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package com.goeuro.sync4j.utils;

import javax.annotation.Nonnull;
import java.io.IOException;
import java.io.InputStream;
import java.io.UncheckedIOException;
import java.nio.file.Path;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import static java.nio.file.Files.newInputStream;
import static java.util.Base64.getEncoder;

public final class Digests {

    @Nonnull
    public static String md5HashAsStringOf(@Nonnull Path source) {
        return md5HashAsStringOf(() -> newInputStream(source));
    }

    @Nonnull
    public static String md5HashAsStringOf(@Nonnull InputStreamOpener source) {
        final byte[] hash = md5HashOf(source);
        return getEncoder().encodeToString(hash);
    }

    @Nonnull
    public static byte[] md5HashOf(@Nonnull InputStreamOpener source) {
        try (final InputStream is = source.open()) {
            return md5HashOf(is);
        } catch (final IOException e) {
            throw new UncheckedIOException(e);
        }
    }

    @Nonnull
    public static byte[] md5HashOf(@Nonnull InputStream is) throws IOException {
        final MessageDigest digest = newMd5Digest();
        final byte[] buf = new byte[8172];
        int read = is.read(buf);
        while (read >= 0) {
            digest.update(buf, 0, read);
            read = is.read(buf);
        }
        return digest.digest();
    }

    @Nonnull
    public static MessageDigest newMd5Digest() {
        try {
            return MessageDigest.getInstance("MD5");
        } catch (final NoSuchAlgorithmException e) {
            throw new RuntimeException("There is no MD5 digester available.", e);
        }
    }

    @FunctionalInterface
    public interface InputStreamOpener {
        @Nonnull
        InputStream open() throws IOException;
    }

}