/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.avro.io;

import java.io.IOException;
import java.nio.ByteBuffer;

import org.apache.avro.AvroTypeException;
import org.apache.avro.Schema;
import org.apache.avro.io.parsing.Parser;
import org.apache.avro.io.parsing.Symbol;
import org.apache.avro.io.parsing.ValidatingGrammarGenerator;
import org.apache.avro.util.Utf8;

/**
 * An implementation of {@link Decoder} that ensures that the sequence
 * of operations conforms to a schema.
 * <p/>
 * Use {@link DecoderFactory#validatingDecoder(Schema, Decoder)} to construct
 * and configure.
 * <p/>
 * ValidatingDecoder is not thread-safe.
 * @see Decoder
 * @see DecoderFactory
 */
public class ValidatingDecoder extends ParsingDecoder
  implements Parser.ActionHandler {
  protected Decoder in;

  ValidatingDecoder(Symbol root, Decoder in) throws IOException {
    super(root);
    this.configure(in);
  }

  ValidatingDecoder(Schema schema, Decoder in) throws IOException {
    this(getSymbol(schema), in);
  }
  
  private static Symbol getSymbol(Schema schema) {
    if (null == schema) {
      throw new NullPointerException("Schema cannot be null");
    }
    return new ValidatingGrammarGenerator().generate(schema);
  }

  /** Re-initialize, reading from a new underlying Decoder. */
  public ValidatingDecoder configure(Decoder in) throws IOException {
    this.parser.reset();
    this.in = in;
    return this;
  }

  @Override
  public void readNull() throws IOException {
    parser.advance(Symbol.NULL);
    in.readNull();
  }
    
  @Override
  public boolean readBoolean() throws IOException {
    parser.advance(Symbol.BOOLEAN);
    return in.readBoolean();
  }

  @Override
  public int readInt() throws IOException {
    parser.advance(Symbol.INT);
    return in.readInt();
  }
    
  @Override
  public long readLong() throws IOException {
    parser.advance(Symbol.LONG);
    return in.readLong();
  }

  @Override
  public float readFloat() throws IOException {
    parser.advance(Symbol.FLOAT);
    return in.readFloat();
  }

  @Override
  public double readDouble() throws IOException {
    parser.advance(Symbol.DOUBLE);
    return in.readDouble();
  }
    
  @Override
  public Utf8 readString(Utf8 old) throws IOException {
    parser.advance(Symbol.STRING);
    return in.readString(old);
  }

  @Override
  public String readString() throws IOException {
    parser.advance(Symbol.STRING);
    return in.readString();
  }

  @Override
  public void skipString() throws IOException {
    parser.advance(Symbol.STRING);
    in.skipString();
  }

  @Override
  public ByteBuffer readBytes(ByteBuffer old) throws IOException {
    parser.advance(Symbol.BYTES);
    return in.readBytes(old);
  }

  @Override
  public void skipBytes() throws IOException {
    parser.advance(Symbol.BYTES);
    in.skipBytes();
  }

  private void checkFixed(int size) throws IOException {
    parser.advance(Symbol.FIXED);
    Symbol.IntCheckAction top = (Symbol.IntCheckAction) parser.popSymbol();
    if (size != top.size) {
      throw new AvroTypeException(
        "Incorrect length for fixed binary: expected " +
        top.size + " but received " + size + " bytes.");
    }
  }
    
  @Override
  public void readFixed(byte[] bytes, int start, int len) throws IOException {
    checkFixed(len);
    in.readFixed(bytes, start, len);
  }

  @Override
  public void skipFixed(int length) throws IOException {
    checkFixed(length);
    in.skipFixed(length);
  }

  @Override
  protected void skipFixed() throws IOException {
    parser.advance(Symbol.FIXED);
    Symbol.IntCheckAction top = (Symbol.IntCheckAction) parser.popSymbol();
    in.skipFixed(top.size);
  }

  @Override
  public int readEnum() throws IOException {
    parser.advance(Symbol.ENUM);
    Symbol.IntCheckAction top = (Symbol.IntCheckAction) parser.popSymbol();
    int result = in.readEnum();
    if (result < 0 || result >= top.size) {
      throw new AvroTypeException(
          "Enumeration out of range: max is " +
          top.size + " but received " + result);
    }
    return result;
  }

  @Override
  public long readArrayStart() throws IOException {
    parser.advance(Symbol.ARRAY_START);
    long result = in.readArrayStart();
    if (result == 0) {
      parser.advance(Symbol.ARRAY_END);
    }
    return result;
  }

  @Override
  public long arrayNext() throws IOException {
    parser.processTrailingImplicitActions();
    long result = in.arrayNext();
    if (result == 0) {
      parser.advance(Symbol.ARRAY_END);
    }
    return result;
  }

  @Override
  public long skipArray() throws IOException {
    parser.advance(Symbol.ARRAY_START);
    for (long c = in.skipArray(); c != 0; c = in.skipArray()) {
      while (c-- > 0) {
        parser.skipRepeater();
      }
    }
    parser.advance(Symbol.ARRAY_END);    
    return 0;
  }

  @Override
  public long readMapStart() throws IOException {
    parser.advance(Symbol.MAP_START);
    long result = in.readMapStart();
    if (result == 0) {
      parser.advance(Symbol.MAP_END);
    }
    return result;
  }

  @Override
  public long mapNext() throws IOException {
    parser.processTrailingImplicitActions();
    long result = in.mapNext();
    if (result == 0) {
      parser.advance(Symbol.MAP_END);
    }
    return result;
  }

  @Override
  public long skipMap() throws IOException {
    parser.advance(Symbol.MAP_START);
    for (long c = in.skipMap(); c != 0; c = in.skipMap()) {
      while (c-- > 0) {
        parser.skipRepeater();
      }
    }
    parser.advance(Symbol.MAP_END);
    return 0;
  }

  @Override
  public int readIndex() throws IOException {
    parser.advance(Symbol.UNION);
    Symbol.Alternative top = (Symbol.Alternative) parser.popSymbol();
    int result = in.readIndex();
    parser.pushSymbol(top.getSymbol(result));
    return result;
  }
  
  @Override
  public Symbol doAction(Symbol input, Symbol top) throws IOException {
    return null;
  }
}

