//******************************
// Written by Peter Golde
// Copyright (c) 2004-2005, Wintellect
//
// Use and restribution of this code is subject to the license agreement 
// contained in the file "License.txt" accompanying this file.
//******************************

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;


namespace Wintellect.PowerCollections
{
    /// <summary>
    /// ReadOnlyDictionaryBase is a base class that can be used to more easily implement the
    /// generic IDictionary&lt;T&gt; and non-generic IDictionary interfaces.
    /// </summary>
    /// <remarks>
    /// <para>To use ReadOnlyDictionaryBase as a base class, the derived class must override
    /// Count, TryGetValue, GetEnumerator. </para>
    /// </remarks>
    /// <typeparam name="TKey">The key type of the dictionary.</typeparam>
    /// <typeparam name="TValue">The value type of the dictionary.</typeparam>
    [Serializable]
    [DebuggerDisplay("{DebuggerDisplayString()}")]
    public abstract class ReadOnlyDictionaryBase<TKey, TValue> : ReadOnlyCollectionBase<KeyValuePair<TKey, TValue>>,
                                                                                                  IDictionary<TKey, TValue>, IDictionary
    {
        /// <summary>
        /// Creates a new DictionaryBase. This must be called from the constructor of the
        /// derived class to specify whether the dictionary is read-only and the name of the
        /// collection.
        /// </summary>
        protected ReadOnlyDictionaryBase()
        {
        }

        /// <summary>
        /// Throws an NotSupportedException stating that this collection cannot be modified.
        /// </summary>
        private void MethodModifiesCollection()
        {
            throw new NotSupportedException(string.Format(Strings.CannotModifyCollection, Util.SimpleClassName(this.GetType())));
        }

        /// <summary>
        /// Adds a new key-value pair to the dictionary. Always throws an exception
        /// indicating that this method is not supported in a read-only dictionary.
        /// </summary>
        /// <param name="key">Key to add.</param>
        /// <param name="value">Value to associated with the key.</param>
        /// <exception cref="NotSupportedException">Always thrown.</exception>
        void IDictionary<TKey, TValue>.Add(TKey key, TValue value)
        {
            MethodModifiesCollection();
        }

        /// <summary>
        /// Removes a key from the dictionary. Always throws an exception
        /// indicating that this method is not supported in a read-only dictionary.
        /// </summary>
        /// <param name="key">Key to remove from the dictionary.</param>
        /// <returns>True if the key was found, false otherwise.</returns>
        /// <exception cref="NotSupportedException">Always thrown.</exception>
        public virtual bool Remove(TKey key)
        {
            MethodModifiesCollection();
            return false;
        }

        /// <summary>
        /// Determines whether a given key is found
        /// in the dictionary.
        /// </summary>
        /// <remarks>The default implementation simply calls TryGetValue and returns
        /// what it returns.</remarks>
        /// <param name="key">Key to look for in the dictionary.</param>
        /// <returns>True if the key is present in the dictionary.</returns>
        public virtual bool ContainsKey(TKey key)
        {
            TValue dummy;
            return TryGetValue(key, out dummy);
        }

        /// <summary>
        /// Determines if this dictionary contains a key equal to <paramref name="key"/>. If so, the value
        /// associated with that key is returned through the value parameter. This method must be overridden 
        /// in the derived class.
        /// </summary>
        /// <param name="key">The key to search for.</param>
        /// <param name="value">Returns the value associated with key, if true was returned.</param>
        /// <returns>True if the dictionary contains key. False if the dictionary does not contain key.</returns>
        public abstract bool TryGetValue(TKey key, out TValue value);

        /// <summary>
        /// The indexer of the dictionary. The set accessor throws an NotSupportedException
        /// stating the dictionary is read-only.
        /// </summary>
        /// <remarks>The get accessor is implemented by calling TryGetValue.</remarks>
        /// <param name="key">Key to find in the dictionary.</param>
        /// <returns>The value associated with the key.</returns>
        /// <exception cref="NotSupportedException">Always thrown from the set accessor, indicating
        /// that the dictionary is read only.</exception>
        /// <exception cref="KeyNotFoundException">Thrown from the get accessor if the key
        /// was not found.</exception>
        public virtual TValue this[TKey key]
        {
            get
            {
                TValue value;
                bool found = TryGetValue(key, out value);
                if (found)
                    return value;
                else
                    throw new KeyNotFoundException(Strings.KeyNotFound);
            }

            set
            {
                MethodModifiesCollection();
            }
        }

