"""Training loop for Alea-mini on a single GPU.

Speed levers vs v1: dataset pre-packed once; length-bucketed batching (minimal
padding); attention mask built on GPU from segment ids (no per-item [L,L] CPU
build + H2D transfer); optional sdpa attention; selectable trunk freeze mode;
--init-from resumes heads+backbone from a checkpoint.
"""
import argparse
import json
import math
import os
import random
import time

import torch
import torch.nn.functional as F

from .dataset import DecisionDataset, row_to_specs
from .losses import bernoulli_brier, choice_loss, crps_loss, pinball_loss
from .model import AleaModel, collate_segments, mask_from_segments
from .packing import pack_request


def set_freeze(model, mode, tail_k=8):
    bb = model.backbone
    if mode == "full":
        return
    for p in bb.parameters():
        p.requires_grad_(False)
    if mode == "tail":
        n = len(bb.layers)
        for layer in bb.layers[n - tail_k:]:
            for p in layer.parameters():
                p.requires_grad_(True)
        for p in bb.norm.parameters():
            p.requires_grad_(True)
    elif mode == "heads":
        pass
    else:
        raise ValueError(mode)


def load_into(model, ckpt_path):
    ck = torch.load(ckpt_path, map_location="cpu", weights_only=False)
    for name, m in zip(["choice", "score", "noul", "regress"],
                       [model.choice_head, model.score_head, model.noul_head,
                        model.regress_head]):
        if name in ck.get("heads", {}):
            m.load_state_dict(ck["heads"][name])
    if ck.get("backbone"):
        model.backbone.load_state_dict(ck["backbone"])
    aux = ck.get("aux", {})
    if model.aux_embed is not None and "aux_embed" in aux:
        model.aux_embed.load_state_dict(aux["aux_embed"], strict=False)
    if model.ngram is not None and "ngram" in aux:
        try:
            model.ngram.load_state_dict(aux["ngram"])
        except Exception:
            pass
    if model.ngram2 is not None and "ngram2" in aux:
        try:
            model.ngram2.load_state_dict(aux["ngram2"])
        except Exception:
            pass
    if getattr(model, "ngram3", None) is not None and "ngram3" in aux:
        try:
            model.ngram3.load_state_dict(aux["ngram3"])
        except Exception:
            pass
    return ck.get("args", {})


def question_losses(outputs, targets, eps=0.0):
    losses = []
    for qres in outputs:
        for r in qres:
            q = targets[r["qid"]]
            if r["qtype"] == "choice":
                qt = torch.tensor(q, device=r["logits"].device)
                if eps > 0 and float(qt.max()) > 0.99:
                    n = qt.numel()
                    qt = (1 - eps) * qt + eps / n
                losses.append(choice_loss(r["logits"][None], qt[None]))
            elif r["qtype"] == "score":
                qt = torch.tensor(q, device=r["logits"].device)
                losses.append(crps_loss(r["logits"][None], qt[None]))
            elif r["qtype"] == "noul":
                qt = torch.tensor(q, device=r["p_yes"].device)
                if eps > 0:
                    qt = (1 - eps) * qt + eps * 0.5
                losses.append(bernoulli_brier(
                    torch.logit(r["p_yes"].clamp(1e-6, 1 - 1e-6))[None],
                    qt[None]))
            elif r["qtype"] == "regress":
                from .heads import TAUS
                qt = torch.tensor(q, device=r["quantiles"].device)
                losses.append(pinball_loss(r["quantiles"][None], qt[None], TAUS))
    return losses


def save_ckpt(model, heads, args, path):
    save = {"heads": {k: m.state_dict() for k, m in
                      zip(["choice", "score", "noul", "regress"], heads)},
            "args": vars(args)}
    if args.train_mode != "heads":
        save["backbone"] = model.backbone.state_dict()
    aux = {}
    if model.aux_embed is not None:
        aux["aux_embed"] = model.aux_embed.state_dict()
    if model.ngram is not None:
        aux["ngram"] = model.ngram.state_dict()
    if getattr(model, "ngram2", None) is not None:
        aux["ngram2"] = model.ngram2.state_dict()
    if getattr(model, "ngram3", None) is not None:
        aux["ngram3"] = model.ngram3.state_dict()
    if aux:
        save["aux"] = aux
    torch.save(save, path)


