examples/trl/prm_train_from_records.py

"""
Train a PRM from pre-collected rollout data stored in checkpoint JSONL files.

Reads checkpoint files written by prm_trainer.py during rollout collection and
builds a soft-label PRM training dataset without re-running any games.

Each checkpoint JSONL row has the form:
    {"checkpoint_id": "<uuid>", "prompt": [...], "response": "...", "outcomes": [0,1,0,0]}

Rows with the same checkpoint_id are grouped and their outcomes averaged into
a true Monte Carlo soft label — the same label that would have been computed
during live training.

Usage:
    python examples/trl/prm_train_from_records.py \\
        --checkpoint-dir prm-checkpoints/Qwen3.5-27B-Instruct-4bit \\
        --epochs 1 2 \\
        --model /nfs/turbo/coe-chaijy-unreplicated/pre-trained-weights/Qwen3.5-27B \\
        --output models/prm/Qwen3.5-27B-Instruct-4bit
"""

from __future__ import annotations

import argparse
import json
import os
import re
import shutil
from collections import defaultdict
from pathlib import Path
import sys

import torch
import torch.nn.functional as F
from transformers import (
    AutoConfig,
    AutoModelForSequenceClassification,
    AutoTokenizer,
    BitsAndBytesConfig,
    DataCollatorWithPadding,
    EarlyStoppingCallback,
    Trainer,
    TrainingArguments,
)
from peft import LoraConfig, TaskType, get_peft_model, prepare_model_for_kbit_training
from datasets import Dataset

# Reuse the static loader from prm_trainer
sys.path.insert(0, str(Path(__file__).parent))


# ---------------------------------------------------------------------------
# BCE trainer (identical to prm_trainer.py)
# ---------------------------------------------------------------------------

class _SoftBCETrainer(Trainer):
    def compute_loss(self, model, inputs, return_outputs=False, **kwargs):
        labels = inputs.pop("labels").float()
        outputs = model(**inputs)
        logits = outputs.logits
        # Handle both num_labels=1 → [batch,1] and num_labels=2 → [batch,2]
        if logits.dim() == 2 and logits.shape[-1] == 2:
            logits = logits[:, 1] - logits[:, 0]  # log-odds for binary
        else:
            logits = logits.squeeze(-1)
        loss = F.binary_cross_entropy_with_logits(logits, labels)
        return (loss, outputs) if return_outputs else loss


# ---------------------------------------------------------------------------
# Data loading
# ---------------------------------------------------------------------------

def resolve_checkpoint_dir(checkpoint_dir: Path, reward_mode: str | None) -> Path:
    """Resolve --checkpoint-dir to the directory that actually holds the JSONL.

    The PRM collector writes per-reward-mode subdirs:
        prm-checkpoints/<model>/success/epoch_*.jsonl
        prm-checkpoints/<model>/bench/epoch_*.jsonl
    so that the two label sets (binary success vs graded bench) never mix. This
    accepts any of:
      * a dir that already has epoch_*.jsonl  -> used as-is (subdir or flat)
      * --reward-mode given                   -> <checkpoint_dir>/<mode>
      * exactly one mode subdir has files     -> auto-pick it (with a note)
      * both modes present, no --reward-mode  -> hard error (must disambiguate),
        because training on a mix of the two label semantics is wrong.
    """
    if list(checkpoint_dir.glob("epoch_*.jsonl")):
        return checkpoint_dir
    if reward_mode is not None:
        return checkpoint_dir / reward_mode
    modes = [m for m in ("success", "bench")
             if list((checkpoint_dir / m).glob("epoch_*.jsonl"))]
    if len(modes) == 1:
        print(f"Auto-detected reward-mode subdir: {checkpoint_dir / modes[0]}")
        return checkpoint_dir / modes[0]
    if len(modes) > 1:
        raise SystemExit(
            f"\n{checkpoint_dir} holds multiple reward modes {modes} with different "
            f"label semantics (binary 'success' vs graded 'bench') — training a mix "
            f"is wrong.\nRe-run with --reward-mode <success|bench>, or point "
            f"--checkpoint-dir at one subdir (e.g. {checkpoint_dir / 'bench'})."
        )
    return checkpoint_dir  # nothing found; load_prm_dataset prints the empty-dir notice


def load_prm_dataset(checkpoint_dir: Path, epoch_nums: list[int] | None,
                     game: str | None = None) -> Dataset:
    """Load checkpoint JSONL files and build a true-MC soft-label PRM dataset.

