import java.util.LinkedList;

public class MyHashMap<K, V> implements MyMap<K, V> {
  // Define the default hash table size. Must be a power of 2
  private static int DEFAULT_INITIAL_CAPACITY = 4;
  
  // Define the maximum hash table size. 1 << 30 is same as 2^30
  private static int MAXIMUM_CAPACITY = 1 << 30; 
  
  // Current hash table capacity. Capacity is a power of 2
  private int capacity;
  
  // Define default load factor
  private static float DEFAULT_MAX_LOAD_FACTOR = 0.75f; 

  // Specify a load factor used in the hash table
  private float loadFactorThreshold; 
     
  // The number of entries in the map
  private int size = 0; 
  
  // Hash table is an array with each cell that is a linked list
  LinkedList<MyMap.Entry<K,V>>[] table;

  /** Construct a map with the default capacity and load factor */
  public MyHashMap() {  
    this(DEFAULT_INITIAL_CAPACITY, DEFAULT_MAX_LOAD_FACTOR);    
  }
  
  /** Construct a map with the specified initial capacity and 
   * default load factor */
  public MyHashMap(int initialCapacity) { 
    this(initialCapacity, DEFAULT_MAX_LOAD_FACTOR);    
  }
  
  /** Construct a map with the specified initial capacity 
   * and load factor */
  public MyHashMap(int initialCapacity, float loadFactorThreshold) { 
    if (initialCapacity > MAXIMUM_CAPACITY)
      this.capacity = MAXIMUM_CAPACITY;
    else
      this.capacity = trimToPowerOf2(initialCapacity);
    
    this.loadFactorThreshold = loadFactorThreshold;    
    table = new LinkedList[capacity];
  }
  
  @Override /** Remove all of the entries from this map */ 
  public void clear() {
    size = 0;
    removeEntries();
  }

  @Override /** Return true if the specified key is in the map */
  public boolean containsKey(K key) {    
    if (get(key) != null)
      return true;
    else
      return false;
  }
  
  @Override /** Return true if this map contains the value */ 
  public boolean containsValue(V value) {
    for (int i = 0; i < capacity; i++) {
      if (table[i] != null) {
        LinkedList<Entry<K, V>> bucket = table[i]; 
        for (Entry<K, V> entry: bucket)
          if (entry.getValue().equals(value)) 
            return true;
      }
    }
    
    return false;
  }
  
  @Override /** Return a set of entries in the map */
  public java.util.Set<MyMap.Entry<K,V>> entrySet() {
    java.util.Set<MyMap.Entry<K, V>> set = 
      new java.util.HashSet<>();
    
    for (int i = 0; i < capacity; i++) {
      if (table[i] != null) {
        LinkedList<Entry<K, V>> bucket = table[i]; 
        for (Entry<K, V> entry: bucket)
          set.add(entry); 
      }
    }
    
    return set;
  }

  @Override /** Return the value that matches the specified key */
  public V get(K key) {
    int bucketIndex = hash(key.hashCode());
    if (table[bucketIndex] != null) {
      LinkedList<Entry<K, V>> bucket = table[bucketIndex]; 
      for (Entry<K, V> entry: bucket)
        if (entry.getKey().equals(key)) 
          return entry.getValue();
    }
    
    return null;
  }
  
  @Override /** Return true if this map contains no entries */
  public boolean isEmpty() {
    return size == 0;
  }  
  
  @Override /** Return a set consisting of the keys in this map */
  public java.util.Set<K> keySet() {
    java.util.Set<K> set = new java.util.HashSet<K>();
    
    for (int i = 0; i < capacity; i++) {
      if (table[i] != null) {
        LinkedList<Entry<K, V>> bucket = table[i]; 
        for (Entry<K, V> entry: bucket)
          set.add(entry.getKey()); 
      }
    }
    
    return set;
  }
      
  @Override /** Add an entry (key, value) into the map */
  public V put(K key, V value) {
    if (get(key) != null) { // The key is already in the map
      int bucketIndex = hash(key.hashCode());
      LinkedList<Entry<K, V>> bucket = table[bucketIndex]; 
      for (Entry<K, V> entry: bucket)
        if (entry.getKey().equals(key)) {
          V oldValue = entry.getValue();
          // Replace old value with new value
          entry.value = value; 
          // Return the old value for the key
          return oldValue;
        }
    }
  
    // Check load factor
    if (size >= capacity * loadFactorThreshold) {
      if (capacity == MAXIMUM_CAPACITY)
        throw new RuntimeException("Exceeding maximum capacity");
      
      rehash();
    }
    
    int bucketIndex = hash(key.hashCode());
    
    // Create a linked list for the bucket if it is not created
    if (table[bucketIndex] == null) {
      table[bucketIndex] = new LinkedList<Entry<K, V>>();
    }

    // Add a new entry (key, value) to hashTable[index]
    table[bucketIndex].add(new MyMap.Entry<K, V>(key, value));

    size++; // Increase size
    
    return value;  
  } 
 
  @Override /** Remove the entries for the specified key */
  public void remove(K key) {
    int bucketIndex = hash(key.hashCode());
    
    // Remove the first entry that matches the key from a bucket
    if (table[bucketIndex] != null) {
      LinkedList<Entry<K, V>> bucket = table[bucketIndex]; 
      for (Entry<K, V> entry: bucket)
        if (entry.getKey().equals(key)) {
          bucket.remove(entry);
          size--; // Decrease size
          break; // Remove just one entry that matches the key
        }
    }
  }
  
  @Override /** Return the number of entries in this map */
  public int size() {
    return size;
  }
  
  @Override /** Return a set consisting of the values in this map */
  public java.util.Set<V> values() {
    java.util.Set<V> set = new java.util.HashSet<>();
    
    for (int i = 0; i < capacity; i++) {
      if (table[i] != null) {
        LinkedList<Entry<K, V>> bucket = table[i]; 
        for (Entry<K, V> entry: bucket)
          set.add(entry.getValue()); 
      }
    }
    
    return set;
  }
  
  /** Hash function */
  private int hash(int hashCode) {
    return supplementalHash(hashCode) & (capacity - 1);
  }
  
  /** Ensure the hashing is evenly distributed */
  private static int supplementalHash(int h) {
    h ^= (h >>> 20) ^ (h >>> 12);
    return h ^ (h >>> 7) ^ (h >>> 4);
  }

  /** Return a power of 2 for initialCapacity */
  private int trimToPowerOf2(int initialCapacity) {
    int capacity = 1;
    while (capacity < initialCapacity) {
      capacity <<= 1;
    }
    
    return capacity;
  }
  
  /** Remove all entries from each bucket */
  private void removeEntries() {
    for (int i = 0; i < capacity; i++) {
      if (table[i] != null) {
        table[i].clear();
      }
    }
  }
  
  /** Rehash the map */
  private void rehash() {
    java.util.Set<Entry<K, V>> set = entrySet(); // Get entries
    capacity <<= 1; // Double capacity    
    table = new LinkedList[capacity]; // Create a new hash table
    size = 0; // Reset size to 0
    
    for (Entry<K, V> entry: set) {
      put(entry.getKey(), entry.getValue()); // Store to new table
    }
  }

  @Override
  public String toString() {
    StringBuilder builder = new StringBuilder("[");
    
    for (int i = 0; i < capacity; i++) {
      if (table[i] != null && table[i].size() > 0) 
        for (Entry<K, V> entry: table[i])
          builder.append(entry);
    }
    
    builder.append("]");
    return builder.toString();
  }
}