/*
    * Copyright (C) 2005-2015 Schlichtherle IT Services.
    * All rights reserved. Use is subject to license terms.
    */
   package net.java.truevfs.comp.zip;
   
   import javax.annotation.concurrent.NotThreadSafe;
   import net.java.truecommons.key.spec.common.AesKeyStrength;
   import static net.java.truecommons.key.spec.common.AesKeyStrength.BITS_128;
  import static net.java.truevfs.comp.zip.LittleEndian.readUShort;
  import static net.java.truevfs.comp.zip.LittleEndian.writeShort;
  
  /**
   * WinZip AES Extra Field.
   *
   * @see     <a href="http://www.winzip.com/win/en/aes_info.htm">AES Encryption Information: Encryption Specification AE-1 and AE-2 (WinZip Computing, S.L.)</a>
   * @see     <a href="http://www.winzip.com/win/en/aes_tips.htm">AES Coding Tips for Developers (WinZip Computing, S.L.)</a>
   * @see     RawZipOutputStream$WinZipAesOutputMethod
   * @author  Christian Schlichtherle
   */
  @NotThreadSafe
  final class WinZipAesExtraField extends ExtraField {
  
      private static final int DATA_SIZE = 7;
      private static final int VENDOR_ID = 'A' | ('E' << 8);
      private static final AesKeyStrength[] KEY_STRENGTHS = AesKeyStrength.values();
  
      /**
       * Entries of this type <em>do</em> include the standard ZIP CRC-32
       * value.
       * For use with {@link #setVendorVersion(int)}/{@link #getVendorVersion()}.
       */
      static final int VV_AE_1 = 1;
  
      /**
       * Entries of this type do <em>not</em> include the standard ZIP CRC-32
       * value.
       * For use with {@link #setVendorVersion(int)}/{@link #getVendorVersion()}.
       */
      static final int VV_AE_2 = 2;
  
      private short vendorVersion = VV_AE_1;
      private byte encryptionStrength = encryptionStrength(BITS_128);
      private short method;
  
      private static byte encryptionStrength(AesKeyStrength keyStrength) {
          return (byte) (keyStrength.ordinal() + 1);
      }
  
      private static AesKeyStrength keyStrength(int encryptionStrength) {
          return KEY_STRENGTHS[(encryptionStrength - 1) & UByte.MAX_VALUE];
      }
  
      @Override
      int getHeaderId() { return WINZIP_AES_ID; }
  
      @Override
      int getDataSize() { return DATA_SIZE; }
  
      /**
       * Returns the vendor version.
       *
       * @see #VV_AE_1
       * @see #VV_AE_2
       */
      int getVendorVersion() { return vendorVersion & UShort.MAX_VALUE; }
  
      /**
       * Sets the vendor version.
       *
       * @see    #VV_AE_1
       * @see    #VV_AE_2
       * @param  vendorVersion the vendor version.
       * @throws IllegalArgumentException
       */
      void setVendorVersion(final int vendorVersion) {
          if (vendorVersion < VV_AE_1 || VV_AE_2 < vendorVersion)
              throw new IllegalArgumentException("" + vendorVersion);
          this.vendorVersion = (short) vendorVersion;
      }
  
      int getVendorId() { return VENDOR_ID; }
  
      AesKeyStrength getKeyStrength() {
          return keyStrength(this.encryptionStrength);
      }
  
      void setKeyStrength(final AesKeyStrength keyStrength) {
          this.encryptionStrength = encryptionStrength(keyStrength);
      }
  
      int getMethod() { return method & UShort.MAX_VALUE; }
  
      void setMethod(final int compressionMethod) {
          assert UShort.check(compressionMethod);
          this.method = (short) compressionMethod;
      }
  
      @Override
     void readFrom(final byte[] buf, int off, final int len) {
         if (DATA_SIZE != len) throw new IllegalArgumentException();
         setVendorVersion(readUShort(buf, off));
         off += 2;
         final int vendorId = (short) readUShort(buf, off);
         off += 2;
         if (VENDOR_ID != vendorId) throw new IllegalArgumentException();
         setKeyStrength(keyStrength(buf[off])); // checked
         off += 1;
         setMethod(readUShort(buf, off));
         // off += 2;
     }
 
     @Override
     void writeTo(byte[] buf, int off) {
         writeShort(this.vendorVersion, buf, off);
         off += 2;
         writeShort(VENDOR_ID, buf, off);
         off += 2;
         buf[off] = this.encryptionStrength;
         off += 1;
         writeShort(this.method, buf, off);
         // off += 2;
     }
 }