import { fail } from './errors.js';

export class BinaryReader {
  readonly bytes: Uint8Array;
  readonly end: number;
  offset: number;
  private readonly view: DataView;

  constructor(bytes: Uint8Array, offset = 0, end = bytes.byteLength) {
    if (offset < 0 || end < offset || end > bytes.byteLength) {
      throw new RangeError('Invalid BinaryReader range');
    }
    this.bytes = bytes;
    this.offset = offset;
    this.end = end;
    this.view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
  }

  ensure(length: number, structure: string): void {
    if (
      !Number.isSafeInteger(length) ||
      length < 0 ||
      this.offset > this.end - length
    ) {
      fail(
        'cab-unexpected-eof',
        `Unexpected end of cabinet while reading ${structure}.`,
        { offset: this.offset, structure }
      );
    }
  }

  readU8(structure: string): number {
    this.ensure(1, structure);
    return this.bytes[this.offset++]!;
  }

  readU16(structure: string): number {
    this.ensure(2, structure);
    const value = this.view.getUint16(this.offset, true);
    this.offset += 2;
    return value;
  }

  readU32(structure: string): number {
    this.ensure(4, structure);
    const value = this.view.getUint32(this.offset, true);
    this.offset += 4;
    return value;
  }

  readBytes(length: number, structure: string): Uint8Array {
    this.ensure(length, structure);
    const result = this.bytes.subarray(this.offset, this.offset + length);
    this.offset += length;
    return result;
  }

  skip(length: number, structure: string): void {
    this.ensure(length, structure);
    this.offset += length;
  }

  readNullTerminatedBytes(maxBytes: number, structure: string): Uint8Array {
    const start = this.offset;
    while (this.offset < this.end && this.bytes[this.offset] !== 0) {
      if (this.offset - start >= maxBytes) {
        fail(
          'cab-name-too-long',
          `Cabinet string exceeds the configured ${maxBytes}-byte limit.`,
          { offset: start, structure }
        );
      }
      this.offset += 1;
    }
    if (this.offset >= this.end) {
      fail('cab-unterminated-string', 'Cabinet string is not NUL-terminated.', {
        offset: start,
        structure,
      });
    }
    const value = this.bytes.subarray(start, this.offset);
    this.offset += 1;
    return value;
  }
}