/*
 * 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.commons.dbutils.wrappers;

import java.io.InputStream;
import java.io.Reader;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.math.BigDecimal;
import java.net.URL;
import java.sql.Blob;
import java.sql.Clob;
import java.sql.Date;
import java.sql.Ref;
import java.sql.ResultSet;
import java.sql.Time;
import java.sql.Timestamp;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.dbutils.ProxyFactory;

/**
 * Decorates a {@code ResultSet} with checks for a SQL NULL value on each
 * {@code getXXX} method. If a column value obtained by a
 * {@code getXXX} method is not SQL NULL, the column value is returned. If
 * the column value is SQL null, an alternate value is returned. The alternate
 * value defaults to the Java {@code null} value, which can be overridden
 * for instances of the class.
 *
 * <p>
 * Usage example:
 * <blockquote>
 * <pre>
 * Connection conn = // somehow get a connection
 * Statement stmt = conn.createStatement();
 * ResultSet resultSet = stmt.executeQuery("SELECT col1, col2 FROM table1");
 *
 * // Wrap the result set for SQL NULL checking
 * SqlNullCheckedResultSet wrapper = new SqlNullCheckedResultSet(resultSet);
 * wrapper.setNullString("---N/A---"); // Set null string
 * wrapper.setNullInt(-999); // Set null integer
 * resultSet = ProxyFactory.instance().createResultSet(wrapper);
 *
 * while (resultSet.next()) {
 *     // If col1 is SQL NULL, value returned will be "---N/A---"
 *     String col1 = resultSet.getString("col1");
 *     // If col2 is SQL NULL, value returned will be -999
 *     int col2 = resultSet.getInt("col2");
 * }
 * resultSet.close();
 * </pre>
 * </blockquote>
 * &lt;/p&gt;
 * <p>Unlike some other classes in DbUtils, this class is NOT thread-safe.</p>
 */
public class SqlNullCheckedResultSet implements InvocationHandler {

    /**
     * Maps normal method names (ie. "getBigDecimal") to the corresponding null
     * Method object (ie. getNullBigDecimal).
     */
    private static final Map<String, Method> NULL_METHODS = new HashMap<>();

    /**
     * The {@code getNull} string prefix.
     * @since 1.4
     */
    private static final String GET_NULL_PREFIX = "getNull";

    static {
        final Method[] methods = SqlNullCheckedResultSet.class.getMethods();
        for (final Method method : methods) {
            final String methodName = method.getName();

            if (methodName.startsWith(GET_NULL_PREFIX)) {
                final String normalName = "get" + methodName.substring(GET_NULL_PREFIX.length());
                NULL_METHODS.put(normalName, method);
            }
        }
    }

    /**
     * The factory to create proxies with.
     */
    private static final ProxyFactory factory = ProxyFactory.instance();

    /**
     * Wraps the {@code ResultSet} in an instance of this class.  This is
     * equivalent to:
     * <pre>
     * ProxyFactory.instance().createResultSet(new SqlNullCheckedResultSet(resultSet));
     * </pre>
     *
     * @param resultSet The {@code ResultSet} to wrap.
     * @return wrapped ResultSet
     */
    public static ResultSet wrap(final ResultSet resultSet) {
        return factory.createResultSet(new SqlNullCheckedResultSet(resultSet));
    }

    private InputStream nullAsciiStream;
    private BigDecimal nullBigDecimal;
    private InputStream nullBinaryStream;
    private Blob nullBlob;
    private boolean nullBoolean;
    private byte nullByte;
    private byte[] nullBytes;
    private Reader nullCharacterStream;
    private Clob nullClob;
    private Date nullDate;
    private double nullDouble;
    private float nullFloat;
    private int nullInt;
    private long nullLong;
    private Object nullObject;
    private Ref nullRef;
    private short nullShort;
    private String nullString;
    private Time nullTime;
    private Timestamp nullTimestamp;
    private URL nullURL;

    /**
     * The wrapped result.
     */
    private final ResultSet resultSet;

