package mp4parser;

import java.io.*;
import java.util.Enumeration;
import java.util.Vector;

public class RandomAccessSequenceFile implements Closeable{
    Enumeration<RandomAccessFile> e;
    private RandomAccessFile rIn;
    private long startOffset = 0;//偏移位置
    private long endOffset = 0;
    private File file = null;//mdathead文件
    public RandomAccessSequenceFile(RandomAccessFile s1, RandomAccessFile s2, long startOffset, long endOffset) throws IOException {
        //startOffset为原文件的偏移起始位置
        this.startOffset = startOffset;
        this.endOffset = endOffset;
        RandomAccessFile mdatHeadIn = getMdatHead(endOffset-startOffset+8);
        Vector<RandomAccessFile> v = new Vector<RandomAccessFile>(2);
//        s2.setLength(endOffset);
        s2.skipBytes((int) startOffset);//跳到偏移字节位置

        v.addElement(s1);
        v.addElement(mdatHeadIn);
        v.addElement(s2);
        e = v.elements();
        try {
            nextStream();
        } catch (IOException ex) {
            // This should never happen
            throw new Error("panic");
        }
    }
    final void nextStream() throws IOException {

        if (rIn != null) {
            rIn.close();
        }

        if (e.hasMoreElements()) {

            rIn =  e.nextElement();
            if (rIn == null)
                throw new NullPointerException();
        }
        else{
            file.delete();//删除创建的临时文件
            rIn = null;
        }
    }

    public int read(byte[] bytes) throws IOException {
//        System.out.println("偏移量"+rIn.getFilePointer());
        if(rIn == null){
            return -1;
        }
        do {
            int n = rIn.read(bytes);
            if (n > 0) {
                return n;
            }
            nextStream();

        } while (rIn != null);
        return -1;
    }
    //实现从任意偏移位置开始
    public void seek(long start) throws IOException {
        if(start>0){
            long n = start;
            while (n-rIn.length()>0){
                n-=rIn.length();
                nextStream();
            }
            rIn.seek(n);
        }

    }

    //mdat头部
    private RandomAccessFile getMdatHead(long size) throws IOException {
        byte[] mdathead = {0x00,0x00,0x00,0x00,0x6d,0x64,0x61,0x74};
        for (int i = 0; i < 4; i++) {
            mdathead[i] = (byte) ((size>>((3-i)*8))&0xff);
//            System.out.println(Long.toBinaryString(mdathead[i]));
        }
//        System.out.println(Long.toBinaryString(mdathead[4]&0xff));
        file = File.createTempFile("mdathead",null);
        FileOutputStream out = new FileOutputStream(file);
        out.write(mdathead);
        out.close();
        return new RandomAccessFile(file,"r");
    }

    @Override
    public void close() throws IOException {
        if(rIn!=null)
            rIn.close();
        while (e.hasMoreElements()) {
            rIn =  e.nextElement();
            if (rIn == null)
                rIn.close();
        }
        file.delete();//删除创建的临时文件
        rIn = null;
    }
}