#!/usr/bin/env python3
"""Generate deterministic gzip-compressed LittleFS web assets."""

from __future__ import annotations

import argparse
import gzip
import os
import shutil
from pathlib import Path


SUPPORTED_SUFFIXES = {".css", ".html", ".ico", ".js", ".json", ".svg"}


def generate_assets(source_directory: Path, output_directory: Path) -> list[Path]:
    source_directory = source_directory.resolve()
    output_directory = output_directory.resolve()
    if not source_directory.is_dir():
        raise ValueError(f"Web source directory does not exist: {source_directory}")
    if source_directory == output_directory:
        raise ValueError("Web source and output directories must differ")

    source_files = sorted(
        path for path in source_directory.rglob("*")
        if path.is_file() and path.suffix.lower() in SUPPORTED_SUFFIXES
    )
    if not source_files:
        raise ValueError(f"No supported web assets found in {source_directory}")

    if output_directory.exists():
        shutil.rmtree(output_directory)
    output_directory.mkdir(parents=True)

    generated_files: list[Path] = []
    for source_path in source_files:
        relative_path = source_path.relative_to(source_directory)
        output_path = output_directory / f"{relative_path}.gz"
        output_path.parent.mkdir(parents=True, exist_ok=True)
        with source_path.open("rb") as source, output_path.open("wb") as output:
            with gzip.GzipFile(
                filename="",
                mode="wb",
                compresslevel=9,
                fileobj=output,
                mtime=0,
            ) as compressed:
                shutil.copyfileobj(source, compressed)
        os.utime(output_path, ns=(0, 0))
        generated_files.append(output_path)

    for directory in sorted(
        (path for path in output_directory.rglob("*") if path.is_dir()),
        reverse=True,
    ):
        os.utime(directory, ns=(0, 0))
    os.utime(output_directory, ns=(0, 0))

    return generated_files


def main() -> int:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--source", type=Path, default=Path("web"))
    parser.add_argument("--output", type=Path, default=Path("data"))
    arguments = parser.parse_args()

    generated_files = generate_assets(arguments.source, arguments.output)
    for path in generated_files:
        print(path)
    return 0


if __name__ == "__main__":
    raise SystemExit(main())