"""The build's pinned tools (tools/build-lock.toml, tools/requirements.txt) and the environment it runs in.

Each tool is downloaded once into build/.cache and checked against its hash, so what a build runs depends on the
repo, not on what the machine has installed. COBBLESURVIVAL_CACHE moves the cache (tools/check_reproducible.py shares
one between its builds: everything in it is checked by hash, so it can't change their result).
"""
import hashlib
import os
import platform
import shutil
import subprocess
import sys
import tarfile
import tomllib
import urllib.request
import venv
from pathlib import Path

ROOT = Path(__file__).resolve().parent.parent
LOCK = tomllib.loads((ROOT / "tools/build-lock.toml").read_text())
CACHE = Path(os.environ.get("COBBLESURVIVAL_CACHE", ROOT / "build/.cache"))
# Nothing the build writes may depend on the machine's clock zone, language or Python's per-run hash seed.
BUILD_ENV = {"TZ": "UTC", "LC_ALL": "C.UTF-8", "PYTHONHASHSEED": "0", "PYTHONUTF8": "1"}


def digest(path, algorithm="sha256"):
    return hashlib.new(algorithm, Path(path).read_bytes()).hexdigest()


def fetch(url, dest, expected, algorithm="sha256"):
    """[dest], downloaded from [url] if it isn't there yet; exits if the file is not the one pinned."""
    if dest.exists() and digest(dest, algorithm) == expected:
        return dest
    dest.parent.mkdir(parents=True, exist_ok=True)
    part = dest.with_name(dest.name + ".part")
    request = urllib.request.Request(url, headers={"User-Agent": "cobblemon-survival-pack build"})
    with urllib.request.urlopen(request, timeout=300) as response, open(part, "wb") as out:
        shutil.copyfileobj(response, out)
    if digest(part, algorithm) != expected:
        part.unlink()
        sys.exit(f"{url} does not match the pinned {algorithm} {expected}")
    part.replace(dest)
    return dest


def download(name):
    """A file listed under [downloads] in tools/build-lock.toml."""
    entry = LOCK["downloads"][name]
    return fetch(entry["url"], CACHE / name, entry["sha256"])


def mod_jar(slug):
    """A mod's jar as pack/mods/<slug>.pw.toml pins it, for the tools that read a mod's own data."""
    meta = tomllib.loads((ROOT / f"pack/mods/{slug}.pw.toml").read_text())
    file = meta["download"]
    return fetch(file["url"], CACHE / "mods" / meta["filename"], file["hash"], file["hash-format"])


def jdk():
    """The pinned JDK's home, the only one Gradle gets to compile with."""
    pin = LOCK["jdk"]
    here = f"{platform.system().lower()}-{platform.machine()}"
    if here != pin["platform"]:
        sys.exit(f"tools/build-lock.toml pins a JDK for {pin['platform']}, this machine is {here}")
    home = CACHE / f"jdk-{pin['version']}"
    if not (home / "bin/javac").exists():
        archive = fetch(pin["url"], CACHE / f"jdk-{pin['version']}.tar.gz", pin["sha256"])
        unpacking = home.with_name(home.name + ".part")
        shutil.rmtree(unpacking, ignore_errors=True)
        unpacking.mkdir(parents=True)
        with tarfile.open(archive) as tar:
            tar.extractall(unpacking, filter="tar")
        shutil.rmtree(home, ignore_errors=True)
        next(unpacking.iterdir()).rename(home)
        unpacking.rmdir()
    return home


def packwiz():
    """The pinned packwiz, built from its pinned commit with the pinned Go."""
    pin = LOCK["packwiz"]
    binary = CACHE / f"packwiz-{pin['version']}" / "packwiz"
    if not binary.exists():
        if not shutil.which("go"):
            sys.exit("building the pinned packwiz needs Go (https://go.dev/dl/)")
        env = os.environ | {"GOBIN": str(binary.parent), "GOTOOLCHAIN": pin["go"], "GOFLAGS": "-trimpath"}
        subprocess.run(["go", "install", f"{pin['module']}@{pin['version']}"], env=env, check=True)
    return binary


def enter_venv():
    """Re-runs the calling script in a private venv with exactly tools/requirements.txt and the build's environment."""
    requirements = ROOT / "tools/requirements.txt"
    home = CACHE / f"venv-{digest(requirements)[:12]}"
    if Path(sys.prefix) == home and all(os.environ.get(k) == v for k, v in BUILD_ENV.items()):
        return
    if f"{sys.version_info[0]}.{sys.version_info[1]}" != LOCK["python"]:
        print(f"warning: tools/build-lock.toml pins Python {LOCK['python']}, this is {sys.version.split()[0]}", file=sys.stderr)
    python = home / "bin/python"
    if not python.exists():
        venv.create(home, with_pip=True)
        subprocess.run([python, "-m", "pip", "install", "--quiet", "--require-hashes", "-r", requirements], check=True)
    os.execve(python, [str(python), sys.argv[0], *sys.argv[1:]], os.environ | BUILD_ENV)