// 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.Immutable;
using System.Composition;
using System.Linq;
using System.Threading;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Completion;
using Microsoft.CodeAnalysis.Completion.Providers;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp.Completion.Providers;

[ExportCompletionProvider(nameof(PartialMethodCompletionProvider), LanguageNames.CSharp), Shared]
[ExtensionOrder(After = nameof(OverrideCompletionProvider))]
[method: ImportingConstructor]
[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
internal sealed partial class PartialMethodCompletionProvider() : AbstractPartialMethodCompletionProvider
{
    internal override string Language => LanguageNames.CSharp;

    protected override bool IncludeAccessibility(IMethodSymbol method, CancellationToken cancellationToken)
    {
        var declaration = (MethodDeclarationSyntax)method.DeclaringSyntaxReferences[0].GetSyntax(cancellationToken);
        foreach (var mod in declaration.Modifiers)
        {
            switch (mod.Kind())
            {
                case SyntaxKind.PublicKeyword:
                case SyntaxKind.ProtectedKeyword:
                case SyntaxKind.InternalKeyword:
                case SyntaxKind.PrivateKeyword:
                    return true;
            }
        }

        return false;
    }

    protected override SyntaxNode GetSyntax(SyntaxToken token)
    {
        return token.GetAncestor<EventFieldDeclarationSyntax>()
            ?? token.GetAncestor<EventDeclarationSyntax>()
            ?? token.GetAncestor<PropertyDeclarationSyntax>()
            ?? token.GetAncestor<IndexerDeclarationSyntax>()
            ?? (SyntaxNode?)token.GetAncestor<MethodDeclarationSyntax>()
            ?? throw ExceptionUtilities.UnexpectedValue(token);
    }

    protected override TextSpan GetTargetSelectionSpan(SyntaxNode caretTarget)
    {
        var methodDeclaration = (MethodDeclarationSyntax)caretTarget;
        return CompletionUtilities.GetTargetSelectionSpanForInsertedMember(methodDeclaration);
    }

    protected override SyntaxToken GetToken(CompletionItem completionItem, SyntaxTree tree, CancellationToken cancellationToken)
    {
        var tokenSpanEnd = MemberInsertionCompletionItem.GetTokenSpanEnd(completionItem);
        return tree.FindTokenOnLeftOfPosition(tokenSpanEnd, cancellationToken);
    }

    public override bool IsInsertionTrigger(SourceText text, int characterPosition, CompletionOptions options)
        => text[characterPosition] == ' ' ||
           (options.TriggerOnTypingLetters && CompletionUtilities.IsStartingNewWord(text, characterPosition));

    public override ImmutableHashSet<char> TriggerCharacters { get; } = CompletionUtilities.SpaceTriggerCharacter;

    protected override bool IsPartial(IMethodSymbol method)
    {
        var declarations = method.DeclaringSyntaxReferences.Select(r => r.GetSyntax()).OfType<MethodDeclarationSyntax>();
        return declarations.Any(d => d.Body == null && d.Modifiers.Any(SyntaxKind.PartialKeyword));
    }

    protected override bool IsPartialMethodCompletionContext(SyntaxTree tree, int position, CancellationToken cancellationToken, out DeclarationModifiers modifiers, out SyntaxToken token)
    {
        var touchingToken = tree.FindTokenOnLeftOfPosition(position, cancellationToken);
        var targetToken = touchingToken.GetPreviousTokenIfTouchingWord(position);
        var text = tree.GetText(cancellationToken);

        token = targetToken;

        modifiers = default;

        if (targetToken.Kind() is SyntaxKind.VoidKeyword or SyntaxKind.PartialKeyword ||
            (targetToken.Kind() == SyntaxKind.IdentifierToken && targetToken.HasMatchingText(SyntaxKind.PartialKeyword)))
        {
            return !IsOnSameLine(touchingToken.GetNextToken(), touchingToken, text) &&
                VerifyModifiers(tree, position, cancellationToken, out modifiers);
        }

        return false;
    }

    private static bool VerifyModifiers(SyntaxTree tree, int position, CancellationToken cancellationToken, out DeclarationModifiers modifiers)
    {
        var touchingToken = tree.FindTokenOnLeftOfPosition(position, cancellationToken);
        var token = touchingToken.GetPreviousToken();

        var foundPartial = touchingToken.IsKindOrHasMatchingText(SyntaxKind.PartialKeyword);
        var foundAsync = false;

        while (IsOnSameLine(token, touchingToken, tree.GetText(cancellationToken)))
        {
            if (token.IsKindOrHasMatchingText(SyntaxKind.AsyncKeyword))
            {
                foundAsync = true;
            }

            foundPartial = foundPartial || token.IsKindOrHasMatchingText(SyntaxKind.PartialKeyword);

            token = token.GetPreviousToken();
        }

        modifiers = new DeclarationModifiers(isAsync: foundAsync, isPartial: true);

        return foundPartial;
    }

    private static bool IsOnSameLine(SyntaxToken syntaxToken, SyntaxToken touchingToken, SourceText text)
    {
        return !syntaxToken.IsKind(SyntaxKind.None)
            && !touchingToken.IsKind(SyntaxKind.None)
            && text.Lines.IndexOf(syntaxToken.SpanStart) == text.Lines.IndexOf(touchingToken.SpanStart);
    }

    protected override string GetDisplayText(IMethodSymbol method, SemanticModel semanticModel, int position)
        => method.ToMinimalDisplayString(semanticModel, position, SignatureDisplayFormat);
}