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"""Rescore existing unconditional samples with independent causal language models.

This leaves the canonical GPT-2 Large metrics untouched. Run from the repository
root with the dlb-eval environment and one free GPU.
"""

from __future__ import annotations

import argparse
from dataclasses import asdict
import json
import math
from pathlib import Path

from dlb.io import atomic_json_write, sha256_file, validate_samples
from evaluation.generative_perplexity import compute_gen_ppl


ROOT = Path(__file__).resolve().parents[1]
MODELS = {
    "pythia-1b": (
        "EleutherAI/pythia-1b",
        "f73d7dcc545c8bd326d8559c8ef84ffe92fea6b2",
        ["*.json", "model.safetensors"],
    ),
    "opt-1.3b": (
        "facebook/opt-1.3b",
        "3f5c25d0bc631cb57ac65913f76e22c2dfb61d62",
        ["*.json", "pytorch_model.bin", "merges.txt", "vocab.json"],
    ),
}
DATASETS = ("lm1b", "owt")
GENERATORS = ("fmlm", "duo_dcd", "duo_di4c", "mdlm_sdtt", "mdlm_di4c")
STEPS = (1, 2, 4)
SAMPLE_COUNT = 1024
CONTEXT_LENGTH = 1024


def scorer_class():
    import torch
    import torch.nn.functional as functional

    class Float32LossScorer:
        def __init__(self, model):
            self.model = model

        def eval(self):
            self.model.eval()
            return self

        def score_batch(self, input_ids, attention_mask):
            ids = torch.as_tensor(input_ids, dtype=torch.long, device="cuda")
            mask = torch.as_tensor(attention_mask, dtype=torch.bool, device="cuda")
            with torch.inference_mode():
                logits = self.model(input_ids=ids, attention_mask=mask).logits
                labels = ids[:, 1:].clone()
                valid = mask[:, 1:]
                labels.masked_fill_(~valid, -100)
                loss = functional.cross_entropy(
                    logits[:, :-1, :].float().reshape(-1, logits.size(-1)),
                    labels.reshape(-1),
                    ignore_index=-100,
                    reduction="sum",
                )
            return float(loss.item()), int(valid.sum().item())

    return Float32LossScorer


def load_model(model_key: str):
    import torch
    from huggingface_hub import snapshot_download
    from transformers import AutoModelForCausalLM, AutoTokenizer

    repo_id, revision, patterns = MODELS[model_key]
    snapshot = Path(
        snapshot_download(repo_id=repo_id, revision=revision, allow_patterns=patterns)
    )
    tokenizer = AutoTokenizer.from_pretrained(snapshot, local_files_only=True)
    tokenizer.padding_side = "right"
    tokenizer.truncation_side = "right"
    if tokenizer.pad_token_id is None:
        tokenizer.pad_token = tokenizer.eos_token
    model = AutoModelForCausalLM.from_pretrained(
        snapshot, local_files_only=True, dtype=torch.float32
    ).to("cuda").eval()
    return scorer_class()(model), tokenizer, snapshot


def sample_path(dataset: str, generator: str, steps: int) -> Path:
    return ROOT / "results" / "samples" / dataset / generator / f"steps_{steps}" / "samples.jsonl"


def output_path(output_root: Path, model_key: str, dataset: str, generator: str, steps: int) -> Path:
    return output_root / model_key / dataset / generator / f"steps_{steps}.json"


def valid_existing(path: Path, sample_sha: str, model_key: str) -> bool:
    if not path.is_file():
        return False
    try:
        row = json.loads(path.read_text(encoding="utf-8"))
        ppl = row["generative_perplexity"]
        return (
            row["samples_sha256"] == sample_sha
            and row["sample_count"] == SAMPLE_COUNT
            and ppl["model_id"] == MODELS[model_key][0]
            and ppl["model_revision"] == MODELS[model_key][1]
            and ppl["forward_dtype"] == "float32"
            and ppl["valid_token_count"] > 0
            and math.isfinite(ppl["perplexity"])
        )
    except (KeyError, TypeError, ValueError, OSError):
        return False


def main() -> None:
    import torch
    import transformers

    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--model", choices=(*MODELS, "all"), default="all")
    parser.add_argument("--output-root", type=Path, default=ROOT / "results" / "ppl_rescore_20260923")
    parser.add_argument("--batch-size", type=int, default=8)
    parser.add_argument("--smoke-samples", type=int, default=0)
    args = parser.parse_args()
    if args.batch_size < 1 or args.smoke_samples < 0:
        parser.error("batch-size must be positive and smoke-samples must be nonnegative")

    # Validate the entire input matrix before loading a scorer or writing results.
    inputs = {}
    for dataset in DATASETS:
        for generator in GENERATORS:
            for steps in STEPS:
                path = sample_path(dataset, generator, steps)
                validate_samples(path, expected=SAMPLE_COUNT)
                inputs[(dataset, generator, steps)] = (path, sha256_file(path))
    print(f"Validated {len(inputs)} sample files x {SAMPLE_COUNT} samples", flush=True)

    model_keys = tuple(MODELS) if args.model == "all" else (args.model,)
    for model_key in model_keys:
        pending = [
            (dataset, generator, steps)
            for dataset in DATASETS
            for generator in GENERATORS
            for steps in STEPS
            if args.smoke_samples or not valid_existing(
                output_path(args.output_root, model_key, dataset, generator, steps),
                inputs[(dataset, generator, steps)][1], model_key,
            )
        ]
        if not pending:
            print(f"{model_key}: all {len(inputs)} outputs already validated", flush=True)
            continue
        scorer, tokenizer, snapshot = load_model(model_key)
        print(f"{model_key}: loaded {snapshot}; pending={len(pending)}", flush=True)
        for index, (dataset, generator, steps) in enumerate(pending, 1):
            path, sample_sha = inputs[(dataset, generator, steps)]
            with path.open(encoding="utf-8") as handle:
                texts = [json.loads(line)["text"] for line in handle]
            if args.smoke_samples:
                texts = texts[:args.smoke_samples]
            result = compute_gen_ppl(
                texts, scorer, tokenizer, batch_size=args.batch_size,
                max_length=CONTEXT_LENGTH,
                model_revision=MODELS[model_key][1],
                tokenizer_revision=MODELS[model_key][1],
            )
            metric = {
                **asdict(result),
                "model_id": MODELS[model_key][0],
                "tokenizer_id": MODELS[model_key][0],
                "model_snapshot": str(snapshot),
                "tokenizer_snapshot": str(snapshot),
                "forward_dtype": "float32",
                "loss_dtype": "float32",
                "torch_version": torch.__version__,
                "transformers_version": transformers.__version__,
                "offline_scoring": True,
            }
            print(
                f"{model_key} {index}/{len(pending)} {dataset}/{generator}/{steps} "
                f"samples={len(texts)} tokens={result.valid_token_count} "
                f"ppl={result.perplexity:.6f}", flush=True,
            )
            if args.smoke_samples:
                break
            atomic_json_write(
                output_path(args.output_root, model_key, dataset, generator, steps),
                {
                    "schema_version": 1,
                    "evaluation": "independent_unconditional_ppl_rescore",
                    "samples": str(path),
                    "samples_sha256": sample_sha,
                    "sample_count": SAMPLE_COUNT,
                    "dataset": dataset,
                    "generator": generator,
                    "steps": steps,
                    "generative_perplexity": metric,
                },
            )


if __name__ == "__main__":
    main()