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"""Paper Algorithm 2, 300 oracle queries x 10 independent trials.

Run only inside a case-owned SLURM job. --resume resumes at a query boundary;
it never warm-starts a new posterior draw from a previous iteration's model.
"""
import json
import time
from pathlib import Path

from common import (case_guard, config_hash, hardware_record, load_config,
                    load_data, model_state_on_cpu, negative_total_flow_rates, parse_args, predict,
                    restore_rng, rng_state, save_json, save_torch, seed_all,
                    write_csv)
import torch
from model.NOTS import NOTS


def fit_posterior(cfg, xs, ys, seed, iteration, loss_file):
    # New model, all fresh weights and optimizer state on every invocation.
    model = NOTS(**cfg['model']).to(xs.device)
    tc = cfg['training']
    if tc['normalization'] != 'none':
        raise ValueError('Audited paper-priority protocol requires physical-space MSE')
    optimizer = torch.optim.AdamW(model.parameters(), lr=tc['lr'], weight_decay=0)
    scheduler = torch.optim.lr_scheduler.CosineAnnealingLR(optimizer, T_max=tc['epochs'])
    model.train()
    for epoch in range(tc['epochs']):
        mse_total = loss_total = 0.0
        count = 0
        for first in range(0, len(xs), tc['batch_size']):
            bx, by = xs[first:first + tc['batch_size']], ys[first:first + tc['batch_size']]
            optimizer.zero_grad(set_to_none=True)
            pressure = model(bx)
            mse = (pressure - by).square().mean()
            penalty = model.l2_penalty()
            loss = mse + tc['lambda_reg'] * penalty
            if not torch.isfinite(loss):
                raise FloatingPointError(f'Nonfinite training loss seed={seed} query={iteration}')
            loss.backward()
            optimizer.step()
            mse_total += mse.item() * len(bx)
            loss_total += loss.item() * len(bx)
            count += len(bx)
        lr = scheduler.get_last_lr()[0]
        scheduler.step()
        record = {'seed': seed, 'iteration': iteration, 'epoch': epoch + 1,
                  'n_observations': len(xs), 'mse': mse_total / count,
                  'loss': loss_total / count, 'lr': lr}
        with open(loss_file, 'a') as f:
            f.write(json.dumps(record) + '\n')
        print('TRAIN ' + json.dumps(record), flush=True)
    return model


@torch.no_grad()
def observed_mse(model, xs, ys, batch_size):
    err = 0.0
    for first in range(0, len(xs), batch_size):
        err += (model(xs[first:first + batch_size]) - ys[first:first + batch_size]).square().sum().item()
    return err / ys.numel()


def trial(cfg, seed, x, oracle_y, truth, noise_std, data_meta, resume):
    out = Path(cfg['paths']['output_dir'])
    rd = out / 'results' / f'trial_{seed}'
    rd.mkdir(parents=True, exist_ok=True)
    state_file = rd / 'resume.pt'
    fingerprint = config_hash(cfg)
    seed_all(seed)
    records, indices, noisy_y = [], [], []
    model = None
    if resume and state_file.exists():
        state = torch.load(state_file, map_location='cpu', weights_only=False)
        if state['config_hash'] != fingerprint or state['data_sha256'] != data_meta['sha256']:
            raise RuntimeError('Resume config/data differs from original experiment')
        records, indices = state['records'], state['indices']
        noisy_y = list(state['noisy_y'].to(x.device).unbind())
        restore_rng(state['rng'])
        if len(records) == cfg['experiment']['iterations'] and 'final_model_state' in state:
            model = NOTS(**cfg['model']).to(x.device)
            model.load_state_dict(state['final_model_state'], strict=True)
        print(f'RESUME seed={seed} completed_queries={len(records)}', flush=True)
    elif state_file.exists():
        raise FileExistsError(f'{state_file} exists; use --resume to avoid overwriting an experiment')
    start = time.monotonic()
    for t in range(len(records), cfg['experiment']['iterations']):
        tick = time.monotonic()
        acquisition = None
        if t < cfg['experiment']['n_init']:
            chosen = torch.randint(len(x), ()).item()
        else:
            fit_x = x[torch.tensor(indices, device=x.device)]
            fit_y = torch.stack(noisy_y)
            model = fit_posterior(cfg, fit_x, fit_y, seed, t + 1, rd / 'training_loss.jsonl')
            values = negative_total_flow_rates(predict(model, x, cfg['experiment']['prediction_batch_size']), x)
            chosen = values.argmax().item()
            acquisition = values[chosen].item()
        # Only the selected pressure becomes an observed training example.
        observation = oracle_y[chosen] + torch.randn_like(oracle_y[chosen]) * noise_std
        indices.append(chosen)
        noisy_y.append(observation)
        regret = truth.max().item() - truth[chosen].item()
        cumulative = sum(row['regret'] for row in records) + regret
        row = {'iteration': t + 1, 'candidate_index': chosen,
               'outcome': truth[chosen].item(),
               'observation': negative_total_flow_rates(observation.unsqueeze(0), x[chosen:chosen + 1]).item(),
               'acquisition': acquisition, 'regret': regret,
               'cumulative_regret': cumulative, 'average_regret': cumulative / (t + 1),
               'n_observations_used_for_fit': t,
               'elapsed_seconds': time.monotonic() - tick}
        records.append(row)
        write_csv(rd / 'trajectory.csv', records)
        boundary_state = {'config_hash': fingerprint, 'data_sha256': data_meta['sha256'],
                          'records': records, 'indices': indices,
                          'noisy_y': torch.stack(noisy_y).cpu(), 'rng': rng_state()}
        if t + 1 == cfg['experiment']['iterations']:
            boundary_state['final_model_state'] = model_state_on_cpu(model)
        save_torch(state_file, boundary_state)
        print(f'QUERY seed={seed} ' + json.dumps(row), flush=True)
        save_json(rd / 'progress.json', {'seed': seed, 'completed_queries': len(records),
                                        'status': 'running', 'last_metrics': row})
    checkpoint_path = out / 'weight' / f'trial_{seed}.pt'
    if model is None:
        # A completed trial needs no extra posterior draw after resumption.
        if not checkpoint_path.exists():
            raise RuntimeError('Completed trajectory lacks final trained checkpoint')
        return checkpoint_path
    # Final model was fit before the 300th oracle query (299 observations).
    used_indices = indices[:-1]
    final_train_mse = observed_mse(model, x[torch.tensor(used_indices, device=x.device)],
                                   torch.stack(noisy_y[:-1]), cfg['training']['batch_size'])
    checkpoint = {'model_state': model_state_on_cpu(model),
                  'model_config': cfg['model'], 'normalization': {'kind': 'identity'},
                  'seed': seed, 'iteration': len(records), 'fit_indices': used_indices,
                  'n_fit_observations': len(used_indices), 'train_mse': final_train_mse,
                  'config_hash': fingerprint, 'data_sha256': data_meta['sha256'],
                  'selection_rule': 'minimum observed training MSE among final trial models; test never used'}
    save_torch(checkpoint_path, checkpoint)
    # This is sequential within one allocation, so no concurrent writers.
    best_path = out / 'weight/best_model.pt'
    old_mse = float('inf')
    if best_path.exists():
        old_mse = torch.load(best_path, map_location='cpu', weights_only=False)['train_mse']
    if final_train_mse < old_mse:
        save_torch(best_path, checkpoint)
    save_json(rd / 'progress.json', {'seed': seed, 'completed_queries': len(records),
                                    'status': 'completed', 'last_metrics': records[-1],
                                    'checkpoint': str(checkpoint_path), 'train_mse': final_train_mse,
                                    'seconds_this_invocation': time.monotonic() - start})
    print(f'TRIAL_COMPLETE seed={seed} average_regret={records[-1]["average_regret"]:.9g} train_mse={final_train_mse:.9g}', flush=True)
    return checkpoint_path


