"""Cascade-EP trainer (zil mode): train L DISTINCT standard transformer blocks with the
interleaved reverse-sweep energy rule — per layer: update z_l (gamma=1, SUM units), then
read that layer's theta-grad from its LOCAL energy term. Numerically == BP restructured
as local two-factor rules; inference = plain forward (standard LLM).
Twin of casc_bp_train.py (same seed => same init & data stream)."""
import argparse, math, pickle, time
import numpy as np, torch, torch.nn as nn, torch.nn.functional as F
from pathlib import Path

ap = argparse.ArgumentParser()
ap.add_argument('--tag', default='casc_ep6')
ap.add_argument('--L', type=int, default=6); ap.add_argument('--C', type=int, default=256)
ap.add_argument('--H', type=int, default=8); ap.add_argument('--T', type=int, default=256)
ap.add_argument('--B', type=int, default=24); ap.add_argument('--steps', type=int, default=4000)
ap.add_argument('--lr', type=float, default=3e-4); ap.add_argument('--warmup', type=int, default=200)
ap.add_argument('--beta', type=float, default=0.03); ap.add_argument('--seed', type=int, default=0)
ap.add_argument('--save_every', type=int, default=1000); ap.add_argument('--log', type=int, default=200)
ap.add_argument('--wandb', default=''); ap.add_argument('--wandb_run', default='')
args = ap.parse_args()
torch.manual_seed(args.seed)
dev = 'cuda' if torch.cuda.is_available() else 'cpu'

DD = Path('/home/yurenh2/ept/ep_run/data/tinystories_bpe')
vocab = pickle.load(open(DD / 'meta.pkl', 'rb'))['vocab_size']

def get_batch(split):
    data = np.memmap(DD / ('train.bin' if split == 'train' else 'val.bin'), dtype=np.uint16, mode='r')
    ix = torch.randint(len(data) - args.T - 1, (args.B,))
    x = torch.stack([torch.from_numpy(data[i:i + args.T].astype(np.int64)) for i in ix])
    y = torch.stack([torch.from_numpy(data[i + 1:i + 1 + args.T].astype(np.int64)) for i in ix])
    return x.to(dev), y.to(dev)

class Block(nn.Module):
    def __init__(self, C, H):
        super().__init__()
        self.ln1, self.ln2 = nn.LayerNorm(C), nn.LayerNorm(C)
        self.attn = nn.MultiheadAttention(C, H, batch_first=True)
        self.ff = nn.Sequential(nn.Linear(C, 4 * C), nn.GELU(), nn.Linear(4 * C, C))
    def forward(self, z, mask):
        h = self.ln1(z); a, _ = self.attn(h, h, h, attn_mask=mask, need_weights=False)
        z = z + a; return z + self.ff(self.ln2(z))

tok = nn.Embedding(vocab, args.C).to(dev)
pos = nn.Embedding(args.T, args.C).to(dev)
blocks = nn.ModuleList([Block(args.C, args.H) for _ in range(args.L)]).to(dev)
mask = torch.triu(torch.full((args.T, args.T), float('-inf'), device=dev), 1)
readout = lambda z: z @ tok.weight.t()
io_params = list(tok.parameters()) + list(pos.parameters())
all_params = io_params + list(blocks.parameters())
blk_params = [list(b.parameters()) for b in blocks]
opt = torch.optim.AdamW(all_params, lr=args.lr, weight_decay=1e-4)
sched = torch.optim.lr_scheduler.LambdaLR(opt, lambda s: min(1.0, (s + 1) / max(args.warmup, 1)))
NBT = args.B * args.T

