// 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;
using System.Collections.Generic;
using System.Diagnostics;
using System.Reflection.Internal;
using System.Reflection.Metadata.Ecma335;

namespace System.Reflection.Metadata
{
    public readonly struct ImportDefinitionCollection : IEnumerable<ImportDefinition>
    {
        private readonly MemoryBlock _block;

        internal ImportDefinitionCollection(MemoryBlock block)
        {
            _block = block;
        }

        public Enumerator GetEnumerator()
        {
            return new Enumerator(_block);
        }

        IEnumerator<ImportDefinition> IEnumerable<ImportDefinition>.GetEnumerator()
        {
            return GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        public struct Enumerator : IEnumerator<ImportDefinition>
        {
            private BlobReader _reader;
            private ImportDefinition _current;

            internal Enumerator(MemoryBlock block)
            {
                _reader = new BlobReader(block);
                _current = default(ImportDefinition);
            }

            /// <exception cref="BadImageFormatException">Invalid blob format.</exception>
            public bool MoveNext()
            {
                if (_reader.RemainingBytes == 0)
                {
                    return false;
                }

                var kind = (ImportDefinitionKind)_reader.ReadByte();

                switch (kind)
                {
                    case ImportDefinitionKind.ImportType:
                        _current = new ImportDefinition(
                            kind,
                            typeOrNamespace: _reader.ReadTypeHandle());

                        break;

                    case ImportDefinitionKind.ImportNamespace:
                        _current = new ImportDefinition(
                            kind,
                            typeOrNamespace: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()));

                        break;

                    case ImportDefinitionKind.ImportAssemblyNamespace:
                        _current = new ImportDefinition(
                            kind,
                            assembly: MetadataTokens.AssemblyReferenceHandle(_reader.ReadCompressedInteger()),
                            typeOrNamespace: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()));

                        break;

                    case ImportDefinitionKind.ImportAssemblyReferenceAlias:
                        _current = new ImportDefinition(
                            kind,
                            alias: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()));

                        break;

                    case ImportDefinitionKind.AliasAssemblyReference:
                        _current = new ImportDefinition(
                            kind,
                            alias: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()),
                            assembly: MetadataTokens.AssemblyReferenceHandle(_reader.ReadCompressedInteger()));

                        break;

                    case ImportDefinitionKind.AliasType:
                        _current = new ImportDefinition(
                            kind,
                            alias: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()),
                            typeOrNamespace: _reader.ReadTypeHandle());

                        break;

                    case ImportDefinitionKind.ImportXmlNamespace:
                    case ImportDefinitionKind.AliasNamespace:
                        _current = new ImportDefinition(
                            kind,
                            alias: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()),
                            typeOrNamespace: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()));

                        break;

                    case ImportDefinitionKind.AliasAssemblyNamespace:
                        _current = new ImportDefinition(
                            kind,
                            alias: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()),
                            assembly: MetadataTokens.AssemblyReferenceHandle(_reader.ReadCompressedInteger()),
                            typeOrNamespace: MetadataTokens.BlobHandle(_reader.ReadCompressedInteger()));

                        break;

                    default:
                        throw new BadImageFormatException(SR.Format(SR.InvalidImportDefinitionKind, kind));
                }

                return true;
            }

            public ImportDefinition Current
            {
                get { return _current; }
            }

            object IEnumerator.Current
            {
                get { return _current; }
            }

            public void Reset()
            {
                _reader.Reset();
                _current = default(ImportDefinition);
            }

            void IDisposable.Dispose()
            {
            }
        }
    }
}