Add bibliography link to citation in Zotero.

ZoteroLinkCitation.vb

Public Sub ZoteroLinkCitation()

    ' get selected area (if applicable)
    Dim nStart&, nEnd&
    nStart = Selection.Start
    nEnd = Selection.End

    ' toggle screen updating
    Application.ScreenUpdating = False

    ' define variables
    Dim title As String
    Dim titleAnchor As String
    Dim style As String
    Dim fieldCode As String
    Dim numOrYear As String
    Dim pos&, n1&, n2&, n3&

    ActiveWindow.View.ShowFieldCodes = True
    Selection.Find.ClearFormatting

    ' find the Zotero bibliography
    With Selection.Find
        .Text = "^d ADDIN ZOTERO_BIBL"
        .Replacement.Text = ""
        .Forward = True
        .Wrap = wdFindContinue
        .Format = False
        .MatchCase = False
        .MatchWholeWord = False
        .MatchWildcards = False
        .MatchSoundsLike = False
        .MatchAllWordForms = False
    End With
    Selection.Find.Execute

    ' add bookmark for the Zotero bibliography
    With ActiveDocument.Bookmarks
        .Add Range:=Selection.Range, Name:="Zotero_Bibliography"
        .DefaultSorting = wdSortByName
        .ShowHidden = True
    End With

    ' loop through each field in the document
    For Each aField In ActiveDocument.Fields
        ' check if the field is a Zotero in-text reference
        '##################################################
        If InStr(aField.Code, "ADDIN ZOTERO_ITEM") > 0 Then
            fieldCode = aField.Code
            '#############
            ' Prepare
            ' Plain citation== Format of Textfield shown
            ' must be in Brackets
            Dim plain_Cit As String
            plCitStrBeg = """plainCitation"":""["
            plCitStrEnd = "]"""
            n1 = InStr(fieldCode, plCitStrBeg)
            n1 = n1 + Len(plCitStrBeg)
            n2 = InStr(Mid(fieldCode, n1, Len(fieldCode) - n1), plCitStrEnd) - 1 + n1
            plain_Cit = Mid$(fieldCode, n1 - 1, n2 - n1 + 2)
            'Reference 'as shown' in word as a string

            'Title array in fieldCode (all referenced Titles within this field)
            Dim array_RefTitle(32) As String
            i = 0
            Do While InStr(fieldCode, """title"":""") > 0
                n1 = InStr(fieldCode, """title"":""") + Len("""title"":""")
                n2 = InStr(Mid(fieldCode, n1, Len(fieldCode) - n1), """,""") - 1 + n1
                If n2 < n1 Then 'Exception the type 'Article'
                    n2 = InStr(Mid(fieldCode, n1, Len(fieldCode) - n1), "}") - 1 + n1 - 1
                End If
                array_RefTitle(i) = Mid(fieldCode, n1, n2 - n1)
                fieldCode = Mid(fieldCode, n2 + 1, Len(fieldCode) - n2 - 1)
                i = i + 1
            Loop
            Titles_in_Cit = i

            'Number array with References shown in PlainCit
            'Numer is equal or less than Titels, depending on the type
            '[3], [8]-[10]; [2]-[4]; [2], [4], [5]
            ' All citations have to be in Brackets each! [3], [8] not [3, 8]
            ' This doesnt work otherwise!
            ' --> treatment of other delimiters could be implemented here
            Dim RefNumber(32) As String
            i = 0
            Do While (InStr(plain_Cit, "]") Or InStr(plain_Cit, "[")) > 0
                n1 = InStr(plain_Cit, "[")
                n2 = InStr(plain_Cit, "]")
                RefNumber(i) = Mid(plain_Cit, n1 + 1, n2 - (n1 + 1))
                plain_Cit = Mid(plain_Cit, n2 + 1, Len(plain_Cit) - (n2 + 1) + 1)
                i = i + 1
            Loop
            Refs_in_Cit = i
            'treat only the shown references (skip the rest)
            '[3], [8]-[10] --> skip [9]
            'Order of titles given from fieldcode, not checked!
            If Titles_in_Cit > Refs_in_Cit Then
                array_RefTitle(Refs_in_Cit - 1) = array_RefTitle(Titles_in_Cit - 1)
                i = 1
                Do While Refs_in_Cit + i <= Titles_in_Cit
                    array_RefTitle(Refs_in_Cit + i - 1) = ""
                    i = i + 1
                Loop
            End If