def random_baseline(cfg, truth):
    out = Path(cfg['paths']['output_dir']) / 'results'
    for seed in cfg['experiment']['seeds']:
        # Isolated stream, same fixed candidate pool, repeated queries permitted.
        generator = torch.Generator().manual_seed(seed)
        choices = torch.randint(len(truth), (cfg['experiment']['iterations'],), generator=generator)
        regrets = truth.cpu().max() - truth.cpu()[choices]
        records = []
        cumulative = 0.0
        for t, (idx, regret) in enumerate(zip(choices.tolist(), regrets.tolist()), 1):
            cumulative += regret
            records.append({'iteration': t, 'candidate_index': idx, 'regret': regret,
                            'cumulative_regret': cumulative, 'average_regret': cumulative / t})
        write_csv(out / f'rs_{seed}.csv', records)
        print(f'RS seed={seed} average_regret={records[-1]["average_regret"]:.9g}', flush=True)


def main():
    parser = parse_args(__doc__)
    parser.add_argument('--resume', action='store_true')
    parser.add_argument('--seed', type=int, help='Optional single configured trial for recovery')
    args = parser.parse_args()
    cfg = load_config(args.config)
    device = case_guard(cfg)
    if cfg['experiment']['iterations'] != 300 or len(cfg['experiment']['seeds']) != 10:
        raise ValueError('Formal experiment requires 300 queries and 10 independent seeds')
    x, y, meta = load_data(cfg)
    out = Path(cfg['paths']['output_dir'])
    save_json(out / 'results/data_manifest.json', meta)
    save_json(out / 'results/hardware.json', hardware_record())
    x, y = x.to(device), y.to(device)
    truth = negative_total_flow_rates(y, x)
    # Appendix D.3 specifies a variance ratio, hence the square root here.
    noise_std = (cfg['experiment']['noise_variance_fraction'] * y.var(dim=0, correction=1)).sqrt()
    save_torch(out / 'results/oracle.pt', {'objectives': truth.cpu(), 'noise_std': noise_std.cpu(),
                                          'best_index': truth.argmax().item(), 'worst_index': truth.argmin().item(),
                                          'data_sha256': meta['sha256']})
    print(f'ORACLE max={truth.max().item():.9g} min={truth.min().item():.9g} ' + json.dumps(meta), flush=True)
    seeds = [args.seed] if args.seed is not None else cfg['experiment']['seeds']
    if not set(seeds).issubset(cfg['experiment']['seeds']):
        raise ValueError('Seed is outside configured independent trials')
    if cfg['experiment']['run_random_baseline']:
        random_baseline(cfg, truth)
    for seed in seeds:
        trial(cfg, seed, x, y, truth, noise_std, meta, args.resume)
    print('TRAINING_REQUEST_FINISHED', flush=True)


if __name__ == '__main__':
    main()