        /// <summary>
        /// Shows the string representation of the dictionary. The string representation contains
        /// a list of the mappings in the dictionary.
        /// </summary>
        /// <returns>The string representation of the dictionary.</returns>
        public override string ToString()
        {
            bool firstItem = true;

            System.Text.StringBuilder builder = new System.Text.StringBuilder();

            builder.Append("{");

            // Call ToString on each item and put it in.
            foreach (KeyValuePair<TKey, TValue> pair in this) {
                if (!firstItem)
                    builder.Append(", ");

                if (pair.Key == null)
                    builder.Append("null");
                else
                    builder.Append(pair.Key.ToString());

                builder.Append("->");

                if (pair.Value == null)
                    builder.Append("null");
                else
                    builder.Append(pair.Value.ToString());

                firstItem = false;
            }

            builder.Append("}");
            return builder.ToString();
        }

       #region IDictionary<TKey,TValue> Members

        /// <summary>
        /// Returns a collection of the keys in this dictionary. 
        /// </summary>
        /// <value>A read-only collection of the keys in this dictionary.</value>
        public virtual ICollection<TKey> Keys
        {
            get { return new KeysCollection(this); }
        }

        /// <summary>
        /// Returns a collection of the values in this dictionary. The ordering of 
        /// values in this collection is the same as that in the Keys collection.
        /// </summary>
        /// <value>A read-only collection of the values in this dictionary.</value>
        public virtual ICollection<TValue> Values
        {
            get { return new ValuesCollection(this); }
        }

        #endregion

        #region ICollection<KeyValuePair<TKey,TValue>> Members

        /// <summary>
        /// Determines if a dictionary contains a given KeyValuePair. This implementation checks to see if the
        /// dictionary contains the given key, and if the value associated with the key is equal to (via object.Equals)
        /// the value.
        /// </summary>
        /// <param name="item">A KeyValuePair containing the Key and Value to check for.</param>
        /// <returns></returns>
        public override bool Contains(KeyValuePair<TKey, TValue> item)
        {
            if (this.ContainsKey(item.Key)) {
                return (object.Equals(this[item.Key], item.Value));
            }
            else {
                return false;
            }
        }

        #endregion

        #region IDictionary Members

        /// <summary>
        /// Adds a key-value pair to the collection. Always throws an exception
        /// indicating that this method is not supported in a read-only dictionary.
        /// </summary>
        /// <param name="key">Key to add to the dictionary.</param>
        /// <param name="value">Value to add to the dictionary.</param>
        /// <exception cref="NotSupportedException">Always thrown.</exception>
        void IDictionary.Add(object key, object value)
        {
            MethodModifiesCollection();
        }

        /// <summary>
        /// Clears this dictionary. Always throws an exception
        /// indicating that this method is not supported in a read-only dictionary.
        /// </summary>
        /// <exception cref="NotSupportedException">Always thrown.</exception>
        void IDictionary.Clear()
        {
            MethodModifiesCollection();
        }

        /// <summary>
        /// Determines if this dictionary contains a key equal to <paramref name="key"/>. The dictionary
        /// is not changed. Calls the (overridden) ContainsKey method. If key is not of the correct
        /// TKey for the dictionary, false is returned.
        /// </summary>
        /// <param name="key">The key to search for.</param>
        /// <returns>True if the dictionary contains key. False if the dictionary does not contain key.</returns>
        bool IDictionary.Contains(object key)
        {
            if (key is TKey || key == null)
                return ContainsKey((TKey)key);
            else
                return false;
        }