    Checkpoint files are named ``epoch_NNNNN_shardSS_<game>.jsonl``. Passing
    ``game`` restricts the load to that game's files (for a per-game PRM); the
    default pools every game into one PRM.
    """
    scores_by_id: dict[str, list[float]] = defaultdict(list)
    meta_by_id: dict[str, dict] = {}

    if game is not None:
        # Same sanitisation the collector applies to game names in filenames.
        g = re.sub(r"[^A-Za-z0-9._-]", "_", game)
        # The game token is the full suffix before .jsonl, so no game name can
        # be a false prefix of another (e.g. wordle vs wordle_withclue).
        available = sorted(checkpoint_dir.glob(f"epoch_*_{g}.jsonl"))
    else:
        available = sorted(checkpoint_dir.glob("epoch_*.jsonl"))
    if epoch_nums is not None:
        available = [p for p in available if int(p.stem.split("_")[1]) in epoch_nums]

    if not available:
        print(f"No checkpoint files found in {checkpoint_dir}")
        return Dataset.from_list([])

    for path in available:
        n_rows = 0
        with open(path) as f:
            for line in f:
                if not line.strip():
                    continue
                row = json.loads(line)
                cid = row["checkpoint_id"]
                scores_by_id[cid].extend(row["outcomes"])
                if cid not in meta_by_id:
                    meta_by_id[cid] = {
                        "prompt": row["prompt"],
                        "response": row["response"],
                    }
                n_rows += 1
        print(f"  {path.name}: {n_rows} checkpoint rows")

    examples = []
    for cid, scores in scores_by_id.items():
        info = meta_by_id[cid]
        examples.append({
            "prompt": info["prompt"],
            "completion": [{"role": "assistant", "content": info["response"]}],
            "label": sum(scores) / len(scores),
            "n_rollouts": len(scores),
        })

    print(f"\nTotal unique (state, response) pairs: {len(examples)}")
    _print_label_distribution(examples)
    return Dataset.from_list(examples)


def load_prm_dataset_from_interactions(
    records_dir: Path,
    epoch_nums: list[int] | None,
    player_name: str,
    branching_factor: int,
) -> Dataset:
    """Load from interactions.json files using sequential branch grouping.

    Branches are written in order: checkpoint 0 → branches 1-N,
    checkpoint 1 → branches N+1-2N, etc.  Grouping by N recovers the true
    MC groups without needing the checkpoint_id field.
    """
    examples = []

    available_epochs = sorted(records_dir.glob("epoch_*"))
    if epoch_nums is not None:
        available_epochs = [
            p for p in available_epochs
            if p.is_dir() and int(p.name.split("_")[1]) in epoch_nums
        ]

    for epoch_dir in available_epochs:
        # Collect all branch files grouped by instance directory
        instance_dirs = sorted({
            f.parent.parent
            for f in epoch_dir.rglob("interactions.json")
        })

        for instance_dir in instance_dirs:
            branch_files = sorted(instance_dir.glob("branch_*/interactions.json"),
                                  key=lambda p: int(p.parent.name.split("_")[1]))
            if not branch_files:
                continue

            # Load all branches for this instance
            branches = []
            for bf in branch_files:
                d = json.loads(bf.read_text())
                outcome = 1.0 if d.get("Success", 0) else 0.0

