package class10_3_HashMaps_start;

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.Objects;
import java.util.Set;

public class HashMap<K,V> implements Map<K,V> {
    public static final int CAPACITY = 10;
    private LinkedList<Entry>[] table = (LinkedList<Entry>[]) new LinkedList[CAPACITY];

    private class Entry{
        private K key;
        private V value;

        public Entry(K key, V value) {
            this.key = key;
            this.value = value;
        }

        @Override
        public boolean equals(Object obj) {
            return Objects.equals(key,key.equals(((Entry)obj).key.equals(key)));
        }
    }


    /**
     * Returns the number of elements in this set (its cardinality).  If this
     * set contains more than {@code Integer.MAX_VALUE} elements, returns
     * {@code Integer.MAX_VALUE}.
     *
     * @return the number of elements in this set (its cardinality)
     */
    @Override
    public int size() {
        return 0;
    }

    /**
     * Returns {@code true} if this set contains no elements.
     *
     * @return {@code true} if this set contains no elements
     */
    @Override
    public boolean isEmpty() {
        return false;
    }

    /**
     * Returns {@code true} if this map contains a mapping for the specified
     * key.  More formally, returns {@code true} if and only if
     * this map contains a mapping for a key {@code k} such that
     * {@code Objects.equals(key, k)}.  (There can be
     * at most one such mapping.)
     *
     * @param key key whose presence in this map is to be tested
     * @return {@code true} if this map contains a mapping for the specified
     * key
     * @throws ClassCastException   if the key is of an inappropriate type for
     *                              this map
     *                              (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified key is null and this map
     *                              does not permit null keys
     *                              (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     */
    @Override
    public boolean containsKey(Object key) {
        return false;
    }

    /**
     * Returns {@code true} if this map maps one or more keys to the
     * specified value.  More formally, returns {@code true} if and only if
     * this map contains at least one mapping to a value {@code v} such that
     * {@code Objects.equals(value, v)}.  This operation
     * will probably require time linear in the map size for most
     * implementations of the {@code Map} interface.
     *
     * @param value value whose presence in this map is to be tested
     * @return {@code true} if this map maps one or more keys to the
     * specified value
     * @throws ClassCastException   if the value is of an inappropriate type for
     *                              this map
     *                              (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified value is null and this
     *                              map does not permit null values
     *                              (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     */
    @Override
    public boolean containsValue(Object value) {
        return false;
    }

    /**
     * Returns the value to which the specified key is mapped,
     * or {@code null} if this map contains no mapping for the key.
     *
     * <p>More formally, if this map contains a mapping from a key
     * {@code k} to a value {@code v} such that
     * {@code Objects.equals(key, k)},
     * then this method returns {@code v}; otherwise
     * it returns {@code null}.  (There can be at most one such mapping.)
     *
     * <p>If this map permits null values, then a return value of
     * {@code null} does not <i>necessarily</i> indicate that the map
     * contains no mapping for the key; it's also possible that the map
     * explicitly maps the key to {@code null}.  The {@link #containsKey
     * containsKey} operation may be used to distinguish these two cases.
     *
     * @param key the key whose associated value is to be returned
     * @return the value to which the specified key is mapped, or
     * {@code null} if this map contains no mapping for the key
     * @throws ClassCastException   if the key is of an inappropriate type for
     *                              this map
     *                              (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified key is null and this map
     *                              does not permit null keys
     *                              (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     */
    @Override
    public V get(Object key) {
        return null;
    }

    /**
     * Associates the specified value with the specified key in this map
     * (optional operation).  If the map previously contained a mapping for
     * the key, the old value is replaced by the specified value.  (A map
     * {@code m} is said to contain a mapping for a key {@code k} if and only
     * if {@link #containsKey(Object) m.containsKey(k)} would return
     * {@code true}.)
     *
     * @param key   key with which the specified value is to be associated
     * @param value value to be associated with the specified key
     * @return the previous value associated with {@code key}, or
     * {@code null} if there was no mapping for {@code key}.
     * (A {@code null} return can also indicate that the map
     * previously associated {@code null} with {@code key},
     * if the implementation supports {@code null} values.)
     * @throws UnsupportedOperationException if the {@code put} operation
     *                                       is not supported by this map
     * @throws ClassCastException            if the class of the specified key or value
     *                                       prevents it from being stored in this map
     * @throws NullPointerException          if the specified key or value is null
     *                                       and this map does not permit null keys or values
     * @throws IllegalArgumentException      if some property of the specified key
     *                                       or value prevents it from being stored in this map
     */
    @Override
    public V put(K key, V value) {
        int hash = key.hashCode();
        int index = Math.floorMod(hash,table.length);
        if(table[index] == null) {
            table[index] = new LinkedList<>();
        }
        LinkedList<Entry> entries = table[index]; // WARNING! POTENTIAL BUG!
        // NOTE: this is O(n/capacity) on average just like for the HashSet.
        Entry entry = new Entry(key, value);
        int oldIndex = entries.indexOf(entry);
        if(oldIndex == -1) {
            entries.add(entry);
            return null;
        } else {
            Entry oldEntry = entries.set(oldIndex,entry);
            return oldEntry.value;
        }
    }

