#!/usr/bin/env python3

import argparse
import contextlib
import functools
import os
try:
    from os import process_cpu_count as cpu_count
except ImportError:
    from os import cpu_count
import pathlib
import shutil
import subprocess
import sys
import sysconfig
import tempfile


CHECKOUT = pathlib.Path(__file__).parent.parent.parent

CROSS_BUILD_DIR = CHECKOUT / "cross-build"
BUILD_DIR = CROSS_BUILD_DIR / "build"
HOST_TRIPLE = "wasm32-wasi"
HOST_DIR = CROSS_BUILD_DIR / HOST_TRIPLE

LOCAL_SETUP = CHECKOUT / "Modules" / "Setup.local"
LOCAL_SETUP_MARKER = "# Generated by Tools/wasm/wasi.py\n".encode("utf-8")


def updated_env(updates={}):
    """Create a new dict representing the environment to use.

    The changes made to the execution environment are printed out.
    """
    env_defaults = {}
    # https://reproducible-builds.org/docs/source-date-epoch/
    git_epoch_cmd = ["git", "log", "-1", "--pretty=%ct"]
    try:
        epoch = subprocess.check_output(git_epoch_cmd, encoding="utf-8").strip()
        env_defaults["SOURCE_DATE_EPOCH"] = epoch
    except subprocess.CalledProcessError:
        pass  # Might be building from a tarball.
    # This layering lets SOURCE_DATE_EPOCH from os.environ takes precedence.
    environment = env_defaults | os.environ | updates

    env_diff = {}
    for key, value in environment.items():
        if os.environ.get(key) != value:
            env_diff[key] = value

    print("🌎 Environment changes:")
    for key in sorted(env_diff.keys()):
        print(f"  {key}={env_diff[key]}")

    return environment


def subdir(working_dir, *, clean_ok=False):
    """Decorator to change to a working directory."""
    def decorator(func):
        @functools.wraps(func)
        def wrapper(context):
            try:
                tput_output = subprocess.check_output(["tput", "cols"],
                                                      encoding="utf-8")
                terminal_width = int(tput_output.strip())
            except subprocess.CalledProcessError:
                terminal_width = 80
            print("⎯" * terminal_width)
            print("📁", working_dir)
            if (clean_ok and getattr(context, "clean", False) and
                working_dir.exists()):
                print(f"🚮 Deleting directory (--clean)...")
                shutil.rmtree(working_dir)

            working_dir.mkdir(parents=True, exist_ok=True)

            with contextlib.chdir(working_dir):
                return func(context, working_dir)

        return wrapper

    return decorator


def call(command, *, quiet, **kwargs):
    """Execute a command.

    If 'quiet' is true, then redirect stdout and stderr to a temporary file.
    """
    print("❯", " ".join(map(str, command)))
    if not quiet:
        stdout = None
        stderr = None
    else:
        stdout = tempfile.NamedTemporaryFile("w", encoding="utf-8",
                                             delete=False,
                                             prefix="cpython-wasi-",
                                             suffix=".log")
        stderr = subprocess.STDOUT
        print(f"📝 Logging output to {stdout.name} (--quiet)...")

    subprocess.check_call(command, **kwargs, stdout=stdout, stderr=stderr)


def build_platform():
    """The name of the build/host platform."""
    # Can also be found via `config.guess`.`
    return sysconfig.get_config_var("BUILD_GNU_TYPE")


def build_python_path():
    """The path to the build Python binary."""
    binary = BUILD_DIR / "python"
    if not binary.is_file():
        binary = binary.with_suffix(".exe")
        if not binary.is_file():
            raise FileNotFoundError("Unable to find `python(.exe)` in "
                                    f"{BUILD_DIR}")

    return binary


@subdir(BUILD_DIR, clean_ok=True)
def configure_build_python(context, working_dir):
    """Configure the build/host Python."""
    if LOCAL_SETUP.exists():
        print(f"👍 {LOCAL_SETUP} exists ...")
    else:
        print(f"📝 Touching {LOCAL_SETUP} ...")
        LOCAL_SETUP.write_bytes(LOCAL_SETUP_MARKER)

    configure = [os.path.relpath(CHECKOUT / 'configure', working_dir)]
    if context.args:
        configure.extend(context.args)

    call(configure, quiet=context.quiet)


