Imports System.IO



Public Class Indexer



    Private Files As New Dictionary(Of Integer, String) ' Key = File index, Value = File name

    Private FileNumbers As New Dictionary(Of String, Integer) ' Key = File name, Value = File index

    Private LastAddedFileIndex As Integer = 0



    Private Words As New Dictionary(Of Integer, String) ' Key = Word index, Value = Word

    Private WordNumbers As New Dictionary(Of String, Integer) ' Key = Word, Value = Word index

    Private LastAddedWordIndex As Integer = 0



    Private Index As New Dictionary(Of Integer, WordOccurrences) ' Key = Word index



    ''' <summary>

    ''' Returns the complete list of document numbers.

    ''' </summary>

    ReadOnly Property AllDocumentsNumbers() As Integer()

        Get

            Dim Result(FileNumbers.Count - 1) As Integer

            Dim I As Integer = 0

            For Each Document As KeyValuePair(Of Integer, String) In Files

                Result(I) = Document.Key

                I += 1

            Next

            Return Result

        End Get

    End Property



    ''' <summary>

    ''' Returns the total number of documents indexed.

    ''' </summary>

    ReadOnly Property DocumentCount() As Integer

        Get

            Return Files.Count

        End Get

    End Property



    ''' <summary>

    ''' Returns the name of the document, given its index.

    ''' </summary>

    ReadOnly Property DocumentName(ByVal index As Integer) As String

        Get

            If Files.ContainsKey(index) Then

                Return Files(index)

            Else

                Throw New ApplicationException("Document " + index.ToString + " does not exist in the index.")

            End If

        End Get

    End Property



    ''' <summary>

    ''' Returns the numeric index of the document, given its name.

    ''' </summary>

    ReadOnly Property DocumentNumber(ByVal name As String) As Integer

        Get

            If FileNumbers.ContainsKey(name) Then

                Return FileNumbers(name)

            Else

                Throw New ApplicationException("The document '" + name + "' does not exist in the index.")

            End If

        End Get

    End Property



    ''' <summary>

    ''' Returns the document indices of documents containing the specified words.

    ''' </summary>

    ''' <param name="word">The word to search for.</param>

    Function DocumentsContainingWord(ByVal word As String) As List(Of Integer)



        Dim Result As New List(Of Integer)

        Dim WordIndex As Integer = -1

        If WordNumbers.TryGetValue(word.ToUpper, WordIndex) Then



            Dim Occurrences As WordOccurrences = Nothing

            Dim Found As Boolean = Index.TryGetValue(WordIndex, Occurrences)



            If Not Found Then

                Throw New Exception("The word " + word + " exists in the words collection but not the index itself.")

            Else

                For Each DocumentIndex As Integer In Index(WordIndex).Documents.Keys

                    Result.Add(DocumentIndex)

                Next

            End If



        End If

        Return Result



    End Function



    ''' <summary>

    ''' Returns the number of times the given word occurs in the given document.

    ''' </summary>

    ''' <param name="documentIndex">The document's index to search in.</param>

    ''' <param name="word">The word to search for.</param>

    Function TermFrequency(ByVal documentIndex As Integer, ByVal word As String) As Integer



        Dim Result As Integer = 0



        Dim WordIndex As Integer = -1

        Dim WordFound As Boolean = WordNumbers.TryGetValue(word.ToUpper, WordIndex)

        If WordFound Then



            ' Get the document frequency and return it

            Dim Occurrences As WordOccurrences = Index(WordIndex)

            Occurrences.Documents.TryGetValue(documentIndex, Result)



        End If



        Return Result



    End Function



    ''' <summary>

    ''' Empties the index.

    ''' </summary>

    Public Sub Clear()



        Files.Clear()

        FileNumbers.Clear()



        Words.Clear()

        WordNumbers.Clear()



        LastAddedWordIndex = 0

        LastAddedFileIndex = 0



        Index.Clear()



    End Sub



    ''' <summary>

    ''' Returns the unique words in the given file's contents.

    ''' </summary>

    ''' <param name="fileContents">The textual contents of a file.</param>

    ''' <returns>A list of the unique words in the given text.</returns>

    Private Function GetVocabulary(ByVal fileContents As String) As String()



        fileContents = fileContents.ToUpper

        Dim WordsInFile As String() = SplitIntoFixedWords(fileContents)

        Dim Vocabulary As New SortedList(Of String, Integer)

        For Each Word As String In WordsInFile

            If Not Vocabulary.ContainsKey(Word) Then Vocabulary.Add(Word, 0)

        Next

        Dim Result(Vocabulary.Count - 1) As String

        Vocabulary.Keys.CopyTo(Result, 0)

        Return Result



    End Function



    ''' <summary>

    ''' Returns the number of times each word occurs in the given document.

