Option Explicit

Private Type NMHDR
    hWndFrom As Long
    idFrom As Long
    code As Long
End Type

Private Type CHARRANGE
    cpMin As Long
    cpMax As Long
End Type

Private Type ENLINK
    hdr As NMHDR
    msg As Long
    wParam As Long
    lParam As Long
    chrg As CHARRANGE
End Type

Private Type TEXTRANGE
    chrg As CHARRANGE
    lpstrText As String
End Type

'Used to change the window procedure which kick-starts the subclassing
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" ( _
ByVal hwnd As Long, _
ByVal nIndex As Long, _
ByVal dwNewLong As Long) As Long

'Used to call the default window procedure for the parent
Private Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" ( _
ByVal lpPrevWndFunc As Long, _
ByVal hwnd As Long, _
ByVal msg As Long, _
ByVal wParam As Long, _
ByVal lParam As Long) As Long

'Used to set and retrieve various information
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" ( _
ByVal hwnd As Long, _
ByVal wMsg As Long, _
ByVal wParam As Long, _
lParam As Any) As Long

'Used to copy... memory... from pointers
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" ( _
Destination As Any, _
Source As Any, _
ByVal Length As Long)

'Used to launch the URL in the user's default browser
Private Declare Function ShellExecute Lib "shell32" Alias "ShellExecuteA" ( _
ByVal hwnd As Long, _
ByVal lpOperation As String, _
ByVal lpFile As String, _
ByVal lpParameters As String, _
ByVal lpDirectory As String, _
ByVal nShowCmd As Long) As Long

Const WM_NOTIFY = &H4E
Const EM_SETEVENTMASK = &H445
Const EM_GETEVENTMASK = &H43B
Const EM_GETTEXTRANGE = &H44B
Const EM_AUTOURLDETECT = &H45B
Const EN_LINK = &H70B

Const WM_LBUTTONDBLCLK = &H203
Const WM_LBUTTONDOWN = &H201
Const WM_LBUTTONUP = &H202
Const WM_MOUSEMOVE = &H200
Const WM_RBUTTONDBLCLK = &H206
Const WM_RBUTTONDOWN = &H204
Const WM_RBUTTONUP = &H205
Const WM_SETCURSOR = &H20

Const CFE_LINK = &H20
Const ENM_LINK = &H4000000
Const GWL_WNDPROC = (-4)
Const SW_SHOW = 5

Dim lOldProc As Long 'Old windowproc
Dim hWndRTB As Long 'hWnd of RTB
Dim hWndParent As Long 'hWnd of parent window


Public Sub DisableURLDetect()

'Don't want to unsubclass a non-subclassed window

    If lOldProc Then
        'Stop URL detection
        SendMessage hWndRTB, EM_AUTOURLDETECT, 0, ByVal 0
        'Reset the window procedure (stop the subclassing)
        SetWindowLong hWndParent, GWL_WNDPROC, lOldProc
        'Set this to 0 so we can subclass again in future
        lOldProc = 0
    End If

End Sub

Public Sub EnableURLDetect(ByVal hWndTextbox As Long, _
                           ByVal hWndOwner As Long)

'Don't want to subclass twice!

    If lOldProc = 0 Then
        'Subclass!
        lOldProc = SetWindowLong(hWndOwner, GWL_WNDPROC, AddressOf WndProc)
        'Tell the RTB to inform us when stuff happens to URLs
        SendMessage hWndTextbox, EM_SETEVENTMASK, 0, ByVal ENM_LINK Or SendMessage(hWndTextbox, EM_GETEVENTMASK, 0, 0)
        'Tell the RTB to start automatically detecting URLs
        SendMessage hWndTextbox, EM_AUTOURLDETECT, 1, ByVal 0
        hWndParent = hWndOwner
        hWndRTB = hWndTextbox
    End If

End Sub

Public Function IsDebug() As Boolean

    On Error GoTo ErrorHandler
    Debug.Print 1 / 0
    IsDebug = False

Exit Function

ErrorHandler:
    IsDebug = True

End Function

Public Function WndProc(ByVal hwnd As Long, _
                        ByVal uMsg As Long, _
                        ByVal wParam As Long, _
                        ByVal lParam As Long) As Long

Dim uHead As NMHDR
Dim eLink As ENLINK
Dim eText As TEXTRANGE
Dim sText As String
Dim lLen  As Long

    'Which message?
    Select Case uMsg
    Case WM_NOTIFY
        'Ooo! A notify message! Something exciting must be happening...
        'Copy the notification header into our structure from the pointer
        CopyMemory uHead, ByVal lParam, Len(uHead)
        'Peek inside the structure
        If uHead.hWndFrom = hWndRTB Then
            If uHead.code = EN_LINK Then
                'Yay! Some kind of kinky linky message.
                'Now that we know its a link message, we can copy the whole ENLINK structure
                'into our structure
                CopyMemory eLink, ByVal lParam, Len(eLink)
                'What kind of message?
                Select Case eLink.msg
                Case WM_LBUTTONUP
                    'Clicked the link!
                    'Set up out TEXTRANGE struct
                    With eText
                        .chrg.cpMin = eLink.chrg.cpMin
                        .chrg.cpMax = eLink.chrg.cpMax
                        .lpstrText = Space$(1024)
                        'Tell the RTB to fill out our TEXTRANGE with the text
                    End With 'eText
                    lLen = SendMessage(hWndRTB, EM_GETTEXTRANGE, 0, eText)
                    'Trim the text
                    sText = Left$(eText.lpstrText, lLen)
                    'Launch the browser
                    ShellExecute hWndParent, vbNullString, sText, vbNullString, vbNullString, SW_SHOW
                    'Other miscellaneous messages
                Case WM_LBUTTONDOWN
                Case WM_LBUTTONDBLCLK
                Case WM_RBUTTONDBLCLK
                Case WM_RBUTTONDOWN
                Case WM_RBUTTONUP
                Case WM_SETCURSOR
                End Select
            End If
        End If
    End Select
    sText = vbNullChar
    'Call the stored window procedure to let it handle all the messages
    WndProc = CallWindowProc(lOldProc, hwnd, uMsg, wParam, lParam)

End Function

If IsDebug = False Then
    EnableURLDetect txtChat.hWnd, Me.hWnd
End If

If IsDebug = False Then
    DisableURLDetect
End If

Public Function IsDebug() As Boolean

    On Error GoTo ErrorHandler
    Debug.Print 1 / 0
    IsDebug = False

Exit Function

ErrorHandler:
    IsDebug = True

End Function

EnableURLDetect txtChat.hWnd, Me.hWnd

DisableURLDetect