/*
* Copyright (c) 2012 The Broad Institute
* 
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following
* conditions:
* 
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
* 
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
* THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

package org.broadinstitute.sting.utils;

import com.google.java.contract.Ensures;
import com.google.java.contract.Requires;
import net.sf.samtools.SAMFileHeader;
import net.sf.samtools.SAMProgramRecord;
import net.sf.samtools.util.StringUtil;
import org.apache.log4j.Logger;
import org.broadinstitute.sting.gatk.GenomeAnalysisEngine;
import org.broadinstitute.sting.gatk.io.StingSAMFileWriter;
import org.broadinstitute.sting.utils.text.TextFormattingUtils;

import java.math.BigInteger;
import java.net.InetAddress;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.*;

/**
 * Created by IntelliJ IDEA.
 * User: depristo
 * Date: Feb 24, 2009
 * Time: 10:12:31 AM
 * To change this template use File | Settings | File Templates.
 */
public class Utils {
    /** our log, which we want to capture anything from this class */
    private static Logger logger = Logger.getLogger(Utils.class);

    public static final float JAVA_DEFAULT_HASH_LOAD_FACTOR = 0.75f;

    /**
     * Boolean xor operation.  Only true if x != y.
     *
     * @param x a boolean
     * @param y a boolean
     * @return true if x != y
     */
    public static boolean xor(final boolean x, final boolean y) {
        return x != y;
    }

    /**
     * Calculates the optimum initial size for a hash table given the maximum number
     * of elements it will need to hold. The optimum size is the smallest size that
     * is guaranteed not to result in any rehash/table-resize operations.
     *
     * @param maxElements  The maximum number of elements you expect the hash table
     *                     will need to hold
     * @return             The optimum initial size for the table, given maxElements
     */
    public static int optimumHashSize ( int maxElements ) {
        return (int)(maxElements / JAVA_DEFAULT_HASH_LOAD_FACTOR) + 2;
    }

    /**
     * Compares two objects, either of which might be null.
     *
     * @param lhs One object to compare.
     * @param rhs The other object to compare.
     *
     * @return True if the two objects are equal, false otherwise.
     */
    public static boolean equals(Object lhs, Object rhs) {
        if (lhs == null && rhs == null) return true;
        else if (lhs == null) return false;
        else return lhs.equals(rhs);
    }

    public static <T> List<T> cons(final T elt, final List<T> l) {
        List<T> l2 = new ArrayList<T>();
        l2.add(elt);
        if (l != null) l2.addAll(l);
        return l2;
    }

    public static void warnUser(final String msg) {
        warnUser(logger, msg);
    }
    
    public static void warnUser(final Logger logger, final String msg) {
        logger.warn(String.format("********************************************************************************"));
        logger.warn(String.format("* WARNING:"));
        logger.warn(String.format("*"));
        prettyPrintWarningMessage(logger, msg);
        logger.warn(String.format("********************************************************************************"));
    }

    /**
     * pretty print the warning message supplied
     *
     * @param logger logger for the message
     * @param message the message
     */
    private static void prettyPrintWarningMessage(Logger logger, String message) {
        StringBuilder builder = new StringBuilder(message);
        while (builder.length() > 70) {
            int space = builder.lastIndexOf(" ", 70);
            if (space <= 0) space = 70;
            logger.warn(String.format("* %s", builder.substring(0, space)));
            builder.delete(0, space + 1);
        }
        logger.warn(String.format("* %s", builder));
    }

    public static ArrayList<Byte> subseq(char[] fullArray) {
        byte[] fullByteArray = new byte[fullArray.length];
        StringUtil.charsToBytes(fullArray, 0, fullArray.length, fullByteArray, 0);
        return subseq(fullByteArray);
    }

    public static ArrayList<Byte> subseq(byte[] fullArray) {
        return subseq(fullArray, 0, fullArray.length - 1);
    }

    public static ArrayList<Byte> subseq(byte[] fullArray, int start, int end) {
        assert end < fullArray.length;
        ArrayList<Byte> dest = new ArrayList<Byte>(end - start + 1);
        for (int i = start; i <= end; i++) {
            dest.add(fullArray[i]);
        }
        return dest;
    }

    public static String baseList2string(List<Byte> bases) {
        byte[] basesAsbytes = new byte[bases.size()];
        int i = 0;
        for (Byte b : bases) {
            basesAsbytes[i] = b;
            i++;
        }
        return new String(basesAsbytes);
    }

