// 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;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Diagnostics;
using System.Text;
using System.Threading;
using Microsoft.CodeAnalysis.Collections;
using Microsoft.CodeAnalysis.PooledObjects;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis
{
    /// <summary>
    /// Represents a mutable bag of diagnostics. You can add diagnostics to the bag,
    /// and also get all the diagnostics out of the bag (the bag implements
    /// IEnumerable&lt;Diagnostics&gt;. Once added, diagnostics cannot be removed, and no ordering
    /// is guaranteed.
    /// 
    /// It is ok to Add diagnostics to the same bag concurrently on multiple threads.
    /// It is NOT ok to Add concurrently with Clear or Free operations.
    /// </summary>
    /// <remarks>The bag is optimized to be efficient when containing zero errors.</remarks>
    [DebuggerDisplay("{GetDebuggerDisplay(), nq}")]
    [DebuggerTypeProxy(typeof(DebuggerProxy))]
    internal class DiagnosticBag
    {
        // The lazyBag field is populated lazily -- the first time an error is added.
        private ConcurrentQueue<Diagnostic>? _lazyBag;

        /// <summary>
        /// Return true if the bag is completely empty - not even containing void diagnostics.
        /// </summary>
        /// <remarks>
        /// This exists for short-circuiting purposes. Use <see cref="System.Linq.Enumerable.Any{T}(IEnumerable{T})"/>
        /// to get a resolved Tuple(Of NamedTypeSymbol, ImmutableArray(Of Diagnostic)) (i.e. empty after eliminating void diagnostics).
        /// </remarks>
        public bool IsEmptyWithoutResolution
        {
            get
            {
                // It should be safe to access this here, since we normally have a collect phase and
                // then a report phase, and we shouldn't be called during the "report" phase. We
                // also never remove diagnostics, so the worst that happens is that we don't return
                // an element that is added a split second after this is called.
                ConcurrentQueue<Diagnostic>? bag = _lazyBag;
                return bag == null || bag.IsEmpty;
            }
        }

        /// <summary>
        /// Returns true if the bag has any diagnostics with DefaultSeverity=Error. Does not consider warnings or informationals
        /// or warnings promoted to error via /warnaserror.
        /// </summary>
        /// <remarks>
        /// Resolves any lazy diagnostics in the bag.
        /// 
        /// Generally, this should only be called by the creator (modulo pooling) of the bag (i.e. don't use bags to communicate -
        /// if you need more info, pass more info).
        /// </remarks>
        public bool HasAnyErrors()
        {
            if (IsEmptyWithoutResolution)
            {
                return false;
            }

            foreach (Diagnostic diagnostic in Bag)
            {
                if (diagnostic.DefaultSeverity == DiagnosticSeverity.Error)
                {
                    return true;
                }
            }

            return false;
        }

        /// <summary>
        /// Returns true if the bag has any non-lazy diagnostics with DefaultSeverity=Error. Does not consider warnings or informationals
        /// or warnings promoted to error via /warnaserror.
        /// </summary>
        /// <remarks>
        /// Does not resolve any lazy diagnostics in the bag.
        /// 
        /// Generally, this should only be called by the creator (modulo pooling) of the bag (i.e. don't use bags to communicate -
        /// if you need more info, pass more info).
        /// </remarks>
        internal bool HasAnyResolvedErrors()
        {
            if (IsEmptyWithoutResolution)
            {
                return false;
            }

            foreach (Diagnostic diagnostic in Bag)
            {
                if ((diagnostic as DiagnosticWithInfo)?.HasLazyInfo != true && diagnostic.DefaultSeverity == DiagnosticSeverity.Error)
                {
                    return true;
                }
            }

            return false;
        }

        /// <summary>
        /// Add a diagnostic to the bag.
        /// </summary>
        public void Add(Diagnostic diag)
        {
            ConcurrentQueue<Diagnostic> bag = this.Bag;
            bag.Enqueue(diag);
        }

