/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.util.internal;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Iterator;
  import java.util.List;
  
  import static io.netty.util.internal.ObjectUtil.*;
  
  /**
   * String utility class.
   */
  public final class StringUtil {
  
      public static final String EMPTY_STRING = "";
      public static final String NEWLINE = SystemPropertyUtil.get("line.separator", "\n");
  
      public static final char DOUBLE_QUOTE = '\"';
      public static final char COMMA = ',';
      public static final char LINE_FEED = '\n';
      public static final char CARRIAGE_RETURN = '\r';
      public static final char TAB = '\t';
      public static final char SPACE = 0x20;
  
      private static final String[] BYTE2HEX_PAD = new String[256];
      private static final String[] BYTE2HEX_NOPAD = new String[256];
      private static final byte[] HEX2B;
  
      /**
       * 2 - Quote character at beginning and end.
       * 5 - Extra allowance for anticipated escape characters that may be added.
       */
      private static final int CSV_NUMBER_ESCAPE_CHARACTERS = 2 + 5;
      private static final char PACKAGE_SEPARATOR_CHAR = '.';
  
      static {
          // Generate the lookup table that converts a byte into a 2-digit hexadecimal integer.
          for (int i = 0; i < BYTE2HEX_PAD.length; i++) {
              String str = Integer.toHexString(i);
              BYTE2HEX_PAD[i] = i > 0xf ? str : ('0' + str);
              BYTE2HEX_NOPAD[i] = str;
          }
          // Generate the lookup table that converts an hex char into its decimal value:
          // the size of the table is such that the JVM is capable of save any bounds-check
          // if a char type is used as an index.
          HEX2B = new byte[Character.MAX_VALUE + 1];
          Arrays.fill(HEX2B, (byte) -1);
          HEX2B['0'] = 0;
          HEX2B['1'] = 1;
          HEX2B['2'] = 2;
          HEX2B['3'] = 3;
          HEX2B['4'] = 4;
          HEX2B['5'] = 5;
          HEX2B['6'] = 6;
          HEX2B['7'] = 7;
          HEX2B['8'] = 8;
          HEX2B['9'] = 9;
          HEX2B['A'] = 10;
          HEX2B['B'] = 11;
          HEX2B['C'] = 12;
          HEX2B['D'] = 13;
          HEX2B['E'] = 14;
          HEX2B['F'] = 15;
          HEX2B['a'] = 10;
          HEX2B['b'] = 11;
          HEX2B['c'] = 12;
          HEX2B['d'] = 13;
          HEX2B['e'] = 14;
          HEX2B['f'] = 15;
      }
  
      private StringUtil() {
          // Unused.
      }
  
      /**
       * Get the item after one char delim if the delim is found (else null).
       * This operation is a simplified and optimized
       * version of {@link String#split(String, int)}.
       */
      public static String substringAfter(String value, char delim) {
          int pos = value.indexOf(delim);
          if (pos >= 0) {
             return value.substring(pos + 1);
         }
         return null;
     }
 
     /**
      * Get the item before one char delim if the delim is found (else null).
      * This operation is a simplified and optimized
      * version of {@link String#split(String, int)}.
      */
     public static String substringBefore(String value, char delim) {
         int pos = value.indexOf(delim);
         if (pos >= 0) {
             return value.substring(0, pos);
         }
         return null;
     }
 
     /**
      * Checks if two strings have the same suffix of specified length
      *
      * @param s   string
      * @param p   string
      * @param len length of the common suffix
      * @return true if both s and p are not null and both have the same suffix. Otherwise - false
      */
     public static boolean commonSuffixOfLength(String s, String p, int len) {
         return s != null && p != null && len >= 0 && s.regionMatches(s.length() - len, p, p.length() - len, len);
     }
 
     /**
      * Converts the specified byte value into a 2-digit hexadecimal integer.
      */
     public static String byteToHexStringPadded(int value) {
         return BYTE2HEX_PAD[value & 0xff];
     }
 
