Conditional Installation with NSIS - nsis

Question

I need to make an installer that will also act as a repair/uninstall program if the concerned software is already installed.
I managed to make a custom page that check if the program exists and display buttons depending on that (the registry key creation is only for testing purpose and should be included in installation process).
For example, an Install button appears if the program isn't installed.
Here is the code doing this :
Page Custom MyCustomPage
var button
var buttonRepair
var buttonUninstall
var dialog
Function MyCustomPage
ReadRegStr $R0 HKLM ${P_DIR_REGKEY} "Version"
${If} ${Errors}
Goto NotInstalled
${Else}
Goto Installed
${EndIf}
NotInstalled:
nsDialogs::Create 1018
;Pop $dialog
${NSD_CreateButton} 25% 25% 50% 50% "Install"
Pop $button
EnableWindow $button 1 # start out disabled
WriteRegStr HKLM ${P_DIR_REGKEY} "Version" ${P_VERSION}
WriteRegStr HKLM ${P_DIR_REGKEY} "" "$INSTDIR\asd.exe"
nsDialogs::Show
${NSD_OnClick} $button ManageInstall
Goto MyEnd
Installed:
nsDialogs::Create 1018
Pop $0
${NSD_CreateButton} 12% 12% 25% 25% "Repair"
Pop $buttonRepair
${NSD_CreateButton} 37% 12% 25% 25% "Uninstall"
Pop $buttonUninstall
EnableWindow $button 1 # start out disabled
EnableWindow $button2 1
${NSD_OnClick} $buttonRepair ManageRepair
${NSD_OnClick} $buttonUninstall ManageUninstall
nsDialogs::Show
Goto MyEnd
MyEnd:
Quit
FunctionEnd
Function ManageInstall
MessageBox MB_OK "Installation"
FunctionEnd
Function ManageRepair
MessageBox MB_OK "Repair"
FunctionEnd
Function ManageUninstall
MessageBox MB_OK "Uninstallation"
FunctionEnd
The problem is that it's all managed by functions, and I can't declare new pages macros in them, so I can't continue with the proper installation through sections because of it.
How should I manage the different actions to be taken by the installer to be able to make user friendly pages like a normal install ?
Should I use custom pages for every single action, because it sounds a bit fastidious and complicated ?

Answer 1

I recommend you create a variable named "ACTION", and set its value when the user clicks an option. And then, jump to the next page. Something like this:
# http://nsis.sourceforge.net/Go_to_a_NSIS_page
Function RelGotoPage
IntCmp $R9 0 0 Move Move
StrCmp $R9 "X" 0 Move
StrCpy $R9 "120"
Move:
SendMessage $HWNDPARENT "0x408" "$R9" ""
FunctionEnd
Function GotoNextPage
StrCpy $R9 "1"
Call RelGotoPage
FunctionEnd
Function ManageRepair
StrCpy $ACTION "repair"
Call GotoNextPage
Abort
FunctionEnd
Then, on each page's "pre" function, you need to check it it has to be displayed or not:
Function repairpage
# Do not display this page unless user selected Repair.
${if} "$ACTION" != "repair"
Abort
$[EndIf}
....
FunctionEnd