@subdir(BUILD_DIR)
def make_build_python(context, working_dir):
    """Make/build the build Python."""
    call(["make", "--jobs", str(cpu_count()), "all"],
            quiet=context.quiet)

    binary = build_python_path()
    cmd = [binary, "-c",
            "import sys; "
            "print(f'{sys.version_info.major}.{sys.version_info.minor}')"]
    version = subprocess.check_output(cmd, encoding="utf-8").strip()

    print(f"🎉 {binary} {version}")


def find_wasi_sdk():
    """Find the path to wasi-sdk."""
    if wasi_sdk_path := os.environ.get("WASI_SDK_PATH"):
        return pathlib.Path(wasi_sdk_path)
    elif (default_path := pathlib.Path("/opt/wasi-sdk")).exists():
        return default_path


def wasi_sdk_env(context):
    """Calculate environment variables for building with wasi-sdk."""
    wasi_sdk_path = context.wasi_sdk_path
    sysroot = wasi_sdk_path / "share" / "wasi-sysroot"
    env = {"CC": "clang", "CPP": "clang-cpp", "CXX": "clang++",
           "AR": "llvm-ar", "RANLIB": "ranlib"}

    for env_var, binary_name in list(env.items()):
        env[env_var] = os.fsdecode(wasi_sdk_path / "bin" / binary_name)

    if wasi_sdk_path != pathlib.Path("/opt/wasi-sdk"):
        for compiler in ["CC", "CPP", "CXX"]:
            env[compiler] += f" --sysroot={sysroot}"

    env["PKG_CONFIG_PATH"] = ""
    env["PKG_CONFIG_LIBDIR"] = os.pathsep.join(
                                map(os.fsdecode,
                                    [sysroot / "lib" / "pkgconfig",
                                     sysroot / "share" / "pkgconfig"]))
    env["PKG_CONFIG_SYSROOT_DIR"] = os.fsdecode(sysroot)

    env["WASI_SDK_PATH"] = os.fsdecode(wasi_sdk_path)
    env["WASI_SYSROOT"] = os.fsdecode(sysroot)

    env["PATH"] = os.pathsep.join([os.fsdecode(wasi_sdk_path / "bin"),
                                   os.environ["PATH"]])

    return env


@subdir(HOST_DIR, clean_ok=True)
def configure_wasi_python(context, working_dir):
    """Configure the WASI/host build."""
    if not context.wasi_sdk_path or not context.wasi_sdk_path.exists():
        raise ValueError("WASI-SDK not found; "
                        "download from "
                        "https://github.com/WebAssembly/wasi-sdk and/or "
                        "specify via $WASI_SDK_PATH or --wasi-sdk")

    config_site = os.fsdecode(CHECKOUT / "Tools" / "wasm" / "config.site-wasm32-wasi")

    wasi_build_dir = working_dir.relative_to(CHECKOUT)

    python_build_dir = BUILD_DIR / "build"
    lib_dirs = list(python_build_dir.glob("lib.*"))
    assert len(lib_dirs) == 1, f"Expected a single lib.* directory in {python_build_dir}"
    lib_dir = os.fsdecode(lib_dirs[0])
    pydebug = lib_dir.endswith("-pydebug")
    python_version = lib_dir.removesuffix("-pydebug").rpartition("-")[-1]
    sysconfig_data = f"{wasi_build_dir}/build/lib.wasi-wasm32-{python_version}"
    if pydebug:
        sysconfig_data += "-pydebug"

    # Use PYTHONPATH to include sysconfig data which must be anchored to the
    # WASI guest's `/` directory.
    host_runner = context.host_runner.format(GUEST_DIR="/",
                                             HOST_DIR=CHECKOUT,
                                             ENV_VAR_NAME="PYTHONPATH",
                                             ENV_VAR_VALUE=f"/{sysconfig_data}",
                                             PYTHON_WASM=working_dir / "python.wasm")
    env_additions = {"CONFIG_SITE": config_site, "HOSTRUNNER": host_runner}
    build_python = os.fsdecode(build_python_path())
    # The path to `configure` MUST be relative, else `python.wasm` is unable
    # to find the stdlib due to Python not recognizing that it's being
    # executed from within a checkout.
    configure = [os.path.relpath(CHECKOUT / 'configure', working_dir),
                    f"--host={HOST_TRIPLE}",
                    f"--build={build_platform()}",
                    f"--with-build-python={build_python}"]
    if pydebug:
        configure.append("--with-pydebug")
    if context.args:
        configure.extend(context.args)
    call(configure,
         env=updated_env(env_additions | wasi_sdk_env(context)),
         quiet=context.quiet)

    python_wasm = working_dir / "python.wasm"
    exec_script = working_dir / "python.sh"
    with exec_script.open("w", encoding="utf-8") as file:
        file.write(f'#!/bin/sh\nexec {host_runner} {python_wasm} "$@"\n')
    exec_script.chmod(0o755)
    print(f"🏃‍♀️ Created {exec_script} ... ")
    sys.stdout.flush()