    /**
     * Removes the mapping for a key from this map if it is present
     * (optional operation).   More formally, if this map contains a mapping
     * from key {@code k} to value {@code v} such that
     * {@code Objects.equals(key, k)}, that mapping
     * is removed.  (The map can contain at most one such mapping.)
     *
     * <p>Returns the value to which this map previously associated the key,
     * or {@code null} if the map contained no mapping for the key.
     *
     * <p>If this map permits null values, then a return value of
     * {@code null} does not <i>necessarily</i> indicate that the map
     * contained no mapping for the key; it's also possible that the map
     * explicitly mapped the key to {@code null}.
     *
     * <p>The map will not contain a mapping for the specified key once the
     * call returns.
     *
     * @param key key whose mapping is to be removed from the map
     * @return the previous value associated with {@code key}, or
     * {@code null} if there was no mapping for {@code key}.
     * @throws UnsupportedOperationException if the {@code remove} operation
     *                                       is not supported by this map
     * @throws ClassCastException            if the key is of an inappropriate type for
     *                                       this map
     *                                       (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException          if the specified key is null and this
     *                                       map does not permit null keys
     *                                       (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     */
    @Override
    public V remove(Object key) {
        return null;
    }

    /**
     * Copies all of the mappings from the specified map to this map
     * (optional operation).  The effect of this call is equivalent to that
     * of calling {@link #put(Object, Object) put(k, v)} on this map once
     * for each mapping from key {@code k} to value {@code v} in the
     * specified map.  The behavior of this operation is undefined if the
     * specified map is modified while the operation is in progress.
     *
     * @param m mappings to be stored in this map
     * @throws UnsupportedOperationException if the {@code putAll} operation
     *                                       is not supported by this map
     * @throws ClassCastException            if the class of a key or value in the
     *                                       specified map prevents it from being stored in this map
     * @throws NullPointerException          if the specified map is null, or if
     *                                       this map does not permit null keys or values, and the
     *                                       specified map contains null keys or values
     * @throws IllegalArgumentException      if some property of a key or value in
     *                                       the specified map prevents it from being stored in this map
     */
    @Override
    public void putAll(Map<? extends K, ? extends V> m) {

    }


    /**
     * Removes all of the elements from this set (optional operation).
     * The set will be empty after this call returns.
     *
     * @throws UnsupportedOperationException if the {@code clear} method
     *                                       is not supported by this set
     */
    @Override
    public void clear() {

    }

    /**
     * Returns a {@link Set} view of the keys contained in this map.
     * The set is backed by the map, so changes to the map are
     * reflected in the set, and vice-versa.  If the map is modified
     * while an iteration over the set is in progress (except through
     * the iterator's own {@code remove} operation), the results of
     * the iteration are undefined.  The set supports element removal,
     * which removes the corresponding mapping from the map, via the
     * {@code Iterator.remove}, {@code Set.remove},
     * {@code removeAll}, {@code retainAll}, and {@code clear}
     * operations.  It does not support the {@code add} or {@code addAll}
     * operations.
     *
     * @return a set view of the keys contained in this map
     */
    @Override
    public Set<K> keySet() {
        return null;
    }

    /**
     * Returns a {@link Collection} view of the values contained in this map.
     * The collection is backed by the map, so changes to the map are
     * reflected in the collection, and vice-versa.  If the map is
     * modified while an iteration over the collection is in progress
     * (except through the iterator's own {@code remove} operation),
     * the results of the iteration are undefined.  The collection
     * supports element removal, which removes the corresponding
     * mapping from the map, via the {@code Iterator.remove},
     * {@code Collection.remove}, {@code removeAll},
     * {@code retainAll} and {@code clear} operations.  It does not
     * support the {@code add} or {@code addAll} operations.
     *
     * @return a collection view of the values contained in this map
     */
    @Override
    public Collection<V> values() {
        return null;
    }

    /**
     * Returns a {@link Set} view of the mappings contained in this map.
     * The set is backed by the map, so changes to the map are
     * reflected in the set, and vice-versa.  If the map is modified
     * while an iteration over the set is in progress (except through
     * the iterator's own {@code remove} operation, or through the
     * {@code setValue} operation on a map entry returned by the
     * iterator) the results of the iteration are undefined.  The set
     * supports element removal, which removes the corresponding
     * mapping from the map, via the {@code Iterator.remove},
     * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
     * {@code clear} operations.  It does not support the
     * {@code add} or {@code addAll} operations.
     *
     * @return a set view of the mappings contained in this map
     */
    @Override
    public Set<Map.Entry<K, V>> entrySet() {
        return null;
    }

}