    /**
     * join the key value pairs of a map into one string, i.e. myMap = [A->1,B->2,C->3] with a call of:
     * joinMap("-","*",myMap) -> returns A-1*B-2*C-3
     *
     * Be forewarned, if you're not using a map that is aware of the ordering (i.e. HashMap instead of LinkedHashMap)
     * the ordering of the string you get back might not be what you expect! (i.e. C-3*A-1*B-2 vrs A-1*B-2*C-3)
     *
     * @param keyValueSeperator the string to seperate the key-value pairs
     * @param recordSeperator the string to use to seperate each key-value pair from other key-value pairs
     * @param map the map to draw from
     * @param <L> the map's key type
     * @param <R> the map's value type
     * @return a string representing the joined map
     */
    public static <L,R> String joinMap(String keyValueSeperator, String recordSeperator, Map<L,R> map) {
        if (map.size() < 1) { return null; }
        String joinedKeyValues[] = new String[map.size()];
        int index = 0;
        for (L key : map.keySet()) {
           joinedKeyValues[index++] = String.format("%s%s%s",key.toString(),keyValueSeperator,map.get(key).toString());
        }
        return join(recordSeperator,joinedKeyValues);
    }

    /**
     * Splits a String using indexOf instead of regex to speed things up.
     *
     * @param str the string to split.
     * @param delimiter the delimiter used to split the string.
     * @return an array of tokens.
     */
    public static ArrayList<String> split(String str, String delimiter) {
        return split(str, delimiter, 10);
    }

    /**
     * Splits a String using indexOf instead of regex to speed things up.
     *
     * @param str the string to split.
     * @param delimiter the delimiter used to split the string.
     * @param expectedNumTokens The number of tokens expected. This is used to initialize the ArrayList.
     * @return an array of tokens.
     */
    public static ArrayList<String> split(String str, String delimiter, int expectedNumTokens) {
        final ArrayList<String> result =  new ArrayList<String>(expectedNumTokens);

        int delimiterIdx = -1;
        do {
            final int tokenStartIdx = delimiterIdx + 1;
            delimiterIdx = str.indexOf(delimiter, tokenStartIdx);
            final String token = (delimiterIdx != -1 ? str.substring(tokenStartIdx, delimiterIdx) : str.substring(tokenStartIdx) );
            result.add(token);
        } while( delimiterIdx != -1 );

        return result;
    }


    /**
     * join an array of strings given a seperator
     * @param separator the string to insert between each array element
     * @param strings the array of strings
     * @return a string, which is the joining of all array values with the separator
     */
    public static String join(String separator, String[] strings) {
        return join(separator, strings, 0, strings.length);
    }

    public static String join(String separator, String[] strings, int start, int end) {
        if ((end - start) == 0) {
            return "";
        }
        StringBuilder ret = new StringBuilder(strings[start]);
        for (int i = start + 1; i < end; ++i) {
            ret.append(separator);
            ret.append(strings[i]);
        }
        return ret.toString();
    }

    public static String join(String separator, int[] ints) {
        if ( ints == null || ints.length == 0)
            return "";
        else {
            StringBuilder ret = new StringBuilder();
            ret.append(ints[0]);
            for (int i = 1; i < ints.length; ++i) {
                ret.append(separator);
                ret.append(ints[i]);
            }
            return ret.toString();
        }
    }

    /**
     * Create a new list that contains the elements of left along with elements elts
     * @param left a non-null list of elements
     * @param elts a varargs vector for elts to append in order to left
     * @param <T>
     * @return A newly allocated linked list containing left followed by elts
     */
    public static <T> List<T> append(final List<T> left, T ... elts) {
        final List<T> l = new LinkedList<T>(left);
        l.addAll(Arrays.asList(elts));
        return l;
    }

    /**
     * Returns a string of the values in joined by separator, such as A,B,C
     *
     * @param separator
     * @param doubles
     * @return
     */
    public static String join(String separator, double[] doubles) {
        if ( doubles == null || doubles.length == 0)
            return "";
        else {
            StringBuilder ret = new StringBuilder();
            ret.append(doubles[0]);
            for (int i = 1; i < doubles.length; ++i) {
                ret.append(separator);
                ret.append(doubles[i]);
            }
            return ret.toString();
        }
    }

