"""Public metadata-only Git checkouts, without credentials or project hooks."""
import os
import subprocess
import tempfile
from pathlib import Path


def checkout_metadata(url,destination,patterns,branch='master'):
    destination=Path(destination)
    destination.parent.mkdir(parents=True,exist_ok=True)
    env=dict(os.environ,GIT_TERMINAL_PROMPT='0',GIT_LFS_SKIP_SMUDGE='1')
    def git(*args):
        result=subprocess.run(['git','-c','credential.helper=','-c','http.extraHeader=','-c','core.hooksPath=/dev/null','-c','core.deltaBaseCacheLimit=32m',*args],env=env,capture_output=True,text=True,timeout=900)
        if result.returncode:
            raise RuntimeError('Metadata checkout failed: '+result.stderr[-500:])
        return result.stdout.strip()
    if not destination.exists():
        with tempfile.TemporaryDirectory(prefix='metadata-clone-',dir=destination.parent) as tmp:
            stage=Path(tmp)/'repo'
            git('clone','--filter=blob:none','--depth','1','--single-branch','--branch',branch,'--no-checkout',url,str(stage))
            git('-C',str(stage),'sparse-checkout','set','--no-cone',*patterns)
            git('-C',str(stage),'checkout',branch)
            stage.rename(destination)
    else:
        if git('-C',str(destination),'status','--porcelain'):
            raise RuntimeError('Metadata checkout has local changes; refusing to overwrite')
        git('-C',str(destination),'fetch','--filter=blob:none','--depth','1','origin',branch)
        git('-C',str(destination),'checkout','--detach','FETCH_HEAD')
    return git('-C',str(destination),'rev-parse','HEAD')