"""
train_split_model_cuda.py — Train binary Sandhi boundary detector on any
device (CUDA / MPS / CPU), with HuggingFace-dataset support.

This is a device-agnostic extension of train_split_model.py. It reuses the
EXACT same model/dataset classes from train_split_model.py (imported, not
copied), so a checkpoint trained here loads identically in decode_best.py /
decode_v2.py. Nothing in the original files is modified.

What it adds over train_split_model.py:
  * Explicit --device {auto,cuda,mps,cpu} selection (auto = cuda -> mps -> cpu).
  * --data accepts a local path OR "hf://<owner>/<repo>/<file.jsonl>":
      - the file is downloaded to the local HF cache with huggingface_hub
        (works for private repos if HF_TOKEN is set in the environment),
      - then trained on exactly like a local file.
  * Optional --bf16 mixed precision (Ampere/Ada+ safe — A100, L40S, H100...;
    OFF by default so the
    run is numerically identical to the MPS run).
  * --push-checkpoint <owner>/<repo>: uploads model.safetensors + config.json
    to a HuggingFace MODEL repo when training finishes (requires HF_TOKEN).
  * Defaults match the deployed checkpoint (num_modes=32, delay=2,
    latent_dim=128, 2 layers, pos_weight=6.0) so a bare run reproduces the
    same architecture.
  * Config.json is ALWAYS written, so inference picks up num_modes/delay
    instead of inferring them.

Usage:
    # local, same device logic as before (MPS on a Mac, CUDA if available)
    python train_split_model_cuda.py --data data/train_V2_fixed.jsonl \
        --delay 2 --num-modes 32 --out checkpoints/delayed_model_save_fixed

    # train from a HuggingFace dataset (private ok, needs HF_TOKEN)
    python train_split_model_cuda.py \
        --data hf://youruser/sanskrit-sandhi-boundaries-v2/train_V2_fixed.jsonl \
        --delay 2 --num-modes 32 --epochs 3 --batch 32 --grad-accum 4

    # smoke test (minutes anywhere): 500 samples, 2 epochs
    python train_split_model_cuda.py --smoke

    # force a specific device
    python train_split_model_cuda.py --device cuda --data ...
"""

from __future__ import annotations

import argparse
import json
import os
import sys
import random
from typing import Dict, List, Optional, Tuple

import numpy as np
import torch
import torch.nn as nn

# ──────────────────────────────────────────────────────────────────────
# Import the SHARED classes from the original script (single source of
# truth -> guaranteed architecture compatibility with decode_best.py).
# Guard the torch.serialization call: `add_safe_globals` only exists on
# torch >= 2.6. On older torch the import would crash, so fail with a
# clear message instead of a confusing traceback on a paid run.
# ──────────────────────────────────────────────────────────────────────
if not hasattr(torch.serialization, "add_safe_globals"):
    sys.exit(
        "torch >= 2.6 is required (torch.serialization.add_safe_globals missing). "
        "On Modal use the pinned image in modal_train.py; locally upgrade torch."
    )
from train_split_model import (  # noqa: E402
    BinaryBoundaryDataset,
    compute_metrics,
    VOCAB_SIZE,
    PAD_ID,
)

from transformers import Trainer, TrainingArguments, TrainerCallback  # noqa: E402
from model import HybridTimeScaleConfig  # noqa: E402


def build_training_args(**kwargs) -> TrainingArguments:
    """Create TrainingArguments tolerant of old AND new transformers versions.

    * Pre-4.9 transformers lack kwargs like warmup_ratio -> drop them.
    * Pre-4.46 uses evaluation_strategy instead of eval_strategy -> rename.
    * v5.x deprecates warmup_ratio (removal planned in v5.2) in favor of
      warmup_steps, which now accepts a float ratio -> convert automatically.

    Upgrade with `pip install -U transformers` to get full support.
    """
    import inspect

    try:
        import transformers as _tf
        tf_major = int(_tf.__version__.split(".")[0])
    except Exception:
        tf_major = 4

    if tf_major >= 5 and "warmup_ratio" in kwargs:
        kwargs["warmup_steps"] = kwargs.pop("warmup_ratio")

    fields = getattr(TrainingArguments, "__dataclass_fields__", None)
    known = set(fields) if fields else set(inspect.signature(TrainingArguments.__init__).parameters)

    if "eval_strategy" in kwargs and "eval_strategy" not in known and "evaluation_strategy" in known:
        kwargs["evaluation_strategy"] = kwargs.pop("eval_strategy")

    unknown = [k for k in kwargs if k not in known]
    if unknown:
        print(f"[warn] transformers too old for kwargs {unknown} — dropping them "
              f"(pip install -U transformers to enable)", file=sys.stderr)
        for k in unknown:
            kwargs.pop(k)

    return TrainingArguments(**kwargs)


class PushCheckpointCallback(TrainerCallback):
    """Push every saved checkpoint to an HF model repo the moment it is saved.

