# /// script
# dependencies = ["trl>=1.9.0", "peft>=0.7.0", "transformers>=4.44", "datasets", "accelerate"]
# ///
"""SakThai 0.5B improvement experiments, scored on sakthai-bench-v1.

Two modes, selected by SAK_MODE, each changing ONE variable from the run before it
so the bench table attributes the difference to a single cause:

  lora-masked  LoRA (same config as the v7 baseline) + prompt masking.
               vs the baseline this isolates *masking*.
  full-masked  Full fine-tune of all 494M params + prompt masking.
               vs lora-masked this isolates *LoRA vs full fine-tune*.

Prompt masking: the baseline computes loss over the whole rendered string,
including a system prompt that carries the entire <tools> schema block — so much
of the gradient teaches the model to reproduce schemas rather than call them.
Here each assistant turn becomes its own prompt/completion pair and TRL's
completion_only_loss masks the prompt. This also roughly doubles the number of
supervised examples (2050 conversations -> ~3822 turns).

Adapters/models are pushed to *-exp-<mode> repos so the baseline v2 artifacts are
never overwritten by an experiment. This script does NOT evaluate: scoring is done
once, for all variants together, by eval_bench.py in the sakthai-bench-v1 repo, so
every number in a comparison comes from the same scorer.
"""
import os, json, gc, random, hashlib, urllib.request
from collections import Counter
import torch
import torch.nn.functional as F
from datasets import load_dataset, Dataset
from transformers import AutoModelForCausalLM, AutoTokenizer
from peft import LoraConfig, get_peft_model
from trl import SFTTrainer, SFTConfig

MODE = os.environ.get("SAK_MODE", "lora-masked")
assert MODE in ("lora-masked", "full-masked"), MODE
SEED = int(os.environ.get("SAK_SEED", "20260729"))
# Trainer seed is SEPARATE from the data seed above. Conflating them is what broke
# every -v2 run: the 19:30 revision passed seed=SEED into SFTConfig, moving the
# trainer seed off its previous default of 42, and all four runs then hit NaN at
# epoch 0.756 — at 4e-4 AND at 2e-5, so the LR was never the cause. Keep 42 unless
# you are deliberately probing seed sensitivity, and change ONE of these at a time.
TRAINER_SEED = int(os.environ.get("SAK_TRAINER_SEED", "42"))
EPOCHS = int(os.environ.get("SAK_EPOCHS", "3"))
TAG = os.environ.get("SAK_TAG", "v2")
random.seed(SEED)

USER, BASE_MODEL = "Nanthasit", "Qwen/Qwen2.5-0.5B-Instruct"
OLD_MERGED = f"{USER}/sakthai-context-0.5b-merged"
OUT_REPO   = f"{USER}/sakthai-context-0.5b-exp-{MODE}-{TAG}"
DATASET    = f"{USER}/sakthai-combined-v7"
BENCH      = f"{USER}/sakthai-bench-v2"
EXCLUDE_URL = f"https://huggingface.co/datasets/{BENCH}/resolve/main/train_exclude_fingerprints.json"
MAX_LEN = int(os.environ.get("SAK_MAXLEN", "1536"))
MAX_TURNS_PER_CONV, PARALLEL_OVERSAMPLE = 4, 3
# Selection is ~90% but argument accuracy is 43.6% — that gap is now the target.
# Rank is the main capacity lever for memorising argument shapes; dropout and
# sequence length are the secondary ones (the latter because over-length pairs
# are dropped, and long prompts are where argument-heavy calls live).
RANK = int(os.environ.get("SAK_RANK", "16"))
DROPOUT = float(os.environ.get("SAK_DROPOUT", "0.05"))

tokenizer = AutoTokenizer.from_pretrained(BASE_MODEL)
if tokenizer.pad_token is None:
    tokenizer.pad_token = tokenizer.eos_token

