package com.atlassian.plugins.rest.common.expand.parameter;
   
   import com.google.common.collect.Sets;
   import org.apache.commons.lang.StringUtils;
   
   import static java.util.Arrays.asList;
   
   import java.util.SortedSet;
   import java.util.regex.Pattern;
  
  final class IndexParser {
      private static final String INDEX = "-?\\d+";
      private static final String RANGE = "(?:" + INDEX + ")?:(?:" + INDEX + ")?";
  
      private static final Pattern INDEX_PATTERN = Pattern.compile(INDEX);
      private static final Pattern RANGE_PATTERN = Pattern.compile(RANGE);
  
      public final static Indexes ALL = new RangeIndexes(null, null);
      public final static Indexes EMPTY = new EmptyIndexes();
  
      private IndexParser() {
      }
  
      static Indexes parse(String indexes) {
          if (StringUtils.isBlank(indexes)) {
              return ALL;
          } else if (INDEX_PATTERN.matcher(indexes).matches()) {
              return new SimpleIndexes(Integer.parseInt(indexes));
          } else if (RANGE_PATTERN.matcher(indexes).matches()) {
              final String leftAsString = StringUtils.substringBefore(indexes, ":");
              final String rightAsString = StringUtils.substringAfter(indexes, ":");
              return new RangeIndexes(
                      StringUtils.isNotBlank(leftAsString) ? Integer.parseInt(leftAsString) : null,
                      StringUtils.isNotBlank(rightAsString) ? Integer.parseInt(rightAsString) : null);
          } else {
              return EMPTY;
          }
      }
  
      static class SimpleIndexes implements Indexes {
          private final int index;
  
          SimpleIndexes(int index) {
              this.index = index;
          }
  
          public boolean isRange() {
              return false;
          }
  
          public int getMinIndex(int size) {
              return getIndex(size);
          }
  
          public int getMaxIndex(int size) {
              return getIndex(size);
          }
  
          private int getIndex(int size) {
              return isInBound(index, size) ? toPositiveIndex(index, size) : -1;
          }
  
          public boolean contains(int i, int size) {
              return isInBound(index, size) && toPositiveIndex(index, size) == i;
          }
  
          public SortedSet<Integer> getIndexes(int size) {
              return isInBound(index, size) ? Sets.newTreeSet(asList(toPositiveIndex(index, size))) : Sets.<Integer>newTreeSet();
          }
      }
  
      static class RangeIndexes implements Indexes {
          private final Integer left;
          private final Integer right;
  
          RangeIndexes(Integer left, Integer right) {
              this.left = left;
              this.right = right;
          }
  
          public boolean isRange() {
              return true;
          }
  
          public int getMinIndex(int size) {
              return actualLeft(size);
          }
  
          public int getMaxIndex(int size) {
              return actualRight(size);
          }
  
          public boolean contains(int index, int size) {
              if (!isInBound(index, size)) {
                  return false;
              }
  
              final int p = toPositiveIndex(index, size);
              return p >= actualLeft(size) && p <= actualRight(size);
         }
 
         public SortedSet<Integer> getIndexes(int size) {
             final SortedSet<Integer> allIndexes = Sets.newTreeSet();
             final int actualLeft = actualLeft(size);
             final int actualRight = actualRight(size);
             if (actualLeft != -1 && actualRight != -1) {
                 for (int i = actualLeft; i <= actualRight; i++) {
                     allIndexes.add(i);
                 }
             }
             return allIndexes;
         }
 
         /**
          * Will calculate the actual positive index matching {link #left}.
          * <ul>
          * <li>If the index is negative it will calculate a positive value,</li>
          * <li>If the size of the list is 0 it will return -1,</li>
          * <li>If the index is not specified or  less than 0, then 0 is returned</li>
          * <li>If the index is greater than the {@code size} of the list then -1 is returned</li>
          * <li>else the positive value of the index is returned.</li>
          * </ul>
          *
          * @param size the size of the list to consider.
          * @return the actual 'left' index as defined.
          * @see #actualRight(int)
          */
         private int actualLeft(int size) {
             if (size == 0) {
                 return -1;
             }
 
             if (left == null) {
                 return 0;
             }
 
             final int positiveLeft = toPositiveIndex(left, size);
             if (positiveLeft < 0) {
                 return 0;
             } else if (positiveLeft >= size) {
                 return -1;
             } else {
                 return positiveLeft;
             }
         }
 
         /**
          * Will calculate the actual positive index matching {link #right}.
          * <ul>
          * <li>If the index is negative it will calculate a positive value,</li>
          * <li>If the size of the list is 0 it will return -1,</li>
          * <li>If the index is not specified or greater than {@code size - 1}, then {@code size - 1} is returned</li>
          * <li>If the index is less than 0 then -1 is returned</li>
          * <li>else the positive value of the index is returned.</li>
          * </ul>
          *
          * @param size the size of the list to consider.
          * @return the actual 'right' index as defined.
          * @see #actualLeft(int)
          */
         private int actualRight(int size) {
             if (size == 0) {
                 return -1;
             }
 
             if (right == null) {
                 return size - 1;
             }
 
             final int positiveRight = toPositiveIndex(right, size);
             if (positiveRight < 0) {
                 return -1;
             } else if (positiveRight >= size - 1) {
                 return size - 1;
             } else {
                 return positiveRight;
             }
         }
     }
 
     private static class EmptyIndexes implements Indexes {
         public boolean isRange() {
             return false;
         }
 
         public int getMinIndex(int size) {
             return -1;
         }
 
         public int getMaxIndex(int size) {
             return -1;
         }
 
         public boolean contains(int index, int size) {
             return false;
         }
 
         public SortedSet<Integer> getIndexes(int size) {
             return Sets.newTreeSet();
         }
 
     }
 
     private static int toPositiveIndex(int i, int size) {
         return i < 0 ? i + size : i;
     }
 
     private static boolean isInBound(int i, int size) {
         final int p = toPositiveIndex(i, size);
         return p >= 0 && p < size;
     }
 }