/*
    * Licensed to The Apereo Foundation under one or more contributor license
    * agreements. See the NOTICE file distributed with this work for additional
    * information regarding copyright ownership.
    *
    *
    * The Apereo Foundation licenses this file to you under the Educational
    * Community 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://opensource.org/licenses/ecl2.txt
   *
   * 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.opencastproject.util.data;
  
  import java.lang.reflect.Array;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Dictionary;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Hashtable;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.NoSuchElementException;
  import java.util.Optional;
  import java.util.Set;
  
  /**
   * This class provides functions to ease and secure the handling of collections by supporting a type safe -- at least to
   * the extent Java's type system allows -- immutable and more functional style.
   *
   * Note that all functions do <i>not</i> mutate input collections unless otherwise stated.
   *
   * @deprecated By now, all of this is natively available in Java.
   */
  @Deprecated
  public final class Collections {
    private Collections() {
    }
  
    // TODO check all clients of this method since it potentially breaks!
    @SuppressWarnings("unchecked")
    private static <A, B> Collection<A> buildFrom(Collection<B> as) {
      try {
        return as.getClass().newInstance();
      } catch (Exception e) {
        throw new IllegalArgumentException("Type " + as.getClass() + " needs a parameterless constructor");
      }
    }
  
    /** Return the head of list <code>as</code> or <code>none</code>. */
    public static <A> Optional<A> head(List<A> as) {
      if (!as.isEmpty()) {
        return Optional.of(as.get(0));
      } else {
        return Optional.empty();
      }
    }
  
    /** Make a string from a collection separating each element by <code>sep</code>. */
    public static String mkString(Collection<?> as, String sep) {
      final StringBuilder b = new StringBuilder();
      for (Object a : as)
        b.append(a).append(sep);
      return b.substring(0, Math.max(b.length() - sep.length(), 0));
    }
  
    /** Append source collection <code>as</code> to <code>target</code>. */
    public static <A, T extends Collection<A>, S extends Iterable<? extends A>> T appendTo(T target, S as) {
      for (A a : as)
        target.add(a);
      return target;
    }
  
    /** Append source collections <code>as</code> to <code>target</code>. */
    @SafeVarargs
    public static <A, T extends Collection<A>, S extends Iterable<? extends A>> T appendToM(T target, S... as) {
      for (S s : as) {
        for (A a : s)
          target.add(a);
      }
      return target;
    }
  
    /** Append source collections <code>as</code> to <code>target</code>. */
    @SafeVarargs
    public static <A, T extends Collection<A>, X extends A> T appendToA(T target, X... as) {
      java.util.Collections.addAll(target, as);
      return target;
   }
 
   /** Concatenates two iterables into a new list. */
   public static <A, M extends Iterable<? extends A>> List<A> concat(M as, M bs) {
     List<A> x = new ArrayList<>();
     for (A a : as)
       x.add(a);
     for (A b : bs)
       x.add(b);
     return x;
   }
 
   /**
    * Merge two maps where <code>b</code> takes precedence.
    *
    * @return a new immutable map
    */
   public static <A, B> Map<A, B> merge(Map<? extends A, ? extends B> a, Map<? extends A, ? extends B> b) {
     final Map<A, B> x = new HashMap<>();
     x.putAll(a);
     x.putAll(b);
     return java.util.Collections.unmodifiableMap(x);
   }
 
   /** Drain all elements of <code>as</code> into a list. */
   public static <A> List<A> toList(Iterator<? extends A> as) {
     final List<A> t = new ArrayList<>();
     while (as.hasNext()) {
       t.add(as.next());
     }
     return t;
   }
 
   /** Drain all elements of <code>as</code> into a list. */
   public static <A> List<A> toList(Collection<A> as) {
     return new ArrayList<>(as);
   }
 
   /**
    * Return the list as is or nil, if <code>as</code> is null.
    * 
    * @deprecated use {@link #nullToNil(java.util.List)}
    */
   @Deprecated
   public static <A> List<A> mkList(List<A> as) {
     return as != null ? as : Collections.<A> nil();
   }
 
   /** Return the list as is or nil, if <code>as</code> is null. */
   public static <A> List<A> nullToNil(List<A> as) {
     return as != null ? as : Collections.<A> nil();
   }
 
   /** Create a list from an array. */
   @SafeVarargs
   public static <A> List<A> list(A... as) {
     final List<A> t = new ArrayList<>();
     java.util.Collections.addAll(t, as);
     return t;
   }
 
   /** Create a list from an array. */
   @SafeVarargs
   public static <A> List<A> nonNullList(A... as) {
     final List<A> t = new ArrayList<>();
     for (A a : as) {
       if (null != a) {
         t.add(a);
       }
     }
     return t;
   }
 
