; EnvVarUpdate.nsh
; Adds/removes a value from a Windows environment variable (PATH-style, semicolon-delimited)
; Usage:
;   ${EnvVarUpdate} $0 "PATH" "A" "HKLM" "$INSTDIR"   ; append
;   ${UnEnvVarUpdate} $0 "PATH" "HKLM" "$INSTDIR"      ; remove

!ifndef ENVVARUPDATE_NSH
!define ENVVARUPDATE_NSH

!include "LogicLib.nsh"
!include "WinMessages.nsh"

; --------------------------------------------------------------------------
; Macro: _EnvVarUpdate
; Action: "A" = Append, "P" = Prepend, "R" = Remove
; --------------------------------------------------------------------------
!macro _EnvVarUpdate OUTVAR EnvVarName Action RegLoc PathString

  Push $0
  Push $1
  Push $2
  Push $3
  Push $4
  Push $5

  ; Read current value
  ReadRegStr $1 ${RegLoc} \
    "SYSTEM\CurrentControlSet\Control\Session Manager\Environment" \
    "${EnvVarName}"

  ; Strip trailing semicolon
  StrCpy $5 $1 1 -1
  ${If} $5 == ";"
    StrCpy $1 $1 -1
  ${EndIf}

  ; Check if PathString already exists
  Push "${PathString}"
  Push $1
  Call _EnvVarUpdateStrStr
  Pop $2   ; $2 = position, or "" if not found

  ${If} "${Action}" == "A"
    ${If} $2 == ""
      ${If} $1 == ""
        StrCpy $3 "${PathString}"
      ${Else}
        StrCpy $3 "$1;${PathString}"
      ${EndIf}
      WriteRegExpandStr ${RegLoc} \
        "SYSTEM\CurrentControlSet\Control\Session Manager\Environment" \
        "${EnvVarName}" "$3"
    ${EndIf}
  ${ElseIf} "${Action}" == "P"
    ${If} $2 == ""
      ${If} $1 == ""
        StrCpy $3 "${PathString}"
      ${Else}
        StrCpy $3 "${PathString};$1"
      ${EndIf}
      WriteRegExpandStr ${RegLoc} \
        "SYSTEM\CurrentControlSet\Control\Session Manager\Environment" \
        "${EnvVarName}" "$3"
    ${EndIf}
  ${ElseIf} "${Action}" == "R"
    ${If} $2 != ""
      ; Remove entry
      StrLen $4 "${PathString}"
      StrCpy $0 $1 $2           ; everything before the match
      IntOp $4 $2 + $4          ; position after the match
      StrCpy $5 $1 "" $4        ; everything after the match
      ; Strip leading/trailing semicolons from join point
      StrCpy $4 $5 1
      ${If} $4 == ";"
        StrCpy $5 $5 "" 1
      ${EndIf}
      StrCpy $4 $0 1 -1
      ${If} $4 == ";"
        StrCpy $0 $0 -1
      ${EndIf}
      ${If} $0 == ""
        StrCpy $3 $5
      ${ElseIf} $5 == ""
        StrCpy $3 $0
      ${Else}
        StrCpy $3 "$0;$5"
      ${EndIf}
      WriteRegExpandStr ${RegLoc} \
        "SYSTEM\CurrentControlSet\Control\Session Manager\Environment" \
        "${EnvVarName}" "$3"
    ${EndIf}
  ${EndIf}

  ; Broadcast change to all windows
  SendMessage ${HWND_BROADCAST} ${WM_SETTINGCHANGE} 0 "STR:Environment" /TIMEOUT=5000

  Pop $5
  Pop $4
  Pop $3
  Pop $2
  Pop $1
  Pop $0

!macroend

; Helper: find substring position (returns "" if not found)
Function _EnvVarUpdateStrStr
  Exch $R0   ; haystack
  Exch
  Exch $R1   ; needle
  Push $R2
  Push $R3
  Push $R4
  Push $R5
  StrLen $R3 $R1
  StrLen $R4 $R0
  IntOp $R4 $R4 - $R3
  StrCpy $R2 0
loop:
  IntCmp $R2 $R4 done done
  StrCpy $R5 $R0 $R3 $R2
  StrCmp $R5 $R1 found
  IntOp $R2 $R2 + 1
  Goto loop
found:
  StrCpy $R0 $R2
  Goto end
done:
  StrCpy $R0 ""
end:
  Pop $R5
  Pop $R4
  Pop $R3
  Pop $R2
  Pop $R1
  Exch $R0
FunctionEnd

!define EnvVarUpdate  `!insertmacro _EnvVarUpdate`
!define UnEnvVarUpdate `!insertmacro _EnvVarUpdate "" "${__LINE__}" "R"`

!endif ; ENVVARUPDATE_NSH