#!/usr/bin/env python3
"""Inspect a source asset, or explicitly download a commit-pinned GitHub asset."""
import argparse
import hashlib
import json
from pathlib import Path
import urllib.parse
import urllib.request


def github_raw_url(url):
    parsed = urllib.parse.urlsplit(url)
    parts = parsed.path.split('/')
    if parsed.hostname != 'github.com' or len(parts) < 6 or parts[3] != 'blob':
        raise ValueError('Expected a GitHub blob URL')
    owner, repo, revision = parts[1], parts[2], parts[4]
    if len(revision) != 40 or any(c not in '0123456789abcdef' for c in revision.lower()):
        raise ValueError('Source URL is not pinned to a full commit')
    raw_path = '/'.join([owner, repo, revision] + parts[5:])
    return 'https://raw.githubusercontent.com/' + urllib.parse.quote(urllib.parse.unquote(raw_path), safe='/')


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('manifest', type=Path)
    parser.add_argument('sample_id')
    parser.add_argument('--download', action='store_true')
    parser.add_argument('--output', type=Path)
    args = parser.parse_args()
    record = next((r for r in map(json.loads, args.manifest.open()) if r['sample_id'] == args.sample_id), None)
    if record is None:
        parser.error('Sample ID not found')
    info = {k: record[k] for k in ['sample_id', 'source_asset_id', 'source_url', 'source_file_type',
                                  'source_sha256', 'historical_license', 'observed_license_url', 'provenance_flags']}
    if record['source_group'] == 'github':
        info['download_url'] = github_raw_url(record['source_url'])
    else:
        info['download_method'] = 'Use the original Sketchfab page and its official download flow.'
    print(json.dumps(info, indent=2, ensure_ascii=False))
    if not args.download:
        return
    if record['source_group'] != 'github':
        parser.error('Automatic Sketchfab downloads are not implemented; use the official source flow.')
    if args.output is None:
        parser.error('--download requires --output')
    if args.output.exists():
        parser.error('Output already exists; select a new path')
    partial = args.output.with_name(args.output.name + '.partial')
    digest = hashlib.sha256()
    created = False
    try:
        with partial.open('xb') as out:
            created = True
            with urllib.request.urlopen(info['download_url'], timeout=60) as response:
                for chunk in iter(lambda: response.read(1024 * 1024), b''):
                    out.write(chunk)
                    digest.update(chunk)
        if digest.hexdigest() != record['source_sha256']:
            raise ValueError('Source SHA-256 mismatch; upstream content or a Git LFS pointer may differ')
        partial.rename(args.output)
    except Exception:
        if created and partial.exists():
            partial.unlink()
        raise
    print('Verified source asset saved to ' + str(args.output))


if __name__ == '__main__':
    main()