        /// <summary>
        /// Add multiple diagnostics to the bag.
        /// </summary>
        public void AddRange<T>(ImmutableArray<T> diagnostics) where T : Diagnostic
        {
            if (!diagnostics.IsDefaultOrEmpty)
            {
                ConcurrentQueue<Diagnostic> bag = this.Bag;
                for (int i = 0; i < diagnostics.Length; i++)
                {
                    bag.Enqueue(diagnostics[i]);
                }
            }
        }

        /// <summary>
        /// Add multiple diagnostics to the bag.
        /// </summary>
        public void AddRange(IEnumerable<Diagnostic> diagnostics)
        {
            foreach (Diagnostic diagnostic in diagnostics)
            {
                this.Bag.Enqueue(diagnostic);
            }
        }

        /// <summary>
        /// Add another DiagnosticBag to the bag.
        /// </summary>
        public void AddRange(DiagnosticBag bag)
        {
            if (!bag.IsEmptyWithoutResolution)
            {
                AddRange(bag.Bag);
            }
        }

        /// <summary>
        /// Add another DiagnosticBag to the bag and free the argument.
        /// </summary>
        public void AddRangeAndFree(DiagnosticBag bag)
        {
            AddRange(bag);
            bag.Free();
        }

        /// <summary>
        /// Seal the bag so no further errors can be added, while clearing it and returning the old set of errors.
        /// Return the bag to the pool.
        /// </summary>
        public ImmutableArray<TDiagnostic> ToReadOnlyAndFree<TDiagnostic>(bool forceResolution = true) where TDiagnostic : Diagnostic
        {
            ConcurrentQueue<Diagnostic>? oldBag = _lazyBag;
            Free();

            return ToReadOnlyCore<TDiagnostic>(oldBag, forceResolution);
        }

        public ImmutableArray<Diagnostic> ToReadOnlyAndFree(bool forceResolution = true)
        {
            return ToReadOnlyAndFree<Diagnostic>(forceResolution);
        }

        public ImmutableArray<TDiagnostic> ToReadOnly<TDiagnostic>(bool forceResolution = true) where TDiagnostic : Diagnostic
        {
            ConcurrentQueue<Diagnostic>? oldBag = _lazyBag;
            return ToReadOnlyCore<TDiagnostic>(oldBag, forceResolution);
        }

        public ImmutableArray<Diagnostic> ToReadOnly(bool forceResolution = true)
        {
            return ToReadOnly<Diagnostic>(forceResolution);
        }

        private static ImmutableArray<TDiagnostic> ToReadOnlyCore<TDiagnostic>(ConcurrentQueue<Diagnostic>? oldBag, bool forceResolution) where TDiagnostic : Diagnostic
        {
            if (oldBag == null)
            {
                return ImmutableArray<TDiagnostic>.Empty;
            }

            ArrayBuilder<TDiagnostic> builder = ArrayBuilder<TDiagnostic>.GetInstance();

            foreach (TDiagnostic diagnostic in oldBag) // Cast should be safe since all diagnostics should be from same language.
            {
                if (forceResolution)
                {
                    if (diagnostic.Severity != InternalDiagnosticSeverity.Void)
                    {
                        Debug.Assert(diagnostic.Severity != InternalDiagnosticSeverity.Unknown); //Info access should have forced resolution.
                        builder.Add(diagnostic);
                    }
                }
                else
                {
                    builder.Add(diagnostic);
                }
            }

            return builder.ToImmutableAndFree();
        }

        /// <remarks>
        /// Generally, this should only be called by the creator (modulo pooling) of the bag (i.e. don't use bags to communicate -
        /// if you need more info, pass more info).
        /// </remarks>
        public IEnumerable<Diagnostic> AsEnumerable()
        {
            ConcurrentQueue<Diagnostic> bag = this.Bag;

            bool foundVoid = false;

            foreach (Diagnostic diagnostic in bag)
            {
                if (diagnostic.Severity == InternalDiagnosticSeverity.Void)
                {
                    foundVoid = true;
                    break;
                }
            }

            return foundVoid
                ? AsEnumerableFiltered()
                : bag;
        }

