//------------------------------------------------------------------------------
// <copyright file="EventHandlerList.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>                                                                
//------------------------------------------------------------------------------

namespace System.ComponentModel {
    using System;
    using System.Diagnostics.CodeAnalysis;
    using System.Security.Permissions;

    /// <devdoc>
    ///    <para>Provides a simple list of delegates. This class cannot be inherited.</para>
    /// </devdoc>
    [HostProtection(SharedState = true)]
    public sealed class EventHandlerList : IDisposable {
        
        ListEntry head;
        Component parent;

        /// <devdoc>
        ///    Creates a new event handler list.
        /// </devdoc>
        [SuppressMessage("Microsoft.Security", "CA2122:DoNotIndirectlyExposeMethodsWithLinkDemands")]
        public EventHandlerList()
        {
        }

        /// <devdoc>
        ///     Creates a new event handler list.  The parent component is used to check the component's
        ///     CanRaiseEvents property.
        /// </devdoc>
        [SuppressMessage("Microsoft.Security", "CA2122:DoNotIndirectlyExposeMethodsWithLinkDemands")]
        internal EventHandlerList(Component parent)
        {
            this.parent = parent;
        }

        /// <devdoc>
        ///    <para>Gets or sets the delegate for the specified key.</para>
        /// </devdoc>
        public Delegate this[object key] {
            [SuppressMessage("Microsoft.Security", "CA2122:DoNotIndirectlyExposeMethodsWithLinkDemands")]
            get {
                ListEntry e = null;
                if (parent == null || parent.CanRaiseEventsInternal)
                {
                    e = Find(key);
                }
                if (e != null) {
                    return e.handler;
                }
                else {
                    return null;
                }
            }
            set {
                ListEntry e = Find(key);
                if (e != null) {
                    e.handler = value;
                }
                else {
                    head = new ListEntry(key, value, head);
                }
            }
        }

        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [SuppressMessage("Microsoft.Security", "CA2122:DoNotIndirectlyExposeMethodsWithLinkDemands")]
        public void AddHandler(object key, Delegate value) {
            ListEntry e = Find(key);
            if (e != null) {
                e.handler = Delegate.Combine(e.handler, value);
            }
            else {
                head = new ListEntry(key, value, head);
            }
        }

        /// <devdoc> allows you to add a list of events to this list </devdoc>
        public void AddHandlers(EventHandlerList listToAddFrom) {
         
            ListEntry currentListEntry = listToAddFrom.head;
            while (currentListEntry != null) {
                AddHandler(currentListEntry.key, currentListEntry.handler);
                currentListEntry = currentListEntry.next;
            }
        }

        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        public void Dispose() {
            head = null;
        }

        private ListEntry Find(object key) {
            ListEntry found = head;
            while (found != null) {
                if (found.key == key) {
                    break;
                }
                found = found.next;
            }
            return found;
        }

        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [SuppressMessage("Microsoft.Security", "CA2122:DoNotIndirectlyExposeMethodsWithLinkDemands")]
        public void RemoveHandler(object key, Delegate value) {
            ListEntry e = Find(key);
            if (e != null) {
                e.handler = Delegate.Remove(e.handler, value);
            }
            // else... no error for removal of non-existant delegate
            //
        }

        private sealed class ListEntry {
            internal ListEntry next;
            internal object key;
            internal Delegate handler;

            public ListEntry(object key, Delegate handler, ListEntry next) {
                this.next = next;
                this.key = key;
                this.handler = handler;
            }
        }
    }


}