@subdir(HOST_DIR)
def make_wasi_python(context, working_dir):
    """Run `make` for the WASI/host build."""
    call(["make", "--jobs", str(cpu_count()), "all"],
             env=updated_env(),
             quiet=context.quiet)

    exec_script = working_dir / "python.sh"
    subprocess.check_call([exec_script, "--version"])


def build_all(context):
    """Build everything."""
    steps = [configure_build_python, make_build_python, configure_wasi_python,
             make_wasi_python]
    for step in steps:
        step(context)

def clean_contents(context):
    """Delete all files created by this script."""
    if CROSS_BUILD_DIR.exists():
        print(f"🧹 Deleting {CROSS_BUILD_DIR} ...")
        shutil.rmtree(CROSS_BUILD_DIR)

    if LOCAL_SETUP.exists():
        with LOCAL_SETUP.open("rb") as file:
            if file.read(len(LOCAL_SETUP_MARKER)) == LOCAL_SETUP_MARKER:
                print(f"🧹 Deleting generated {LOCAL_SETUP} ...")


def main():
    default_host_runner = (f"{shutil.which('wasmtime')} run "
                        # Make sure the stack size will work for a pydebug
                        # build.
                        # The 8388608 value comes from `ulimit -s` under Linux
                        # which equates to 8291 KiB.
                        "--wasm max-wasm-stack=8388608 "
                        # Use WASI 0.2 primitives.
                        "--wasi preview2 "
                        # Enable thread support; causes use of preview1.
                        #"--wasm threads=y --wasi threads=y "
                        # Map the checkout to / to load the stdlib from /Lib.
                        "--dir {HOST_DIR}::{GUEST_DIR} "
                        # Set PYTHONPATH to the sysconfig data.
                        "--env {ENV_VAR_NAME}={ENV_VAR_VALUE}")

    parser = argparse.ArgumentParser()
    subcommands = parser.add_subparsers(dest="subcommand")
    build = subcommands.add_parser("build", help="Build everything")
    configure_build = subcommands.add_parser("configure-build-python",
                                             help="Run `configure` for the "
                                             "build Python")
    make_build = subcommands.add_parser("make-build-python",
                                        help="Run `make` for the build Python")
    configure_host = subcommands.add_parser("configure-host",
                                            help="Run `configure` for the "
                                                 "host/WASI (pydebug builds "
                                                 "are inferred from the build "
                                                 "Python)")
    make_host = subcommands.add_parser("make-host",
                                       help="Run `make` for the host/WASI")
    clean = subcommands.add_parser("clean", help="Delete files and directories "
                                                 "created by this script")
    for subcommand in build, configure_build, make_build, configure_host, make_host:
        subcommand.add_argument("--quiet", action="store_true", default=False,
                        dest="quiet",
                        help="Redirect output from subprocesses to a log file")
    for subcommand in configure_build, configure_host:
        subcommand.add_argument("--clean", action="store_true", default=False,
                        dest="clean",
                        help="Delete any relevant directories before building")
    for subcommand in build, configure_build, configure_host:
        subcommand.add_argument("args", nargs="*",
                                help="Extra arguments to pass to `configure`")
    for subcommand in build, configure_host:
        subcommand.add_argument("--wasi-sdk", type=pathlib.Path,
                                dest="wasi_sdk_path",
                                default=find_wasi_sdk(),
                                help="Path to wasi-sdk; defaults to "
                                     "$WASI_SDK_PATH or /opt/wasi-sdk")
        subcommand.add_argument("--host-runner", action="store",
                        default=default_host_runner, dest="host_runner",
                        help="Command template for running the WASI host "
                             "(default designed for wasmtime 14 or newer: "
                                f"`{default_host_runner}`)")

    context = parser.parse_args()

    dispatch = {"configure-build-python": configure_build_python,
                "make-build-python": make_build_python,
                "configure-host": configure_wasi_python,
                "make-host": make_wasi_python,
                "build": build_all,
                "clean": clean_contents}
    dispatch[context.subcommand](context)


if  __name__ == "__main__":
    main()