     /**
      * Converts the specified byte value into a 2-digit hexadecimal integer and appends it to the specified buffer.
      */
     public static <T extends Appendable> T byteToHexStringPadded(T buf, int value) {
         try {
             buf.append(byteToHexStringPadded(value));
         } catch (IOException e) {
             PlatformDependent.throwException(e);
         }
         return buf;
     }
 
     /**
      * Converts the specified byte array into a hexadecimal value.
      */
     public static String toHexStringPadded(byte[] src) {
         return toHexStringPadded(src, 0, src.length);
     }
 
     /**
      * Converts the specified byte array into a hexadecimal value.
      */
     public static String toHexStringPadded(byte[] src, int offset, int length) {
         return toHexStringPadded(new StringBuilder(length << 1), src, offset, length).toString();
     }
 
     /**
      * Converts the specified byte array into a hexadecimal value and appends it to the specified buffer.
      */
     public static <T extends Appendable> T toHexStringPadded(T dst, byte[] src) {
         return toHexStringPadded(dst, src, 0, src.length);
     }
 
     /**
      * Converts the specified byte array into a hexadecimal value and appends it to the specified buffer.
      */
     public static <T extends Appendable> T toHexStringPadded(T dst, byte[] src, int offset, int length) {
         final int end = offset + length;
         for (int i = offset; i < end; i++) {
             byteToHexStringPadded(dst, src[i]);
         }
         return dst;
     }
 
     /**
      * Converts the specified byte value into a hexadecimal integer.
      */
     public static String byteToHexString(int value) {
         return BYTE2HEX_NOPAD[value & 0xff];
     }
 
     /**
      * Converts the specified byte value into a hexadecimal integer and appends it to the specified buffer.
      */
     public static <T extends Appendable> T byteToHexString(T buf, int value) {
         try {
             buf.append(byteToHexString(value));
         } catch (IOException e) {
             PlatformDependent.throwException(e);
         }
         return buf;
     }
 
     /**
      * Converts the specified byte array into a hexadecimal value.
      */
     public static String toHexString(byte[] src) {
         return toHexString(src, 0, src.length);
     }
 
     /**
      * Converts the specified byte array into a hexadecimal value.
      */
     public static String toHexString(byte[] src, int offset, int length) {
         return toHexString(new StringBuilder(length << 1), src, offset, length).toString();
     }
 
     /**
      * Converts the specified byte array into a hexadecimal value and appends it to the specified buffer.
      */
     public static <T extends Appendable> T toHexString(T dst, byte[] src) {
         return toHexString(dst, src, 0, src.length);
     }
 
     /**
      * Converts the specified byte array into a hexadecimal value and appends it to the specified buffer.
      */
     public static <T extends Appendable> T toHexString(T dst, byte[] src, int offset, int length) {
         assert length >= 0;
         if (length == 0) {
             return dst;
         }
 
         final int end = offset + length;
         final int endMinusOne = end - 1;
         int i;
 
         // Skip preceding zeroes.
         for (i = offset; i < endMinusOne; i++) {
             if (src[i] != 0) {
                 break;
             }
         }
 
         byteToHexString(dst, src[i++]);
         int remaining = end - i;
         toHexStringPadded(dst, src, i, remaining);
 
         return dst;
     }
 
     /**
      * Helper to decode half of a hexadecimal number from a string.
      * @param c The ASCII character of the hexadecimal number to decode.
      * Must be in the range {@code [0-9a-fA-F]}.
      * @return The hexadecimal value represented in the ASCII character
      * given, or {@code -1} if the character is invalid.
      */
     public static int decodeHexNibble(final char c) {
         // Character.digit() is not used here, as it addresses a larger
         // set of characters (both ASCII and full-width latin letters).
         return HEX2B[c];
     }
 