# ── Manual ChatML renderer (Qwen's template cannot render this data) ──────
def _text(c):
    return "" if c is None else (c if isinstance(c, str) else json.dumps(c, ensure_ascii=False))
def _tools_block(tools):
    if not tools: return ""
    sigs = "\n".join(json.dumps(t, ensure_ascii=False) for t in tools)
    return ("\n\n# Tools\n\nYou may call one or more functions. Signatures are within "
            "<tools></tools>:\n<tools>\n" + sigs + "\n</tools>\n\nFor each call return:\n"
            "<tool_call>\n{\"name\": <name>, \"arguments\": <json>}\n</tool_call>")
def _assistant_body(m):
    body = _text(m.get("content"))
    for tc in (m.get("tool_calls") or []):
        fn = tc.get("function", tc); a = fn.get("arguments", "{}")
        if not isinstance(a, str): a = json.dumps(a, ensure_ascii=False)
        body += ("\n" if body else "") + '<tool_call>\n{"name": "%s", "arguments": %s}\n</tool_call>' % (fn.get("name", ""), a)
    return body
def _render_msg(m, tools_sys):
    r = m.get("role")
    if r == "system": return "<|im_start|>system\n" + _text(m.get("content")) + _tools_block(tools_sys) + "<|im_end|>\n"
    if r == "user":   return "<|im_start|>user\n" + _text(m.get("content")) + "<|im_end|>\n"
    if r == "tool":   return "<|im_start|>user\n<tool_response>\n" + _text(m.get("content")) + "\n</tool_response><|im_end|>\n"
    if r == "assistant": return "<|im_start|>assistant\n" + _assistant_body(m) + "<|im_end|>\n"
    return ""
def render_chatml(messages, tools, add_generation_prompt=False):
    messages = messages or []
    out = []
    if not (messages and messages[0].get("role") == "system") and tools:
        out.append("<|im_start|>system\nYou are a helpful assistant." + _tools_block(tools) + "<|im_end|>\n")
    for i, m in enumerate(messages):
        out.append(_render_msg(m, tools if (i == 0 and m.get("role") == "system") else None))
    if add_generation_prompt: out.append("<|im_start|>assistant\n")
    return "".join(out)

def fingerprint(messages):
    return hashlib.sha1(json.dumps(messages, sort_keys=True, ensure_ascii=False).encode()).hexdigest()

# ── Data: explode into prompt/completion pairs, one per assistant turn ────
with urllib.request.urlopen(EXCLUDE_URL) as r:
    _ex = json.load(r)
EXCLUDE, HELD_OUT_TOOLS = set(_ex["fingerprints"]), set(_ex["held_out_tools"])

def _keep(ex):
    if fingerprint(ex["messages"]) in EXCLUDE:
        return False
    names = {(t.get("function") or {}).get("name") or t.get("name") for t in (ex.get("tools") or [])}
    return not (names & HELD_OUT_TOOLS)

raw = load_dataset(DATASET, split="train").filter(_keep)
print(f"conversations after bench exclusion: {len(raw)} | "
      f"rank={RANK} dropout={DROPOUT} max_len={MAX_LEN}")

pairs = []
for ex in raw:
    msgs, tools = ex["messages"], (ex.get("tools") or None)
    idxs = [i for i, m in enumerate(msgs) if m.get("role") == "assistant"]
    # Cap long conversations: 6% of them would otherwise contribute 20% of rows.
    if len(idxs) > MAX_TURNS_PER_CONV:
        idxs = sorted(random.sample(idxs, MAX_TURNS_PER_CONV))
    for i in idxs:
        completion = _assistant_body(msgs[i])
        if not completion.strip():
            continue
        gold = [(tc.get("function") or {}).get("name") for tc in (msgs[i].get("tool_calls") or [])]
        gold = [n for n in gold if n]
        pair = {
            "prompt": render_chatml(msgs[:i], tools, add_generation_prompt=True),
            "completion": completion + "<|im_end|>",
        }
        # Exploding to turn level collapses parallel calls to ~5% of turns (most
        # assistant turns in multi-turn chats are plain replies after a tool
        # result), while the bench is 30% parallel. Oversample so the training
        # mix is not itself the reason parallel scores move.
        pairs.extend([pair] * (PARALLEL_OVERSAMPLE if len(gold) > 1 else 1))
print("prompt/completion pairs:", len(pairs))
DUP_CAP = int(os.environ.get("SAK_DUP_CAP", "0"))  # 0 = off; N = keep at most N copies of an identical pair
def cap_duplicates(pairs, cap):
    """Keep at most `cap` copies of each identical (prompt, completion) pair.
    cap <= 0 disables (returns the list unchanged)."""
    if cap <= 0:
        return list(pairs)
    seen, out = Counter(), []
    for p in pairs:
        k = _key(p)
        if seen[k] < cap:
            out.append(p)
            seen[k] += 1
    return out
def _key(p):
    return (p["prompt"], p["completion"])
pairs = cap_duplicates(pairs, DUP_CAP)
print(f"after SAK_DUP_CAP={DUP_CAP}: {len(pairs)} pairs")

train_ds = Dataset.from_list(pairs)
_before = len(train_ds)
train_ds = train_ds.filter(
    lambda e: len(tokenizer(e["prompt"] + e["completion"]).input_ids) <= MAX_LEN)
print(f"dropped {_before - len(train_ds)} pairs over {MAX_LEN} tokens; training on {len(train_ds)}")

