// 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.Generic;
using System.Collections.Immutable;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Shared.Utilities;

namespace Microsoft.CodeAnalysis.Completion.Providers;

internal sealed class GlobalAssemblyCacheCompletionHelper
{
    private static readonly Lazy<List<string>> s_lazyAssemblySimpleNames =
        new(() => [.. GlobalAssemblyCache.Instance.GetAssemblySimpleNames()]);

    private readonly CompletionItemRules _itemRules;

    public GlobalAssemblyCacheCompletionHelper(CompletionItemRules itemRules)
    {
        Debug.Assert(itemRules != null);
        _itemRules = itemRules;
    }

    public Task<ImmutableArray<CompletionItem>> GetItemsAsync(string directoryPath, CancellationToken cancellationToken)
        => Task.Run(() => GetItems(directoryPath, cancellationToken));

    // internal for testing
    internal ImmutableArray<CompletionItem> GetItems(string directoryPath, CancellationToken cancellationToken)
    {
        using var resultDisposer = ArrayBuilder<CompletionItem>.GetInstance(out var result);

        var comma = directoryPath.IndexOf(',');
        if (comma >= 0)
        {
            var partialName = directoryPath[..comma];
            foreach (var identity in GetAssemblyIdentities(partialName))
            {
                result.Add(CommonCompletionItem.Create(
                    identity.GetDisplayName(), displayTextSuffix: "", glyph: Glyph.Assembly, rules: _itemRules));
            }
        }
        else
        {
            foreach (var displayName in s_lazyAssemblySimpleNames.Value)
            {
                cancellationToken.ThrowIfCancellationRequested();
                result.Add(CommonCompletionItem.Create(
                    displayName, displayTextSuffix: "", glyph: Glyph.Assembly, rules: _itemRules));
            }
        }

        return result.ToImmutableAndClear();
    }

    private static IEnumerable<AssemblyIdentity> GetAssemblyIdentities(string partialName)
        => IOUtilities.PerformIO(() => GlobalAssemblyCache.Instance.GetAssemblyIdentities(partialName), []);
}