    /**
     * Constructs a new instance of
     * {@code SqlNullCheckedResultSet}
     * to wrap the specified {@code ResultSet}.
     * @param resultSet ResultSet to wrap
     */
    public SqlNullCheckedResultSet(final ResultSet resultSet) {
        this.resultSet = resultSet;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getAsciiStream} method.
     *
     * @return the value
     */
    public InputStream getNullAsciiStream() {
        return this.nullAsciiStream;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getBigDecimal} method.
     *
     * @return the value
     */
    public BigDecimal getNullBigDecimal() {
        return this.nullBigDecimal;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getBinaryStream} method.
     *
     * @return the value
     */
    public InputStream getNullBinaryStream() {
        return this.nullBinaryStream;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getBlob} method.
     *
     * @return the value
     */
    public Blob getNullBlob() {
        return this.nullBlob;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getBoolean} method.
     *
     * @return the value
     */
    public boolean getNullBoolean() {
        return this.nullBoolean;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getByte} method.
     *
     * @return the value
     */
    public byte getNullByte() {
        return this.nullByte;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getBytes} method.
     *
     * @return the value
     */
    public byte[] getNullBytes() {
        if (this.nullBytes == null) {
            return null;
        }
        return this.nullBytes.clone();
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getCharacterStream} method.
     *
     * @return the value
     */
    public Reader getNullCharacterStream() {
        return this.nullCharacterStream;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getClob} method.
     *
     * @return the value
     */
    public Clob getNullClob() {
        return this.nullClob;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getDate} method.
     *
     * @return the value
     */
    public Date getNullDate() {
        return this.nullDate != null ? new Date(this.nullDate.getTime()) : null;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getDouble} method.
     *
     * @return the value
     */
    public double getNullDouble() {
        return this.nullDouble;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getFloat} method.
     *
     * @return the value
     */
    public float getNullFloat() {
        return this.nullFloat;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getInt} method.
     *
     * @return the value
     */
    public int getNullInt() {
        return this.nullInt;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getLong} method.
     *
     * @return the value
     */
    public long getNullLong() {
        return this.nullLong;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getObject} method.
     *
     * @return the value
     */
    public Object getNullObject() {
        return this.nullObject;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getRef} method.
     *
     * @return the value
     */
    public Ref getNullRef() {
        return this.nullRef;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getShort} method.
     *
     * @return the value
     */
    public short getNullShort() {
        return this.nullShort;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getString} method.
     *
     * @return the value
     */
    public String getNullString() {
        return this.nullString;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getTime} method.
     *
     * @return the value
     */
    public Time getNullTime() {
        return this.nullTime != null ? new Time(this.nullTime.getTime()) : null;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getTimestamp} method.
     *
     * @return the value
     */
    public Timestamp getNullTimestamp() {
        if (this.nullTimestamp == null) {
            return null;
        }

        final Timestamp ts = new Timestamp(this.nullTimestamp.getTime());
        ts.setNanos(this.nullTimestamp.getNanos());
        return ts;
    }

    /**
     * Returns the value when a SQL null is encountered as the result of
     * invoking a {@code getURL} method.
     *
     * @return the value
     */
    public URL getNullURL() {
        return this.nullURL;
    }

    /**
     * Intercepts calls to {@code get*} methods and calls the appropriate
     * {@code getNull*} method if the {@code ResultSet} returned
     * {@code null}.
     *
     * @see java.lang.reflect.InvocationHandler#invoke(Object, java.lang.reflect.Method, Object[])
     * @param proxy Not used; all method calls go to the internal result set
     * @param method The method to invoke on the result set
     * @param args The arguments to pass to the result set
     * @return null checked result
     * @throws Throwable error
     */
    @Override
    public Object invoke(final Object proxy, final Method method, final Object[] args)
        throws Throwable {

        final Object result = method.invoke(this.resultSet, args);

        final Method nullMethod = NULL_METHODS.get(method.getName());