                # Extract player turns as (gm_prompt, player_response) pairs
                turns = []
                for turn in d.get("turns", []):
                    gm_prompt = player_response = None
                    for msg in turn:
                        act = msg.get("action", {})
                        if (msg.get("from") == "GM" and msg.get("to") == player_name
                                and act.get("type") == "send message"):
                            gm_prompt = act["content"]
                        elif (msg.get("from") == player_name and msg.get("to") == "GM"
                              and act.get("type") == "get message"):
                            player_response = act["content"]
                    if gm_prompt is not None and player_response is not None:
                        turns.append((gm_prompt, player_response))

                branches.append({"turns": turns, "outcome": outcome})

            # Group sequentially by branching_factor
            n = branching_factor
            n_groups = len(branches) // n
            for g in range(n_groups):
                group = branches[g * n: (g + 1) * n]
                outcomes = [b["outcome"] for b in group]

                # The shared prefix is turns 0..g from any branch (they're identical)
                # The diverging step is turn g; prompt = conversation before turn g
                ref = group[0]["turns"]
                if g >= len(ref):
                    continue  # base game was shorter than expected

                # Build conversation history up to (not including) turn g
                prompt: list[dict] = []
                for t in range(g):
                    gm_msg, player_resp = ref[t]
                    prompt.append({"role": "user", "content": gm_msg})
                    prompt.append({"role": "assistant", "content": player_resp})
                # Add the GM message that precedes the diverging response
                prompt.append({"role": "user", "content": ref[g][0]})
                response = ref[g][1]

                examples.append({
                    "prompt": prompt,
                    "completion": [{"role": "assistant", "content": response}],
                    "label": sum(outcomes) / len(outcomes),
                    "n_rollouts": len(outcomes),
                })

        print(f"  {epoch_dir.name}: done")

    print(f"\nTotal checkpoint groups: {len(examples)}")
    _print_label_distribution(examples)
    return Dataset.from_list(examples)


# ---------------------------------------------------------------------------
# Helpers
# ---------------------------------------------------------------------------

def _print_label_distribution(examples: list[dict]):
    labels = [e["label"] for e in examples]
    buckets = {"0.0": 0, "(0,0.5)": 0, "0.5": 0, "(0.5,1)": 0, "1.0": 0}
    for l in labels:
        if l == 0.0:     buckets["0.0"] += 1
        elif l < 0.5:    buckets["(0,0.5)"] += 1
        elif l == 0.5:   buckets["0.5"] += 1
        elif l < 1.0:    buckets["(0.5,1)"] += 1
        else:            buckets["1.0"] += 1
    avg = sum(labels) / len(labels) if labels else 0
    print(f"Label distribution (n={len(labels)}, mean={avg:.3f}):")
    for bucket, count in buckets.items():
        bar = "#" * min(count, 60)
        print(f"  {bucket:>10}  {bar} ({count})")


def _tokenize_batch(batch, tokenizer, max_length=1024):
    texts = []
    for prompt, completion in zip(batch["prompt"], batch["completion"]):
        messages = prompt + completion
        text = tokenizer.apply_chat_template(
            messages, tokenize=False, add_generation_prompt=False
        )
        texts.append(text)
    encoded = tokenizer(
        texts,
        truncation=True,
        max_length=max_length,     # left-truncate keeps the response (scored end)
        truncation_side="left",
        padding=False,
    )
    encoded["labels"] = batch["label"]
    return encoded


