#!/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"

LOCAL_SETUP = CHECKOUT / "Modules" / "Setup.local"
LOCAL_SETUP_MARKER = b"# Generated by Tools/wasm/wasi.py\n"

WASMTIME_VAR_NAME = "WASMTIME"
WASMTIME_HOST_RUNNER_VAR = f"{{{WASMTIME_VAR_NAME}}}"


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):
            nonlocal working_dir

            if callable(working_dir):
                working_dir = working_dir(context)
            try:
                tput_output = subprocess.check_output(
                    ["tput", "cols"], encoding="utf-8"
                )
            except subprocess.CalledProcessError:
                terminal_width = 80
            else:
                terminal_width = int(tput_output.strip())
            print("⎯" * terminal_width)
            print("📁", working_dir)
            if (
                clean_ok
                and getattr(context, "clean", False)
                and working_dir.exists()
            ):
                print("🚮 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(
                f"Unable to find `python(.exe)` in {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(lambda context: CROSS_BUILD_DIR / context.host_triple, 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.
    args = {
        "GUEST_DIR": "/",
        "HOST_DIR": CHECKOUT,
        "ENV_VAR_NAME": "PYTHONPATH",
        "ENV_VAR_VALUE": f"/{sysconfig_data}",
        "PYTHON_WASM": working_dir / "python.wasm",
    }
    # Check dynamically for wasmtime in case it was specified manually via
    # `--host-runner`.
    if WASMTIME_HOST_RUNNER_VAR in context.host_runner:
        if wasmtime := shutil.which("wasmtime"):
            args[WASMTIME_VAR_NAME] = wasmtime
        else:
            raise FileNotFoundError(
                "wasmtime not found; download from "
                "https://github.com/bytecodealliance/wasmtime"
            )
    host_runner = context.host_runner.format_map(args)
    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={context.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(lambda context: CROSS_BUILD_DIR / context.host_triple)
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"{WASMTIME_HOST_RUNNER_VAR} 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"
    )
    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}`)",
        )
    for subcommand in build, configure_host, make_host:
        subcommand.add_argument(
            "--host-triple",
            action="store",
            default="wasm32-wasip1",
            help="The target triple for the WASI host build",
        )

    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()