        /// <summary>
        /// Removes the key (and associated value) from the collection that is equal to the passed in key. Always throws an exception
        /// indicating that this method is not supported in a read-only dictionary.
        /// </summary>
        /// <param name="key">The key to remove.</param>
        /// <exception cref="NotSupportedException">Always thrown.</exception>
        void IDictionary.Remove(object key)
        {
            MethodModifiesCollection();
        }

        /// <summary>
        /// Returns an enumerator that enumerates all the entries in the dictionary. Each entry is 
        /// returned as a DictionaryEntry.
        /// The entries are enumerated in the same orders as the (overridden) GetEnumerator
        /// method.
        /// </summary>
        /// <returns>An enumerator for enumerating all the elements in the OrderedDictionary.</returns>		
        IDictionaryEnumerator IDictionary.GetEnumerator()
        {
            // You can't implement this directly with an iterator, because iterators automatically implement
            // IEnumerator, not IDictionaryEnumerator. We use the helper class DictionaryEnumeratorWrapper.
            return new DictionaryEnumeratorWrapper(this.GetEnumerator());
        }

        /// <summary>
        /// Returns an enumerator that enumerates all the entries in the dictionary. Each entry is 
        /// returned as a DictionaryEntry.
        /// The entries are enumerated in the same orders as the (overridden) GetEnumerator
        /// method.
        /// </summary>
        /// <returns>An enumerator for enumerating all the elements in the OrderedDictionary.</returns>		
        IEnumerator IEnumerable.GetEnumerator()
        {
            return ((IDictionary)this).GetEnumerator();
        }

        /// <summary>
        /// Returns whether this dictionary is fixed size. 
        /// </summary>
        /// <value>Always returns true.</value>
        bool IDictionary.IsFixedSize
        {
            get { return true; }
        }

        /// <summary>
        /// Returns if this dictionary is read-only. 
        /// </summary>
        /// <value>Always returns true.</value>
        bool IDictionary.IsReadOnly
        {
            get { return true; }
        }

        /// <summary>
        /// Returns a collection of all the keys in the dictionary. The values in this collection will
        /// be enumerated in the same order as the (overridden) GetEnumerator method.
        /// </summary>
        /// <value>The collection of keys.</value>
        ICollection IDictionary.Keys
        {
            get { return new KeysCollection(this); }
        }

        /// <summary>
        /// Returns a collection of all the values in the dictionary. The values in this collection will
        /// be enumerated in the same order as the (overridden) GetEnumerator method.
        /// </summary>
        /// <value>The collection of values.</value>
        ICollection IDictionary.Values
        {
            get { return new ValuesCollection(this); }
        }

        /// <summary>
        /// Gets the value associated with a given key. When getting a value, if this
        /// key is not found in the collection, then null is returned. If the key is not of the correct type 
        /// for this dictionary, null is returned.
        /// </summary>
        /// <value>The value associated with the key, or null if the key was not present.</value>
        /// <exception cref="NotSupportedException">Always thrown from the set accessor, indicating
        /// that the dictionary is read only.</exception>
        object IDictionary.this[object key]
        {
            get
            {
                if (key is TKey || key == null) {
                    TKey theKey = (TKey)key;
                    TValue theValue;

                    // The IDictionary (non-generic) indexer returns null for not found, instead of
                    // throwing an exception like the generic IDictionary indexer.
                    if (TryGetValue(theKey, out theValue))
                        return theValue;
                    else
                        return null;
                }
                else {
                    return null;
                }
            }
            set
            {
                MethodModifiesCollection();
            }
        }

        #endregion

        /// <summary>
        /// Display the contents of the dictionary in the debugger. This is intentionally private, it is called
        /// only from the debugger due to the presence of the DebuggerDisplay attribute. It is similar
        /// format to ToString(), but is limited to 250-300 characters or so, so as not to overload the debugger.
        /// </summary>
        /// <returns>The string representation of the items in the collection, similar in format to ToString().</returns>
        new internal string DebuggerDisplayString()
        {
            const int MAXLENGTH = 250;

            bool firstItem = true;

            System.Text.StringBuilder builder = new System.Text.StringBuilder();

            builder.Append("{");