    /**
     * Returns a string of the form elt1.toString() [sep elt2.toString() ... sep elt.toString()] for a collection of
     * elti objects (note there's no actual space between sep and the elti elements).  Returns
     * "" if collection is empty.  If collection contains just elt, then returns elt.toString()
     *
     * @param separator the string to use to separate objects
     * @param objects a collection of objects.  the element order is defined by the iterator over objects
     * @param <T> the type of the objects
     * @return a non-null string
     */
    public static <T> String join(final String separator, final Collection<T> objects) {
        if (objects.isEmpty()) { // fast path for empty collection
            return "";
        } else {
            final Iterator<T> iter = objects.iterator();
            final T first = iter.next();

            if ( ! iter.hasNext() ) // fast path for singleton collections
                return first.toString();
            else { // full path for 2+ collection that actually need a join
                final StringBuilder ret = new StringBuilder(first.toString());
                while(iter.hasNext()) {
                    ret.append(separator);
                    ret.append(iter.next().toString());
                }
                return ret.toString();
            }
        }
    }

    public static <T> String join(final String separator, final T ... objects) {
        return join(separator, Arrays.asList(objects));
    }

    /**
     * Create a new string thats a n duplicate copies of s
     * @param s the string to duplicate
     * @param nCopies how many copies?
     * @return a string
     */
    public static String dupString(final String s, int nCopies) {
        if ( s == null || s.equals("") ) throw new IllegalArgumentException("Bad s " + s);
        if ( nCopies < 1 ) throw new IllegalArgumentException("nCopies must be >= 1 but got " + nCopies);

        final StringBuilder b = new StringBuilder();
        for ( int i = 0; i < nCopies; i++ )
            b.append(s);
        return b.toString();
    }

    public static String dupString(char c, int nCopies) {
        char[] chars = new char[nCopies];
        Arrays.fill(chars, c);
        return new String(chars);
    }

    public static byte[] dupBytes(byte b, int nCopies) {
        byte[] bytes = new byte[nCopies];
        Arrays.fill(bytes, b);
        return bytes;
    }

    // trim a string for the given character (i.e. not just whitespace)
    public static String trim(String str, char ch) {
        char[] array = str.toCharArray();


        int start = 0;
        while ( start < array.length && array[start] == ch )
            start++;

        int end = array.length - 1;
        while ( end > start && array[end] == ch )
            end--;

        return str.substring(start, end+1);
    }

    /**
     * Splits expressions in command args by spaces and returns the array of expressions.
     * Expressions may use single or double quotes to group any individual expression, but not both.
     * @param args Arguments to parse.
     * @return Parsed expressions.
     */
    public static String[] escapeExpressions(String args) {
        // special case for ' and " so we can allow expressions
        if (args.indexOf('\'') != -1)
            return escapeExpressions(args, "'");
        else if (args.indexOf('\"') != -1)
            return escapeExpressions(args, "\"");
        else
            return args.trim().split(" +");
    }

    /**
     * Splits expressions in command args by spaces and the supplied delimiter and returns the array of expressions.
     * @param args Arguments to parse.
     * @param delimiter Delimiter for grouping expressions.
     * @return Parsed expressions.
     */
    private static String[] escapeExpressions(String args, String delimiter) {
        String[] command = {};
        String[] split = args.split(delimiter);
        String arg;
        for (int i = 0; i < split.length - 1; i += 2) {
            arg = split[i].trim();
            if (arg.length() > 0) // if the unescaped arg has a size
                command = Utils.concatArrays(command, arg.split(" +"));
            command = Utils.concatArrays(command, new String[]{split[i + 1]});
        }
        arg = split[split.length - 1].trim();
        if (split.length % 2 == 1) // if the command ends with a delimiter
            if (arg.length() > 0) // if the last unescaped arg has a size
                command = Utils.concatArrays(command, arg.split(" +"));
        return command;
    }

