import {FileProviderInterface} from './file-provider-interface';

/**
 * Checks if bigint can be converted to number and convert it if possible
 * @param bigint bigint to be converted
 * @returns number
 */
const toNumber = (bigint: bigint) => {
  if (bigint > Number.MAX_SAFE_INTEGER) {
    throw new Error('Offset is out of bounds');
  }
  return Number(bigint);
};

/**
 * Provides file data using DataView
 * @deprecated - will be replaced with ReadableFile
 */
export class DataViewFile implements FileProviderInterface {
  /** The DataView from which data is provided */
  private file: DataView;

  constructor(file: DataView) {
    this.file = file;
  }

  async destroy(): Promise<void> {}

  /**
   * Gets an unsigned 8-bit integer at the specified byte offset from the start of the file.
   * @param offset The offset, in bytes, from the start of the file where to read the data.
   */
  async getUint8(offset: bigint): Promise<number> {
    return this.file.getUint8(toNumber(offset));
  }

  /**
   * Gets an unsigned 16-bit intege at the specified byte offset from the start of the file.
   * @param offset The offset, in bytes, from the start of the file where to read the data.
   */
  async getUint16(offset: bigint): Promise<number> {
    return this.file.getUint16(toNumber(offset), true);
  }

  /**
   * Gets an unsigned 32-bit integer at the specified byte offset from the start of the file.
   * @param offset The offset, in bytes, from the start of the file where to read the data.
   */
  async getUint32(offset: bigint): Promise<number> {
    return this.file.getUint32(toNumber(offset), true);
  }

  /**
   * Gets an unsigned 64-bit integer at the specified byte offset from the start of the file.
   * @param offset The offset, in bytes, from the start of the file where to read the data.
   */
  async getBigUint64(offset: bigint): Promise<bigint> {
    return this.file.getBigUint64(toNumber(offset), true);
  }

  /**
   * returns an ArrayBuffer whose contents are a copy of this file bytes from startOffset, inclusive, up to endOffset, exclusive.
   * @param startOffset The offset, in bytes, from the start of the file where to start reading the data.
   * @param endOffset The offset, in bytes, from the start of the file where to end reading the data.
   */
  async slice(startOffset: bigint, endOffset: bigint): Promise<ArrayBuffer> {
    return this.file.buffer.slice(toNumber(startOffset), toNumber(endOffset));
  }

  /** the length (in bytes) of the data. */
  get length() {
    return BigInt(this.file.byteLength);
  }
}