Merge pull request #28 from adlange/4-add-combinations-calculation

#4 add getNumberOfPossibleCombinations method to ReadableIdGenerator …

Author: adlange

CHANGELOG.md

@@ -6,6 +6,8 @@
 
 * new module `readable-ids-dictionary-english-adjective-noun`
 * fix parent BOM creation and artifact packaging
+* add `getNumberOfPossibleCombinations()` method to `ReadableIdGenerator`
+* add `getNumberOfPossibleCombinations()` method to `TokenDictionary` interface
 * improve documentation
 
 ##  0.0.1

README.md

@@ -209,6 +209,13 @@ generated. Because all dictionaries have the same probability of being selected
 duplicates among the IDs can be much higher when using another significantly smaller dictionary compared to the use of a
 single, extensive dictionary.
 
+You can get the estimated number of possible combinations possible from the given dictionaries, assuming that there are
+no duplicates / overlaps within the dictionaries and that a good `RandomGenerator` is used:
+
+```java
+long possibleCombinations = generator.getNumberOfPossibleCombinations();
+```
+
 ### Using Multiple Modules of readable-ids
 
 To avoid having to maintain the module version individually, it is advisable to use the BOM.

readable-ids-core/src/main/java/de/adrianlange/readableids/ReadableIdGenerator.java

@@ -97,6 +97,18 @@ public String nextId() {
     return tokenJoiner.joinTokens(idFromDictionary);
   }
 
+  /**
+   * Returns the number of possible combinations of tokens for all dictionaries.
+   *
+   * @return Number of possible combinations
+   */
+  public long getNumberOfPossibleCombinations() {
+
+    return tokenDictionaries.stream()
+            .map(TokenDictionary::getNumberOfPossibleCombinations)
+            .reduce(0L, Long::sum);
+  }
+
   private String[] getIdFromDictionary() {
 
     var dictionary = tokenDictionaries.get(randomGenerator.nextInt(tokenDictionaries.size()));

readable-ids-core/src/main/java/de/adrianlange/readableids/tokendictionary/AppendNumberDictionary.java

@@ -52,4 +52,10 @@ public String[] getTokensAtPositions(int[] positions) {
     tokensAtPositions[positionsForParent.length] = String.valueOf(positions[positionsForParent.length] + minimalValueInc);
     return tokensAtPositions;
   }
+
+  @Override
+  public long getNumberOfPossibleCombinations() {
+
+    return parentTokenDictionary.getNumberOfPossibleCombinations() * (long) (maximalValueExc - minimalValueInc);
+  }
 }

readable-ids-core/src/main/java/de/adrianlange/readableids/tokendictionary/PrependAmountGermanDictionary.java

@@ -37,6 +37,12 @@ public String[] getTokensAtPositions(int[] positions) {
     return tokensAtPositions;
   }
 
+  @Override
+  public long getNumberOfPossibleCombinations() {
+
+    return parentTokenDictionary.getNumberOfPossibleCombinations() * (long) (MAXIMAL_VALUE - MINIMAL_VALUE);
+  }
+
   private static String getAmountString(int amount) {
 
     return switch (amount) {

readable-ids-core/src/main/java/de/adrianlange/readableids/tokendictionary/SimpleTokenDictionary.java

@@ -32,4 +32,14 @@ public String[] getTokensAtPositions(int[] positions) {
     }
     return tokens;
   }
+
+  @Override
+  public long getNumberOfPossibleCombinations() {
+
+    long numberOfCombinations = 1;
+    for (var tokenArray : dictionary) {
+      numberOfCombinations *= tokenArray.length;
+    }
+    return numberOfCombinations;
+  }
 }

readable-ids-core/src/main/java/de/adrianlange/readableids/tokendictionary/TokenDictionary.java

@@ -20,4 +20,11 @@ public interface TokenDictionary {
    * @return Array of tokens, which form the ID in the end
    */
   String[] getTokensAtPositions(int[] positions);
+
+  /**
+   * Returns the number of possible combinations of tokens in the dictionary. If the dictionary is empty, it also returns <var>1</var>, since it returns the singe empty value.
+   *
+   * @return Number of possible combinations
+   */
+  long getNumberOfPossibleCombinations();
 }