    /**
     * Concatenates two String arrays.
     * @param A First array.
     * @param B Second array.
     * @return Concatenation of A then B.
     */
    public static String[] concatArrays(String[] A, String[] B) {
       String[] C = new String[A.length + B.length];
       System.arraycopy(A, 0, C, 0, A.length);
       System.arraycopy(B, 0, C, A.length, B.length);
       return C;
    }

    /**
     * Appends String(s) B to array A.
     * @param A First array.
     * @param B Strings to append.
     * @return A with B(s) appended.
     */
    public static String[] appendArray(String[] A, String... B) {
        return concatArrays(A, B);
    }

    public static <T extends Comparable<T>> List<T> sorted(Collection<T> c) {
        return sorted(c, false);
    }

    public static <T extends Comparable<T>> List<T> sorted(Collection<T> c, boolean reverse) {
        List<T> l = new ArrayList<T>(c);
        Collections.sort(l);
        if ( reverse ) Collections.reverse(l);
        return l;
    }

    public static <T extends Comparable<T>, V> List<V> sorted(Map<T,V> c) {
        return sorted(c, false);
    }

    public static <T extends Comparable<T>, V> List<V> sorted(Map<T,V> c, boolean reverse) {
        List<T> t = new ArrayList<T>(c.keySet());
        Collections.sort(t);
        if ( reverse ) Collections.reverse(t);

        List<V> l = new ArrayList<V>();
        for ( T k : t ) {
            l.add(c.get(k));
        }
        return l;
    }

    /**
     * Reverse a byte array of bases
     *
     * @param bases  the byte array of bases
     * @return the reverse of the base byte array
     */
    static public byte[] reverse(byte[] bases) {
        byte[] rcbases = new byte[bases.length];

        for (int i = 0; i < bases.length; i++) {
            rcbases[i] = bases[bases.length - i - 1];
        }

        return rcbases;
    }

    static public final <T> List<T> reverse(final List<T> l) {
        final List<T> newL = new ArrayList<T>(l);
        Collections.reverse(newL);
        return newL;
    }

    /**
     * Reverse an int array of bases
     *
     * @param bases  the int array of bases
     * @return the reverse of the base int array
     */
    static public int[] reverse(int[] bases) {
        int[] rcbases = new int[bases.length];

        for (int i = 0; i < bases.length; i++) {
            rcbases[i] = bases[bases.length - i - 1];
        }

        return rcbases;
    }

    /**
     * Reverse (NOT reverse-complement!!) a string
     *
     * @param bases  input string
     * @return the reversed string
     */
    static public String reverse(String bases) {
        return new String( reverse( bases.getBytes() )) ;
    }

    public static boolean isFlagSet(int value, int flag) {
        return ((value & flag) == flag);
    }

    /**
     * Helper utility that calls into the InetAddress system to resolve the hostname.  If this fails,
     * unresolvable gets returned instead.
     *
     * @return
     */
    public static final String resolveHostname() {
        try {
            return InetAddress.getLocalHost().getCanonicalHostName();
        }
        catch (java.net.UnknownHostException uhe) { // [beware typo in code sample -dmw]
            return "unresolvable";
            // handle exception
        }
    }


    public static byte [] arrayFromArrayWithLength(byte[] array, int length) {
        byte [] output = new byte[length];
        for (int j = 0; j < length; j++)
            output[j] = array[(j % array.length)];
        return output;
    }

    public static void fillArrayWithByte(byte[] array, byte value) {
        for (int i=0; i<array.length; i++)
            array[i] = value;
    }

    /**
     * Creates a program record for the program, adds it to the list of program records (@PG tags) in the bam file and sets
     * up the writer with the header and presorted status.
     *
     * @param toolkit             the engine
     * @param originalHeader      original header
     * @param KEEP_ALL_PG_RECORDS whether or not to keep all the other program records already existing in this BAM file
     * @param programRecord       the program record for this program
     */
    public static SAMFileHeader setupWriter(GenomeAnalysisEngine toolkit, SAMFileHeader originalHeader, boolean KEEP_ALL_PG_RECORDS, SAMProgramRecord programRecord) {
        SAMFileHeader header = originalHeader.clone();
        List<SAMProgramRecord> oldRecords = header.getProgramRecords();
        List<SAMProgramRecord> newRecords = new ArrayList<SAMProgramRecord>(oldRecords.size()+1);
        for ( SAMProgramRecord record : oldRecords )
            if ( (programRecord != null && !record.getId().startsWith(programRecord.getId())) || KEEP_ALL_PG_RECORDS )
                newRecords.add(record);

        if (programRecord != null) {
            newRecords.add(programRecord);
            header.setProgramRecords(newRecords);
        }
        return header;
    }