    With --push-checkpoint set, each checkpoint-<step>/ directory is uploaded
    to hf://<repo>/checkpoints/step-<step>/ as soon as the Trainer writes it.
    A mid-run kill (budget gone, instance recycled, Ctrl-C) therefore never
    loses progress: the best-so-far weights are already on the Hub. The final
    push_checkpoint() still uploads the best model to the repo root.
    """

    def __init__(self, repo_id: str):
        self.repo_id = repo_id
        self._api = None

    def _hub(self):
        if self._api is None:
            from huggingface_hub import HfApi
            self._api = HfApi()
            self._api.create_repo(repo_id=self.repo_id, repo_type="model", exist_ok=True)
        return self._api

    def on_save(self, args, state, control, **kwargs):
        step = state.global_step
        ckpt_dir = os.path.join(args.output_dir, f"checkpoint-{step}")
        if not os.path.isdir(ckpt_dir):
            return
        try:
            self._hub().upload_folder(
                repo_id=self.repo_id,
                folder_path=ckpt_dir,
                repo_type="model",
                path_in_repo=f"checkpoints/step-{step}",
                commit_message=f"checkpoint step {step}",
            )
            print(f"[push] checkpoint-{step} -> hf://{self.repo_id}/checkpoints/step-{step}",
                  file=sys.stderr)
        except Exception as e:  # never let a push failure kill training
            print(f"[push] WARNING: failed to push checkpoint-{step}: {e}",
                  file=sys.stderr)


def get_model_class(backbone: str):
    """Return the BinaryBoundaryModel class for the chosen backbone.

    * 'local': train_split_model.BinaryBoundaryModel (model.py math) — the
      default, byte-identical to the original training path.
    * 'hf':    hybrid_boundary_model.HybridBoundaryModel — built on the
      HuggingFace CodeIsAbstract/HybridTimeScale backbone (chunked parallel
      linear attention, explicit position_ids, KV-cache support). State-dict
      keys are identical (blocks.*, head.*, pos_weight), so checkpoints
      trained this way load in decode_best.py / decode_v2.py with zero
      changes. Requires the HF model.py: pip install the package, set
      HYBRID_HF_MODEL_PATH, or drop it at hf_backbone/model.py.
    """
    if backbone == "local":
        from train_split_model import BinaryBoundaryModel
        return BinaryBoundaryModel
    if backbone == "hf":
        from hybrid_boundary_model import HybridBoundaryModel
        return HybridBoundaryModel
    sys.exit(f"[error] unknown --backbone {backbone} (local|hf)")


# ---------------------------------------------------------------------------
# HF dataset resolution
# ---------------------------------------------------------------------------

def resolve_data_path(data_arg: str) -> str:
    """Turn --data into a local jsonl path.

    Accepts:
      * a local path (used as-is), or
      * hf://<owner>/<repo>/<file>  -> downloaded via huggingface_hub to the
        local HF cache (private repos work when HF_TOKEN is set).
    """
    if not data_arg.startswith("hf://"):
        if not os.path.exists(data_arg):
            sys.exit(f"[error] data file not found: {data_arg}")
        return data_arg

    spec = data_arg[len("hf://"):]
    parts = spec.split("/")
    if len(parts) < 3:
        sys.exit(
            f"[error] hf:// spec must be hf://<owner>/<repo>/<file>: {data_arg}"
        )
    repo_id = f"{parts[0]}/{parts[1]}"
    filename = "/".join(parts[2:])

    from huggingface_hub import hf_hub_download
    try:
        path = hf_hub_download(repo_id=repo_id, filename=filename,
                               repo_type="dataset")
    except Exception as e:
        sys.exit(
            f"[error] failed to download {repo_id}/{filename} from HF.\n"
            f"  If the repo is private, set HF_TOKEN (e.g. HF_TOKEN=... or "
            f"modal.Secret.from_name('hf-token')).\n  detail: {e}"
        )
    print(f"Downloaded dataset to HF cache: {path}", file=sys.stderr)
    return path