     /**
      * Helper to decode half of a hexadecimal number from a string.
      * @param b The ASCII character of the hexadecimal number to decode.
      * Must be in the range {@code [0-9a-fA-F]}.
      * @return The hexadecimal value represented in the ASCII character
      * given, or {@code -1} if the character is invalid.
      */
     public static int decodeHexNibble(final byte b) {
         // Character.digit() is not used here, as it addresses a larger
         // set of characters (both ASCII and full-width latin letters).
         return HEX2B[b];
     }
 
     /**
      * Decode a 2-digit hex byte from within a string.
      */
     public static byte decodeHexByte(CharSequence s, int pos) {
         int hi = decodeHexNibble(s.charAt(pos));
         int lo = decodeHexNibble(s.charAt(pos + 1));
         if (hi == -1 || lo == -1) {
             throw new IllegalArgumentException(String.format(
                     "invalid hex byte '%s' at index %d of '%s'", s.subSequence(pos, pos + 2), pos, s));
         }
         return (byte) ((hi << 4) + lo);
     }
 
     /**
      * Decodes part of a string with <a href="https://en.wikipedia.org/wiki/Hex_dump">hex dump</a>
      *
      * @param hexDump a {@link CharSequence} which contains the hex dump
      * @param fromIndex start of hex dump in {@code hexDump}
      * @param length hex string length
      */
     public static byte[] decodeHexDump(CharSequence hexDump, int fromIndex, int length) {
         if (length < 0 || (length & 1) != 0) {
             throw new IllegalArgumentException("length: " + length);
         }
         if (length == 0) {
             return EmptyArrays.EMPTY_BYTES;
         }
         byte[] bytes = new byte[length >>> 1];
         for (int i = 0; i < length; i += 2) {
             bytes[i >>> 1] = decodeHexByte(hexDump, fromIndex + i);
         }
         return bytes;
     }
 
     /**
      * Decodes a <a href="https://en.wikipedia.org/wiki/Hex_dump">hex dump</a>
      */
     public static byte[] decodeHexDump(CharSequence hexDump) {
         return decodeHexDump(hexDump, 0, hexDump.length());
     }
 
     /**
      * Generates a class name from a {@link Class}. Similar to {@link Class#getName()}, but null-safe.
      */
     public static String className(Object o) {
         if (o == null) {
             return "null_object";
         } else {
             return o.getClass().getName();
         }
     }
 
     /**
      * The shortcut to {@link #simpleClassName(Class) simpleClassName(o.getClass())}.
      */
     public static String simpleClassName(Object o) {
         if (o == null) {
             return "null_object";
         } else {
             return simpleClassName(o.getClass());
         }
     }
 
     /**
      * Generates a simplified name from a {@link Class}.  Similar to {@link Class#getSimpleName()}, but it works fine
      * with anonymous classes.
      */
     public static String simpleClassName(Class<?> clazz) {
         String className = checkNotNull(clazz, "clazz").getName();
         final int lastDotIdx = className.lastIndexOf(PACKAGE_SEPARATOR_CHAR);
         if (lastDotIdx > -1) {
             return className.substring(lastDotIdx + 1);
         }
         return className;
     }
 
     /**
      * Escapes the specified value, if necessary according to
      * <a href="https://tools.ietf.org/html/rfc4180#section-2">RFC-4180</a>.
      *
      * @param value The value which will be escaped according to
      *              <a href="https://tools.ietf.org/html/rfc4180#section-2">RFC-4180</a>
      * @return {@link CharSequence} the escaped value if necessary, or the value unchanged
      */
     public static CharSequence escapeCsv(CharSequence value) {
         return escapeCsv(value, false);
     }
 