    ''' </summary>

    ''' <param name="fileContents">The document containing words to count.</param>

    Private Function GetWordCounts(ByVal fileContents As String) As Dictionary(Of Integer, Integer)



        ' Create a list of all the words, each set as occurring 0 times

        Dim WordCounts As New Dictionary(Of Integer, Integer)

        For Each Index As Integer In Words.Keys

            WordCounts.Add(Index, 0)

        Next



        ' Count the number of occurrances of every word in this document

        Dim WordsInFile As String() = SplitIntoFixedWords(fileContents)

        For Each Word As String In WordsInFile

            Dim WordIndex As Integer = WordNumbers(Word)

            WordCounts(WordIndex) += 1

        Next



        ' Determine which words have a count greater than zero and include only those in the result

        Dim WordsToInclude As New List(Of Integer)

        For Each WordIndex As Integer In WordCounts.Keys

            If WordCounts(WordIndex) > 0 Then WordsToInclude.Add(WordIndex)

        Next

        Dim Result As New Dictionary(Of Integer, Integer)

        For Each WordIndex As Integer In WordsToInclude

            Result.Add(WordIndex, WordCounts(WordIndex))

        Next



        Return Result



    End Function



    ''' <summary>

    ''' Splits the document into words.

    ''' </summary>

    ''' <param name="fileContents">The document to split into words.</param>

    ''' <returns>The document, split into words.</returns>

    Private Function SplitIntoFixedWords(ByVal fileContents As String) As String()



        fileContents = fileContents.ToUpper

        Dim Words() As String = fileContents.Split(" "c, "!"c, "."c, ":"c, """"c, "-"c, Environment.NewLine)

        Dim WordsToReturn(Words.Length - 1) As String

        Dim Index As Integer = 0

        For Each Word As String In Words

            Word = FixWord(Word)

            If Word <> "" Then

                WordsToReturn(Index) = Word

                Index += 1

            End If

        Next



        ReDim Preserve WordsToReturn(Index - 1)

        Return WordsToReturn



    End Function



    ''' <summary>

    ''' Find each file in the given directory and index it.

    ''' </summary>

    ''' <param name="directory">The directory whose files to index.</param>

    ''' <remarks>Files are not recursed, and so only the files in the specified directory itself will be indexed.</remarks>

    Public Sub AddDirectoryToIndex(ByVal directory As String)



        ' Get the file names

        For Each Filename As String In IO.Directory.GetFiles(directory)

            AddFileName(Filename)

        Next



        ' Phase 1: Build a global vocabulary

        Dim Vocabulary As New SortedList(Of String, Integer)

        For Each File As KeyValuePair(Of Integer, String) In Files



            Dim Contents As String = GetFileContents(File.Value)



            ' Build a vocabulary for the file and add it to the complete list of words

            Dim FileVocabulary As String() = GetVocabulary(Contents)

            For Each Word As String In FileVocabulary

                If Not Vocabulary.ContainsKey(Word) Then Vocabulary.Add(Word, 0)

            Next



        Next



        ' Copy the complete list of words into the global vocabulary

        For Each Word As String In Vocabulary.Keys

            AddWordToVocabulary(Word)

        Next



        ' Phase 2: Determine how many times each word occurs in each document

        For Each File As KeyValuePair(Of Integer, String) In Files



            ' Count each word as it is read in

            Dim Contents As String = GetFileContents(File.Value)

            Dim DocumentWordCount As Dictionary(Of Integer, Integer) = GetWordCounts(Contents)



            ' Store number of times each word occurs in the document (by merging with the global index)

            MergeDocumentWordCount(FileNumbers(File.Value), DocumentWordCount)



        Next



    End Sub



    Public Sub AddFileToIndex(ByVal fileName As String)

        AddFileContentsToIndex(fileName, GetFileContents(fileName))

    End Sub



    Public Sub AddFileToIndex(ByVal virtualFilename As String, ByVal fileName As String)

        AddFileContentsToIndex(virtualFilename, GetFileContents(fileName))

    End Sub



    Public Sub AddFileContentsToIndex(ByVal virtualFilename As String, ByVal contents As String)



        ' Add to the list of files

        Dim FileIndex As Integer = AddFileName(virtualFilename)



        ' Build a vocabulary for the file and add it to the complete list of words

        Dim Vocabulary As New SortedList(Of String, Integer)