        /// <remarks>
        /// Using an iterator to avoid copying the list.  If perf is a problem,
        /// create an explicit enumerator type.
        /// </remarks>
        private IEnumerable<Diagnostic> AsEnumerableFiltered()
        {
            foreach (Diagnostic diagnostic in this.Bag)
            {
                if (diagnostic.Severity != InternalDiagnosticSeverity.Void)
                {
                    Debug.Assert(diagnostic.Severity != InternalDiagnosticSeverity.Unknown); //Info access should have forced resolution.
                    yield return diagnostic;
                }
            }
        }

        internal IEnumerable<Diagnostic> AsEnumerableWithoutResolution()
        {
            // PERF: don't make a defensive copy - callers are internal and won't modify the bag.
            return _lazyBag ?? SpecializedCollections.EmptyEnumerable<Diagnostic>();
        }

        internal int Count => _lazyBag?.Count ?? 0;

        public override string ToString()
        {
            if (this.IsEmptyWithoutResolution)
            {
                // TODO(cyrusn): do we need to localize this?
                return "<no errors>";
            }
            else
            {
                StringBuilder builder = new StringBuilder();
                foreach (Diagnostic diag in Bag) // NOTE: don't force resolution
                {
                    builder.AppendLine(diag.ToString());
                }
                return builder.ToString();
            }
        }

        /// <summary>
        /// Get the underlying concurrent storage, creating it on demand if needed.
        /// NOTE: Concurrent Adding to the bag is supported, but concurrent Clearing is not.
        ///       If one thread adds to the bug while another clears it, the scenario is 
        ///       broken and we cannot do anything about it here.
        /// </summary>
        private ConcurrentQueue<Diagnostic> Bag
        {
            get
            {
                ConcurrentQueue<Diagnostic>? bag = _lazyBag;
                if (bag != null)
                {
                    return bag;
                }

                ConcurrentQueue<Diagnostic> newBag = new ConcurrentQueue<Diagnostic>();
                return Interlocked.CompareExchange(ref _lazyBag, newBag, null) ?? newBag;
            }
        }

        // clears the bag.
        /// NOTE: Concurrent Adding to the bag is supported, but concurrent Clearing is not.
        ///       If one thread adds to the bug while another clears it, the scenario is 
        ///       broken and we cannot do anything about it here.
        internal void Clear()
        {
            ConcurrentQueue<Diagnostic>? bag = _lazyBag;
            if (bag != null)
            {
                _lazyBag = null;
            }
        }

        #region "Poolable"

        internal static DiagnosticBag GetInstance()
        {
            DiagnosticBag bag = s_poolInstance.Allocate();
            return bag;
        }

        internal void Free()
        {
            Clear();
            s_poolInstance.Free(this);
        }

        private static readonly ObjectPool<DiagnosticBag> s_poolInstance = CreatePool(128);
        private static ObjectPool<DiagnosticBag> CreatePool(int size)
        {
            return new ObjectPool<DiagnosticBag>(() => new DiagnosticBag(), size);
        }

        #endregion

        #region Debugger View

        internal sealed class DebuggerProxy
        {
            private readonly DiagnosticBag _bag;

            public DebuggerProxy(DiagnosticBag bag)
            {
                _bag = bag;
            }

            [DebuggerBrowsable(DebuggerBrowsableState.RootHidden)]
            public object[] Diagnostics
            {
                get
                {
                    ConcurrentQueue<Diagnostic>? lazyBag = _bag._lazyBag;
                    if (lazyBag != null)
                    {
                        return lazyBag.ToArray();
                    }
                    else
                    {
                        return Array.Empty<object>();
                    }
                }
            }
        }

        private string GetDebuggerDisplay()
        {
            return "Count = " + (_lazyBag?.Count ?? 0);
        }
        #endregion
    }
}