# ---------------------------------------------------------------------------
# Device selection (explicit override + auto cuda -> mps -> cpu)
# ---------------------------------------------------------------------------

def get_device(device_arg: Optional[str]) -> torch.device:
    if device_arg == "auto" or device_arg is None:
        if torch.cuda.is_available():
            return torch.device("cuda")
        if torch.backends.mps.is_available():
            return torch.device("mps")
        return torch.device("cpu")
    if device_arg == "cuda":
        if not torch.cuda.is_available():
            sys.exit("[error] --device cuda but CUDA is not available")
        return torch.device("cuda")
    if device_arg == "mps":
        if not torch.backends.mps.is_available():
            sys.exit("[error] --device mps but MPS is not available")
        return torch.device("mps")
    if device_arg == "cpu":
        return torch.device("cpu")
    sys.exit(f"[error] unknown --device {device_arg} (auto|cuda|mps|cpu)")


# ---------------------------------------------------------------------------
# HF checkpoint push
# ---------------------------------------------------------------------------

def push_checkpoint(out_dir: str, repo_id: str, config) -> None:
    from huggingface_hub import HfApi, upload_folder
    files = [f for f in os.listdir(out_dir) if f.endswith((".safetensors", ".bin", ".json", ".txt"))]
    print(f"Pushing {len(files)} files from {out_dir} to hf://{repo_id}", file=sys.stderr)
    api = HfApi()
    api.create_repo(repo_id=repo_id, repo_type="model", exist_ok=True)
    upload_folder(repo_id=repo_id, folder_path=out_dir, repo_type="model")
    print(f"Checkpoint pushed to https://huggingface.co/{repo_id}", file=sys.stderr)


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

def main():
    parser = argparse.ArgumentParser(description="Train binary Sandhi boundary detector (CUDA/MPS/CPU).")
    parser.add_argument("--data", default="data/train_V2_fixed.jsonl",
                        help="local jsonl path OR hf://<owner>/<repo>/<file>.jsonl")
    parser.add_argument("--out", default="checkpoints/delayed_model_save_fixed")
    parser.add_argument("--epochs", type=int, default=3)
    parser.add_argument("--batch", type=int, default=32)
    parser.add_argument("--grad-accum", type=int, default=4)
    parser.add_argument("--lr", type=float, default=3e-4)
    parser.add_argument("--max-seq-len", type=int, default=256)
    parser.add_argument("--latent-dim", type=int, default=128)
    parser.add_argument("--num-layers", type=int, default=2,
                        help="number of blocks (requires --layer-types)")
    parser.add_argument("--layer-types", default=None,
                        help="comma-separated block types, e.g. 'linear,softmax' or "
                             "'linear,softmax,linear' or 'linear,linear'. Default: "
                             "linear,softmax (matches the deployed model)")
    parser.add_argument("--num-modes", type=int, default=32,
                        help="Fourier modes; 32 matches the deployed checkpoint")
    parser.add_argument("--pos-weight", type=float, default=6.0,
                        help="Class imbalance weight (boundaries are 1-in-6.5)")
    parser.add_argument("--limit", type=int, default=None)
    parser.add_argument("--smoke", action="store_true")
    parser.add_argument("--delay", type=int, default=2,
                        help="Delayed prediction: model at pos t predicts pos t-N (2 = deployed)")
    parser.add_argument("--device", default="auto", choices=["auto", "cuda", "mps", "cpu"])
    parser.add_argument("--backbone", default="local", choices=["local", "hf"],
                        help="'local' = model.py math (original); 'hf' = HuggingFace "
                             "CodeIsAbstract/HybridTimeScale backbone (chunked linear "
                             "attention, position_ids, KV cache). Same checkpoint format.")
    parser.add_argument("--bf16", action="store_true",
                        help="Use bf16 autocast (Ampere/Ada+ GPUs: A100, L40S, H100...; "
                             "off by default for fp32 parity with MPS)")
    parser.add_argument("--eval-steps", type=int, default=500)
    parser.add_argument("--save-steps", type=int, default=500)
    parser.add_argument("--dataloader-workers", type=int, default=0,
                        help="DataLoader workers (0 = main process). On A100 with "
                             "large batch sizes, 4-8 avoids data-loading stalls.")
    parser.add_argument("--resume", default=None,
                        help="Resume from checkpoint dir (e.g. checkpoints/delayed_model_save_fixed/checkpoint-5500)")
    parser.add_argument("--push-checkpoint", default=None,
                        help="hf repo id (owner/name) to push checkpoints to (needs HF_TOKEN). "
                             "Every saved checkpoint is pushed live to checkpoints/step-<n>/; "
                             "the best model is pushed to the repo root at the end.")
    args = parser.parse_args()