     /**
      * Escapes the specified value, if necessary according to
      * <a href="https://tools.ietf.org/html/rfc4180#section-2">RFC-4180</a>.
      *
      * @param value          The value which will be escaped according to
      *                       <a href="https://tools.ietf.org/html/rfc4180#section-2">RFC-4180</a>
      * @param trimWhiteSpace The value will first be trimmed of its optional white-space characters,
      *                       according to <a href="https://tools.ietf.org/html/rfc7230#section-7">RFC-7230</a>
      * @return {@link CharSequence} the escaped value if necessary, or the value unchanged
      */
     public static CharSequence escapeCsv(CharSequence value, boolean trimWhiteSpace) {
         int length = checkNotNull(value, "value").length();
         int start;
         int last;
         if (trimWhiteSpace) {
             start = indexOfFirstNonOwsChar(value, length);
             last = indexOfLastNonOwsChar(value, start, length);
         } else {
             start = 0;
             last = length - 1;
         }
         if (start > last) {
             return EMPTY_STRING;
         }
 
         int firstUnescapedSpecial = -1;
         boolean quoted = false;
         if (isDoubleQuote(value.charAt(start))) {
             quoted = isDoubleQuote(value.charAt(last)) && last > start;
             if (quoted) {
                 start++;
                 last--;
             } else {
                 firstUnescapedSpecial = start;
             }
         }
 
         if (firstUnescapedSpecial < 0) {
             if (quoted) {
                 for (int i = start; i <= last; i++) {
                     if (isDoubleQuote(value.charAt(i))) {
                         if (i == last || !isDoubleQuote(value.charAt(i + 1))) {
                             firstUnescapedSpecial = i;
                             break;
                         }
                         i++;
                     }
                 }
             } else {
                 for (int i = start; i <= last; i++) {
                     char c = value.charAt(i);
                     if (c == LINE_FEED || c == CARRIAGE_RETURN || c == COMMA) {
                         firstUnescapedSpecial = i;
                         break;
                     }
                     if (isDoubleQuote(c)) {
                         if (i == last || !isDoubleQuote(value.charAt(i + 1))) {
                             firstUnescapedSpecial = i;
                             break;
                         }
                         i++;
                     }
                 }
             }
 
             if (firstUnescapedSpecial < 0) {
                 // Special characters is not found or all of them already escaped.
                 // In the most cases returns a same string. New string will be instantiated (via StringBuilder)
                 // only if it really needed. It's important to prevent GC extra load.
                 return quoted? value.subSequence(start - 1, last + 2) : value.subSequence(start, last + 1);
             }
         }
 
         StringBuilder result = new StringBuilder(last - start + 1 + CSV_NUMBER_ESCAPE_CHARACTERS);
         result.append(DOUBLE_QUOTE).append(value, start, firstUnescapedSpecial);
         for (int i = firstUnescapedSpecial; i <= last; i++) {
             char c = value.charAt(i);
             if (isDoubleQuote(c)) {
                 result.append(DOUBLE_QUOTE);
                 if (i < last && isDoubleQuote(value.charAt(i + 1))) {
                     i++;
                 }
             }
             result.append(c);
         }
         return result.append(DOUBLE_QUOTE);
     }
 
     /**
      * Unescapes the specified escaped CSV field, if necessary according to
      * <a href="https://tools.ietf.org/html/rfc4180#section-2">RFC-4180</a>.
      *
      * @param value The escaped CSV field which will be unescaped according to
      *              <a href="https://tools.ietf.org/html/rfc4180#section-2">RFC-4180</a>
      * @return {@link CharSequence} the unescaped value if necessary, or the value unchanged
      */
     public static CharSequence unescapeCsv(CharSequence value) {
         int length = checkNotNull(value, "value").length();
         if (length == 0) {
             return value;
         }
         int last = length - 1;
         boolean quoted = isDoubleQuote(value.charAt(0)) && isDoubleQuote(value.charAt(last)) && length != 1;
         if (!quoted) {
             validateCsvFormat(value);
             return value;
         }
         StringBuilder unescaped = InternalThreadLocalMap.get().stringBuilder();
         for (int i = 1; i < last; i++) {
             char current = value.charAt(i);
             if (current == DOUBLE_QUOTE) {
                 if (isDoubleQuote(value.charAt(i + 1)) && (i + 1) != last) {
                     // Followed by a double-quote but not the last character
                     // Just skip the next double-quote
                     i++;
                 } else {
                     // Not followed by a double-quote or the following double-quote is the last character
                     throw newInvalidEscapedCsvFieldException(value, i);
                 }
             }
             unescaped.append(current);
         }
         return unescaped.toString();
     }
 
