const INITIAL_STATE = new Uint32Array([
  0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
  0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19
]);

const ROUND_CONSTANTS = new Uint32Array([
  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 rotateRight(value, count) {
  return (value >>> count) | (value << (32 - count));
}

export class Sha256 {
  constructor() {
    this.state = INITIAL_STATE.slice();
    this.schedule = new Uint32Array(64);
    this.buffer = new Uint8Array(64);
    this.bufferLength = 0;
    this.bytes = 0;
    this.finished = false;
  }

  update(value) {
    if (this.finished) throw new Error('SHA-256 digest is already finalized');
    const bytes = value instanceof Uint8Array
      ? value
      : new Uint8Array(value.buffer || value, value.byteOffset || 0, value.byteLength);
    this.bytes += bytes.byteLength;
    let offset = 0;

    if (this.bufferLength) {
      const count = Math.min(64 - this.bufferLength, bytes.byteLength);
      this.buffer.set(bytes.subarray(0, count), this.bufferLength);
      this.bufferLength += count;
      offset = count;
      if (this.bufferLength === 64) {
        this.#compress(this.buffer);
        this.bufferLength = 0;
      }
    }

    while (offset + 64 <= bytes.byteLength) {
      this.#compress(bytes.subarray(offset, offset + 64));
      offset += 64;
    }
    if (offset < bytes.byteLength) {
      this.buffer.set(bytes.subarray(offset), 0);
      this.bufferLength = bytes.byteLength - offset;
    }
    return this;
  }

  #compress(block) {
    const words = this.schedule;
    for (let index = 0; index < 16; index += 1) {
      const offset = index * 4;
      words[index] = ((block[offset] << 24) | (block[offset + 1] << 16) |
        (block[offset + 2] << 8) | block[offset + 3]) >>> 0;
    }
    for (let index = 16; index < 64; index += 1) {
      const x = words[index - 15];
      const y = words[index - 2];
      const sigma0 = rotateRight(x, 7) ^ rotateRight(x, 18) ^ (x >>> 3);
      const sigma1 = rotateRight(y, 17) ^ rotateRight(y, 19) ^ (y >>> 10);
      words[index] = (words[index - 16] + sigma0 + words[index - 7] + sigma1) >>> 0;
    }

    let [a, b, c, d, e, f, g, h] = this.state;
    for (let index = 0; index < 64; index += 1) {
      const choice = (e & f) ^ (~e & g);
      const majority = (a & b) ^ (a & c) ^ (b & c);
      const sum0 = rotateRight(a, 2) ^ rotateRight(a, 13) ^ rotateRight(a, 22);
      const sum1 = rotateRight(e, 6) ^ rotateRight(e, 11) ^ rotateRight(e, 25);
      const first = (h + sum1 + choice + ROUND_CONSTANTS[index] + words[index]) >>> 0;
      const second = (sum0 + majority) >>> 0;
      h = g;
      g = f;
      f = e;
      e = (d + first) >>> 0;
      d = c;
      c = b;
      b = a;
      a = (first + second) >>> 0;
    }

    const values = [a, b, c, d, e, f, g, h];
    for (let index = 0; index < 8; index += 1) {
      this.state[index] = (this.state[index] + values[index]) >>> 0;
    }
  }

  digestHex() {
    if (this.finished) throw new Error('SHA-256 digest is already finalized');
    this.finished = true;
    const tail = new Uint8Array(this.bufferLength + 1 + 8 + 64);
    tail.set(this.buffer.subarray(0, this.bufferLength));
    tail[this.bufferLength] = 0x80;
    const paddedLength = Math.ceil((this.bufferLength + 1 + 8) / 64) * 64;
    const bitHigh = Math.floor(this.bytes / 0x20000000);
    const bitLow = (this.bytes * 8) >>> 0;
    const view = new DataView(tail.buffer);
    view.setUint32(paddedLength - 8, bitHigh, false);
    view.setUint32(paddedLength - 4, bitLow, false);
    for (let offset = 0; offset < paddedLength; offset += 64) {
      this.#compress(tail.subarray(offset, offset + 64));
    }
    return [...this.state].map((word) => word.toString(16).padStart(8, '0')).join('');
  }
}

export async function sha256Blob(blob, { signal } = {}) {
  const hash = new Sha256();
  const reader = blob.stream().getReader();
  let bytesSinceYield = 0;
  try {
    while (true) {
      if (signal?.aborted) throw signal.reason || new DOMException('Aborted', 'AbortError');
      const { done, value } = await reader.read();
      if (done) break;
      const bytes = value instanceof Uint8Array ? value : new Uint8Array(value);
      hash.update(bytes);
      bytesSinceYield += bytes.byteLength;
      if (bytesSinceYield >= 8 * 1024 * 1024) {
        bytesSinceYield = 0;
        if (typeof globalThis.scheduler?.yield === 'function') await globalThis.scheduler.yield();
        else await new Promise((resolve) => setTimeout(resolve, 0));
      }
    }
    return hash.digestHex();
  } catch (error) {
    await reader.cancel(error).catch(() => {});
    throw error;
  }
}
