// 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 System.Threading.Tasks;
using Microsoft.CodeAnalysis.Collections;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Shared.Collections;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.StringIndentation;
using Microsoft.CodeAnalysis.Text;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.CSharp.StringIndentation;

[ExportLanguageService(typeof(IStringIndentationService), LanguageNames.CSharp), Shared]
[method: ImportingConstructor]
[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
internal sealed class CSharpStringIndentationService() : IStringIndentationService
{
    public async Task<ImmutableArray<StringIndentationRegion>> GetStringIndentationRegionsAsync(
        Document document, TextSpan textSpan, CancellationToken cancellationToken)
    {
        var text = await document.GetValueTextAsync(cancellationToken).ConfigureAwait(false);
        var root = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);

        using var result = TemporaryArray<StringIndentationRegion>.Empty;

        using var _ = ArrayBuilder<SyntaxNode>.GetInstance(out var nodeStack);
        nodeStack.Add(root);

        while (nodeStack.TryPop(out var node))
        {
            if (node is InterpolatedStringExpressionSyntax
                {
                    StringStartToken.RawKind: (int)SyntaxKind.InterpolatedMultiLineRawStringStartToken
                } interpolatedString)
            {
                ProcessInterpolatedStringExpression(text, interpolatedString, ref result.AsRef(), cancellationToken);
            }

            foreach (var child in node.ChildNodesAndTokens())
            {
                // Don't bother recursing into nodes that don't hit the requested span, they can never contribute
                // regions of interest.

                var childSpan = child.FullSpan;
                if (childSpan.Start > textSpan.End)
                    break;

                if (childSpan.End < textSpan.Start)
                    continue;

                if (child.AsNode(out var childNode))
                {
                    nodeStack.Add(childNode);
                }
                else if (child.IsToken)
                {
                    if (child.Kind() is SyntaxKind.MultiLineRawStringLiteralToken or SyntaxKind.Utf8MultiLineRawStringLiteralToken)
                        ProcessMultiLineRawStringLiteralToken(text, child.AsToken(), ref result.AsRef(), cancellationToken);
                }
            }
        }

        result.Sort(static (region1, region2) => region1.IndentSpan.CompareTo(region2.IndentSpan));

        return result.ToImmutableAndClear();
    }

    private static void ProcessMultiLineRawStringLiteralToken(
        SourceText text, SyntaxToken token, ref TemporaryArray<StringIndentationRegion> result, CancellationToken cancellationToken)
    {
        // Ignore strings with errors as we don't want to draw a line in a bad place that makes things even harder
        // to understand.
        if (token.ContainsDiagnostics && token.GetDiagnostics().Any(d => d.Severity == DiagnosticSeverity.Error))
            return;

        cancellationToken.ThrowIfCancellationRequested();
        if (!TryGetIndentSpan(text, (ExpressionSyntax)token.GetRequiredParent(), out _, out var indentSpan))
            return;

        result.Add(new StringIndentationRegion(indentSpan));
    }

    private static void ProcessInterpolatedStringExpression(
        SourceText text, InterpolatedStringExpressionSyntax interpolatedString, ref TemporaryArray<StringIndentationRegion> result, CancellationToken cancellationToken)
    {
        // Ignore strings with errors as we don't want to draw a line in a bad place that makes things even harder
        // to understand.
        if (interpolatedString.ContainsDiagnostics)
        {
            var errors = interpolatedString.GetDiagnostics().Where(d => d.Severity == DiagnosticSeverity.Error);
            foreach (var error in errors)
            {
                if (!IsInHole(interpolatedString, error.Location.SourceSpan))
                    return;
            }
        }

        cancellationToken.ThrowIfCancellationRequested();
        if (!TryGetIndentSpan(text, interpolatedString, out var offset, out var indentSpan))
            return;

        using var _ = ArrayBuilder<TextSpan>.GetInstance(out var builder);

        foreach (var content in interpolatedString.Contents)
        {
            if (content is InterpolationSyntax interpolation &&
                !IgnoreInterpolation(text, offset, interpolation))
            {
                builder.Add(interpolation.Span);
            }
        }

        result.Add(new StringIndentationRegion(indentSpan, builder.ToImmutable()));
    }

    private static bool IsInHole(InterpolatedStringExpressionSyntax interpolatedString, TextSpan sourceSpan)
    {
        foreach (var content in interpolatedString.Contents)
        {
            if (content is InterpolationSyntax && content.Span.Contains(sourceSpan))
                return true;
        }

        return false;
    }

    private static bool IgnoreInterpolation(SourceText text, int offset, InterpolationSyntax interpolation)
    {
        // We can ignore the hole if all the content of it is after the region's indentation level.
        // In that case, it's fine to draw the line through the hole as it won't intersect any code
        // (or show up on the right side of the line).

        var holeStartLine = text.Lines.GetLineFromPosition(interpolation.SpanStart).LineNumber;
        var holeEndLine = text.Lines.GetLineFromPosition(interpolation.Span.End).LineNumber;

        for (var i = holeStartLine; i <= holeEndLine; i++)
        {
            var line = text.Lines[i];
            var currentLineOffset = line.GetFirstNonWhitespaceOffset();

            if (currentLineOffset != null && currentLineOffset < offset)
                return false;
        }

        return true;
    }

    private static bool TryGetIndentSpan(SourceText text, ExpressionSyntax expression, out int offset, out TextSpan indentSpan)
    {
        indentSpan = default;

        // get the last line of the literal to determine the indentation string.
        var lastLine = text.Lines.GetLineFromPosition(expression.Span.End);
        var offsetOpt = lastLine.GetFirstNonWhitespaceOffset();

        // We should always have a non-null offset in a multi-line raw string without errors.
        Contract.ThrowIfNull(offsetOpt);
        offset = offsetOpt.Value;
        if (offset == 0)
            return false;

        var firstLine = text.Lines.GetLineFromPosition(expression.SpanStart);

        // A literal without errors must span at least three lines.  Like so:
        //      """
        //      foo
        //      """
        Contract.ThrowIfTrue(lastLine.LineNumber - firstLine.LineNumber < 2);
        indentSpan = TextSpan.FromBounds(firstLine.Start, lastLine.Start + offset);
        return true;
    }
}