     /**
      * Unescapes the specified escaped CSV fields according to
      * <a href="https://tools.ietf.org/html/rfc4180#section-2">RFC-4180</a>.
      *
      * @param value A string with multiple CSV escaped fields which will be unescaped according to
      *              <a href="https://tools.ietf.org/html/rfc4180#section-2">RFC-4180</a>
      * @return {@link List} the list of unescaped fields
      */
     public static List<CharSequence> unescapeCsvFields(CharSequence value) {
         List<CharSequence> unescaped = new ArrayList<CharSequence>(2);
         StringBuilder current = InternalThreadLocalMap.get().stringBuilder();
         boolean quoted = false;
         int last = value.length() - 1;
         for (int i = 0; i <= last; i++) {
             char c = value.charAt(i);
             if (quoted) {
                 switch (c) {
                     case DOUBLE_QUOTE:
                         if (i == last) {
                             // Add the last field and return
                             unescaped.add(current.toString());
                             return unescaped;
                         }
                         char next = value.charAt(++i);
                         if (next == DOUBLE_QUOTE) {
                             // 2 double-quotes should be unescaped to one
                             current.append(DOUBLE_QUOTE);
                             break;
                         }
                         if (next == COMMA) {
                             // This is the end of a field. Let's start to parse the next field.
                             quoted = false;
                             unescaped.add(current.toString());
                             current.setLength(0);
                             break;
                         }
                         // double-quote followed by other character is invalid
                         throw newInvalidEscapedCsvFieldException(value, i - 1);
                     default:
                         current.append(c);
                 }
             } else {
                 switch (c) {
                     case COMMA:
                         // Start to parse the next field
                         unescaped.add(current.toString());
                         current.setLength(0);
                         break;
                     case DOUBLE_QUOTE:
                         if (current.length() == 0) {
                             quoted = true;
                             break;
                         }
                         // double-quote appears without being enclosed with double-quotes
                         // fall through
                     case LINE_FEED:
                         // fall through
                     case CARRIAGE_RETURN:
                         // special characters appears without being enclosed with double-quotes
                         throw newInvalidEscapedCsvFieldException(value, i);
                     default:
                         current.append(c);
                 }
             }
         }
         if (quoted) {
             throw newInvalidEscapedCsvFieldException(value, last);
         }
         unescaped.add(current.toString());
         return unescaped;
     }
 
     /**
      * Validate if {@code value} is a valid csv field without double-quotes.
      *
      * @throws IllegalArgumentException if {@code value} needs to be encoded with double-quotes.
      */
     private static void validateCsvFormat(CharSequence value) {
         int length = value.length();
         for (int i = 0; i < length; i++) {
             switch (value.charAt(i)) {
                 case DOUBLE_QUOTE:
                 case LINE_FEED:
                 case CARRIAGE_RETURN:
                 case COMMA:
                     // If value contains any special character, it should be enclosed with double-quotes
                     throw newInvalidEscapedCsvFieldException(value, i);
                 default:
             }
         }
     }
 
     private static IllegalArgumentException newInvalidEscapedCsvFieldException(CharSequence value, int index) {
         return new IllegalArgumentException("invalid escaped CSV field: " + value + " index: " + index);
     }
 
     /**
      * Get the length of a string, {@code null} input is considered {@code 0} length.
      */
     public static int length(String s) {
         return s == null ? 0 : s.length();
     }
 
     /**
      * Determine if a string is {@code null} or {@link String#isEmpty()} returns {@code true}.
      */
     public static boolean isNullOrEmpty(String s) {
         return s == null || s.isEmpty();
     }
 
