# PythonVenv.cmake — project-wide Python venv shared by every component that
# ships Python tooling (currently MsgUtils; LogReader will join later).
#
# Why a venv at all: PEP 668 distros (Debian/Ubuntu with Python 3.11+, etc.)
# forbid `pip install` into the system or user site-packages. The venv lets
# editable installs work without `--break-system-packages` and without
# polluting the developer's machine.
#
# Why project-level (and not per-component): more than one component needs a
# Python interpreter to install into; pointing each at the same venv keeps
# every installed package mutually importable, avoids duplicate venv setup
# code in every CMakeLists.txt, and makes "where do my Python deps live"
# answerable in one place.
#
# Usage:
#   include(cmake/PythonVenv.cmake)            # creates ${PROJECT_PYTHON}
#   register_python_package(<absolute_dir>)    # pip install -e the given pyproject
#
# Re-installs only when the package's pyproject.toml changes — keyed via a
# build-tree stamp file, so reconfigures stay fast.

if(DEFINED PROJECT_PYTHON_INCLUDED)
    return()
endif()
set(PROJECT_PYTHON_INCLUDED TRUE)

find_package(Python3 REQUIRED COMPONENTS Interpreter)

set(PROJECT_VENV_DIR ${CMAKE_BINARY_DIR}/.venv CACHE INTERNAL "Project Python venv root")
set(PROJECT_PYTHON   ${PROJECT_VENV_DIR}/bin/python CACHE INTERNAL "Project venv python interpreter")

# Probe pip inside the venv. A half-created venv (missing python3-venv on the
# host) can have python but no pip — we want to catch that and report it
# clearly rather than failing on the first `pip install`.
execute_process(
    COMMAND ${PROJECT_PYTHON} -m pip --version
    RESULT_VARIABLE _venv_pip_ok
    OUTPUT_QUIET
    ERROR_QUIET
)
if(NOT _venv_pip_ok EQUAL 0)
    message(STATUS "Creating project Python venv at ${PROJECT_VENV_DIR}")
    file(REMOVE_RECURSE ${PROJECT_VENV_DIR})
    execute_process(
        COMMAND ${Python3_EXECUTABLE} -m venv ${PROJECT_VENV_DIR}
        RESULT_VARIABLE _venv_result
        OUTPUT_VARIABLE _venv_output
        ERROR_VARIABLE _venv_output
    )
    if(NOT _venv_result EQUAL 0 OR NOT EXISTS ${PROJECT_PYTHON})
        message(FATAL_ERROR
            "Failed to create venv at ${PROJECT_VENV_DIR}.\n"
            "Install the venv module (e.g. 'sudo apt install python3-venv' or 'python3-full' on Debian/Ubuntu, "
            "matching your Python version).\n"
            "Output:\n${_venv_output}")
    endif()
    execute_process(
        COMMAND ${PROJECT_PYTHON} -m pip --version
        RESULT_VARIABLE _venv_pip_ok
        OUTPUT_QUIET
        ERROR_QUIET
    )
    if(NOT _venv_pip_ok EQUAL 0)
        message(FATAL_ERROR
            "Venv at ${PROJECT_VENV_DIR} was created but pip is not available inside it. "
            "Install the matching python3-venv package and reconfigure.")
    endif()
endif()

# Editable installs via pyproject.toml require pip >= 21.3. Upgrade once per
# configure; cheap when already up-to-date.
execute_process(
    COMMAND ${PROJECT_PYTHON} -m pip install --upgrade pip --quiet
    RESULT_VARIABLE _pip_upgrade_result
)
if(NOT _pip_upgrade_result EQUAL 0)
    message(FATAL_ERROR "Failed to upgrade pip in project venv (pip returned ${_pip_upgrade_result})")
endif()

# register_python_package(<absolute_dir>)
#
# Installs the pyproject at <absolute_dir> editable into the project venv.
# Re-runs only when <absolute_dir>/pyproject.toml's mtime moves past a stamp
# file in the build tree, so reconfiguring on an unchanged tree is a no-op.
# Stamps are namespaced by the leaf directory name so two pyprojects in
# different directories don't clobber each other.
function(register_python_package _pkg_dir)
    if(NOT IS_ABSOLUTE "${_pkg_dir}")
        message(FATAL_ERROR "register_python_package: path must be absolute: ${_pkg_dir}")
    endif()
    set(_pyproject "${_pkg_dir}/pyproject.toml")
    if(NOT EXISTS "${_pyproject}")
        message(FATAL_ERROR "register_python_package: no pyproject.toml at ${_pkg_dir}")
    endif()

    get_filename_component(_leaf "${_pkg_dir}" NAME)
    set(_stamp "${CMAKE_BINARY_DIR}/python-venv-stamps/${_leaf}.installed")

    # Compare stamp mtime to the pyproject's. IS_NEWER_THAN treats a missing
    # stamp as "older", so first configure always installs.
    if("${_pyproject}" IS_NEWER_THAN "${_stamp}")
        message(STATUS "Installing Python package ${_leaf} into project venv")
        execute_process(
            COMMAND ${PROJECT_PYTHON} -m pip install -e ${_pkg_dir} --quiet
            RESULT_VARIABLE _pip_result
        )
        if(NOT _pip_result EQUAL 0)
            message(FATAL_ERROR "Failed to install ${_leaf} into project venv (pip returned ${_pip_result})")
        endif()
        file(MAKE_DIRECTORY "${CMAKE_BINARY_DIR}/python-venv-stamps")
        file(TOUCH "${_stamp}")
    endif()
endfunction()