@echo off
setlocal enableDelayedExpansion

REM Setup initial vars
set "script_name="
set "thisDir=%~dp0"
set /a tried=0
set "toask=yes"
set "pause_on_error=yes"
set "py2v="
set "py2path="
set "py3v="
set "py3path="
set "pypath="

REM use_py3:
REM   TRUE  = Use if found, use py2 otherwise
REM   FALSE = Use py2
REM   FORCE = Use py3
set "use_py3=TRUE"

REM Get the system32 (or equivalent) path
call :setcomspec
set "syspath=%ComSpec:cmd.exe=%"

goto checkscript

:checkscript
REM Check for our script first
set "looking_for=!script_name!"
if "!script_name!" == "" (
    set "looking_for=%~n0.py or %~n0.command"
    set "script_name=%~n0.py"
    if not exist "!thisDir!\!script_name!" (
        set "script_name=%~n0.command"
    )
)
if not exist "!thisDir!\!script_name!" (
    echo Could not find !looking_for!.
    echo Please make sure to run this script from the same directory
    echo as !looking_for!.
    echo.
    echo Press [enter] to quit.
    pause > nul
    exit /b
)
goto checkpy

:setcomspec
REM Helper method to return the "proper" path to cmd.exe, reg.exe, and where.exe by walking the ComSpec var
REM Prep the LF variable to use the "line feed" approach - requires 2 newlines after it to function
set LF=^


REM Strip double semi-colons
call :undouble "ComSpec" ";"
set "testpath=%ComSpec:;=!LF!%"
REM Let's walk each path and test if cmd.exe, reg.exe, and where.exe exist there
set /a found=0
for /f %%i in ("!testpath!") do (
    REM Only continue if we haven't found it yet
    if NOT "%%i" == "" (
        if !found! lss 1 (
            set "temppath=%%i"
            REM Remove "cmd.exe" from the end if it exists
            if /i "!temppath:~-7!" == "cmd.exe" (
                set "temppath=!temppath:~0,-7!"
            )
            REM Pad the end with a backslash if needed
            if NOT "!temppath:~-1!" == "\" (
                set "temppath=!temppath!\"
            )
            REM Let's see if cmd, reg, and where exist there - and set it if so
            if EXIST "!temppath!cmd.exe" (
                if EXIST "!temppath!reg.exe" (
                    if EXIST "!temppath!where.exe" (
                        set /a found=1
                        set "ComSpec=!temppath!cmd.exe"
                    )
                )
            )
        )
    )
)
goto :EOF

:updatepath
set "spath="
set "upath="
for /f "USEBACKQ tokens=2* delims= " %%i in (`!syspath!reg.exe query "HKCU\Environment" /v "Path" 2^> nul`) do ( if not "%%j" == "" set "upath=%%j" )
for /f "USEBACKQ tokens=2* delims= " %%i in (`!syspath!reg.exe query "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" /v "Path" 2^> nul`) do ( if not "%%j" == "" set "spath=%%j" )
if not "%spath%" == "" (
    REM We got something in the system path
    set "PATH=%spath%"
    if not "!upath!" == "" (
        REM We also have something in the user path
        set "PATH=%PATH%;%upath%"
    )
) else if not "%upath%" == "" (
    set "PATH=%upath%"
)
REM Remove double semicolons from the adjusted PATH
call :undouble "PATH" ";"
goto :EOF

:undouble <string_name> <character>
REM Helper function to strip doubles of a single character out of a string recursively
set "string_name=%~1"
set "character=%~2"
set "check=!%string_name%:%character%%character%=%character%!"
if not "!check!" == "!%~1!" (
    set "!string_name!=!check!"
    call :undouble "%~1" "%~2"
)
goto :EOF

:checkpy
call :updatepath
for /f "USEBACKQ tokens=*" %%x in (`!syspath!where.exe python 2^> nul`) do ( call :checkpyversion "%%x" "py2v" "py2path" "py3v" "py3path" )
for /f "USEBACKQ tokens=*" %%x in (`!syspath!where.exe python3 2^> nul`) do ( call :checkpyversion "%%x" "py2v" "py2path" "py3v" "py3path" )
for /f "USEBACKQ tokens=*" %%x in (`!syspath!where.exe py 2^> nul`) do ( call :checkpyversion "%%x" "py2v" "py2path" "py3v" "py3path" )
set "targetpy=3"
if /i "!use_py3!" == "FALSE" (
    set "targetpy=2"
    set "pypath=!py2path!"
) else if /i "!use_py3!" == "FORCE" (
    set "pypath=!py3path!"
) else if /i "!use_py3!" == "TRUE" (
    set "pypath=!py3path!"
    if "!pypath!" == "" set "pypath=!py2path!"
)
if not "!pypath!" == "" (
    goto runscript
)

if "!pypath!" == "" (
    if %tried% lss 1 (
        if /i "!toask!"=="yes" (
            REM Better ask permission first
            goto askinstall
        ) else (
            goto installpy
        )
    ) else (
        cls
        echo   ###     ###
        echo  # Warning #
        echo ###     ###
        echo.
        REM Couldn't install for whatever reason - give the error message
        echo Python is not installed or not found in your PATH var.
        echo Please install it from https://www.python.org/downloads/windows/
        echo.
        echo Make sure you check the box labeled:
        echo.
        echo "Add Python X.X to PATH"
        echo.
        echo Where X.X is the py version you're installing.
        echo.
        echo Press [enter] to quit.
        pause > nul
        exit /b
    )
)
goto runscript

