/*
 * Copyright Red Hat, Inc. and/or its affiliates
 * and other contributors as indicated by the @author tags and
 * the COPYRIGHT.txt file distributed with this work.
 *
 * Licensed 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.teiid.script.io;

import java.io.IOException;
import java.io.Reader;


/** 
 * Base class for any type of Reader, where data can be read as line by line.
 * The derived classes just need to extend this class and implement the "nextLine()"
 * method to get the full "Reader" functionality.
 * 
 */
public abstract class StringLineReader extends Reader {

    // Current line which is being fed to the reader
    String currentLine = null;
    // Current index of where the reading stopped last time
    int currentLineIndex = 0;

    boolean closed = false;
    
    /** 
     * @see java.io.Reader#close()
     * @since 4.3
     */
    public void close() throws IOException {
        closed = true;
    }

    /** 
     * @see java.io.Reader#read(char[], int, int)
     * @since 4.3
     */
    public int read(char[] cbuf, int off, int len) throws IOException {
        if (closed) {
            throw new IllegalStateException("Reader already closed"); //$NON-NLS-1$
        }

        int srcoff = currentLineIndex;        
        if (currentLine == null || (currentLine != null && (currentLine.length()-currentLineIndex) <= 0)) {            
            currentLine = nextLine();
            currentLineIndex = 0; 
            srcoff = currentLineIndex;
        }
         
        // If we have data available then send it.
        if (currentLine != null) {
            // If requested more than one line limit length to one line
            if (len > (currentLine.length()-currentLineIndex)) {
                len = (currentLine.length()-currentLineIndex);
            }
                                
            // Copy the contents to destination.
            System.arraycopy(currentLine.toCharArray(), srcoff, cbuf, off, len);
            
            // Now move the current index further 
            currentLineIndex = currentLineIndex+len;
            return len;
        }
        return -1;
    }

    /**
     * Get the next line of data from the data source. 
     * @return
     * @throws IOException
     * @since 4.3
     */
    abstract protected String nextLine() throws IOException; 
}