    # Auto-set output dir for delayed models (keeps naming conventions)
    if args.out == "checkpoints/delayed_model_save_fixed" and args.delay > 0:
        args.out = f"checkpoints/delayed_model_save_fixed_delay{args.delay}"

    device = get_device(args.device)
    print(f"Device: {device}", file=sys.stderr)

    # ── Config ──────────────────────────────────────────────────────
    if args.layer_types:
        layer_types = [t.strip() for t in args.layer_types.split(",") if t.strip()]
        valid = {"linear", "softmax"}
        if not layer_types or any(t not in valid for t in layer_types):
            sys.exit(f"[error] --layer-types must be comma-separated values from {valid}")
    else:
        # default pattern: alternate linear/softmax starting with linear
        layer_types = (["linear", "softmax"] * args.num_layers)[: args.num_layers]

    config = HybridTimeScaleConfig(
        vocab_size=VOCAB_SIZE,
        latent_dim=args.latent_dim,
        num_layers=len(layer_types),
        num_modes=args.num_modes,
        layer_types=layer_types,
        time_scale=float(2 * args.num_modes),  # Nyquist: time_scale = 2 * num_modes
        dropout=0.1,
        pad_token_id=PAD_ID,   # shared with train_split_model.py
        bos_token_id=0,
        eos_token_id=0,
        tie_word_embeddings=False,
    )
    # Store delay in config for inference to pick up
    config.delay = args.delay

    model_class = get_model_class(args.backbone)
    model = model_class(config, pos_weight=args.pos_weight)
    n_params = sum(p.numel() for p in model.parameters())
    print(f"Model parameters: {n_params:,} ({n_params/1e6:.2f}M)", file=sys.stderr)
    print(f"  backbone={args.backbone}, latent_dim={args.latent_dim}, num_modes={args.num_modes}, "
          f"layers={layer_types}, delay={args.delay}", file=sys.stderr)

    # ── Data ────────────────────────────────────────────────────────
    if args.smoke:
        args.limit = 500
        args.epochs = 2
        args.eval_steps = 20
        args.save_steps = 20
        print("SMOKE TEST: 500 samples, 2 epochs", file=sys.stderr)

    data_path = resolve_data_path(args.data)
    print(f"Data: {data_path}", file=sys.stderr)

    full_ds = BinaryBoundaryDataset(
        data_path, max_seq_len=args.max_seq_len, delay=args.delay, limit=args.limit
    )
    print(f"Total samples: {len(full_ds)}", file=sys.stderr)
    if args.delay > 0:
        print(f"Delayed prediction: delay={args.delay}, labels shifted +{args.delay}, "
              f"{args.delay} pad chars appended at end", file=sys.stderr)

    # Stratified eval: 1000 samples across complexity bins (deterministic, seed 42)
    random.seed(42)
    indices = list(range(len(full_ds)))
    random.shuffle(indices)

    eval_target = min(1000, len(full_ds) // 10)
    bins: Dict[str, List[int]] = {"1-2": [], "3-5": [], "6-10": [], "11+": []}
    for i in indices:
        nb = full_ds.samples[i].get("n_boundaries", 1)
        if nb <= 2:
            bins["1-2"].append(i)
        elif nb <= 5:
            bins["3-5"].append(i)
        elif nb <= 10:
            bins["6-10"].append(i)
        else:
            bins["11+"].append(i)

    eval_indices: List[int] = []
    per_bin = eval_target // len(bins)
    for key in bins:
        take = min(per_bin, len(bins[key]))
        eval_indices.extend(bins[key][:take])

    eval_set = set(eval_indices)
    train_indices = [i for i in indices if i not in eval_set]

    print(f"Stratified eval: {len(eval_indices)} samples", file=sys.stderr)

    train_subset = torch.utils.data.Subset(full_ds, train_indices)
    eval_subset = torch.utils.data.Subset(full_ds, eval_indices)