:checkpyversion <path> <py2v> <py2path> <py3v> <py3path>
set "version="&for /f "tokens=2* USEBACKQ delims= " %%a in (`"%~1" -V 2^>^&1`) do (
    REM Ensure we have a version number
    call :isnumber "%%a"
    if not "!errorlevel!" == "0" goto :EOF
    set "version=%%a"
)
if not defined version goto :EOF
if "!version:~0,1!" == "2" (
    REM Python 2
    call :comparepyversion "!version!" "!%~2!"
    if "!errorlevel!" == "1" (
        set "%~2=!version!"
        set "%~3=%~1"
    )
) else (
    REM Python 3
    call :comparepyversion "!version!" "!%~4!"
    if "!errorlevel!" == "1" (
        set "%~4=!version!"
        set "%~5=%~1"
    )
)
goto :EOF

:isnumber <check>
set "var="&for /f "delims=0123456789." %%i in ("%~1") do set var=%%i
if defined var (exit /b 1)
exit /b 0

:comparepyversion <version1> <version2> <return>
REM Exits with status 0 if equal, 1 if v1 gtr v2, 2 if v1 lss v2
for /f "tokens=1,2,3 delims=." %%a in ("%~1") do (
    set a1=%%a
    set a2=%%b
    set a3=%%c
)
for /f "tokens=1,2,3 delims=." %%a in ("%~2") do (
    set b1=%%a
    set b2=%%b
    set b3=%%c
)
if not defined a1 set a1=0
if not defined a2 set a2=0
if not defined a3 set a3=0
if not defined b1 set b1=0
if not defined b2 set b2=0
if not defined b3 set b3=0
if %a1% gtr %b1% exit /b 1
if %a1% lss %b1% exit /b 2
if %a2% gtr %b2% exit /b 1
if %a2% lss %b2% exit /b 2
if %a3% gtr %b3% exit /b 1
if %a3% lss %b3% exit /b 2
exit /b 0

:askinstall
cls
echo   ###              ###
echo  # Python Not Found #
echo ###              ###
echo.
echo Python !targetpy! was not found on the system or in the PATH var.
echo.
set /p "menu=Would you like to install it now? [y/n]: "
if /i "!menu!"=="y" (
    REM We got the OK - install it
    goto installpy
) else if "!menu!"=="n" (
    REM No OK here...
    set /a tried=%tried%+1
    goto checkpy
)
REM Incorrect answer - go back
goto askinstall

:installpy
REM This will attempt to download and install python
REM First we get the html for the python downloads page for Windows
set /a tried=%tried%+1
cls
echo   ###               ###
echo  # Installing Python #
echo ###               ###
echo.
echo Gathering info from https://www.python.org/downloads/windows/...
powershell -command "[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; (new-object System.Net.WebClient).DownloadFile('https://www.python.org/downloads/windows/','%TEMP%\pyurl.txt')"
if not exist "%TEMP%\pyurl.txt" (
    goto checkpy
)

echo Parsing for latest...
pushd "%TEMP%"
:: Version detection code slimmed by LussacZheng (https://github.com/corpnewt/gibMacOS/issues/20)
for /f "tokens=9 delims=< " %%x in ('findstr /i /c:"Latest Python !targetpy! Release" pyurl.txt') do ( set "release=%%x" )
popd

echo Found Python !release! -  Downloading...
REM Let's delete our txt file now - we no longer need it
del "%TEMP%\pyurl.txt"

REM At this point - we should have the version number.
REM We can build the url like so: "https://www.python.org/ftp/python/[version]/python-[version]-amd64.exe"
set "url=https://www.python.org/ftp/python/!release!/python-!release!-amd64.exe"
set "pytype=exe"
if "!targetpy!" == "2" (
    set "url=https://www.python.org/ftp/python/!release!/python-!release!.amd64.msi"
    set "pytype=msi"
)
REM Now we download it with our slick powershell command
powershell -command "[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; (new-object System.Net.WebClient).DownloadFile('!url!','%TEMP%\pyinstall.!pytype!')"
REM If it doesn't exist - we bail
if not exist "%TEMP%\pyinstall.!pytype!" (
    goto checkpy
)
REM It should exist at this point - let's run it to install silently
echo Installing...
pushd "%TEMP%"
if /i "!pytype!" == "exe" (
    echo pyinstall.exe /quiet PrependPath=1 Include_test=0 Shortcuts=0 Include_launcher=0
    pyinstall.exe /quiet PrependPath=1 Include_test=0 Shortcuts=0 Include_launcher=0
) else (
    set "foldername=!release:.=!"
    echo msiexec /i pyinstall.msi /qb ADDLOCAL=ALL TARGETDIR="%LocalAppData%\Programs\Python\Python!foldername:~0,2!"
    msiexec /i pyinstall.msi /qb ADDLOCAL=ALL TARGETDIR="%LocalAppData%\Programs\Python\Python!foldername:~0,2!"
)
popd
echo Installer finished with %ERRORLEVEL% status.
REM Now we should be able to delete the installer and check for py again
del "%TEMP%\pyinstall.!pytype!"
REM If it worked, then we should have python in our PATH
REM this does not get updated right away though - let's try
REM manually updating the local PATH var
call :updatepath
goto checkpy
exit /b

:runscript
REM Python found
cls
set "args=%*"
set "args=!args:"=!"
if "!args!"=="" (
    "!pypath!" "!thisDir!!script_name!"
) else (
    "!pypath!" "!thisDir!!script_name!" %*
)
if /i "!pause_on_error!" == "yes" (
    if not "%ERRORLEVEL%" == "0" (
        echo.
        echo Script exited with error code: %ERRORLEVEL%
        echo.
        echo Press [enter] to exit...
        pause > nul
    )
)
goto :EOF