// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Collections.Immutable;
using System.Diagnostics;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.FlowAnalysis
{
    /// <summary>
    /// Encapsulates information about regions of <see cref="BasicBlock"/>s in a <see cref="ControlFlowGraph"/>.
    /// Regions can overlap, but never cross each other boundaries.
    /// </summary>
    public sealed class ControlFlowRegion
    {
        /// <summary>
        /// Region's kind
        /// </summary>
        public ControlFlowRegionKind Kind { get; }

        /// <summary>
        /// Enclosing region. Null for <see cref="ControlFlowRegionKind.Root"/>
        /// </summary>
        public ControlFlowRegion? EnclosingRegion { get; private set; }

        /// <summary>
        /// Target exception type for <see cref="ControlFlowRegionKind.Filter"/>, <see cref="ControlFlowRegionKind.Catch"/>, 
        /// <see cref="ControlFlowRegionKind.FilterAndHandler "/>
        /// </summary>
        public ITypeSymbol? ExceptionType { get; }

        /// <summary>
        /// Ordinal (<see cref="BasicBlock.Ordinal"/>) of the first <see cref="BasicBlock"/> within the region. 
        /// </summary>
        public int FirstBlockOrdinal { get; }

        /// <summary>
        /// Ordinal (<see cref="BasicBlock.Ordinal"/>) of the last <see cref="BasicBlock"/> within the region. 
        /// </summary>
        public int LastBlockOrdinal { get; }

        /// <summary>
        /// Regions nested within this region.
        /// </summary>
        public ImmutableArray<ControlFlowRegion> NestedRegions { get; }

        /// <summary>
        /// Locals for which this region represent the life-time.
        /// </summary>
        public ImmutableArray<ILocalSymbol> Locals { get; }

        /// <summary>
        /// Local functions declared within the region.
        /// </summary>
        public ImmutableArray<IMethodSymbol> LocalFunctions { get; }

        /// <summary>
        /// Capture Ids used for intermediate results within the region.
        /// </summary>
        public ImmutableArray<CaptureId> CaptureIds { get; }

        internal ControlFlowRegion(ControlFlowRegionKind kind, int firstBlockOrdinal, int lastBlockOrdinal,
                        ImmutableArray<ControlFlowRegion> nestedRegions,
                        ImmutableArray<ILocalSymbol> locals,
                        ImmutableArray<IMethodSymbol> methods,
                        ImmutableArray<CaptureId> captureIds,
                        ITypeSymbol? exceptionType,
                        ControlFlowRegion? enclosingRegion)
        {
            Debug.Assert(firstBlockOrdinal >= 0);
            Debug.Assert(lastBlockOrdinal >= firstBlockOrdinal);

            Kind = kind;
            FirstBlockOrdinal = firstBlockOrdinal;
            LastBlockOrdinal = lastBlockOrdinal;
            ExceptionType = exceptionType;
            Locals = locals.NullToEmpty();
            LocalFunctions = methods.NullToEmpty();
            CaptureIds = captureIds.NullToEmpty();
            NestedRegions = nestedRegions.NullToEmpty();
            EnclosingRegion = enclosingRegion;

            foreach (ControlFlowRegion r in NestedRegions)
            {
                Debug.Assert(r.EnclosingRegion == null && r.Kind != ControlFlowRegionKind.Root);
                r.EnclosingRegion = this;
            }
#if DEBUG
            int previousLast;

            switch (kind)
            {
                case ControlFlowRegionKind.TryAndFinally:
                case ControlFlowRegionKind.FilterAndHandler:
                    Debug.Assert(NestedRegions.Length == 2);
                    Debug.Assert(NestedRegions[0].Kind == (kind == ControlFlowRegionKind.TryAndFinally ? ControlFlowRegionKind.Try : ControlFlowRegionKind.Filter));
                    Debug.Assert(NestedRegions[1].Kind == (kind == ControlFlowRegionKind.TryAndFinally ? ControlFlowRegionKind.Finally : ControlFlowRegionKind.Catch));
                    Debug.Assert(NestedRegions[0].FirstBlockOrdinal == firstBlockOrdinal);
                    Debug.Assert(NestedRegions[1].LastBlockOrdinal == lastBlockOrdinal);
                    Debug.Assert(NestedRegions[0].LastBlockOrdinal + 1 == NestedRegions[1].FirstBlockOrdinal);
                    break;

                case ControlFlowRegionKind.TryAndCatch:
                    Debug.Assert(NestedRegions.Length >= 2);
                    Debug.Assert(NestedRegions[0].Kind == ControlFlowRegionKind.Try);
                    Debug.Assert(NestedRegions[0].FirstBlockOrdinal == firstBlockOrdinal);
                    previousLast = NestedRegions[0].LastBlockOrdinal;

                    for (int i = 1; i < NestedRegions.Length; i++)
                    {
                        ControlFlowRegion r = NestedRegions[i];
                        Debug.Assert(previousLast + 1 == r.FirstBlockOrdinal);
                        previousLast = r.LastBlockOrdinal;

                        Debug.Assert(r.Kind == ControlFlowRegionKind.FilterAndHandler || r.Kind == ControlFlowRegionKind.Catch);
                    }

                    Debug.Assert(previousLast == lastBlockOrdinal);
                    break;

                case ControlFlowRegionKind.Root:
                case ControlFlowRegionKind.LocalLifetime:
                case ControlFlowRegionKind.Try:
                case ControlFlowRegionKind.Filter:
                case ControlFlowRegionKind.Catch:
                case ControlFlowRegionKind.Finally:
                case ControlFlowRegionKind.StaticLocalInitializer:
                case ControlFlowRegionKind.ErroneousBody:
                    previousLast = firstBlockOrdinal - 1;

                    foreach (ControlFlowRegion r in NestedRegions)
                    {
                        Debug.Assert(previousLast < r.FirstBlockOrdinal);
                        previousLast = r.LastBlockOrdinal;
                    }

                    Debug.Assert(previousLast <= lastBlockOrdinal);
                    break;

                default:
                    throw ExceptionUtilities.UnexpectedValue(kind);
            }
#endif
        }

        internal bool ContainsBlock(int destinationOrdinal)
        {
            return FirstBlockOrdinal <= destinationOrdinal && LastBlockOrdinal >= destinationOrdinal;
        }
    }
}