import argparse
import hashlib
from pathlib import Path


VALUES = {
    'conservative': {
        'remote_assignment_reserve_bytes': 64 * 1024 * 1024,
        'remote_assignment_max_active': 1,
        'keycheck_queue_max_items': 8192,
        'keycheck_queue_max_bytes': 64 * 1024 * 1024,
    },
    'final': {
        'remote_assignment_reserve_bytes': 2 * 1024 * 1024,
        'remote_assignment_max_active': 50,
        'keycheck_queue_max_items': 131072,
        'keycheck_queue_max_bytes': 128 * 1024 * 1024,
    },
}


def render(payload, mode):
    text = payload.decode('utf-8', errors='strict')
    if '\r' in text:
        raise ValueError('configuration must use LF line endings')
    lines = text.splitlines(keepends=True)
    values = VALUES[mode]
    hard_limit = '  result_bundle_max_event_bytes: 67108864\n'
    if lines.count(hard_limit) != 1:
        raise ValueError('unexpected hard result limit')
    for field in ('remote_assignment_reserve_bytes', 'remote_assignment_max_active'):
        if any(line.startswith(f'  {field}:') for line in lines):
            raise ValueError(f'active configuration already contains {field}')
    index = lines.index(hard_limit) + 1
    lines[index:index] = [
        f"  remote_assignment_reserve_bytes: {values['remote_assignment_reserve_bytes']}\n",
        f"  remote_assignment_max_active: {values['remote_assignment_max_active']}\n",
    ]
    replacements = {
        '  keycheck_queue_max_items: 8192\n': (
            f"  keycheck_queue_max_items: {values['keycheck_queue_max_items']}\n"
        ),
        '  keycheck_queue_max_bytes: 67108864\n': (
            f"  keycheck_queue_max_bytes: {values['keycheck_queue_max_bytes']}\n"
        ),
    }
    for before, after in replacements.items():
        if lines.count(before) != 1:
            raise ValueError(f'unexpected active configuration field: {before.strip()}')
        lines[lines.index(before)] = after
    return ''.join(lines).encode('utf-8')


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('--input', required=True)
    parser.add_argument('--output', required=True)
    parser.add_argument('--mode', choices=tuple(VALUES), required=True)
    parser.add_argument('--expected-sha256', required=True)
    args = parser.parse_args()

    source = Path(args.input)
    destination = Path(args.output)
    payload = source.read_bytes()
    if hashlib.sha256(payload).hexdigest() != args.expected_sha256:
        raise SystemExit('active configuration identity changed')
    rendered = render(payload, args.mode)
    destination.write_bytes(rendered)
    print(hashlib.sha256(rendered).hexdigest())


if __name__ == '__main__':
    main()