        // Check nullMethod != null first so that we don't call wasNull()
        // before a true getter method was invoked on the ResultSet.
        return nullMethod != null && this.resultSet.wasNull()
            ? nullMethod.invoke(this, (Object[]) null)
            : result;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getAsciiStream} method.
     *
     * @param nullAsciiStream the value
     */
    public void setNullAsciiStream(final InputStream nullAsciiStream) {
        this.nullAsciiStream = nullAsciiStream;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getBigDecimal} method.
     *
     * @param nullBigDecimal the value
     */
    public void setNullBigDecimal(final BigDecimal nullBigDecimal) {
        this.nullBigDecimal = nullBigDecimal;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getBinaryStream} method.
     *
     * @param nullBinaryStream the value
     */
    public void setNullBinaryStream(final InputStream nullBinaryStream) {
        this.nullBinaryStream = nullBinaryStream;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getBlob} method.
     *
     * @param nullBlob the value
     */
    public void setNullBlob(final Blob nullBlob) {
        this.nullBlob = nullBlob;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getBoolean} method.
     *
     * @param nullBoolean the value
     */
    public void setNullBoolean(final boolean nullBoolean) {
        this.nullBoolean = nullBoolean;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getByte} method.
     *
     * @param nullByte the value
     */
    public void setNullByte(final byte nullByte) {
        this.nullByte = nullByte;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getBytes} method.
     *
     * @param nullBytes the value
     */
    public void setNullBytes(final byte[] nullBytes) {
        if (nullBytes != null) {
            this.nullBytes = nullBytes.clone();
        } else {
            this.nullBytes = null;
        }
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getCharacterStream} method.
     *
     * @param nullCharacterStream the value
     */
    public void setNullCharacterStream(final Reader nullCharacterStream) {
        this.nullCharacterStream = nullCharacterStream;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getClob} method.
     *
     * @param nullClob the value
     */
    public void setNullClob(final Clob nullClob) {
        this.nullClob = nullClob;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getDate} method.
     *
     * @param nullDate the value
     */
    public void setNullDate(final Date nullDate) {
        this.nullDate = nullDate != null ? new Date(nullDate.getTime()) : null;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getDouble} method.
     *
     * @param nullDouble the value
     */
    public void setNullDouble(final double nullDouble) {
        this.nullDouble = nullDouble;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getFloat} method.
     *
     * @param nullFloat the value
     */
    public void setNullFloat(final float nullFloat) {
        this.nullFloat = nullFloat;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getInt} method.
     *
     * @param nullInt the value
     */
    public void setNullInt(final int nullInt) {
        this.nullInt = nullInt;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getLong} method.
     *
     * @param nullLong the value
     */
    public void setNullLong(final long nullLong) {
        this.nullLong = nullLong;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getObject} method.
     *
     * @param nullObject the value
     */
    public void setNullObject(final Object nullObject) {
        this.nullObject = nullObject;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getRef} method.
     *
     * @param nullRef the value
     */
    public void setNullRef(final Ref nullRef) {
        this.nullRef = nullRef;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getShort} method.
     *
     * @param nullShort the value
     */
    public void setNullShort(final short nullShort) {
        this.nullShort = nullShort;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getString} method.
     *
     * @param nullString the value
     */
    public void setNullString(final String nullString) {
        this.nullString = nullString;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getTime} method.
     *
     * @param nullTime the value
     */
    public void setNullTime(final Time nullTime) {
        this.nullTime = nullTime != null ? new Time(nullTime.getTime()) : null;
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getTimestamp} method.
     *
     * @param nullTimestamp the value
     */
    public void setNullTimestamp(final Timestamp nullTimestamp) {
        if (nullTimestamp != null) {
            this.nullTimestamp = new Timestamp(nullTimestamp.getTime());
            this.nullTimestamp.setNanos(nullTimestamp.getNanos());
        } else {
            this.nullTimestamp = null;
        }
    }

    /**
     * Sets the value to return when a SQL null is encountered as the result of
     * invoking a {@code getURL} method.
     *
     * @param nullURL the value
     */
    public void setNullURL(final URL nullURL) {
        this.nullURL = nullURL;
    }

}