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Operate the database like a stream
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package org.sql2o;

import org.sql2o.quirks.Quirks;

import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Iterator for a {@link ResultSet}. Tricky part here is getting {@link #hasNext()}
 * to work properly, meaning it can be called multiple times without calling {@link #next()}.
 *
 * @author [email protected]
 */
public abstract class ResultSetIteratorBase implements Iterator {
    // fields needed to read result set
    protected ResultSet rs;
    protected boolean isCaseSensitive;
    protected Quirks quirks;
    protected ResultSetMetaData meta;

    public ResultSetIteratorBase(ResultSet rs, boolean isCaseSensitive, Quirks quirks) {
        this.rs = rs;
        this.isCaseSensitive = isCaseSensitive;
        this.quirks = quirks;
        try {
            meta = rs.getMetaData();
        }
        catch(SQLException ex) {
            throw new Sql2oException("Database error: " + ex.getMessage(), ex);
        }
    }

    // fields needed to properly implement
    private ResultSetValue next; // keep track of next item in case hasNext() is called multiple times
    private boolean resultSetFinished; // used to note when result set exhausted

    public boolean hasNext() {
        // check if we already fetched next item
        if (next != null) {
            return true;
        }

        // check if result set already finished
        if (resultSetFinished) {
            return false;
        }

        // now fetch next item
        next = safeReadNext();

        // check if we got something
        if (next != null) {
            return true;
        }

        // no more items
        resultSetFinished = true;

        return false;
    }

    public T next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }

        T result = next.value;

        next = null;

        return result;
    }

    public void remove() {
        throw new UnsupportedOperationException();
    }

    private ResultSetValue safeReadNext()
    {
        try {
            if (!rs.next())
                return null;
            ResultSetValue resultSetValue = new ResultSetValue(readNext());
            return resultSetValue;
        }
        catch (SQLException ex) {
            throw new Sql2oException("Database error: " + ex.getMessage(), ex);
        }
    }

    protected abstract T readNext() throws SQLException;

    protected String getColumnName(int colIdx) throws SQLException {
        return quirks.getColumnName(meta, colIdx);
    }

    private final class ResultSetValue {
        public final S value;

        public ResultSetValue(S value){
            this.value = value;
        }
    }
}