#!/usr/bin/env python3

from __future__ import annotations

import argparse
import hashlib
import os
import shutil
import subprocess
import sys
import tempfile
from pathlib import Path

ROOT = Path(__file__).resolve().parent
DEFAULT_OUTPUT = ROOT.parent / "docs" / "canvas-4b-design-model-proposal.pdf"
SOURCE_DATE_EPOCH = "1785542400"


def sha256(path: Path) -> str:
    digest = hashlib.sha256()
    with path.open("rb") as handle:
        while chunk := handle.read(1024 * 1024):
            digest.update(chunk)
    return digest.hexdigest()


def source_id() -> str:
    digest = hashlib.sha256()
    paths = [
        ROOT / "paper.md",
        ROOT / "main.tex",
        ROOT / "capyresearch.sty",
        ROOT / "prepare_content.py",
        ROOT / "references.bib",
        *sorted((ROOT / "assets").iterdir()),
    ]
    for path in paths:
        digest.update(path.relative_to(ROOT).as_posix().encode())
        digest.update(b"\0")
        digest.update(path.read_bytes())
        digest.update(b"\0")
    return digest.hexdigest()[:32].upper()


def require_commands() -> None:
    missing = [
        command
        for command in ("pandoc", "latexmk", "lualatex")
        if shutil.which(command) is None
    ]
    if missing:
        raise SystemExit("missing paper build commands: " + ", ".join(missing))


def render(output: Path) -> Path:
    require_commands()
    with tempfile.TemporaryDirectory(prefix="capy-canvas-paper-") as directory:
        build = Path(directory)
        for name in (
            "paper.md",
            "main.tex",
            "capyresearch.sty",
            "prepare_content.py",
            "references.bib",
        ):
            shutil.copy2(ROOT / name, build / name)
        shutil.copytree(ROOT / "assets", build / "assets")
        main = build / "main.tex"
        main.write_text(
            main.read_text().replace("CAPY_PDF_TRAILER_ID", source_id())
        )
        environment = {
            **os.environ,
            "SOURCE_DATE_EPOCH": SOURCE_DATE_EPOCH,
            "FORCE_SOURCE_DATE": "1",
            "TZ": "UTC",
        }
        subprocess.run(
            [sys.executable, "prepare_content.py"],
            cwd=build,
            env=environment,
            check=True,
        )
        subprocess.run(
            [
                "latexmk",
                "-lualatex",
                "-interaction=nonstopmode",
                "-halt-on-error",
                "main.tex",
            ],
            cwd=build,
            env=environment,
            check=True,
        )
        output.parent.mkdir(parents=True, exist_ok=True)
        temporary = output.with_name(f".{output.name}.tmp")
        shutil.copy2(build / "main.pdf", temporary)
        os.replace(temporary, output)
    return output


def main() -> None:
    parser = argparse.ArgumentParser()
    parser.add_argument("--output", type=Path, default=DEFAULT_OUTPUT)
    parser.add_argument(
        "--check",
        action="store_true",
        help="Render to a temporary file and require an exact canonical-PDF match.",
    )
    args = parser.parse_args()
    if args.check:
        with tempfile.TemporaryDirectory(prefix="capy-canvas-paper-check-") as directory:
            rendered = render(Path(directory) / DEFAULT_OUTPUT.name)
            if not DEFAULT_OUTPUT.exists():
                raise SystemExit(f"canonical PDF is missing: {DEFAULT_OUTPUT}")
            if rendered.read_bytes() != DEFAULT_OUTPUT.read_bytes():
                raise SystemExit(
                    "canonical PDF is stale: "
                    f"expected {sha256(rendered)}, found {sha256(DEFAULT_OUTPUT)}"
                )
            print(f"paper is reproducible: {sha256(rendered)}")
        return
    rendered = render(args.output.expanduser().resolve())
    print(f"rendered {rendered} ({sha256(rendered)})")


if __name__ == "__main__":
    main()