// 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.Generic;
using System.Collections.Immutable;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.Internal.Log;
using Microsoft.CodeAnalysis.LanguageService;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Shared.Extensions.ContextQuery;
using Microsoft.CodeAnalysis.Text;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.Completion.Providers;

internal abstract partial class AbstractKeywordCompletionProvider<TContext> : LSPCompletionProvider
    where TContext : SyntaxContext
{
    private static readonly EqualityComparer<CompletionItem> s_comparer = EqualityComparer<CompletionItem>.Create(
        static (x, y) => x?.DisplayText == y?.DisplayText,
        static x => x.DisplayText.GetHashCode());

    private readonly ImmutableArray<IKeywordRecommender<TContext>> _keywordRecommenders;

    protected AbstractKeywordCompletionProvider(ImmutableArray<IKeywordRecommender<TContext>> keywordRecommenders)
        => _keywordRecommenders = keywordRecommenders;

    protected abstract CompletionItem CreateItem(RecommendedKeyword keyword, TContext context, CancellationToken cancellationToken);

    public override async Task ProvideCompletionsAsync(CompletionContext context)
    {
        var cancellationToken = context.CancellationToken;

        using (Logger.LogBlock(FunctionId.Completion_KeywordCompletionProvider_GetItemsWorker, cancellationToken))
        {
            context.AddItems(await context.Document.GetUnionItemsFromDocumentAndLinkedDocumentsAsync(
                s_comparer,
                d => RecommendCompletionItemsAsync(d, context, cancellationToken)).ConfigureAwait(false));
        }
    }

    private async Task<ImmutableArray<CompletionItem>> RecommendCompletionItemsAsync(Document document, CompletionContext context, CancellationToken cancellationToken)
    {
        var position = context.Position;
        var syntaxContext = (TContext)await context.GetSyntaxContextWithExistingSpeculativeModelAsync(document, cancellationToken).ConfigureAwait(false);
        var keywords = await RecommendKeywordsAsync(document, position, syntaxContext, cancellationToken).ConfigureAwait(false);
        return keywords.SelectAsArray(k => CreateItem(k, syntaxContext, cancellationToken));
    }

    private async Task<ImmutableArray<RecommendedKeyword>> RecommendKeywordsAsync(
        Document document,
        int position,
        TContext context,
        CancellationToken cancellationToken)
    {
        var syntaxTree = await document.GetRequiredSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
        var syntaxFacts = document.GetRequiredLanguageService<ISyntaxFactsService>();
        if (syntaxFacts.IsInNonUserCode(syntaxTree, position, cancellationToken))
            return [];

        using var _ = ArrayBuilder<RecommendedKeyword>.GetInstance(out var result);
        foreach (var recommender in _keywordRecommenders)
        {
            var keywords = recommender.RecommendKeywords(position, context, cancellationToken);
            result.AddRange(keywords.NullToEmpty());
        }

        result.RemoveDuplicates();
        return result.ToImmutableAndClear();
    }

    public sealed override Task<TextChange?> GetTextChangeAsync(Document document, CompletionItem item, char? ch, CancellationToken cancellationToken)
        => Task.FromResult((TextChange?)new TextChange(item.Span, item.DisplayText));
}