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package edu.stanford.protege.webprotege.filemanager;

import com.google.common.base.Charsets;
import com.google.common.io.Files;

import javax.annotation.Nonnull;
import java.io.File;
import java.io.IOException;
import java.util.function.Supplier;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Matthew Horridge
 * Stanford Center for Biomedical Informatics Research
 * 10 Mar 2017
 *
 * A utility class for reading the latest contents of a file into a string.  When the method for getting
 * the contents is called, the fileSupplier is checked to ensure that the latest contents are returned.  Contents
 * are cached in memory.
 */
public class FileContents {

    private final Supplier fileSupplier;

    private long lastTimestamp = 0;

    private String cachedTemplate = "";

    public FileContents(@Nonnull Supplier fileSupplier) {
        this.fileSupplier = checkNotNull(fileSupplier);
    }

    @Nonnull
    public File getFile() {
        return fileSupplier.get();
    }

    public boolean exists() {
        return getFile().exists();
    }

    /**
     * Gets the contents of the specified file as a string.
     * @return The contents as a string.
     */
    @Nonnull
    public synchronized String getContents() {
        try {
            File file = getFile();
            if (file.exists() && file.lastModified() > lastTimestamp) {
                cachedTemplate = Files.toString(file, Charsets.UTF_8);
                lastTimestamp = file.lastModified();
            }
            return cachedTemplate;
        } catch (IOException e) {
            return "Could not read file: " + e.getMessage();
        }
    }
}