# ── Train ────────────────────────────────────────────────────────────────
model = AutoModelForCausalLM.from_pretrained(BASE_MODEL, torch_dtype=torch.bfloat16, device_map="cuda")
model.config.use_cache = False
if MODE == "lora-masked":
    model = get_peft_model(model, LoraConfig(
        r=RANK, lora_alpha=2 * RANK, lora_dropout=DROPOUT, bias="none",
        task_type="CAUSAL_LM", use_rslora=True,
        target_modules=["q_proj","k_proj","v_proj","o_proj","gate_proj","up_proj","down_proj"]))
    model.print_trainable_parameters()
    # 4e-4 (sqrt-scaled for batch 64) is marginally unstable: it survives 3 epochs
    # but diverges to NaN by 6. Overridable so longer runs can drop it.
    lr = float(os.environ.get("SAK_LR", "4e-4"))
else:
    # Full fine-tune needs a far lower LR than LoRA; 4e-4 would destroy the base.
    lr = float(os.environ.get("SAK_LR", "2e-5"))
    print("full fine-tune: all", sum(p.numel() for p in model.parameters()), "params trainable")

args = SFTConfig(output_dir=f"out-{MODE}-{TAG}", num_train_epochs=EPOCHS, seed=TRAINER_SEED,
                 per_device_train_batch_size=32, gradient_accumulation_steps=2,
                 learning_rate=lr, gradient_checkpointing=False,
                 lr_scheduler_type="cosine", warmup_ratio=0.1, logging_steps=5,
                 save_strategy="no", bf16=True, max_length=MAX_LEN,
                 completion_only_loss=True,          # mask the prompt
                 push_to_hub=False, report_to="none", run_name=f"sakthai-0.5b-{MODE}-{TAG}")
def zero_nonfinite_grads(model):
    """If ANY parameter gradient is non-finite, zero ALL gradients (making the
    next optimizer step a no-op) and return the offender count. Finite grads
    are left untouched and 0 is returned."""
    bad = [n for n, p in model.named_parameters()
           if p.grad is not None and not torch.isfinite(p.grad).all()]
    if bad:
        for p in model.parameters():
            if p.grad is not None:
                p.grad.zero_()
    return len(bad)

def reforward_diagnostics(model, input_ids, attention_mask, labels):
    """No-grad reforward WITHOUT labels (fused linear+CE models return
    logits=None when labels are passed — the bug that killed the first two
    diagnostic runs). Manual shifted cross-entropy over unmasked labels."""
    with torch.no_grad():
        out = model(input_ids=input_ids, attention_mask=attention_mask)
        logits = out.logits
        result = {
            "logits_nan": bool(torch.isnan(logits).any()),
            "logits_inf": bool(torch.isinf(logits).any()),
            "loss": None,
        }
        shifted = logits[:, :-1].float()
        targets = labels[:, 1:]
        mask = targets != -100
        if mask.any():
            result["loss"] = float(F.cross_entropy(shifted[mask], targets[mask]))
    return result

class NanGuard(SFTTrainer):
    _events = 0
    def training_step(self, model, inputs, num_items_in_batch=None):
        ids, labels = inputs["input_ids"], inputs["labels"]
        loss = super().training_step(model, inputs, num_items_in_batch)
        n_bad = zero_nonfinite_grads(model)
        if n_bad or not torch.isfinite(loss):
            NanGuard._events += 1
            print(f"\n!!! non-finite ({n_bad} grad params) event #{NanGuard._events} "
                  f"at step {self.state.global_step} epoch {self.state.epoch}")
            print(">>> gradients zeroed - update skipped, training continues")
            if NanGuard._events <= 2:
                try:
                    unmasked = (labels != -100).sum(-1)
                    print("unmasked labels/row:", unmasked.tolist())
                    diag = reforward_diagnostics(model, ids, inputs.get("attention_mask"), labels)
                    print("reforward:", diag)
                    for k in range(ids.shape[0]):
                        txt = tokenizer.decode(ids[k], skip_special_tokens=False).replace(tokenizer.pad_token, "")
                        print(f"--- row {k} unmasked={unmasked[k].item()}: {repr(txt[-250:])}")
                except Exception as e:
                    import traceback; print("diag failed (continuing):", e); traceback.print_exc()
            return torch.zeros_like(loss)
        return loss

trainer = NanGuard(model=model, args=args, train_dataset=train_ds, processing_class=tokenizer)
trainer.train()
if NanGuard._events:
    print(f"NanGuard skipped {NanGuard._events} poisoned micro-batches; weights stayed clean.")

if MODE == "lora-masked":
    merged = trainer.model.merge_and_unload()
else:
    merged = trainer.model
merged.push_to_hub(OUT_REPO); tokenizer.push_to_hub(OUT_REPO)
print(f"pushed -> {OUT_REPO}")

print(f"\nDone: {MODE}. Score it with eval_bench.py from the bench repo:")
print(f"  SAK_MODELS={OUT_REPO} -> Nanthasit/sakthai-bench-v1/eval_bench.py")