// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
//
//
// Description: Base class for DataTemplateKey, TableTemplateKey.
//
 
using System.Reflection;
using System.ComponentModel;
using System.Windows.Markup;
 
namespace System.Windows
{
    /// <summary> The TemplateKey object is used as the resource key for data templates</summary>
    [TypeConverter(typeof(TemplateKeyConverter))]
    public abstract class TemplateKey : ResourceKey, ISupportInitialize
    {
        /// <summary> Constructor (called by derived classes only) </summary>
        protected TemplateKey(TemplateType templateType)
        {
            _dataType = null;   // still needs to be initialized
            _templateType = templateType;
        }
 
        /// <summary> Constructor (called by derived classes only) </summary>
        protected TemplateKey(TemplateType templateType, object dataType)
        {
            Exception ex = ValidateDataType(dataType, "dataType");
            if (ex != null)
                throw ex;
 
            _dataType = dataType;
            _templateType = templateType;
        }
 
#region ISupportInitialize
 
        /// <summary>Begin Initialization</summary>
        void ISupportInitialize.BeginInit()
        {
            _initializing = true;
        }
 
        /// <summary>End Initialization, verify that internal state is consistent</summary>
        void ISupportInitialize.EndInit()
        {
            if (_dataType == null)
            {
                throw new InvalidOperationException(SR.Format(SR.PropertyMustHaveValue, "DataType", this.GetType().Name));
            }
 
            _initializing = false;
        }
 
#endregion ISupportInitialize
 
        /// <summary>
        /// The type for which the template is designed.  This is either
        /// a Type (for object data), or a string (for XML data).  In the latter
        /// case the string denotes the XML tag name.
        /// </summary>
        public object DataType
        {
            get { return _dataType; }
            set
            {
                if (!_initializing)
                    throw new InvalidOperationException(SR.Format(SR.PropertyIsInitializeOnly, "DataType", this.GetType().Name));
                if (_dataType != null && value != _dataType)
                    throw new InvalidOperationException(SR.Format(SR.PropertyIsImmutable, "DataType", this.GetType().Name));
 
                Exception ex = ValidateDataType(value, "value");
                if (ex != null)
                    throw ex;
 
                _dataType = value;
            }
        }
 
        /// <summary> Override of Object.GetHashCode() </summary>
        public override int GetHashCode()
        {
            // note that the hash code can change, but only during intialization
            // and only once (DataType can only be changed once, from null to
            // non-null, and that can only happen during [Begin/End]Init).
            // Technically this is still a violation of the "constant during
            // lifetime" rule, however in practice this is acceptable.  It is
            // very unlikely that someone will put a TemplateKey into a hashtable
            // before it is initialized.
 
            int hashcode = (int)_templateType;
 
            if (_dataType != null)
            {
                hashcode += _dataType.GetHashCode();
            }
 
            return hashcode;
        }
 
        /// <summary> Override of Object.Equals() </summary>
        public override bool Equals(object o)
        {
            TemplateKey key = o as TemplateKey;
            if (key != null)
            {
                return  _templateType == key._templateType &&
                        Object.Equals(_dataType, key._dataType);
            }
            return false;
        }
 
        /// <summary> Override of Object.ToString() </summary>
        public override string ToString()
        {
            Type type = DataType as Type;
            return (DataType != null)
                    ?   string.Create(TypeConverterHelper.InvariantEnglishUS, $"{this.GetType().Name}({DataType})")
                    :   string.Create(TypeConverterHelper.InvariantEnglishUS, $"{this.GetType().Name}(null)");
        }
 
        /// <summary>
        ///     Allows SystemResources to know which assembly the template might be defined in.
        /// </summary>
        public override Assembly Assembly
        {
            get
            {
                Type type = _dataType as Type;
                if (type != null)
                {
                    return type.Assembly;
                }
 
                return null;
            }
        }
 
        /// <summary> The different types of templates that use TemplateKey </summary>
        protected enum TemplateType
        {
            /// <summary> DataTemplate </summary>
            DataTemplate,
            /// <summary> TableTemplate </summary>
            TableTemplate,
        }
 
        // Validate against these rules
        //  1. dataType must not be null (except at initialization, which is tested at EndInit)
        //  2. dataType must be either a Type (object data) or a string (XML tag name)
        //  3. dataType cannot be typeof(Object)
        internal static Exception ValidateDataType(object dataType, string argName)
        {
            Exception result = null;
 
            if (dataType == null)
            {
                result = new ArgumentNullException(argName);
            }
            else if (!(dataType is Type) && !(dataType is String))
            {
                result = new ArgumentException(SR.Format(SR.MustBeTypeOrString, dataType.GetType().Name), argName);
            }
            else if (typeof(Object).Equals(dataType))
            {
                result = new ArgumentException(SR.DataTypeCannotBeObject, argName);
            }
 
            return result;
        }
 
        private object _dataType;
        private TemplateType _templateType;
        private bool _initializing;
    }
}