        For Each Word As String In GetVocabulary(contents)

            If Not Vocabulary.ContainsKey(Word) Then Vocabulary.Add(Word, 0)

        Next



        ' Copy the complete list of words into the global vocabulary

        For Each Word As String In Vocabulary.Keys

            If Not WordNumbers.ContainsKey(Word) Then AddWordToVocabulary(Word)

        Next



        ' Count each word as it is read in

        Dim DocumentWordCount As Dictionary(Of Integer, Integer) = GetWordCounts(contents)



        ' Store number of times each word occurs in the document (by merging with the global index)

        MergeDocumentWordCount(FileIndex, DocumentWordCount)



    End Sub



    Public Sub RemoveDocumentFromIndex(ByVal virtualFilename As String)



        ' Check the file exists

        If Not FileNumbers.ContainsKey(virtualFilename) Then

            Throw New ApplicationException("The document '" + virtualFilename + "' does not exist in the index.")

        End If



        ' Remove the file from the list of files

        Dim DocumentIndex As Integer = FileNumbers(virtualFilename)

        Files.Remove(DocumentIndex)

        FileNumbers.Remove(virtualFilename)



        ' Process each word in the index

        Dim WordsToRemove As New List(Of Integer)

        For Each Word As KeyValuePair(Of Integer, WordOccurrences) In Index

            Dim WordIndex As Integer = Word.Key

            Dim Occurrences As WordOccurrences = Word.Value



            ' Remove the word from the index

            If Occurrences.Documents.ContainsKey(DocumentIndex) Then



                ' Remove the document from the word

                Dim OccurrencesInDocument As Integer = Occurrences.Documents(DocumentIndex)

                Occurrences.Occurrences -= OccurrencesInDocument

                Occurrences.Documents.Remove(DocumentIndex)



                ' This word no longer exists in any document

                If Occurrences.Documents.Count = 0 Then WordsToRemove.Add(WordIndex)



            End If



        Next



        ' Remove WordOccurrences objects that are no longer needed, as well as unused words in vocabulary

        For Each WordIndex As Integer In WordsToRemove

            Index.Remove(WordIndex)

            WordNumbers.Remove(Words(WordIndex))

            Words.Remove(WordIndex)

        Next



    End Sub



    ''' <summary>

    ''' Loads all of the text in the given file, and return it.

    ''' </summary>

    ''' <param name="filename">The file whose contents to retrieve.</param>

    Private Function GetFileContents(ByVal filename As String) As String



        Dim File As New IO.StreamReader(filename)

        Dim Contents As String = File.ReadToEnd

        File.Close()

        File.Dispose()

        Return Contents



    End Function



    ''' <summary>

    ''' Strips the words of all non-alphanumeric characters.

    ''' </summary>

    ''' <param name="word">The word to 'fix'.</param>

    ''' <returns>The word without any symbol characters.</returns>

    Private Function FixWord(ByVal word As String) As String



        Dim Result As String = ""

        For Each C As Char In word

            Select Case C

                Case "a"c To "z"c, "A"c To "Z"c, "0"c To "9"c : Result += C

            End Select

        Next

        Return Result



    End Function



    ''' <summary>

    ''' Merges the document words count into the global index.

    ''' </summary>

    ''' <param name="documentFilenameIndex">The index of the document whose word counts to merge.</param>

    ''' <param name="documentWordCount">A list of word indices and word counts.</param>

    Private Sub MergeDocumentWordCount(ByVal documentFilenameIndex As Integer, _

                                       ByVal documentWordCount As Dictionary(Of Integer, Integer))



        For Each WordIndex As Integer In documentWordCount.Keys

            Dim WordOccurrences As Integer = documentWordCount(WordIndex)

            If Index.ContainsKey(WordIndex) Then

                With Index(WordIndex)

                    .Occurrences += WordOccurrences

                    .Documents.Add(documentFilenameIndex, WordOccurrences)

                End With

            Else

                Index.Add(WordIndex, New WordOccurrences(WordOccurrences, documentFilenameIndex))

            End If

        Next



    End Sub



    Private Function AddWordToVocabulary(ByVal word As String) As Integer



        ' Determine the next word index to use

        Dim WordIndex As Integer = LastAddedWordIndex

        While Words.ContainsKey(WordIndex)

            WordIndex += 1

        End While

        LastAddedWordIndex = WordIndex



        ' Add the word to the vocabulary

        Words.Add(WordIndex, word)

        WordNumbers.Add(word, WordIndex)



