' 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.Collections.Generic
Imports System.Linq
Imports System.Runtime.InteropServices
Imports Microsoft.CodeAnalysis.Text
Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
Imports TypeKind = Microsoft.CodeAnalysis.TypeKind

Namespace Microsoft.CodeAnalysis.VisualBasic
    ''' <summary>
    ''' This class is used to validate the compiler options.
    ''' </summary>
    Friend Module OptionsValidator
        ''' <summary>
        ''' Parse the project level imports, adding errors to the errorBag as necessary
        ''' </summary>
        Friend Function ParseImports(importsClauses As IEnumerable(Of String), diagnostics As DiagnosticBag) As GlobalImport()
            Debug.Assert(diagnostics IsNot Nothing)

            Dim importsClauseArray = importsClauses.Select(AddressOf StringExtensions.Unquote).ToArray()

            If importsClauseArray.Length > 0 Then
                ' Create a file with Import statement for each imported name, and parse it. Use two newlines
                ' after each to avoid issues with implicit line continuation.
                Dim importFileText As String = importsClauseArray.Select(Function(name) "Imports " + name + vbCrLf + vbCrLf).Aggregate(Function(a, b) a & b)
                Dim tree = VisualBasicSyntaxTree.ParseText(SourceText.From(importFileText), VisualBasicParseOptions.Default, "")

                ' Extract all the parsed imports back out.
                Dim parsedImportList As New List(Of GlobalImport)
                Dim importList As SyntaxList(Of ImportsStatementSyntax) = tree.GetCompilationUnitRoot().Imports
                For i = 0 To importList.Count - 1
                    Dim statement = importList(i)
                    Dim importsClausesSyntaxList As SeparatedSyntaxList(Of ImportsClauseSyntax) = statement.ImportsClauses

                    If importsClauses.Count > 0 Then
                        Dim clause As ImportsClauseSyntax = importsClausesSyntaxList(0)
                        Dim syntaxErrors As IEnumerable(Of Diagnostic) = clause.GetSyntaxErrors(tree)

                        If importsClausesSyntaxList.Count > 1 Then
                            ' Only allow one import clause per name. If more than one is found, report "expected end of statement".
                            syntaxErrors = syntaxErrors.Concat(New VBDiagnostic(New DiagnosticInfo(MessageProvider.Instance, ERRID.ERR_ExpectedEOS), importsClausesSyntaxList(1).GetLocation()))
                        End If

                        Dim import = New GlobalImport(clause, importsClauseArray(i))

                        Dim errors = From diag In syntaxErrors
                                     Select import.MapDiagnostic(diag)

                        diagnostics.AddRange(errors)

                        If Not errors.Any(Function(diag) diag.Severity = DiagnosticSeverity.Error) Then
                            ' only add imports without syntax errors.
                            parsedImportList.Add(import)
                        End If

                    End If
                Next

                Return parsedImportList.ToArray()
            Else
                Return Array.Empty(Of GlobalImport)
            End If
        End Function

        ''' <summary>
        ''' Validate and parse the root namespace. If the root namespace string is a valid namespace name, the parsed
        ''' version is returned. Otherwise Nothing is returned.
        ''' </summary>
        Friend Function IsValidNamespaceName(name As String) As Boolean
            Debug.Assert(name IsNot Nothing)

            ' TODO: consider calling Syntax.ParseName and analyze the result (reject () or 
            ' type characters instead of reimplementing a lot of logic in IsValidRootNamespaceComponent.

            ' PERF: Avoid allocations from String.Split
            Dim start As Integer = 0
            Do
                Dim index = name.IndexOf("."c, start)
                If Not IsValidRootNamespaceComponent(name, start, If(index < 0, name.Length, index), allowEscaping:=True) Then
                    ' ERRID.ERR_BadNamespaceName1
                    Return False
                End If
                If index < 0 Then Exit Do
                start = index + 1
            Loop

            Return True
        End Function

        ''' <summary>
        ''' Check if a string is a valid component of the root namespace. We use the usual
        ''' VB identifier rules, but don't check for keywords (this is the same as previous versions).
        ''' </summary>
        Private Function IsValidRootNamespaceComponent(name As String, start As Integer, [end] As Integer, allowEscaping As Boolean) As Boolean
            Debug.Assert(name IsNot Nothing)

            ' Empty string is not valid.
            If start = [end] Then
                Return False
            End If

            Dim lastIdentifierCharacterIndex As Integer = [end] - 1

            If allowEscaping AndAlso SyntaxFacts.ReturnFullWidthOrSelf(name(start)) = SyntaxFacts.FULLWIDTH_LEFT_SQUARE_BRACKET Then
                If SyntaxFacts.ReturnFullWidthOrSelf(name(lastIdentifierCharacterIndex)) <> SyntaxFacts.FULLWIDTH_RIGHT_SQUARE_BRACKET Then
                    Return False
                End If

                Return IsValidRootNamespaceComponent(name, start + 1, lastIdentifierCharacterIndex, allowEscaping:=False)
            End If

            If Not SyntaxFacts.IsIdentifierStartCharacter(name(start)) Then
                Return False
            End If

            ' an identifier starting with an underscore must at least consist of two characters
            If ([end] - start) = 1 AndAlso SyntaxFacts.ReturnFullWidthOrSelf(name(start)) = SyntaxFacts.FULLWIDTH_LOW_LINE Then
                Return False
            End If

            For i = start + 1 To lastIdentifierCharacterIndex
                If Not SyntaxFacts.IsIdentifierPartCharacter(name(i)) Then
                    Return False
                End If
            Next

            Return True
        End Function
    End Module
End Namespace