// 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.Concurrent;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
using Microsoft.CodeAnalysis.Shared.Extensions;
 
namespace Microsoft.CodeAnalysis.Shared.Utilities
{
    using TreeMap = ConcurrentDictionary<(SyntaxTree tree, int namespaceId), ImmutableDictionary<INamespaceOrTypeSymbol, IAliasSymbol>>;
 
    internal static class AliasSymbolCache
    {
        private static readonly ConditionalWeakTable<Compilation, TreeMap> s_treeAliasMap = new();
 
        /// <summary>
        /// Returns <see langword="true"/> if items were already cached for this <paramref name="semanticModel"/> and
        /// <paramref name="namespaceId"/>, <see langword="false"/> otherwise.  Callers should use this value to
        /// determine if they should call <see cref="AddAliasSymbols"/> or not.  A result of <see langword="true"/> does
        /// *not* mean that <paramref name="aliasSymbol"/> is non-<see langword="null"/>.
        /// </summary>
        public static bool TryGetAliasSymbol(
            SemanticModel semanticModel,
            int namespaceId,
            INamespaceOrTypeSymbol targetSymbol,
            out IAliasSymbol? aliasSymbol)
        {
            semanticModel = semanticModel.GetOriginalSemanticModel();
 
            aliasSymbol = null;
            if (!s_treeAliasMap.TryGetValue(semanticModel.Compilation, out var treeMap) ||
                !treeMap.TryGetValue((semanticModel.SyntaxTree, namespaceId), out var symbolMap))
            {
                // maps aren't available.  Caller needs to call back into us to add aliases for this scope.
                return false;
            }
 
            // map was available.  see if it contains an alias to this target.  This is considered successful regardless
            // of whether we find a mapping or not.
            symbolMap.TryGetValue(targetSymbol, out aliasSymbol);
            return true;
        }
 
        public static void AddAliasSymbols(SemanticModel semanticModel, int namespaceId, IEnumerable<IAliasSymbol> aliasSymbols)
        {
            // given semantic model must be the original semantic model for now
            var treeMap = s_treeAliasMap.GetValue(semanticModel.Compilation, static _ => new TreeMap());
 
            // check again to see whether somebody has beaten us
            var key = (tree: semanticModel.SyntaxTree, namespaceId);
            if (treeMap.ContainsKey(key))
                return;
 
            var builder = ImmutableDictionary.CreateBuilder<INamespaceOrTypeSymbol, IAliasSymbol>();
            foreach (var alias in aliasSymbols)
            {
                if (builder.ContainsKey(alias.Target))
                    continue;
 
                // only put the first one.
                builder.Add(alias.Target, alias);
            }
 
            // Use namespace id rather than holding onto namespace node directly, that will keep the tree alive as long
            // as the compilation is alive. In the current design, a node can come and go even if compilation is alive
            // through recoverable tree.
            treeMap.TryAdd(key, builder.ToImmutable());
        }
    }
}