' 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.
 
Imports System.ComponentModel.Composition
Imports System.Threading
Imports Microsoft.CodeAnalysis.AutomaticCompletion
Imports Microsoft.CodeAnalysis.Diagnostics
Imports Microsoft.CodeAnalysis.Formatting
Imports Microsoft.CodeAnalysis.Host.Mef
Imports Microsoft.CodeAnalysis.Options
Imports Microsoft.CodeAnalysis.Text
Imports Microsoft.VisualStudio.Commanding
Imports Microsoft.VisualStudio.Language.Intellisense.AsyncCompletion
Imports Microsoft.VisualStudio.Text.Editor
Imports Microsoft.VisualStudio.Text.Editor.Commanding.Commands
Imports Microsoft.VisualStudio.Text.Operations
Imports Microsoft.VisualStudio.Utilities
 
Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.AutomaticCompletion
    ' <summary>
    ' visual basic automatic line ender command handler
    ' </summary>
    <Export(GetType(ICommandHandler))>
    <ContentType(ContentTypeNames.VisualBasicContentType)>
    <Name(PredefinedCommandHandlerNames.AutomaticLineEnder)>
    <Order(Before:=PredefinedCompletionNames.CompletionCommandHandler)>
    Friend Class AutomaticLineEnderCommandHandler
        Inherits AbstractAutomaticLineEnderCommandHandler
 
        <ImportingConstructor>
        <Obsolete(MefConstruction.ImportingConstructorMessage, True)>
        Public Sub New(undoRegistry As ITextUndoHistoryRegistry,
                       editorOperations As IEditorOperationsFactoryService,
                       editorOptionsService As EditorOptionsService)
 
            MyBase.New(undoRegistry, editorOperations, editorOptionsService)
        End Sub
 
        Protected Overrides Sub NextAction(editorOperation As IEditorOperations, nextAction As Action)
            ' let the next action run
            nextAction()
        End Sub
 
        Protected Overrides Function TreatAsReturn(document As ParsedDocument, caretPosition As Integer, cancellationToken As CancellationToken) As Boolean
            ' No special handling in VB.
            Return False
        End Function
 
        Protected Overrides Sub ModifySelectedNode(args As AutomaticLineEnderCommandArgs, document As ParsedDocument, selectedNode As SyntaxNode, addBrace As Boolean, caretPosition As Integer, fallbackOptions As StructuredAnalyzerConfigOptions, cancellationToken As CancellationToken)
        End Sub
 
        Protected Overrides Function GetValidNodeToModifyBraces(document As ParsedDocument, caretPosition As Integer, cancellationToken As CancellationToken) As (SyntaxNode, Boolean)?
            Return Nothing
        End Function
 
        Protected Overrides Function FormatBasedOnEndToken(document As ParsedDocument, position As Integer, formattingOptions As SyntaxFormattingOptions, cancellationToken As CancellationToken) As IList(Of TextChange)
            ' vb does automatic line commit
            ' no need to do explicit formatting
            Return SpecializedCollections.EmptyList(Of TextChange)
        End Function
 
        Protected Overrides Function GetEndingString(document As ParsedDocument, position As Integer) As String
            ' prepare expansive information from document
            Dim root = document.Root
            Dim text = document.Text
 
            ' get line where the caret is on
            Dim line = text.Lines.GetLineFromPosition(position)
 
            ' find line break token if there is one
            Dim lastToken = CType(root.FindTokenOnLeftOfPosition(line.End, includeSkipped:=False), SyntaxToken)
            lastToken = If(lastToken.Kind = SyntaxKind.EndOfFileToken, lastToken.GetPreviousToken(includeZeroWidth:=True), lastToken)
 
            ' find last token of the line
            If lastToken.Kind = SyntaxKind.None OrElse line.End < lastToken.Span.End Then
                Return Nothing
            End If
 
            ' properly ended
            If Not lastToken.IsMissing AndAlso lastToken.IsLastTokenOfStatementWithEndOfLine() Then
                Return Nothing
            End If
 
            ' so far so good. check whether we need to add explicit line continuation here
            Dim nonMissingToken = If(lastToken.IsMissing, lastToken.GetPreviousToken(), lastToken)
 
            ' now we have the last token, check whether it is at a valid location
            If (line.Span.Contains(nonMissingToken.Span.End)) Then
                ' make sure that there is no trailing text after last token on the line if it is not at the end of the line
                Dim endingString = text.ToString(TextSpan.FromBounds(nonMissingToken.Span.End, line.End))
                If Not String.IsNullOrWhiteSpace(endingString) Then
                    Return Nothing
                End If
            End If
 
            ' check whether implicit line continuation is allowed
            If SyntaxFacts.AllowsTrailingImplicitLineContinuation(CType(nonMissingToken, SyntaxToken)) Then
                Return Nothing
            End If
 
            Dim nextToken = nonMissingToken.GetNextToken(includeZeroWidth:=True)
 
            ' if there is skipped token between previous and next token, don't do anything
            If nonMissingToken.TrailingTrivia.Concat(nextToken.LeadingTrivia).Any(AddressOf HasSkippedText) Then
                Return Nothing
            End If
 
            If nextToken.IsLastTokenOfStatementWithEndOfLine() Then
                Return " _"
            End If
 
            Dim nextNonMissingToken = nextToken.GetNextNonZeroWidthTokenOrEndOfFile()
            If nextNonMissingToken.Kind = SyntaxKind.EndOfFileToken Then
                Return Nothing
            End If
 
            Return If(SyntaxFacts.AllowsLeadingImplicitLineContinuation(CType(nextToken, SyntaxToken)), Nothing, " _")
        End Function
 
        Private Shared Function HasSkippedText(trivia As SyntaxTrivia) As Boolean
            Return trivia.Kind = SyntaxKind.SkippedTokensTrivia
        End Function
    End Class
End Namespace