connectors/file/src/main/java/org/apache/edgent/connectors/file/runtime/TextFileReader.java

/*
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you 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 org.apache.edgent.connectors.file.runtime;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;

import org.apache.edgent.function.BiFunction;
import org.apache.edgent.function.Consumer;
import org.apache.edgent.function.Function;
import org.apache.edgent.oplet.OpletContext;
import org.apache.edgent.oplet.core.Pipe;
import org.slf4j.Logger;

public class TextFileReader extends Pipe<String,String> {

    private static final long serialVersionUID = 1L;
    private static final Logger trace = FileConnector.getTrace();
    private volatile String encoding = "UTF-8";
    private volatile Charset charset;
    private volatile boolean shutdown;
    private volatile Function<String,String> preFn = path -> null;
    private volatile BiFunction<String,Exception,String> postFn = (path,exc) -> null;

    private void setShutdown(boolean b) {
        shutdown = b;
    }

    private boolean isShutdown() {
        return shutdown;
    }
    
    private String getEncoding() {
        return encoding;
    }
    
    public void setPre(Function<String,String> preFn) {
        if (preFn == null)
            this.preFn = path -> null;
        else
            this.preFn = preFn;
    }
    
    public void setPost(BiFunction<String,Exception,String> postFn) {
        if (postFn == null)
            this.postFn = (path,exc) -> null;
        else
            this.postFn = postFn;
    }

    @Override
    public synchronized void initialize(OpletContext<String,String> context) {
        super.initialize(context);

        charset = Charset.forName(getEncoding());
    }
    
    private void pre(String pathname, Consumer<String> dst) {
        String preStr = preFn.apply(pathname);
        if (preStr != null)
            dst.accept(preStr);
    }
    
    private void post(String pathname, Exception e, Consumer<String> dst) {
        String postStr = postFn.apply(pathname, e);
        if (postStr != null)
            dst.accept(postStr);
    }

    @Override
    public void accept(String pathname) {
        trace.trace("reading path={}", pathname);
        Consumer<String> dst = getDestination();
        pre(pathname, dst);
        Path path = new File(pathname).toPath();
        Exception exc = null;
        int nlines = 0;
        try (BufferedReader br = Files.newBufferedReader(path, charset)) {
            for (int i = 0;;i++) {
                if (i % 10 == 0 && isShutdown())
                    break;
                String line = br.readLine();
                if (line == null)
                    break;
                nlines++;
                dst.accept(line);
            }
        }
        catch (IOException e) {
            trace.error("Error processing file '{}'", pathname, e);
            exc = e;
        }
        finally {
            trace.trace("done reading nlines={} path={} ", nlines, pathname);
            post(pathname, exc, dst);
        }
    }

    @Override
    public void close() throws Exception {
        setShutdown(true);
    }
}