#!/usr/bin/env python3
"""Flatten and minify the site's CSS imports without changing their order.

The page HTML loads css/main.css. Keeping this file as a generated bundle removes
the browser's serial @import chain while the individual files under css/ remain
the editable source of truth.
"""
import argparse
import posixpath
import re
import subprocess
import sys
import tempfile
from pathlib import Path

ROOT = Path(__file__).resolve().parent.parent
OUTPUT = ROOT / "css" / "main.css"
SOURCE = ROOT / "css" / "source.css"
IMPORT_RE = re.compile(r"@import\s+['\"]([^'\"]+\.css)(?:\?v=[0-9a-f]{8})?['\"]\s*;", re.I)
URL_RE = re.compile(r"url\(\s*(['\"]?)(\.\.?/[^)'\"\s]+)\1\s*\)", re.I)
LIGHTNINGCSS = "lightningcss-cli@1.33.0"


def rebase_urls(css: str, source: str) -> str:
    """Make relative url() references resolve from css/main.css after bundling."""
    source_dir = posixpath.dirname(source)

    def replace(match: re.Match) -> str:
        quote, value = match.groups()
        target = posixpath.normpath(posixpath.join(source_dir, value))
        from_bundle = posixpath.relpath(target, "css")
        return f"url({quote}{from_bundle}{quote})"

    return URL_RE.sub(replace, css)


def build(output: Path) -> None:
    source_text = SOURCE.read_text(encoding="utf-8")
    imports = IMPORT_RE.findall(source_text)
    if not imports:
        raise RuntimeError("css/source.css has no CSS imports to bundle")
    chunks = []
    for import_path in imports:
        rel = posixpath.normpath(posixpath.join("css", import_path))
        path = ROOT / rel
        if not path.is_file():
            raise FileNotFoundError(f"Missing CSS source: {rel}")
        chunks.append(rebase_urls(path.read_text(encoding="utf-8"), rel))
    input_path = ROOT / "css" / ".main.build.css"
    input_path.write_text("\n".join(chunks), encoding="utf-8", newline="\n")
    try:
        subprocess.run(
            ["npx", "--yes", LIGHTNINGCSS, str(input_path), "--minify", "--output-file", str(output)],
            cwd=ROOT,
            check=True,
        )
    finally:
        input_path.unlink(missing_ok=True)


def main() -> int:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--check", action="store_true", help="fail if css/main.css is stale")
    args = parser.parse_args()
    if not SOURCE.is_file():
        raise FileNotFoundError("Missing CSS source aggregator: css/source.css")
    if args.check:
        with tempfile.NamedTemporaryFile(prefix="msos-main-", suffix=".css", dir=ROOT / "css", delete=False) as tmp:
            temp_output = Path(tmp.name)
        try:
            build(temp_output)
            if temp_output.read_bytes() != OUTPUT.read_bytes():
                print("css/main.css is stale; run tools/build_css_bundle.py", file=sys.stderr)
                return 1
        finally:
            temp_output.unlink(missing_ok=True)
        print(f"CSS bundle is current ({OUTPUT.stat().st_size:,} bytes)")
        return 0
    build(OUTPUT)
    print(f"Wrote css/main.css ({OUTPUT.stat().st_size:,} bytes)")
    return 0


if __name__ == "__main__":
    try:
        raise SystemExit(main())
    except Exception as exc:
        print(f"CSS bundle failed: {exc}", file=sys.stderr)
        raise SystemExit(1)