (c < 0x800) {
      utf8.push(0xc0 | (c >> 6), 0x80 | (c & 0x3f))
    } else if (c < 0xd800 || c >= 0xe000) {
      utf8.push(0xe0 | (c >> 12), 0x80 | ((c >> 6) & 0x3f), 0x80 | (c & 0x3f))
    } else {
      i++
      c = 0x10000 + (((c & 0x3ff) << 10) | (str.charCodeAt(i) & 0x3ff))
      utf8.push(
        0xf0 | (c >> 18),
        0x80 | ((c >> 12) & 0x3f),
        0x80 | ((c >> 6) & 0x3f),
        0x80 | (c & 0x3f)
      )
    }
  }
  return utf8
}

const HEX = '0123456789abcdef'

/** SHA-256 → hex 문자열 */
export function sha256(message: string): string {
  const bytes = toBytes(message)
  const l = bytes.length
  const bitLen = l * 8

  bytes.push(0x80)
  while (bytes.length % 64 !== 56) bytes.push(0)
  // 64-bit length (high 32 bits = 0 for our use)
  for (let i = 0; i < 4; i++) bytes.push(0)
  bytes.push((bitLen >>> 24) & 0xff, (bitLen >>> 16) & 0xff, (bitLen >>> 8) & 0xff, bitLen & 0xff)

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

  const w = new Array(64)
  for (let off = 0; off < bytes.length; off += 64) {
    for (let i = 0; i < 16; i++) {
      w[i] =
        (bytes[off + i * 4] << 24) |
        (bytes[off + i * 4 + 1] << 16) |
        (bytes[off + i * 4 + 2] << 8) |
        bytes[off + i * 4 + 3]
    }
    for (let i = 16; i < 64; i++) {
      const s0 = rrot(w[i - 15], 7) ^ rrot(w[i - 15], 18) ^ (w[i - 15] >>> 3)
      const s1 = rrot(w[i - 2], 17) ^ rrot(w[i - 2], 19) ^ (w[i - 2] >>> 10)
      w[i] = (w[i - 16] + s0 + w[i - 7] + s1) | 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 S1 = rrot(e, 6) ^ rrot(e, 11) ^ rrot(e, 25)
      const ch = (e & f) ^ (~e & g)
      const t1 = (h + S1 + ch + K[i] + w[i]) | 0
      const S0 = rrot(a, 2) ^ rrot(a, 13) ^ rrot(a, 22)
      const maj = (a & b) ^ (a & c) ^ (b & c)
      const t2 = (S0 + maj) | 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 out = [h0, h1, h2, h3, h4, h5, h6, h7]
  let hex = ''
  for (const n of out) {
    for (let s = 28; s >= 0; s -= 4) hex += HEX[(n >>> s) & 0xf]
  }
  return hex
}