def main():
    ap = argparse.ArgumentParser()
    ap.add_argument("--train", default="data/train.jsonl")
    ap.add_argument("--dev", default="data/dev.jsonl")
    ap.add_argument("--out", default="runs/alea_mini")
    ap.add_argument("--model", default="Qwen/Qwen3-0.6B")
    ap.add_argument("--init-from", default=None, help="checkpoint to resume")
    ap.add_argument("--epochs", type=float, default=1.0)
    ap.add_argument("--batch", type=int, default=8)
    ap.add_argument("--accum", type=int, default=4)
    ap.add_argument("--lr-head", type=float, default=2e-4)
    ap.add_argument("--lr-backbone", type=float, default=2e-5)
    ap.add_argument("--train-mode", default="tail",
                    choices=["heads", "tail", "full"])
    ap.add_argument("--tail-k", type=int, default=8)
    ap.add_argument("--use-aux-embed", action="store_true",
                    help="add second trainable embedding table (~155M params)")
    ap.add_argument("--use-ngram", action="store_true",
                    help="add hashed n-gram encoder (~100M params)")
    ap.add_argument("--use-ngram2", action="store_true",
                    help="second n-gram bank, orders 5-8, 512k buckets")
    ap.add_argument("--use-ngram3", action="store_true",
                    help="multi-hash n-gram bank, orders 3-6, K=2 tables")
    ap.add_argument("--lr-aux", type=float, default=3e-4,
                    help="lr for aux_embed/ngram modules (fresh params)")
    ap.add_argument("--attn", default="sdpa", choices=["eager", "sdpa"])
    ap.add_argument("--max-len", type=int, default=2048)
    ap.add_argument("--token-budget", type=int, default=24576,
                    help="cap batch by tokens: batch_n*max_len <= budget")
    ap.add_argument("--max-items", type=int, default=0)
    ap.add_argument("--save-every", type=int, default=1000)
    ap.add_argument("--seed", type=int, default=0)
    ap.add_argument("--label-smooth", type=float, default=0.0)
    args = ap.parse_args()

    torch.manual_seed(args.seed)
    random.seed(args.seed)
    dev = torch.device("cuda" if torch.cuda.is_available() else "cpu")

    from transformers import AutoTokenizer
    tok = AutoTokenizer.from_pretrained(args.model)
    model = AleaModel(args.model, attn_impl=args.attn,
                      use_aux_embed=args.use_aux_embed,
                      use_ngram=args.use_ngram, use_ngram2=args.use_ngram2,
                      use_ngram3=args.use_ngram3).to(dev)
    model.backbone.gradient_checkpointing_enable()
    if args.init_from:
        prev = load_into(model, args.init_from)
        print(f"resumed from {args.init_from}")
    set_freeze(model, args.train_mode, args.tail_k)

    heads = [model.choice_head, model.score_head, model.noul_head,
             model.regress_head]
    head_params = [p for m in heads for p in m.parameters()]
    bb_params = [p for p in model.backbone.parameters() if p.requires_grad]
    groups = [{"params": head_params, "lr": args.lr_head}]
    if bb_params:
        groups.append({"params": bb_params, "lr": args.lr_backbone})
    aux_params = [p for m in (model.aux_embed, model.ngram, model.ngram2,
                              getattr(model, "ngram3", None)) if m is not None
                  for p in m.parameters()]
    if aux_params:
        groups.append({"params": aux_params, "lr": args.lr_aux})
    opt = torch.optim.AdamW(groups, weight_decay=0.01)

