/**
 * SQL-DK
 * Copyright © 2014 František Kučera (frantovo.cz)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
package info.globalcode.sql.dk.batch;

import info.globalcode.sql.dk.Parameter;
import info.globalcode.sql.dk.SQLCommand;
import info.globalcode.sql.dk.SQLCommandNumbered;
import java.io.DataInputStream;
import java.io.InputStream;
import static info.globalcode.sql.dk.batch.BatchConstants.*;
import static info.globalcode.sql.dk.Functions.toHex;
import info.globalcode.sql.dk.SQLType;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 *
 * @author Ing. František Kučera (frantovo.cz)
 */
public class BatchDecoder {

	public Batch decode(InputStream in) throws BatchException {
		return new BatchFromStream(new DataInputStream(in));
	}

	private class BatchFromStream implements Batch {

		private DataInputStream in;
		private boolean hasNext;

		public BatchFromStream(DataInputStream in) throws BatchException {
			this.in = in;
			hasNext = verifyHeader();
		}

		@Override
		public boolean hasNext() throws BatchException {
			return hasNext;
		}

		@Override
		public SQLCommand next() throws BatchException {
			try {
				String sql = readNextString();

				int paramCount = in.readInt();
				List<Parameter> parameters = new ArrayList<>(paramCount);

				for (int i = 0; i < paramCount; i++) {
					SQLType type = SQLType.valueOf(in.readInt());
					String value = readNextString();
					parameters.add(new Parameter(value, type));
				}

				hasNext = verifyHeader();

				SQLCommand sqlCommand = new SQLCommandNumbered(sql, parameters);
				return sqlCommand;
			} catch (IOException e) {
				throw new BatchException("Unable to read batch", e);
			}
		}

		private String readNextString() throws IOException {
			byte[] buffer = new byte[in.readInt()];
			in.read(buffer);
			return new String(buffer, CHARSET);
		}

		/**
		 * @return true if correct batch header was found | false if EOF was found
		 * @throws BatchException if unexpected data was found (not batch header nor EOF)
		 */
		private boolean verifyHeader() throws BatchException {
			try {
				byte[] buffer = new byte[BATCH_HEADER.length];
				int bytesRead = in.read(buffer);

				if (bytesRead == BATCH_HEADER.length && Arrays.equals(buffer, BATCH_HEADER)) {
					return true;
				} else if (bytesRead == -1) {
					return false;
				} else {
					throw new BatchException("This is not SQL-DK batch: " + toHex(buffer));
				}
			} catch (IOException e) {
				throw new BatchException("Unable to read batch header", e);
			}
		}
	}
}