package MD5;

import java.lang.reflect.*;

public class MD5 {
    /* 下面這些S11-S44實際上是一個4*4的矩陣，在原始的C實現中是用#define 實現的，
    這里把它們實現成為static final是表示了只讀，切能在同一個進程空間內的多個
    Instance間共享*/
        static final int S11 = 7;
        static final int S12 = 12;
        static final int S13 = 17;
        static final int S14 = 22;

        static final int S21 = 5;
        static final int S22 = 9;
        static final int S23 = 14;
        static final int S24 = 20;

        static final int S31 = 4;
        static final int S32 = 11;
        static final int S33 = 16;
        static final int S34 = 23;

        static final int S41 = 6;
        static final int S42 = 10;
        static final int S43 = 15;
        static final int S44 = 21;

        static final byte[] PADDING = { -128, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
        /* 下面的三個成員是MD5計算過程中用到的3個核心數據，在原始的C實現中
           被定義到MD5_CTX結構中
        
         */
        private long[] state = new long[4];  // state (ABCD)
        private long[] count = new long[2];  // number of bits, modulo 2^64 (lsb first)
        private byte[] buffer = new byte[64]; // input buffer
        
    /* digestHexStr是MD5的唯一一個公共成員，是最新一次計算結果的
    　 16進制ASCII表示.
    */
        public String digestHexStr;
        
        /* digest,是最新一次計算結果的2進制內部表示，表示128bit的MD5值.
    */
        private byte[] digest = new byte[16];
        
    /*
      getMD5ofStr是類MD5最主要的公共方法，入口參數是你想要進行MD5變換的字符串
      返回的是變換完的結果，這個結果是從公共成員digestHexStr取得的．
    */
        public String getMD5ofStr(String inbuf) {
                md5Init();
                md5Update(inbuf.getBytes(), inbuf.length());
                md5Final();
                digestHexStr = "";
                for (int i = 0; i < 16; i++) {
                        digestHexStr += byteHEX(digest[i]);
                }
                return digestHexStr;

        }
        // 這是MD5這個類的標準構造函數，JavaBean要求有一個public的并且沒有參數的構造函數
        public MD5() {
                md5Init();

                return;
        }
        


        /* md5Init是一個初始化函數，初始化核心變量，裝入標準的幻數 */
        private void md5Init() {
                count[0] = 0L;
                count[1] = 0L;
                ///* Load magic initialization constants.

                state[0] = 0x67452301L;
                state[1] = 0xefcdab89L;
                state[2] = 0x98badcfeL;
                state[3] = 0x10325476L;

                return;
        }
        /* F, G, H ,I 是4個基本的MD5函數，在原始的MD5的C實現中，由于它們是
        簡單的位運算，可能出于效率的考慮把它們實現成了宏，在java中，我們把它們
     　　實現成了private方法，名字保持了原來C中的。 */

        private long F(long x, long y, long z) {
                return (x & y) | ((~x) & z);

        }
        private long G(long x, long y, long z) {
                return (x & z) | (y & (~z));

        }
        private long H(long x, long y, long z) {
                return x ^ y ^ z;
        }

        private long I(long x, long y, long z) {
                return y ^ (x | (~z));
        }
        
       /* 
          FF,GG,HH和II將調用F,G,H,I進行近一步變換
          FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4.
          Rotation is separate from addition to prevent recomputation.
       */  

        private long FF(long a, long b, long c, long d, long x, long s,
                long ac) {
                a += F (b, c, d) + x + ac;
                a = ((int) a << s) | ((int) a >>> (32 - s));
                a += b;
                return a;
        }

        private long GG(long a, long b, long c, long d, long x, long s,
                long ac) {
                a += G (b, c, d) + x + ac;
                a = ((int) a << s) | ((int) a >>> (32 - s));
                a += b;
                return a;
        }
        private long HH(long a, long b, long c, long d, long x, long s,
                long ac) {
                a += H (b, c, d) + x + ac;
                a = ((int) a << s) | ((int) a >>> (32 - s));
                a += b;
                return a;
        }
        private long II(long a, long b, long c, long d, long x, long s,
                long ac) {
                a += I (b, c, d) + x + ac;
                a = ((int) a << s) | ((int) a >>> (32 - s));
                a += b;
                return a;
        }
        /*
         md5Update是MD5的主計算過程，inbuf是要變換的字節串，inputlen是長度，這個
         函數由getMD5ofStr調用，調用之前需要調用md5init，因此把它設計成private的
        */
        private void md5Update(byte[] inbuf, int inputLen) {

                int i, index, partLen;
                byte[] block = new byte[64];
                index = (int)(count[0] >>> 3) & 0x3F;
                // /* Update number of bits */
                if ((count[0] += (inputLen << 3)) < (inputLen << 3))
                        count[1]++;
                count[1] += (inputLen >>> 29);

                partLen = 64 - index;

                // Transform as many times as possible.
                if (inputLen >= partLen) {
                        md5Memcpy(buffer, inbuf, index, 0, partLen);
                        md5Transform(buffer);

                        for (i = partLen; i + 63 < inputLen; i += 64) {

                                md5Memcpy(block, inbuf, 0, i, 64);
                                md5Transform (block);
                        }
                        index = 0;

                } else

                        i = 0;

                ///* Buffer remaining input */
                md5Memcpy(buffer, inbuf, index, i, inputLen - i);

        }
        
        /*
          md5Final整理和填寫輸出結果
        */
        private void md5Final () {
                byte[] bits = new byte[8];
                int index, padLen;

                ///* Save number of bits */
                Encode (bits, count, 8);