    # ── Training args ───────────────────────────────────────────────
    # fp32 by default (numerically identical to the MPS run). bf16 is opt-in
    # and safe on A100/H100 (loss is computed in fp32 internally).
    use_bf16 = args.bf16 and device.type == "cuda"

    training_args = build_training_args(
        output_dir=args.out,
        num_train_epochs=args.epochs,
        per_device_train_batch_size=args.batch,
        per_device_eval_batch_size=args.batch,
        gradient_accumulation_steps=args.grad_accum,
        learning_rate=args.lr,
        warmup_ratio=0.05,
        lr_scheduler_type="cosine",
        weight_decay=0.01,
        max_grad_norm=0.5,
        logging_steps=10,
        eval_strategy="steps",
        eval_steps=args.eval_steps,
        save_strategy="steps",
        save_steps=args.save_steps,
        save_total_limit=3,
        load_best_model_at_end=True,
        metric_for_best_model="f1",
        greater_is_better=True,
        report_to="none",
        fp16=False,
        bf16=use_bf16,
        dataloader_num_workers=args.dataloader_workers,
        gradient_checkpointing=False,
        seed=42,
        use_cpu=(device.type == "cpu"),
        remove_unused_columns=False,
    )

    # ── Resume ──────────────────────────────────────────────────────
    resume_from = args.resume
    if resume_from:
        if os.path.isdir(resume_from):
            print(f"Loading weights from {resume_from}", file=sys.stderr)
            from safetensors.torch import load_file
            sd_path = os.path.join(resume_from, "model.safetensors")
            if not os.path.exists(sd_path):
                sd_path = os.path.join(resume_from, "pytorch_model.bin")
                state_dict = torch.load(sd_path, map_location="cpu", weights_only=False)
            else:
                state_dict = load_file(sd_path)
            state_dict = {k.replace("_orig_mod.", ""): v for k, v in state_dict.items()}
            model.load_state_dict(state_dict, strict=False)
            print(f"Weights loaded (fresh LR schedule, no optimizer state)", file=sys.stderr)
        else:
            print(f"[warn] {resume_from} not found, starting fresh", file=sys.stderr)
            resume_from = None

    # ── Trainer ─────────────────────────────────────────────────────
    # Same custom trainer as train_split_model.py: keep labels in inputs so
    # the model can compute the (imbalanced) BCE loss itself.
    class BoundaryTrainer(Trainer):
        def compute_loss(self, model, inputs, return_outputs=False, num_items_in_batch=None):
            outputs = model(**inputs)
            loss = outputs["loss"] if isinstance(outputs, dict) else outputs[0]
            return (loss, outputs) if return_outputs else loss

        def prediction_step(self, model, inputs, prediction_loss_only, ignore_keys=None):
            inputs = self._prepare_inputs(inputs)
            with torch.no_grad():
                outputs = model(**inputs)
                loss = outputs.get("loss")
                logits = outputs.get("logits")
                labels = inputs.get("labels")
            if loss is not None and torch.isnan(loss):
                print(f"[DEBUG] NaN loss! inputs keys: {list(inputs.keys())}", file=sys.stderr)
                print(f"[DEBUG] labels sum: {inputs['labels'].sum().item()}", file=sys.stderr)
            if loss is not None:
                loss = loss.detach().cpu()
            if logits is not None:
                logits = logits.detach().cpu()
            if labels is not None:
                labels = labels.detach().cpu()
            return (loss, logits, labels)

    trainer = BoundaryTrainer(
        model=model,
        args=training_args,
        train_dataset=train_subset,
        eval_dataset=eval_subset,
        compute_metrics=compute_metrics,
    )

    # Live checkpoint push (every save — never loses a mid-run kill)
    if args.push_checkpoint:
        trainer.add_callback(PushCheckpointCallback(args.push_checkpoint))

    # ── Train ───────────────────────────────────────────────────────
    print(f"\nStarting training: {args.epochs} epochs, {len(train_indices)} samples "
          f"on {device.type}", file=sys.stderr)
    print(f"Effective batch size: {args.batch * args.grad_accum}", file=sys.stderr)
    print(f"Mixed precision: {'bf16' if use_bf16 else 'fp32'}", file=sys.stderr)
    print(file=sys.stderr)

    trainer.train()

    # ── Save ────────────────────────────────────────────────────────
    trainer.save_model(args.out)
    config.save_pretrained(args.out)
    print(f"\nModel saved to {args.out}", file=sys.stderr)

    # ── Final eval ──────────────────────────────────────────────────
    metrics = trainer.evaluate()
    print(f"\nFinal eval:", file=sys.stderr)
    for k, v in metrics.items():
        print(f"  {k}: {v}", file=sys.stderr)

    # ── Optional push to HF ─────────────────────────────────────────
    if args.push_checkpoint:
        push_checkpoint(args.out, args.push_checkpoint, config)


if __name__ == "__main__":
    main()