        ' Return the index

        Return WordIndex



    End Function



    Private Function AddFileName(ByVal fileName As String) As Integer



        ' Determine the next file name index to use

        Dim FileNameIndex As Integer = LastAddedFileIndex

        While Files.ContainsKey(FileNameIndex)

            FileNameIndex += 1

        End While

        LastAddedFileIndex = FileNameIndex



        ' Add the word to the vocabulary

        Files.Add(FileNameIndex, fileName)

        FileNumbers.Add(fileName, FileNameIndex)



        ' Return the index

        Return FileNameIndex



    End Function



    Public Shared Function LoadIndex(ByVal fileName As String) As Indexer



        Dim Result As New Indexer



        ' Get list of files

        Using File As New BinaryReader(New FileStream(fileName, FileMode.Open))



            Dim FileCount As Integer = File.ReadInt32

            Result.Files.Clear()

            Result.FileNumbers.Clear()

            For I As Integer = 1 To FileCount

                Dim DocumentIndex As Integer = File.ReadInt32

                Dim DocumentName As String = File.ReadString

                Result.Files.Add(DocumentIndex, DocumentName)

                Result.FileNumbers.Add(DocumentName, DocumentIndex)

            Next



            ' Get global vocabulary

            Dim VocabularyWordCount As Integer = File.ReadInt32

            Result.Words.Clear()

            Result.WordNumbers.Clear()

            For I As Integer = 1 To VocabularyWordCount

                Dim WordIndex As Integer = File.ReadInt32

                Dim Word As String = File.ReadString

                Result.Words.Add(WordIndex, Word)

                Result.WordNumbers.Add(Word, WordIndex)

            Next



            ' Get the main part of the index

            Dim IndexEntriesCount As Integer = File.ReadInt32

            Result.Index.Clear()

            For A As Integer = 1 To IndexEntriesCount

                Dim MainKey As Integer = File.ReadInt32

                Dim Occurrences As Integer = File.ReadInt32

                Dim DocumentCount As Integer = File.ReadInt32

                Dim Documents(DocumentCount - 1) As Integer

                For B As Integer = 0 To DocumentCount - 1

                    Documents(B) = File.ReadInt32

                Next

                Result.Index.Add(MainKey, New WordOccurrences(Occurrences, Documents))

            Next



            ' Close the file

            File.Close()



        End Using



        Return Result



    End Function



    Public Sub Save(ByVal fileName As String)



        ' Write list of files

        Dim File As New BinaryWriter(New FileStream(fileName, FileMode.Create))

        File.Write(Files.Count)

        For Each IndexedFilename As KeyValuePair(Of Integer, String) In Files

            File.Write(IndexedFilename.Key)

            File.Write(IndexedFilename.Value)

        Next



        ' Write global vocabulary

        File.Write(Words.Count)

        For Each Word As KeyValuePair(Of Integer, String) In Words

            File.Write(Word.Key)

            File.Write(Word.Value)

        Next



        ' Write the main part of the index

        File.Write(Index.Count)

        For Each IndexEntry As KeyValuePair(Of Integer, WordOccurrences) In Index

            File.Write(IndexEntry.Key)

            File.Write(IndexEntry.Value.Occurrences)

            File.Write(IndexEntry.Value.Documents.Count)

            For Each DocumentEntry As KeyValuePair(Of Integer, Integer) In IndexEntry.Value.Documents

                File.Write(DocumentEntry.Key)

            Next

        Next



        ' Close the file

        File.Close()



    End Sub



    ''' <summary>

    ''' Returns a string describing the index in full.

    ''' </summary>

    ''' <remarks>

    ''' The index is returned in the following format:

    ''' 

    ''' WORD: TotalOccurrances {DocumentFilename|DocumentOccurrances,...}

    ''' </remarks>

    Overrides Function ToString() As String



        ' Write out every word...

        Dim Result As New Text.StringBuilder

        For Each WordIndex As Integer In Index.Keys

            With Index(WordIndex)

                Result.Append(Words(WordIndex)).Append(": ").Append(.Occurrences).Append(" {")



                ' ...and every occurrance of the word...

                Dim CommaRequired As Boolean = False

                For Each DocumentIndex As Integer In .Documents.Keys

                    Dim DocumentFilename As String = Files(DocumentIndex)

                    Dim DocumentOccurrances As Integer = .Documents(DocumentIndex)

                    If CommaRequired Then Result.Append(",") Else CommaRequired = True

                    Result.Append(DocumentFilename).Append("|").Append(DocumentOccurrances.ToString)

                Next

            End With

            Result.Append("}").Append(Environment.NewLine)

        Next

        Return Result.ToString



    End Function



End Class