package mobvista.dmp.common;

import com.google.common.collect.Lists;
import org.apache.hadoop.io.ArrayFile;
import org.apache.hadoop.io.IOUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.*;
import java.util.Iterator;
import java.util.List;

/**
 * author: houying
 * date  : 16-10-31
 * desc  :
 */
public abstract class ListCache<T> implements Iterable<T> {
    private static final Logger logger = LoggerFactory.getLogger(ListCache.class);

    private List<T> list;
    private boolean isWriteFile;
    private Iterator<T> iterator;
    private BufferedWriter writer;
    private File file;
    private boolean isClosed;

    private ListCache() {
        isWriteFile = false;
        list = Lists.newLinkedList();
        writer = null;
        isClosed = false;
    }

    public void add(T t) throws IOException {
        if (isWriteFile) {
            addIntoFile(t);
        } else {
            addIntoList(t);
        }
    }

    protected void addIntoList(T t) throws IOException {
        if (list.size() < 1000) {
            list.add(t);
        } else if (list.size() == 1000){ //刚刚到达阈值，将list的元素刷入文件
            logger.info("list size is larger than 1000, switch to file cache!");
            if (writer == null) {
                file = new File("list-cache" + System.currentTimeMillis() +".txt");
                writer = new BufferedWriter(new FileWriter(file));
            }
            for (T element: list) {
                writeLine(element, writer);
                writer.newLine();
            }
            writeLine(t, writer);
            writer.newLine();
            writer.flush();
            isWriteFile = true;
        }
    }

    private void addIntoFile(T t) throws IOException {
        writeLine(t, writer);
        writer.newLine();
    }

    public void flushAndClose() throws IOException {
        if (isWriteFile) {
            writer.close();
        }
        isClosed = true;
    }

    @Override
    public Iterator<T> iterator() {
        if (!isClosed) {
            throw new IllegalStateException("did not call flushAndClose() for ListCache");
        }
        if (iterator == null) {
            if (!isWriteFile) {
                iterator = list.iterator();
            } else {
                try {
                    iterator = new FileIterator(file);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
            }
        }
        return iterator;
    }

    public class FileIterator implements Iterator<T> {

        private BufferedReader reader;
        private String nextLine;

        public FileIterator(File file) throws FileNotFoundException {
            reader = new BufferedReader(new FileReader(file));
            nextLine = null;
        }

        @Override
        public boolean hasNext() {
            try {
                nextLine = reader.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (nextLine == null) {
                try {
                    reader.close();
                    file.delete();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                return false;
            } else {
                return true;
            }
        }

        @Override
        public T next() {
            return readLine(nextLine);
        }

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

    protected abstract void writeLine(T element, Writer writer) throws IOException;

    protected abstract T readLine(String nextLine);

    public static ListCache<String> newStringListCache() {
        return new ListCache<String>() {
            @Override
            protected void writeLine(String element, Writer writer) throws IOException {
                writer.write(element);
            }

            @Override
            protected String readLine(String nextLine) {
                return nextLine;
            }
        };
    }

    public static void main(String[] args) throws IOException {
        ListCache<String> listCache = ListCache.newStringListCache();
        for (int i = 0; i < 1001; i++) {
            listCache.add(i + "");
        }
        listCache.flushAndClose();
        for (String s: listCache) {
            System.out.println(s);
        }
    }
}