/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.codec.digest;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.fail;
  
  import java.io.FileNotFoundException;
  import java.io.FileOutputStream;
  import java.io.PrintStream;
  import java.lang.reflect.Constructor;
  import java.nio.charset.StandardCharsets;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Properties;
  import java.util.Random;
  import java.util.zip.CRC32;
  import java.util.zip.Checksum;
  
  import org.junit.jupiter.api.Test;
  
  /**
   * Unit test to verify that the pure-Java CRC32 algorithm gives the same results as the built-in implementation.
   *
   * Copied from Hadoop 2.6.3 (Renamed TestPureJavaCrc32 to PureJavaCrc32Test).
   */
  public class PureJavaCrc32Test {
  
      /**
       * Performance tests to compare performance of the Pure Java implementation to the built-in java.util.zip implementation. This can be run from the command
       * line with:
       *
       * java -cp path/to/test/classes:path/to/common/classes \ 'org.apache.hadoop.util.TestPureJavaCrc32$PerformanceTest'
       *
       * The output is in JIRA table format.
       */
      public static class PerformanceTest {
          private static final class BenchResult {
              /** CRC value */
              final long value;
              /** Speed (MB per second) */
              final double mbps;
  
              BenchResult(final long value, final double mbps) {
                  this.value = value;
                  this.mbps = mbps;
              }
          }
  
          public static final int MAX_LEN = 32 * 1024 * 1024; // up to 32MB chunks
  
          public static final int BYTES_PER_SIZE = MAX_LEN * 4;
          static final Class<? extends Checksum> zip = CRC32.class;
          static final List<Class<? extends Checksum>> CRCS = new ArrayList<>();
  
          static {
              CRCS.add(zip);
              CRCS.add(PureJavaCrc32.class);
          }
  
          private static BenchResult doBench(final Class<? extends Checksum> clazz, final int numThreads, final byte[] bytes, final int size) throws Exception {
  
              final Thread[] threads = new Thread[numThreads];
              final BenchResult[] results = new BenchResult[threads.length];
  
              {
                  final int trials = BYTES_PER_SIZE / size;
                  final double mbProcessed = trials * size / 1024.0 / 1024.0;
                  final Constructor<? extends Checksum> ctor = clazz.getConstructor();
  
                  for (int i = 0; i < threads.length; i++) {
                      final int index = i;
                      threads[i] = new Thread() {
                          final Checksum crc = ctor.newInstance();
  
                          @Override
                          public void run() {
                              final long st = System.nanoTime();
                              crc.reset();
                              for (int trialIndex = 0; trialIndex < trials; trialIndex++) {
                                  crc.update(bytes, 0, size);
                              }
                              final long et = System.nanoTime();
                              final double secondsElapsed = (et - st) / 1000000000.0d;
                              results[index] = new BenchResult(crc.getValue(), mbProcessed / secondsElapsed);
                         }
                     };
                 }
             }
 
             for (final Thread thread : threads) {
                 thread.start();
             }
             for (final Thread thread : threads) {
                 thread.join();
             }
 
             final long expected = results[0].value;
             double sum = results[0].mbps;
             for (int i = 1; i < results.length; i++) {
                 if (results[i].value != expected) {
                     throw new AssertionError(clazz.getSimpleName() + " results not matched.");
                 }
                 sum += results[i].mbps;
             }
             return new BenchResult(expected, sum / results.length);
         }
 
         private static void doBench(final List<Class<? extends Checksum>> crcs, final byte[] bytes, final int size, final PrintStream out) throws Exception {
             final String numBytesStr = " #Bytes ";
             final String numThreadsStr = "#T";
             final String diffStr = "% diff";
 
             out.print('|');
             printCell(numBytesStr, 0, out);
             printCell(numThreadsStr, 0, out);
             for (int i = 0; i < crcs.size(); i++) {
                 final Class<? extends Checksum> c = crcs.get(i);
                 out.print('|');
                 printCell(c.getSimpleName(), 8, out);
                 for (int j = 0; j < i; j++) {
                     printCell(diffStr, diffStr.length(), out);
                 }
             }
             out.printf("\n");
 
             for (int numThreads = 1; numThreads <= 16; numThreads <<= 1) {
                 out.printf("|");
                 printCell(String.valueOf(size), numBytesStr.length(), out);
                 printCell(String.valueOf(numThreads), numThreadsStr.length(), out);
 