   /** The empty list. */
   @SuppressWarnings("unchecked")
   public static <A> List<A> nil() {
     return java.util.Collections.EMPTY_LIST;
   }
 
   /** The empty list. */
   @SuppressWarnings("unchecked")
   public static <A> List<A> nil(Class<A> type) {
     return java.util.Collections.EMPTY_LIST;
   }
 
   /** Construct a new list by prepending an element to a given list. */
   public static <A> List<A> cons(A a, List<? extends A> as) {
     final List<A> target = new ArrayList<>(as.size() + 1);
     target.add(a);
     target.addAll(as);
     return target;
   }
 
   /** Create a set from an array. */
   @SafeVarargs
   public static <A> Set<A> set(A... as) {
     final Set<A> t = new HashSet<>(as.length);
     java.util.Collections.addAll(t, as);
     return t;
   }
 
   /** Create a set from a list. */
   public static <A> Set<A> toSet(List<A> as) {
     Set<A> r = new HashSet<>(as.size());
     for (A a : as)
       r.add(a);
     return r;
   }
 
   /** Create a map from a list of tuples (K, V). */
   @SafeVarargs
   public static <K, V> Map<K, V> map(Tuple<? extends K, ? extends V>... ts) {
     final Map<K, V> map = new HashMap<>(ts.length);
     for (Tuple<? extends K, ? extends V> t : ts) {
       map.put(t.getA(), t.getB());
     }
     return map;
   }
 
   /** Create a dictionary from a list of tuples (K, V). */
   @SafeVarargs
   public static <K, V> Dictionary<K, V> dict(Tuple<? extends K, ? extends V>... ts) {
     final Dictionary<K, V> dict = new Hashtable<>(ts.length);
     for (Tuple<? extends K, ? extends V> t : ts) {
       dict.put(t.getA(), t.getB());
     }
     return dict;
   }
 
   /** Create an array from a collection. */
   @SuppressWarnings("unchecked")
   public static <A, B extends A> A[] toArray(Class<A> elemType, Collection<B> a) {
     return a.toArray((A[]) Array.newInstance(elemType, a.size()));
   }
 
   /** Convert a collection of {@link Double}s into an array of primitive type. */
   public static double[] toDoubleArray(Collection<Double> as) {
     final double[] target = new double[as.size()];
     int i = 0;
     for (Double a : as) {
       target[i] = a;
       i++;
     }
     return target;
   }
 
   /** Create an iterator form an array. */
   @SafeVarargs
   public static <A> Iterator<A> iterator(final A... as) {
     return new Iterator<A>() {
       private int i = 0;
 
       @Override
       public boolean hasNext() {
         return as.length > i;
       }
 
       @Override
       public A next() {
         if (i < as.length) {
           return as[i++];
         } else {
           throw new NoSuchElementException();
         }
       }
 
       @Override
       public void remove() {
         throw new UnsupportedOperationException();
       }
     };
   }
 
   /** Create an iterator that repeats <code>a</code> for the said times. */
   public static <A, X extends A> Iterator<A> repeat(final X a, final int times) {
     return new Iterator<A>() {
       private int count = times;
 
       @Override
       public boolean hasNext() {
         return count > 0;
       }
 
       @Override
       public A next() {
         count--;
         return a;
       }
 
       @Override
       public void remove() {
         throw new UnsupportedOperationException();
       }
     };
   }
 
   /** Join two iterators. */
   public static <A> Iterator<A> join(final Iterator<A> a, final Iterator<A> b) {
     return new Iterator<A>() {
       @Override
       public boolean hasNext() {
         return a.hasNext() || b.hasNext();
       }
 
       @Override
       public A next() {
         return a.hasNext() ? a.next() : b.next();
       }
 
       @Override
       public void remove() {
         throw new UnsupportedOperationException();
       }
     };
   }
 
   /**
    * Make an Iterator usable in a for comprehension like this:
    *
    * <pre>
    *   Iterator&lt;A&gt; as = ...
    *   for (A a : forc(as)) {
    *     ...
    *   }
    * </pre>
    */
   public static <A> Iterable<A> forc(final Iterator<A> as) {
     return new Iterable<A>() {
       @Override
       public Iterator<A> iterator() {
         return as;
       }
     };
   }
 
   /** Concat (aka flatten) a collection of collections by concatenating them all. [[a]] -&gt; [a] */
   public static <A, M extends Collection<? extends Collection<A>>> List<A> concat(M as) {
     final List<A> target = new ArrayList<>(as.size());
     for (Collection<A> a : as) {
       target.addAll(a);
     }
     return target;
   }
 
 }