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

namespace System.Reflection.Metadata
{
    /// <summary>
    /// Debug information associated with a method definition. Stored in debug metadata.
    /// </summary>
    /// <remarks>
    /// See https://github.com/dotnet/runtime/blob/main/src/libraries/System.Reflection.Metadata/specs/PortablePdb-Metadata.md#methoddebuginformation-table-0x31.
    /// </remarks>
    public readonly struct MethodDebugInformation
    {
        private readonly MetadataReader _reader;

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

        internal MethodDebugInformation(MetadataReader reader, MethodDebugInformationHandle handle)
        {
            _reader = reader;
            _rowId = handle.RowId;
        }

        private MethodDebugInformationHandle Handle => MethodDebugInformationHandle.FromRowId(_rowId);

        /// <summary>
        /// Returns a blob encoding sequence points, or nil if the method doesn't have sequence points.
        /// Use <see cref="GetSequencePoints()"/> to decode the blob.
        /// </summary>
        public BlobHandle SequencePointsBlob => _reader.MethodDebugInformationTable.GetSequencePoints(Handle);

        /// <summary>
        /// Handle of the single document containing all sequence points of the method,
        /// or nil if the method doesn't have sequence points or spans multiple documents.
        /// </summary>
        public DocumentHandle Document => _reader.MethodDebugInformationTable.GetDocument(Handle);

        /// <summary>
        /// Returns local signature handle, or nil if the method doesn't define any local variables.
        /// </summary>
        public StandaloneSignatureHandle LocalSignature
        {
            get
            {
                if (SequencePointsBlob.IsNil)
                {
                    return default(StandaloneSignatureHandle);
                }

                return StandaloneSignatureHandle.FromRowId(_reader.GetBlobReader(SequencePointsBlob).ReadCompressedInteger());
            }
        }

        /// <summary>
        /// Returns a collection of sequence points decoded from <see cref="SequencePointsBlob"/>.
        /// </summary>
        public SequencePointCollection GetSequencePoints()
        {
            return new SequencePointCollection(_reader.BlobHeap.GetMemoryBlock(SequencePointsBlob), Document);
        }

        /// <summary>
        /// If the method is a MoveNext method of a state machine returns the kickoff method of the state machine, otherwise returns nil handle.
        /// </summary>
        public MethodDefinitionHandle GetStateMachineKickoffMethod()
        {
            return _reader.StateMachineMethodTable.FindKickoffMethod(_rowId);
        }
    }
}