# ---------------------------------------------------------------------------
# Main
# ---------------------------------------------------------------------------

def main():
    parser = argparse.ArgumentParser(
        description="Train PRM from pre-collected rollout checkpoint files"
    )
    parser.add_argument(
        "--checkpoint-dir",
        default="prm-checkpoints/Qwen3.5-27B-Instruct-4bit",
        help="Directory with epoch_NNNNN.jsonl files. May be a per-reward-mode "
             "subdir (e.g. .../success or .../bench) or the parent dir (then use "
             "--reward-mode, or it auto-picks if only one mode is present).",
    )
    parser.add_argument(
        "--reward-mode", choices=["success", "bench"], default=None,
        help="Which reward-mode subdir under --checkpoint-dir to train on "
             "(success = Math-Shepherd binary; bench = graded eval score). "
             "Output is placed under <output>/<reward-mode> unless --output is set.",
    )
    parser.add_argument(
        "--game", default=None,
        help="Train a PER-GAME PRM from only this game's checkpoints "
             "(e.g. 'taboo'). Default: pool all games into one PRM. Output is "
             "nested under <output>/.../<game> unless --output is set.",
    )
    parser.add_argument(
        "--epochs", nargs="+", type=int, default=None,
        help="Epoch numbers to include (default: all available)",
    )
    parser.add_argument(
        "--legacy", action="store_true",
        help="Load from interactions.json files instead of JSONL checkpoints "
             "(use for data collected before checkpoint saving was added)",
    )
    parser.add_argument(
        "--branching-factor", type=int, default=4,
        help="Number of rollouts per checkpoint (used with --legacy)",
    )
    parser.add_argument(
        "--player-name", default="Player 1",
        help="Player name for turn extraction (used with --legacy)",
    )
    parser.add_argument(
        "--model",
        default="/nfs/turbo/coe-chaijy-unreplicated/pre-trained-weights/Qwen3.5-27B",
        help="HuggingFace model ID or local path to use as PRM base",
    )
    parser.add_argument(
        "--output", default="models/prm/Qwen3.5-27B-Instruct-4bit",
        help="Directory to save the trained PRM",
    )
    parser.add_argument(
        "--min-rollouts", type=int, default=1,
        help="Minimum number of rollouts for a training example to be included",
    )
    parser.add_argument(
        "--no-4bit", action="store_true",
        help="Disable 4-bit quantization + LoRA (trains full model, not recommended)",
    )
    parser.add_argument(
        "--bf16-lora", action="store_true",
        help="Load model in bf16 (no quantization) but still apply LoRA. "
             "Uses ~18GB for 9B model but works with torchrun DDP.",
    )
    parser.add_argument(
        "--per-device-batch-size", type=int, default=4,
        help="Per-GPU batch size. Increase to fill GPU memory (default: 4).",
    )
    parser.add_argument(
        "--gradient-accumulation-steps", type=int, default=32,
        help="Gradient accumulation steps. Reduce proportionally when increasing "
             "batch size to keep the same effective batch size (default: 32).",
    )
    parser.add_argument(
        "--resume", action="store_true",
        help="Resume training from the latest checkpoint in --output (if any). "
             "Safe to pass on a fresh run: if no checkpoint exists, trains from "
             "scratch. Relies on save_strategy='epoch' checkpoints.",
    )
    parser.add_argument(
        "--max-length", type=int, default=1024,
        help="Max tokens of (prompt+response) the PRM reads per example "
             "(left-truncated to keep the scored response). Default 1024.",
    )
    args = parser.parse_args()

    checkpoint_dir = resolve_checkpoint_dir(Path(args.checkpoint_dir), args.reward_mode)
    print(f"Using checkpoint dir: {checkpoint_dir}")

    # Keep success/bench PRMs in separate output dirs so they never overwrite
    # each other. If the resolved dir is a reward-mode subdir and --output was
    # left at its default, nest the output under that mode.
    resolved_mode = checkpoint_dir.name if checkpoint_dir.name in ("success", "bench") else None
    default_output = parser.get_default("output")
    if args.output == default_output:
        # Keep success/bench and per-game PRMs in separate output dirs so they
        # never overwrite each other: <output>/<mode>/<game>.
        suffix = Path("")
        if resolved_mode:
            suffix = suffix / resolved_mode
        if args.game:
            suffix = suffix / args.game
        if str(suffix):
            args.output = str(Path(args.output) / suffix)
            print(f"Output dir set to: {args.output}")