    /**
    * Creates a program record for the program, adds it to the list of program records (@PG tags) in the bam file and returns
    * the new header to be added to the BAM writer.
    *
    * @param toolkit             the engine
    * @param KEEP_ALL_PG_RECORDS whether or not to keep all the other program records already existing in this BAM file
    * @param walker              the walker object (so we can extract the command line)
    * @param PROGRAM_RECORD_NAME the name for the PG tag
    * @return a pre-filled header for the bam writer
    */
    public static SAMFileHeader setupWriter(GenomeAnalysisEngine toolkit, SAMFileHeader originalHeader, boolean KEEP_ALL_PG_RECORDS, Object walker, String PROGRAM_RECORD_NAME) {
        final SAMProgramRecord programRecord = createProgramRecord(toolkit, walker, PROGRAM_RECORD_NAME);
        return setupWriter(toolkit, originalHeader, KEEP_ALL_PG_RECORDS, programRecord);
    }

    /**
     * Creates a program record for the program, adds it to the list of program records (@PG tags) in the bam file and sets
     * up the writer with the header and presorted status.
     *
     * @param writer              BAM file writer
     * @param toolkit             the engine
     * @param preSorted           whether or not the writer can assume reads are going to be added are already sorted
     * @param KEEP_ALL_PG_RECORDS whether or not to keep all the other program records already existing in this BAM file
     * @param walker              the walker object (so we can extract the command line)
     * @param PROGRAM_RECORD_NAME the name for the PG tag
     */
    public static void setupWriter(StingSAMFileWriter writer, GenomeAnalysisEngine toolkit, SAMFileHeader originalHeader, boolean preSorted, boolean KEEP_ALL_PG_RECORDS, Object walker, String PROGRAM_RECORD_NAME) {
        SAMFileHeader header = setupWriter(toolkit, originalHeader, KEEP_ALL_PG_RECORDS, walker, PROGRAM_RECORD_NAME);
        writer.writeHeader(header);
        writer.setPresorted(preSorted);
    }


    /**
     * Creates a program record (@PG) tag
     *
     * @param toolkit             the engine
     * @param walker              the walker object (so we can extract the command line)
     * @param PROGRAM_RECORD_NAME the name for the PG tag
     * @return a program record for the tool
     */
    public static SAMProgramRecord createProgramRecord(GenomeAnalysisEngine toolkit, Object walker, String PROGRAM_RECORD_NAME) {
        final SAMProgramRecord programRecord = new SAMProgramRecord(PROGRAM_RECORD_NAME);
        final ResourceBundle headerInfo = TextFormattingUtils.loadResourceBundle("StingText");
        try {
            final String version = headerInfo.getString("org.broadinstitute.sting.gatk.version");
            programRecord.setProgramVersion(version);
        } catch (MissingResourceException e) {
            // couldn't care less if the resource is missing...
        }
        programRecord.setCommandLine(toolkit.createApproximateCommandLineArgumentString(toolkit, walker));
        return programRecord;
    }

    public static <E> Collection<E> makeCollection(Iterable<E> iter) {
        Collection<E> list = new ArrayList<E>();
        for (E item : iter) {
            list.add(item);
        }
        return list;
    }

    /**
     * Returns the number of combinations represented by this collection
     * of collection of options.
     *
     * For example, if this is [[A, B], [C, D], [E, F, G]] returns 2 * 2 * 3 = 12
     *
     * @param options
     * @param <T>
     * @return
     */
    @Requires("options != null")
    public static <T> int nCombinations(final Collection<T>[] options) {
        int nStates = 1;
        for ( Collection<T> states : options ) {
            nStates *= states.size();
        }
        return nStates;
    }

    @Requires("options != null")
    public static <T> int nCombinations(final List<List<T>> options) {
        if ( options.isEmpty() )
            return 0;
        else {
            int nStates = 1;
            for ( Collection<T> states : options ) {
                nStates *= states.size();
            }
            return nStates;
        }
    }