            '#############
            'Make the links
            For Refs = 0 To Refs_in_Cit - 1 Step 1
                title = array_RefTitle(Refs)
                array_RefTitle(Refs) = ""
                ' make title a valid bookmark name
                titleAnchor = title
                titleAnchor = MakeValidBMName(titleAnchor)

                ActiveWindow.View.ShowFieldCodes = False
                Selection.GoTo What:=wdGoToBookmark, Name:="Zotero_Bibliography"

                '' locate the corresponding reference in the bibliography
                '' by searching for its title
                Selection.Find.ClearFormatting
                With Selection.Find
                    .Text = Left(title, 255)
                    .Replacement.Text = ""
                    .Forward = True
                    .Wrap = wdFindContinue
                    .Format = False
                    .MatchCase = False
                    .MatchWholeWord = False
                    .MatchWildcards = False
                    .MatchSoundsLike = False
                    .MatchAllWordForms = False
                End With
                Selection.Find.Execute

                ' select the whole caption (for mouseover tooltip)
                Selection.MoveStartUntil ("["), Count:=wdBackward
                Selection.MoveEndUntil (vbBack)
                lnkcap = "[" & Selection.Text
                lnkcap = Left(lnkcap, 70)

                ' add bookmark for the reference within the bibliography
                Selection.Shrink
                With ActiveDocument.Bookmarks
                    .Add Range:=Selection.Range, Name:=titleAnchor
                    .DefaultSorting = wdSortByName
                    .ShowHidden = True
                End With

                ' jump back to the field
                aField.Select
                ' find and select the numeric part of the field which will become the hyperlink
                Selection.Find.ClearFormatting
                With Selection.Find
                    .Text = RefNumber(Refs)
                    .Replacement.Text = ""
                    .Forward = True
                    .Wrap = wdFindContinue
                    .Format = False
                    .MatchCase = False
                    .MatchWholeWord = False
                    .MatchWildcards = False
                    .MatchSoundsLike = False
                    .MatchAllWordForms = False
                End With
                Selection.Find.Execute

                numOrYear = Selection.Range.Text & ""

                ' store current style
                style = Selection.style
                ' Generate the Hyperlink -->Forward!
                ActiveDocument.Hyperlinks.Add Anchor:=Selection.Range, Address:="", SubAddress:=titleAnchor, ScreenTip:=lnkcap, TextToDisplay:="" & numOrYear
                ' reset the style
                Selection.style = style

                ' comment if you want standard link style
                aField.Select
                With Selection.Font
                    .Underline = wdUnderlineNone
                    .ColorIndex = wdBlack
                End With

            Next Refs 'References in Cit

        End If  'If Zotero-Field
        '#########################

    Next aField ' next field

    ' go back to original range selected
    ActiveWindow.View.ShowFieldCodes = False
    ActiveDocument.Range(nStart, nEnd).Select

End Sub
Function MakeValidBMName(strIn As String)
    Dim pFirstChr As String
    Dim i As Long
    Dim tempStr As String
    strIn = Trim(strIn)
    pFirstChr = Left(strIn, 1)
    If Not pFirstChr Like "[A-Za-z]" Then
        strIn = "A_" & strIn
    End If
    For i = 1 To Len(strIn)
        Select Case Asc(Mid$(strIn, i, 1))
         Case 49 To 57, 65 To 90, 97 To 122
            tempStr = tempStr & Mid$(strIn, i, 1)
         Case Else
            tempStr = tempStr & "_"
        End Select
    Next i
    tempStr = Replace(tempStr, "  ", " ")
    MakeValidBMName = Left(tempStr, 40)
End Function

Code is from Zotero forums.