/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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 com.android.ide.eclipse.gltrace;

import com.android.ide.eclipse.gltrace.GLProtoBuf.GLMessage;
import com.google.protobuf.InvalidProtocolBufferException;

import java.io.EOFException;
import java.io.IOException;
import java.io.RandomAccessFile;

public class TraceFileReader {
    /** Maximum size for a protocol buffer message.
     * The message size is dominated by the size of the compressed framebuffer.
     * Currently, we assume that the maximum is for a 1080p display. Since the buffers compress
     * well, we should probably never get close to this.
     */
    private static final int MAX_PROTOBUF_SIZE = 1920 * 1080 * 100;

    /**
     * Obtain the next protobuf message in this file.
     * @param file file to read from
     * @param offset offset to start reading from
     * @return protobuf message at given offset
     * @throws IOException in case of file I/O errors
     * @throws InvalidProtocolBufferException if protobuf is not well formed
     */
    public GLMessage getMessageAtOffset(RandomAccessFile file, long offset) throws IOException {
        int len;
        byte[] b;
        try {
            if (offset != -1) {
                file.seek(offset);
            }

            len = file.readInt();
            if (len > MAX_PROTOBUF_SIZE) {
                String msg = String.format(
                        "Unexpectedly large (%d bytes) protocol buffer message encountered.",
                        len);
                throw new InvalidProtocolBufferException(msg);
            }

            b = new byte[len];
            file.readFully(b);
        } catch (EOFException e) {
            return null;
        }

        return GLMessage.parseFrom(b);
    }
}