/*
    * SPDX-FileCopyrightText: none
    * SPDX-License-Identifier: CC0-1.0
    */
   
   package dev.metaschema.core.metapath.function;
   
   import java.util.HashMap;
   import java.util.Map;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReadWriteLock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  import java.util.stream.Stream;
  
  import dev.metaschema.core.qname.IEnhancedQName;
  import dev.metaschema.core.util.ObjectUtils;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import edu.umd.cs.findbugs.annotations.Nullable;
  
  /**
   * Provides a catalog of registered function implementations.
   * <p>
   * Functions can be registered using the {@link #registerFunction(IFunction)}
   * method.
   * <p>
   * Previously registered functions can be looked up using the
   * {@link #getFunction(IEnhancedQName, int)} method.
   */
  public class FunctionLibrary implements IFunctionLibrary {
  
    @NonNull
    private final Map<IEnhancedQName, NamedFunctionSet> libraryByQName = new HashMap<>(); // NOPMD - intentional
    @NonNull
    private final ReadWriteLock instanceLock = new ReentrantReadWriteLock();
  
    /**
     * Register the provided function signature.
     *
     * @param function
     *          the function signature to register
     * @throws IllegalArgumentException
     *           if the provided function has the same arity as a previously
     *           registered function with the same name
     */
    public final void registerFunction(@NonNull IFunction function) {
      registerFunctionByQName(function);
    }
  
    private void registerFunctionByQName(@NonNull IFunction function) {
      IEnhancedQName qname = function.getQName();
      IFunction duplicate;
      Lock writeLock = instanceLock.writeLock();
      writeLock.lock();
      try {
        NamedFunctionSet functions = libraryByQName.get(qname);
        if (functions == null) {
          functions = new NamedFunctionSet();
          libraryByQName.put(qname, functions);
        }
        duplicate = functions.addFunction(function);
      } finally {
        writeLock.unlock();
      }
      if (duplicate != null) {
        throw new IllegalArgumentException(String.format("Duplicate functions with same arity: %s shadows %s",
            duplicate.toSignature(), function.toSignature()));
      }
    }
  
    @Override
    public Stream<IFunction> stream() {
      Lock readLock = instanceLock.readLock();
      readLock.lock();
      try {
        return ObjectUtils.notNull(libraryByQName.values().stream().flatMap(NamedFunctionSet::getFunctionsAsStream));
      } finally {
        readLock.unlock();
      }
    }
  
    @Override
    public IFunction getFunction(@NonNull IEnhancedQName name, int arity) {
      IFunction retval = null;
      Lock readLock = instanceLock.readLock();
      readLock.lock();
      try {
        NamedFunctionSet functions = libraryByQName.get(name);
        if (functions != null) {
          retval = functions.getFunctionWithArity(arity);
        }
      } finally {
        readLock.unlock();
      }
      return retval;
    }
  
    private static class NamedFunctionSet {
      private final Map<Integer, IFunction> arityToFunctionMap;
      private IFunction unboundedArity;
 
     public NamedFunctionSet() {
       this.arityToFunctionMap = new HashMap<>();
     }
 
     @SuppressWarnings("null")
     @NonNull
     public Stream<IFunction> getFunctionsAsStream() {
       return arityToFunctionMap.values().stream();
     }
 
     @Nullable
     public IFunction getFunctionWithArity(int arity) {
       IFunction retval = arityToFunctionMap.get(arity);
       if (retval == null && unboundedArity != null && unboundedArity.arity() < arity) {
         retval = unboundedArity;
       }
       return retval;
     }
 
     @Nullable
     public IFunction addFunction(@NonNull IFunction function) {
       IFunction old = arityToFunctionMap.put(function.arity(), function);
       if (function.isArityUnbounded()) {
         unboundedArity = function;
       }
       return old;
     }
   }
 }