def zil_step(x, y):
    """One cascade-EP (zil) gradient computation. Returns free-phase CE for logging;
    leaves grads in p.grad (normalized to CE_mean units)."""
    z0g = tok(x) + pos(torch.arange(args.T, device=dev))[None]
    z0 = z0g.detach()
    with torch.no_grad():
        zs, z = [], z0
        for b in blocks:
            z = b(z, mask); zs.append(z)
        free_ce = F.cross_entropy(readout(zs[-1]).reshape(-1, vocab), y.reshape(-1)).item()
    for p in all_params: p.grad = None
    for l in range(args.L - 1, -1, -1):
        zl = zs[l].detach().requires_grad_(True)
        # 1) state update: gamma=1 in SUM units (top gets the beta-nudge)
        if l + 1 < args.L:
            obj_u = 0.5 * ((zs[l + 1].detach() - blocks[l + 1](zl, mask)) ** 2).sum()
        else:
            obj_u = args.beta * NBT * F.cross_entropy(readout(zl).reshape(-1, vocab), y.reshape(-1))
        g = torch.autograd.grad(obj_u, zl)[0]
        zs[l] = (zl - g).detach()
        # 2) immediate local read: this block's params (+ io at the ends)
        prev = z0g if l == 0 else zs[l - 1].detach()      # l=0 keeps emb graph
        params_l = blk_params[l] + (io_params if l == 0 else [])
        obj_r = 0.5 * ((zs[l] - blocks[l](prev, mask)) ** 2).sum() / NBT
        if l + 1 == args.L:
            obj_r = obj_r + args.beta * F.cross_entropy(readout(zs[l]).reshape(-1, vocab), y.reshape(-1))
            params_l = params_l + [tok.weight]
        seen, uniq = set(), []
        for p in params_l:
            if id(p) not in seen: seen.add(id(p)); uniq.append(p)
        gs = torch.autograd.grad(obj_r, uniq, allow_unused=True)
        for p, gg in zip(uniq, gs):
            if gg is None: continue
            p.grad = gg if p.grad is None else p.grad + gg
    for p in all_params:
        if p.grad is not None: p.grad /= args.beta
    return free_ce

@torch.no_grad()
def evaluate(nb=6):
    tot = 0.0
    for _ in range(nb):
        x, y = get_batch('val')
        z = tok(x) + pos(torch.arange(args.T, device=dev))[None]
        for b in blocks: z = b(z, mask)
        tot += F.cross_entropy(readout(z).reshape(-1, vocab), y.reshape(-1)).item()
    return tot / nb

wb = None
if args.wandb:
    try:
        import wandb as _w
        wb = _w.init(project=args.wandb, name=args.wandb_run or args.tag, id=args.wandb_run or args.tag,
                     resume='allow', config=vars(args))
    except Exception as e:
        print(f'[wandb] disabled ({e})', flush=True)

n = sum(p.numel() for p in all_params)
print(f'[{args.tag}] cascade-EP(zil) L{args.L} C{args.C} H{args.H} T{args.T} beta={args.beta} | {n/1e6:.2f}M | {dev}', flush=True)
best, t0 = 1e9, time.time()
for step in range(args.steps + 1):
    x, y = get_batch('train')
    ce = zil_step(x, y)
    torch.nn.utils.clip_grad_norm_(all_params, 1.0)
    opt.step(); sched.step(); opt.zero_grad(set_to_none=True)
    if step % args.log == 0:
        val = evaluate(); best = min(best, val)
        print(f'step {step:5d}/{args.steps} | train {ce:.4f} val {val:.4f} (best {best:.4f}) '
              f'| {step/max(time.time()-t0,1e-9):.2f} it/s', flush=True)
        if wb is not None:
            try: wb.log({'train_ce': ce, 'val_ce': val, 'best': best}, step=step)
            except Exception: pass
    if step % args.save_every == 0 and step > 0:
        torch.save({'tok': tok.state_dict(), 'pos': pos.state_dict(), 'blocks': blocks.state_dict(),
                    'step': step, 'val': best, 'config': vars(args)}, Path('runs') / f'{args.tag}_s{step}.pt')
print(f'[{args.tag}] DONE best val CE {best:.4f} (BP twin reference: casc_bp6)', flush=True)
if wb is not None:
    try: wb.summary['best_val_ce'] = best; wb.finish()
    except Exception: pass