                 BenchResult expected = null;
                 final List<BenchResult> previous = new ArrayList<>();
                 for (final Class<? extends Checksum> c : crcs) {
                     System.gc();
 
                     final BenchResult result = doBench(c, numThreads, bytes, size);
                     printCell(String.format("%9.1f", result.mbps), c.getSimpleName().length() + 1, out);
 
                     // check result
                     if (c == zip) {
                         expected = result;
                     } else if (expected == null) {
                         fail("The first class is " + c.getName() + " but not " + zip.getName());
                     } else if (result.value != expected.value) {
                         fail(c + " has bugs!");
                     }
 
                     // compare result with previous
                     for (final BenchResult p : previous) {
                         final double diff = (result.mbps - p.mbps) / p.mbps * 100;
                         printCell(String.format("%5.1f%%", diff), diffStr.length(), out);
                     }
                     previous.add(result);
                 }
                 out.printf("\n");
             }
         }
 
         private static void doBench(final List<Class<? extends Checksum>> crcs, final PrintStream out) throws Exception {
             final byte[] bytes = new byte[MAX_LEN];
             new Random().nextBytes(bytes);
 
             // Print header
             out.printf("\nPerformance Table (The unit is MB/sec; #T = #Theads)\n");
 
             // Warm up implementations to get jit going.
             for (final Class<? extends Checksum> c : crcs) {
                 doBench(c, 1, bytes, 2);
                 doBench(c, 1, bytes, 2101);
             }
 
             // Test on a variety of sizes with different number of threads
             for (int size = 32; size <= MAX_LEN; size <<= 1) {
                 doBench(crcs, bytes, size, out);
             }
         }
 
         public static void main(final String args[]) throws Exception {
             printSystemProperties(System.out);
             doBench(CRCS, System.out);
         }
 
         private static void printCell(final String s, final int width, final PrintStream out) {
             final int w = s.length() > width ? s.length() : width;
             out.printf(" %" + w + "s |", s);
         }
 
         private static void printSystemProperties(final PrintStream out) {
             final String[] names = { "java.version", "java.runtime.name", "java.runtime.version", "java.vm.version", "java.vm.vendor", "java.vm.name",
                     "java.vm.specification.version", "java.specification.version", "os.arch", "os.name", "os.version" };
             final Properties p = System.getProperties();
             for (final String n : names) {
                 out.println(n + " = " + p.getProperty(n));
             }
         }
     }
 
     /**
      * Generate a table to perform checksums based on the same CRC-32 polynomial that java.util.zip.CRC32 uses.
      */
     public static class Table {
         /** Generate CRC-32 lookup tables */
         public static void main(final String[] args) throws FileNotFoundException {
             if (args.length != 1) {
                 System.err.println("Usage: " + Table.class.getName() + " <polynomial>");
                 System.exit(1);
             }
             final long polynomial = Long.parseLong(args[0], 16);
 
             final int i = 8;
             final Table t = new Table(i, 16, polynomial);
             final String s = t.toString();
             System.out.println(s);
 
             // print to a file
             try (final PrintStream out = new PrintStream(new FileOutputStream("table" + i + ".txt"), true)) {
                 out.println(s);
             }
         }
 
         private final int[][] tables;
 
         private Table(final int nBits, final int nTables, final long polynomial) {
             tables = new int[nTables][];
             final int size = 1 << nBits;
             for (int i = 0; i < tables.length; i++) {
                 tables[i] = new int[size];
             }
 
