import { InputStream } from './InputStream';

'use strict';

/**
 * Base64DecodeInputStream
 * @author Kazuhiko Arase
 */
export class Base64DecodeInputStream extends InputStream {

  private buffer = 0;
  private buflen = 0;

  constructor(private istream: InputStream) {
    super();
  }

  public readByte(): number {

    while (this.buflen < 8) {

      var c = this.istream.readByte();

      if (c == -1) {

        if (this.buflen == 0) {
          return -1;
        }

        throw 'unexpected end of file./' + this.buflen;

      } else if (c == '='.charCodeAt(0)) {

        this.buflen = 0;
        return -1;

      } else if (Base64DecodeInputStream.isWhitespace(c)) {
        // ignore if whitespace.
        continue;
      }

      this.buffer = (this.buffer << 6) |
        Base64DecodeInputStream.decode(c);
      this.buflen += 6;
    }

    var n = (this.buffer >>> (this.buflen - 8)) & 0xff;
    this.buflen -= 8;
    return n;
  }

  private static isWhitespace(c: number): boolean {
    return c == '\v'.charCodeAt(0) ||
      c == '\t'.charCodeAt(0) ||
      c == '\r'.charCodeAt(0) ||
      c == '\n'.charCodeAt(0);
  }

  private static decode(c: number): number {
    if ('A'.charCodeAt(0) <= c && c <= 'Z'.charCodeAt(0)) {
      return c - 'A'.charCodeAt(0);
    } else if ('a'.charCodeAt(0) <= c && c <= 'z'.charCodeAt(0)) {
      return c - 'a'.charCodeAt(0) + 26;
    } else if ('0'.charCodeAt(0) <= c && c <= '9'.charCodeAt(0)) {
      return c - '0'.charCodeAt(0) + 52;
    } else if (c == '+'.charCodeAt(0)) {
      return 62;
    } else if (c == '/'.charCodeAt(0)) {
      return 63;
    } else {
      throw 'c:' + c;
    }
  }
}