    if args.legacy:
        print("=== Loading dataset from interactions.json (legacy, group-by-N MC) ===")
        dataset = load_prm_dataset_from_interactions(
            checkpoint_dir, args.epochs, args.player_name, args.branching_factor
        )
    else:
        scope = f"game='{args.game}'" if args.game else "all games (pooled)"
        print(f"=== Loading dataset from checkpoint JSONL files (true MC) — {scope} ===")
        dataset = load_prm_dataset(checkpoint_dir, args.epochs, args.game)

    if args.min_rollouts > 1:
        before = len(dataset)
        dataset = dataset.filter(lambda row: row["n_rollouts"] >= args.min_rollouts)
        print(f"After min_rollouts={args.min_rollouts} filter: {len(dataset)} / {before}")

    if len(dataset) == 0:
        print("No training examples after filtering. Exiting.")
        return

    print(f"\n=== Tokenising ({len(dataset)} examples) ===")
    tokenizer = AutoTokenizer.from_pretrained(args.model)
    if tokenizer.pad_token is None:
        tokenizer.pad_token = tokenizer.eos_token
        tokenizer.pad_token_id = tokenizer.eos_token_id

    tokenized = dataset.map(
        lambda batch: _tokenize_batch(batch, tokenizer, args.max_length),
        batched=True,
        remove_columns=dataset.column_names,
        desc="Tokenising",
    )

    split = tokenized.train_test_split(test_size=0.1, seed=42)
    print(f"Train: {len(split['train'])}  Val: {len(split['test'])}")

    prm_config = AutoConfig.from_pretrained(args.model, num_labels=1)
    if hasattr(prm_config, "classifier_dropout"):
        prm_config.classifier_dropout = 0.05
    prm_config.pad_token_id = tokenizer.pad_token_id

    if args.no_4bit:
        print(f"\n=== Loading PRM classifier (full bf16, no LoRA) from: {args.model} ===")
        prm_classifier = AutoModelForSequenceClassification.from_pretrained(
            args.model, config=prm_config, torch_dtype=torch.bfloat16
        )
    elif args.bf16_lora:
        print(f"\n=== Loading PRM classifier (bf16 + LoRA) from: {args.model} ===")
        prm_classifier = AutoModelForSequenceClassification.from_pretrained(
            args.model, config=prm_config, torch_dtype=torch.bfloat16
        )
        lora_config = LoraConfig(
            task_type=TaskType.SEQ_CLS,
            r=16,
            lora_alpha=32,
            lora_dropout=0.05,
            target_modules=["q_proj", "v_proj"],
        )
        prm_classifier = get_peft_model(prm_classifier, lora_config)
        prm_classifier.config.pad_token_id = tokenizer.pad_token_id
        prm_classifier.print_trainable_parameters()
    else:
        print(f"\n=== Loading PRM classifier (4-bit + LoRA) from: {args.model} ===")
        bnb_config = BitsAndBytesConfig(
            load_in_4bit=True,
            bnb_4bit_quant_type="nf4",
            bnb_4bit_compute_dtype=torch.bfloat16,
        )
        # Under DDP (launched via torchrun), each rank must load a FULL copy of
        # the model on its OWN single GPU — `device_map="auto"` would shard one
        # model across all visible GPUs, which is incompatible with DDP. When
        # LOCAL_RANK is set, pin to that rank's GPU; otherwise fall back to the
        # single-process "auto" placement.
        local_rank = int(os.environ.get("LOCAL_RANK", -1))
        device_map = {"": local_rank} if local_rank != -1 else "auto"
        prm_classifier = AutoModelForSequenceClassification.from_pretrained(
            args.model,
            config=prm_config,
            quantization_config=bnb_config,
            device_map=device_map,
        )
        # use_reentrant=False is required for gradient checkpointing under DDP
        # (the reentrant variant breaks DDP's autograd hooks); harmless otherwise.
        prm_classifier = prepare_model_for_kbit_training(
            prm_classifier,
            use_gradient_checkpointing=True,
            gradient_checkpointing_kwargs={"use_reentrant": False},
        )
        lora_config = LoraConfig(
            task_type=TaskType.SEQ_CLS,
            r=16,
            lora_alpha=32,
            lora_dropout=0.05,
            target_modules=["q_proj", "v_proj"],
        )
        prm_classifier = get_peft_model(prm_classifier, lora_config)
        prm_classifier.config.pad_token_id = tokenizer.pad_token_id
        prm_classifier.print_trainable_parameters()

