// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Immutable;
using System.Reflection.Metadata.Ecma335;

namespace System.Reflection.Metadata
{
    public readonly struct EventDefinition
    {
        private readonly MetadataReader _reader;

        // Workaround: JIT doesn't generate good code for nested structures, so use RowId.
        private readonly int _rowId;

        internal EventDefinition(MetadataReader reader, EventDefinitionHandle handle)
        {
            _reader = reader;
            _rowId = handle.RowId;
        }

        private EventDefinitionHandle Handle
        {
            get { return EventDefinitionHandle.FromRowId(_rowId); }
        }

        public StringHandle Name
        {
            get
            {
                return _reader.EventTable.GetName(Handle);
            }
        }

        public EventAttributes Attributes
        {
            get
            {
                return _reader.EventTable.GetFlags(Handle);
            }
        }

        public EntityHandle Type
        {
            get
            {
                return _reader.EventTable.GetEventType(Handle);
            }
        }

        public CustomAttributeHandleCollection GetCustomAttributes()
        {
            return new CustomAttributeHandleCollection(_reader, Handle);
        }

        /// <summary>
        /// Returns a handle to the type that declares this event.
        /// </summary>
        public TypeDefinitionHandle GetDeclaringType()
        {
            return _reader.GetDeclaringType(Handle);
        }

        public EventAccessors GetAccessors()
        {
            int adder = 0;
            int remover = 0;
            int fire = 0;
            ImmutableArray<MethodDefinitionHandle>.Builder? other = null;

            ushort methodCount;
            int firstRowId = _reader.MethodSemanticsTable.FindSemanticMethodsForEvent(Handle, out methodCount);
            for (ushort i = 0; i < methodCount; i++)
            {
                int rowId = firstRowId + i;
                switch (_reader.MethodSemanticsTable.GetSemantics(rowId))
                {
                    case MethodSemanticsAttributes.Adder:
                        adder = _reader.MethodSemanticsTable.GetMethod(rowId).RowId;
                        break;

                    case MethodSemanticsAttributes.Remover:
                        remover = _reader.MethodSemanticsTable.GetMethod(rowId).RowId;
                        break;

                    case MethodSemanticsAttributes.Raiser:
                        fire = _reader.MethodSemanticsTable.GetMethod(rowId).RowId;
                        break;

                    case MethodSemanticsAttributes.Other:
                        other ??= ImmutableArray.CreateBuilder<MethodDefinitionHandle>();

                        other.Add(_reader.MethodSemanticsTable.GetMethod(rowId));
                        break;
                }
            }

            var otherAccessors = other?.ToImmutable() ?? ImmutableArray<MethodDefinitionHandle>.Empty;
            return new EventAccessors(adder, remover, fire, otherAccessors);
        }
    }
}