"""One-time export from an explicit historical Git revision, never a runtime seed."""
import argparse
import json
import os
from pathlib import Path
import re
import subprocess

ROOT = Path(__file__).resolve().parents[1]
BASELINE = '25c5e83d08eae4277fe429a692955bd3bb2e717f'  # Last main revision before database-backed documents.


def export(ref):
    commit = subprocess.check_output(['git', 'rev-parse', '--verify', ref + '^{commit}'], cwd=ROOT, text=True).strip()

    def read(name):
        return subprocess.check_output(['git', 'show', f'{commit}:{name}'], cwd=ROOT).decode()

    catalog = json.loads(read('content/catalog.json'))
    names = subprocess.check_output(['git', 'ls-tree', '-r', '--name-only', commit, '--', 'content/docs'], cwd=ROOT, text=True).splitlines()
    documents = []
    for name in sorted(n for n in names if n.endswith('.md')):
        source = name.removeprefix('content/docs/').removesuffix('.md')
        metadata = catalog['documents'][source]
        collection = next(c for c in catalog['collections'] if not c['path'] or source.startswith(c['path'] + '/'))
        content = read(name)
        title = re.search(r'^# (.+)$', content, re.M)
        documents.append(dict(slug=metadata['slug'], sourceSlug=source, category=metadata['category'],
            title=title[1].strip() if title else source, content=content,
            group=metadata.get('group', collection['title']), collection=metadata.get('collection', collection['title']),
            description=metadata.get('description', collection['description']),
            draft=metadata.get('draft', False), featured=metadata.get('featured', False), revision=1))
    if not documents:
        raise ValueError('Refusing empty migration')
    return dict(format='tabularium-documents-v1', documents=documents)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--ref', default=BASELINE)
    parser.add_argument('--output', type=Path, required=True)
    args = parser.parse_args()
    payload = export(args.ref)
    args.output.parent.mkdir(parents=True, exist_ok=True)
    descriptor = os.open(args.output, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
    with os.fdopen(descriptor, 'w') as output:
        json.dump(payload, output, ensure_ascii=False)
    print(f"Exported {len(payload['documents'])} documents; source is immutable Git history")