            // Call ToString on each item and put it in.
            foreach (KeyValuePair<TKey, TValue> pair in this) {
                if (builder.Length >= MAXLENGTH) {
                    builder.Append(", ...");
                    break;
                }

                if (!firstItem)
                    builder.Append(", ");

                if (pair.Key == null)
                    builder.Append("null");
                else
                    builder.Append(pair.Key.ToString());

                builder.Append("->");

                if (pair.Value == null)
                    builder.Append("null");
                else
                    builder.Append(pair.Value.ToString());

                firstItem = false;
            }

            builder.Append("}");
            return builder.ToString();
        }


        #region Keys and Values collections

        /// <summary>
        /// A private class that implements ICollection&lt;TKey&gt; and ICollection for the
        /// Keys collection. The collection is read-only.
        /// </summary>
        [Serializable]
        private sealed class KeysCollection : ReadOnlyCollectionBase<TKey>
        {
            private ReadOnlyDictionaryBase<TKey, TValue> myDictionary;

            /// <summary>
            /// Constructor.
            /// </summary>
            /// <param name="myDictionary">The dictionary this is associated with.</param>
            public KeysCollection(ReadOnlyDictionaryBase<TKey, TValue> myDictionary)
            {
                this.myDictionary = myDictionary;
            }

            public override int Count
            {
                get { return myDictionary.Count; }
            }

            public override IEnumerator<TKey> GetEnumerator()
            {
                foreach (KeyValuePair<TKey, TValue> pair in myDictionary)
                    yield return pair.Key;
            }

            public override bool Contains(TKey key)
            {
                return myDictionary.ContainsKey(key);
            }
        }

        /// <summary>
        /// A private class that implements ICollection&lt;TKey&gt; and ICollection for the
        /// Values collection. The collection is read-only.
        /// </summary>
        [Serializable]
        private sealed class ValuesCollection : ReadOnlyCollectionBase<TValue>
        {
            private ReadOnlyDictionaryBase<TKey, TValue> myDictionary;

            public ValuesCollection(ReadOnlyDictionaryBase<TKey, TValue> myDictionary)
            {
                this.myDictionary = myDictionary;
            }

            public override int Count
            {
                get { return myDictionary.Count; }
            }

            public override IEnumerator<TValue> GetEnumerator()
            {
                foreach (KeyValuePair<TKey, TValue> pair in myDictionary)
                    yield return pair.Value;
            }
        }

        #endregion

        /// <summary>
        /// A class that wraps a IDictionaryEnumerator around an IEnumerator that
        /// enumerates KeyValuePairs. This is useful in implementing IDictionary, because
        /// IEnumerator can be implemented with an iterator, but IDictionaryEnumerator cannot.
        /// </summary>
        [Serializable]
        private class DictionaryEnumeratorWrapper : IDictionaryEnumerator
        {
            private IEnumerator<KeyValuePair<TKey, TValue>> enumerator;

            /// <summary>
            /// Constructor.
            /// </summary>
            /// <param name="enumerator">The enumerator of KeyValuePairs that is being wrapped.</param>
            public DictionaryEnumeratorWrapper(IEnumerator<KeyValuePair<TKey, TValue>> enumerator)
            {
                this.enumerator = enumerator;
            }

            public DictionaryEntry Entry
            {
                get
                {
                    KeyValuePair<TKey, TValue> pair = enumerator.Current;
                    DictionaryEntry entry = new DictionaryEntry();
                    if (pair.Key != null)
                        entry.Key = pair.Key;
                    entry.Value = pair.Value;

                    return entry;
                }
            }

            public object Key
            {
                get
                {
                    KeyValuePair<TKey, TValue> pair = enumerator.Current;

                    return pair.Key;
                }
            }

            public object Value
            {
                get
                {
                    KeyValuePair<TKey, TValue> pair = enumerator.Current;
                    return pair.Value;
                }
            }

            public void Reset()
            {
                throw new NotSupportedException(Strings.ResetNotSupported);
            }


            public bool MoveNext()
            {
                return enumerator.MoveNext();
            }


            public object Current
            {
                get
                {
                    return Entry;
                }
            }
        }
    }
}