/** Chunk size used when rebuilding attachment blobs from disk without blocking the UI thread. */
export const ATTACHMENT_BLOB_READ_CHUNK_SIZE_BYTES = 256 * 1024;

/** Number of bytes encoded per chunk to keep base64 encoding off the call stack. */
const BASE64_ENCODE_CHUNK_SIZE = 0x8000;

/** Decode a base64 payload into bytes for Blob construction. */
export function decodeBase64ToUint8Array(base64: string): Uint8Array {
  const binary = atob(base64);
  const bytes = new Uint8Array(binary.length);

  for (let index = 0; index < binary.length; index++) {
    bytes[index] = binary.charCodeAt(index);
  }

  return bytes;
}

/** Encode bytes into a base64 payload, chunked so large buffers cannot overflow the call stack. */
export function encodeUint8ArrayToBase64(bytes: Uint8Array): string {
  let binary = '';

  for (let offset = 0; offset < bytes.length; offset += BASE64_ENCODE_CHUNK_SIZE) {
    const chunk = bytes.subarray(offset, offset + BASE64_ENCODE_CHUNK_SIZE);

    binary += String.fromCharCode(...chunk);
  }

  return btoa(binary);
}

/** Returns the decoded byte length of a base64 payload without allocating the bytes. */
export function base64DecodedByteLength(base64: string): number {
  const padding = base64.endsWith('==') ? 2 : base64.endsWith('=') ? 1 : 0;

  return Math.max(0, Math.floor((base64.length * 3) / 4) - padding);
}

/** Yield control back to the browser so long attachment hydration cannot freeze Electron. */
export function yieldToAttachmentHydrationLoop(): Promise<void> {
  return new Promise((resolve) => {
    setTimeout(resolve, 0);
  });
}