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package com.formkiq.server.util;

import java.nio.charset.StandardCharsets;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.commons.codec.binary.Base64;

/**
 * String helper utilities.
 *
 */
public final class Strings {

    /** Default deliminator to use to encode strings. */
    public static final String DEFAULT_DELIM = ":";

    /** Regex to extract label / value. */
    private static final Pattern EXTRACT_LABEL_VALUE = Pattern
            .compile("^(.*)\\[(.*)\\]$");

    /**
     * Decodes string using deliminator and Base64.
     * @param base64 {@link String}
     * @param deliminator {@link String}
     * @return String[]
     */
    public static String[] decode(final String base64,
            final String deliminator) {
        byte[] bytes = Base64.decodeBase64(base64);
        String s = new String(bytes, StandardCharsets.UTF_8);
        return s.split(deliminator);
    }

    /**
     * Encodes two strings together using deliminator and Base64.
     * @param s0 {@link String}
     * @param s1 {@link String}
     * @param deliminator {@link String}
     * @return {@link String}
     */
    public static String encode(final String s0, final String s1,
            final String deliminator) {

        String encoded = s0 + deliminator + s1;

        byte[] bytes = Base64
                .encodeBase64(encoded.getBytes(StandardCharsets.UTF_8));
        return new String(bytes, StandardCharsets.UTF_8);
    }

    /**
     * Generate Token based off of Offset / Max Results.
     * @param offset int
     * @param maxResults int
     * @return {@link String}
     */
    public static String generateOffsetToken(final int offset,
            final int maxResults) {
        return encode("" + offset, "" + maxResults, DEFAULT_DELIM);
    }

    /**
     * Get Max Results from Token.
     * @param token {@link String}
     * @param defaultMaxResults int
     * @return int
     */
    public static int getMaxResults(final String token,
            final int defaultMaxResults) {

        try {
            String s = decode(token, DEFAULT_DELIM)[1];
            return Integer.parseInt(s);
        } catch (NullPointerException | ArrayIndexOutOfBoundsException
                | NumberFormatException e) {
            return defaultMaxResults;
        }
    }

    /**
     * Get Offset from token.
     * @param token {@link String}
     * @return int
     */
    public static int getOffset(final String token) {
        try {
            String s = decode(token, DEFAULT_DELIM)[0];
            return Integer.parseInt(s);
        } catch (NullPointerException | ArrayIndexOutOfBoundsException
                | NumberFormatException e) {
            return 0;
        }
    }

    /**
     * private constructor.
     */
    private Strings() {
    }

    /**
     * Extract Label / Value from String.
     * @param s {@link String}
     * @return String[]
     */
    public static String[] extractLabelAndValue(final String s) {

        if (s != null) {

            Matcher m = EXTRACT_LABEL_VALUE.matcher(s);
            if (m.matches()) {
                return new String[] { m.group(1), m.group(2)};
            }

            return new String[] { s, s };
        }

        return new String[] { "", "" };
    }
}