    training_args = TrainingArguments(
        output_dir=args.output,
        per_device_train_batch_size=args.per_device_batch_size,
        gradient_accumulation_steps=args.gradient_accumulation_steps,
        learning_rate=3e-5,
        adam_beta1=0.9,
        adam_beta2=0.95,
        weight_decay=0.0,
        num_train_epochs=50,
        eval_strategy="epoch",
        save_strategy="epoch",
        # load_best_model_at_end=False on purpose: under multi-node DDP its
        # end-of-train GPU reload intermittently throws CUDA "device busy/
        # unavailable" (cudaErrorDevicesUnavailable) during teardown and fails
        # the whole job AFTER training already succeeded. We instead copy the
        # best checkpoint (by eval_loss, still tracked below) on rank 0 after
        # train() — a pure file copy, no GPU op, so it can't crash.
        load_best_model_at_end=False,
        metric_for_best_model="eval_loss",
        greater_is_better=False,
        bf16=True,
        logging_steps=1,
        report_to="none",
        # Under DDP, only the LoRA adapter params require grad and all are used
        # in the forward, so disabling the unused-param search is both correct
        # and faster. Ignored when not running distributed.
        ddp_find_unused_parameters=False,
    )

    trainer = _SoftBCETrainer(
        model=prm_classifier,
        args=training_args,
        train_dataset=split["train"],
        eval_dataset=split["test"],
        data_collator=DataCollatorWithPadding(tokenizer),
        # Scaling-LLM-Test-Time-Compute (App. D) selects the checkpoint with the
        # LOWEST val loss. With only ~373 val examples and ~26 steps/epoch, val
        # loss is noisy, so patience=5 avoids stopping on a transient uptick
        # before the true minimum (we copy that best checkpoint out below).
        callbacks=[EarlyStoppingCallback(early_stopping_patience=5)],
    )

    print("\n=== Training ===")
    # Resume from the latest epoch checkpoint if --resume and one exists;
    # otherwise train from scratch (passing resume on a checkpoint-less dir errors,
    # so guard on an existing checkpoint-* subdir).
    resume = bool(args.resume) and any(Path(args.output).glob("checkpoint-*"))
    if resume:
        print(f"Resuming from latest checkpoint in {args.output}")
    trainer.train(resume_from_checkpoint=resume)

    # Save the final PRM on rank 0 ONLY, by copying the BEST checkpoint's adapter
    # (no GPU reload -> avoids the cudaErrorDevicesUnavailable crash). Falls back
    # to save_model() if no best checkpoint was recorded (e.g. no eval ran).
    if trainer.is_world_process_zero():
        out = Path(args.output)
        out.mkdir(parents=True, exist_ok=True)
        best = trainer.state.best_model_checkpoint
        if best and Path(best).is_dir():
            print(f"Best checkpoint (lowest eval_loss): {best}")
            for fn in ("adapter_model.safetensors", "adapter_config.json",
                       "adapter_model.bin", "README.md", "chat_template.jinja"):
                src = Path(best) / fn
                if src.exists():
                    shutil.copy2(src, out / fn)
        else:
            print("No best checkpoint recorded; saving current model state.")
            trainer.save_model()
        tokenizer.save_pretrained(args.output)
        print(f"\nPRM saved to {args.output}")


if __name__ == "__main__":
    main()