     /**
      * Find the index of the first non-white space character in {@code s} starting at {@code offset}.
      *
      * @param seq    The string to search.
      * @param offset The offset to start searching at.
      * @return the index of the first non-white space character or &lt;{@code -1} if none was found.
      */
     public static int indexOfNonWhiteSpace(CharSequence seq, int offset) {
         for (; offset < seq.length(); ++offset) {
             if (!Character.isWhitespace(seq.charAt(offset))) {
                 return offset;
             }
         }
         return -1;
     }
 
     /**
      * Find the index of the first white space character in {@code s} starting at {@code offset}.
      *
      * @param seq    The string to search.
      * @param offset The offset to start searching at.
      * @return the index of the first white space character or &lt;{@code -1} if none was found.
      */
     public static int indexOfWhiteSpace(CharSequence seq, int offset) {
         for (; offset < seq.length(); ++offset) {
             if (Character.isWhitespace(seq.charAt(offset))) {
                 return offset;
             }
         }
         return -1;
     }
 
     /**
      * Determine if {@code c} lies within the range of values defined for
      * <a href="https://unicode.org/glossary/#surrogate_code_point">Surrogate Code Point</a>.
      *
      * @param c the character to check.
      * @return {@code true} if {@code c} lies within the range of values defined for
      * <a href="https://unicode.org/glossary/#surrogate_code_point">Surrogate Code Point</a>. {@code false} otherwise.
      */
     public static boolean isSurrogate(char c) {
         return c >= '\uD800' && c <= '\uDFFF';
     }
 
     private static boolean isDoubleQuote(char c) {
         return c == DOUBLE_QUOTE;
     }
 
     /**
      * Determine if the string {@code s} ends with the char {@code c}.
      *
      * @param s the string to test
      * @param c the tested char
      * @return true if {@code s} ends with the char {@code c}
      */
     public static boolean endsWith(CharSequence s, char c) {
         int len = s.length();
         return len > 0 && s.charAt(len - 1) == c;
     }
 
     /**
      * Trim optional white-space characters from the specified value,
      * according to <a href="https://tools.ietf.org/html/rfc7230#section-7">RFC-7230</a>.
      *
      * @param value the value to trim
      * @return {@link CharSequence} the trimmed value if necessary, or the value unchanged
      */
     public static CharSequence trimOws(CharSequence value) {
         final int length = value.length();
         if (length == 0) {
             return value;
         }
         int start = indexOfFirstNonOwsChar(value, length);
         int end = indexOfLastNonOwsChar(value, start, length);
         return start == 0 && end == length - 1 ? value : value.subSequence(start, end + 1);
     }
 
     /**
      * Returns a char sequence that contains all {@code elements} joined by a given separator.
      *
      * @param separator for each element
      * @param elements to join together
      *
      * @return a char sequence joined by a given separator.
      */
     public static CharSequence join(CharSequence separator, Iterable<? extends CharSequence> elements) {
         ObjectUtil.checkNotNull(separator, "separator");
         ObjectUtil.checkNotNull(elements, "elements");
 
         Iterator<? extends CharSequence> iterator = elements.iterator();
         if (!iterator.hasNext()) {
             return EMPTY_STRING;
         }
 
         CharSequence firstElement = iterator.next();
         if (!iterator.hasNext()) {
             return firstElement;
         }
 
         StringBuilder builder = new StringBuilder(firstElement);
         do {
             builder.append(separator).append(iterator.next());
         } while (iterator.hasNext());
 
         return builder;
     }
 
     /**
      * @return {@code length} if no OWS is found.
      */
     private static int indexOfFirstNonOwsChar(CharSequence value, int length) {
         int i = 0;
         while (i < length && isOws(value.charAt(i))) {
             i++;
         }
         return i;
     }
 
     /**
      * @return {@code start} if no OWS is found.
      */
     private static int indexOfLastNonOwsChar(CharSequence value, int start, int length) {
         int i = length - 1;
         while (i > start && isOws(value.charAt(i))) {
             i--;
         }
         return i;
     }
 
     private static boolean isOws(char c) {
         return c == SPACE || c == TAB;
     }
 
 }