    /**
     * Make all combinations of N size of objects
     *
     * if objects = [A, B, C]
     * if N = 1 => [[A], [B], [C]]
     * if N = 2 => [[A, A], [B, A], [C, A], [A, B], [B, B], [C, B], [A, C], [B, C], [C, C]]
     *
     * @param objects
     * @param n
     * @param <T>
     * @param withReplacement if false, the resulting permutations will only contain unique objects from objects
     * @return
     */
    public static <T> List<List<T>> makePermutations(final List<T> objects, final int n, final boolean withReplacement) {
        final List<List<T>> combinations = new ArrayList<List<T>>();

        if ( n <= 0 )
            ;
        else if ( n == 1 ) {
            for ( final T o : objects )
                combinations.add(Collections.singletonList(o));
        } else {
            final List<List<T>> sub = makePermutations(objects, n - 1, withReplacement);
            for ( List<T> subI : sub ) {
                for ( final T a : objects ) {
                    if ( withReplacement || ! subI.contains(a) )
                        combinations.add(Utils.cons(a, subI));
                }
            }
        }

        return combinations;
    }

    /**
     * Convenience function that formats the novelty rate as a %.2f string
     *
     * @param known number of variants from all that are known
     * @param all number of all variants
     * @return a String novelty rate, or NA if all == 0
     */
    public static String formattedNoveltyRate(final int known, final int all) {
        return formattedPercent(all - known, all);
    }

    /**
     * Convenience function that formats the novelty rate as a %.2f string
     *
     * @param x number of objects part of total that meet some criteria
     * @param total count of all objects, including x
     * @return a String percent rate, or NA if total == 0
     */
    public static String formattedPercent(final long x, final long total) {
        return total == 0 ? "NA" : String.format("%.2f", (100.0*x) / total);
    }

    /**
     * Convenience function that formats a ratio as a %.2f string
     *
     * @param num  number of observations in the numerator
     * @param denom number of observations in the denumerator
     * @return a String formatted ratio, or NA if all == 0
     */
    public static String formattedRatio(final long num, final long denom) {
        return denom == 0 ? "NA" : String.format("%.2f", num / (1.0 * denom));
    }

    /**
     * Create a constant map that maps each value in values to itself
     * @param values
     * @param <T>
     * @return
     */
    public static <T> Map<T, T> makeIdentityFunctionMap(Collection<T> values) {
        Map<T,T> map = new HashMap<T, T>(values.size());
        for ( final T value : values )
            map.put(value, value);
        return Collections.unmodifiableMap(map);
    }

    /**
     * Divides the input list into a list of sublists, which contains group size elements (except potentially the last one)
     *
     * list = [A, B, C, D, E]
     * groupSize = 2
     * result = [[A, B], [C, D], [E]]
     *
     * @param list
     * @param groupSize
     * @return
     */
    public static <T> List<List<T>> groupList(final List<T> list, final int groupSize) {
        if ( groupSize < 1 ) throw new IllegalArgumentException("groupSize >= 1");

        final List<List<T>> subLists = new LinkedList<List<T>>();
        int n = list.size();
        for ( int i = 0; i < n; i += groupSize ) {
            subLists.add(list.subList(i, Math.min(i + groupSize, n)));
        }
        return subLists;
    }

    /**
     * @see #calcMD5(byte[])
     */
    public static String calcMD5(final String s) throws NoSuchAlgorithmException {
        return calcMD5(s.getBytes());
    }

    /**
     * Calculate the md5 for bytes, and return the result as a 32 character string
     *
     * @param bytes the bytes to calculate the md5 of
     * @return the md5 of bytes, as a 32-character long string
     * @throws NoSuchAlgorithmException
     */
    @Ensures({"result != null", "result.length() == 32"})
    public static String calcMD5(final byte[] bytes) throws NoSuchAlgorithmException {
        if ( bytes == null ) throw new IllegalArgumentException("bytes cannot be null");
        final byte[] thedigest = MessageDigest.getInstance("MD5").digest(bytes);
        final BigInteger bigInt = new BigInteger(1, thedigest);

        String md5String = bigInt.toString(16);
        while (md5String.length() < 32) md5String = "0" + md5String; // pad to length 32
        return md5String;
    }
}