    warmup_frac = 0.03
    def lr_lambda(s):
        wu = max(1, int(total_steps * warmup_frac))
        if s < wu:
            return s / wu
        p = (s - wu) / max(1, total_steps - wu)
        return 0.5 * (1 + math.cos(math.pi * min(1.0, p)))

    print("pre-packing dataset...", flush=True)
    ds = DecisionDataset(args.train, tok, max_len=args.max_len)
    if args.max_items:
        ds.rows = ds.rows[: args.max_items]
    items = []
    skipped = 0
    for row in ds.rows:
        try:
            state, qs, targets = row_to_specs(row)
            pk = pack_request(tok, state, qs, max_len=args.max_len)
            items.append((pk, targets))
        except ValueError:
            skipped += 1
    n = len(items)
    print(f"packed {n} (skipped {skipped}) trainable="
          f"{sum(p.numel() for p in model.parameters() if p.requires_grad)/1e6:.1f}M",
          flush=True)

    # token-budget batching: sort by length, then chunk so that
    # batch_size * max_len_in_batch <= token_budget (long items -> small
    # batches, short items -> up to --batch wide)
    lengths = [len(p.input_ids) for p, _ in items]
    order = sorted(range(n), key=lambda i: lengths[i])
    batches, cur, cur_max = [], [], 0
    for i in order:
        new_max = max(cur_max, lengths[i])
        if cur and ((len(cur) + 1) * new_max > args.token_budget
                    or len(cur) >= args.batch):
            batches.append(cur)
            cur, cur_max = [], 0
            new_max = lengths[i]
        cur.append(i)
        cur_max = new_max
    if cur:
        batches.append(cur)
    steps_per_epoch = math.ceil(len(batches) / args.accum)
    total_steps = int(steps_per_epoch * args.epochs)
    sched = torch.optim.lr_scheduler.LambdaLR(opt, lr_lambda)
    pad_id = tok.pad_token_id if tok.pad_token_id is not None else tok.eos_token_id

    os.makedirs(args.out, exist_ok=True)
    step, micro, running = 0, 0, 0.0
    t0 = time.time()
    model.train()

    done = False
    while not done:
        random.shuffle(batches)
        for batch_idx in batches:
            packeds = [items[i][0] for i in batch_idx]
            targs = [items[i][1] for i in batch_idx]
            ids, pos, seg, qof, oof = collate_segments(packeds, pad_id)
            ids, pos = ids.to(dev), pos.to(dev)
            mask = mask_from_segments(seg.to(dev), qof.to(dev),
                                      oof.to(dev)).to(torch.bfloat16)

            out = model(ids, mask, pos, packeds)
            losses = []
            for qi, qres in enumerate(out):
                losses += question_losses([qres], targs[qi],
                                          getattr(args, "label_smooth", 0.0))
            loss = torch.stack(losses).mean() / args.accum
            loss.backward()
            running += loss.item() * args.accum
            micro += 1

            if micro % args.accum == 0:
                torch.nn.utils.clip_grad_norm_(
                    [p for g in groups for p in g["params"]], 1.0)
                opt.step()
                sched.step()
                opt.zero_grad(set_to_none=True)
                step += 1
                if step % 50 == 0:
                    el = time.time() - t0
                    mem = torch.cuda.max_memory_allocated() / 2**30
                    print(f"step {step}/{total_steps} "
                          f"loss={running/(50*args.accum):.4f} "
                          f"{el/step:.2f}s/step peak={mem:.1f}GB", flush=True)
                    running = 0.0
                if step % args.save_every == 0 or step == total_steps:
                    ck = os.path.join(args.out, f"step{step}.pt")
                    save_ckpt(model, heads, args, ck)
                    print(f"saved {ck}", flush=True)
                if step >= total_steps:
                    done = True
                    break
        if step >= total_steps:
            break

    save_ckpt(model, heads, args, os.path.join(args.out, "final.pt"))
    print("done")


if __name__ == "__main__":
    main()