             // compute the first table
             final int[] first = tables[0];
             for (int i = 0; i < first.length; i++) {
                 int crc = i;
                 for (int j = 0; j < nBits; j++) {
                     if ((crc & 1) == 1) {
                         crc >>>= 1;
                         crc ^= polynomial;
                     } else {
                         crc >>>= 1;
                     }
                 }
                 first[i] = crc;
             }
 
             // compute the remaining tables
             final int mask = first.length - 1;
             for (int j = 1; j < tables.length; j++) {
                 final int[] previous = tables[j - 1];
                 final int[] current = tables[j];
                 for (int i = 0; i < current.length; i++) {
                     current[i] = previous[i] >>> nBits ^ first[previous[i] & mask];
                 }
             }
         }
 
         @Override
         public String toString() {
             final StringBuilder b = new StringBuilder();
 
             final String tableFormat = String.format("T%d_", Integer.numberOfTrailingZeros(tables[0].length)) + "%d";
             final String startFormat = "  private static final int " + tableFormat + "_start = %d*256;";
 
             for (int j = 0; j < tables.length; j++) {
                 b.append(String.format(startFormat, j, j));
                 b.append("\n");
             }
 
             b.append("  private static final int[] T = new int[] {");
             for (final String s : toStrings(tableFormat)) {
                 b.append("\n");
                 b.append(s);
             }
             b.setCharAt(b.length() - 2, '\n');
             b.append(" };\n");
             return b.toString();
         }
 
         String[] toStrings(final String nameFormat) {
             final String[] s = new String[tables.length];
             for (int j = 0; j < tables.length; j++) {
                 final int[] t = tables[j];
                 final StringBuilder b = new StringBuilder();
                 b.append(String.format("    /* " + nameFormat + " */", j));
                 for (int i = 0; i < t.length;) {
                     b.append("\n    ");
                     for (int k = 0; k < 4; k++) {
                         b.append(String.format("0x%08X, ", t[i++]));
                     }
                 }
                 s[j] = b.toString();
             }
             return s;
         }
     }
 
     private final CRC32 theirs = new CRC32();
 
     private final PureJavaCrc32 ours = new PureJavaCrc32();
 
     private void checkOnBytes(final byte[] bytes, final boolean print) {
         theirs.reset();
         ours.reset();
         checkSame();
 
         for (final byte b : bytes) {
             ours.update(b);
             theirs.update(b);
             checkSame();
         }
 
         if (print) {
             System.out.println("theirs:\t" + Long.toHexString(theirs.getValue()) + "\nours:\t" + Long.toHexString(ours.getValue()));
         }
 
         theirs.reset();
         ours.reset();
 
         ours.update(bytes, 0, bytes.length);
         theirs.update(bytes, 0, bytes.length);
         if (print) {
             System.out.println("theirs:\t" + Long.toHexString(theirs.getValue()) + "\nours:\t" + Long.toHexString(ours.getValue()));
         }
 
         checkSame();
 
         if (bytes.length >= 10) {
             ours.update(bytes, 5, 5);
             theirs.update(bytes, 5, 5);
             checkSame();
         }
     }
 
     private void checkSame() {
         assertEquals(theirs.getValue(), ours.getValue());
     }
 
     @Test
     public void testCorrectness() throws Exception {
         checkSame();
 
         theirs.update(104);
         ours.update(104);
         checkSame();
 
         checkOnBytes(new byte[] { 40, 60, 97, -70 }, false);
 
         checkOnBytes("hello world!".getBytes(StandardCharsets.UTF_8), false);
 
         final Random random1 = new Random();
         final Random random2 = new Random();
         for (int i = 0; i < 10000; i++) {
             final byte[] randomBytes = new byte[random1.nextInt(2048)];
             random2.nextBytes(randomBytes);
             checkOnBytes(randomBytes, false);
         }
 
     }
 }