import json
import os
import warnings
from pathlib import Path
from typing import Optional

#import llama
import torch
from fairscale.nn.model_parallel.initialize import initialize_model_parallel
from torch import nn
from transformers import (
    AutoModelForCausalLM,
    LlamaForCausalLM,
    LlamaTokenizer,
    MistralForCausalLM,
    GemmaTokenizer,
    GemmaForCausalLM
)

from finetune import data_provider, extra_args, get_batch, loss_func, model_provider
from megatron import get_args, update_num_microbatches
from megatron.arguments import parse_args
from megatron.initialize import initialize_megatron, set_jit_fusion_options
from megatron.training import (
    _setup_model_and_optimizer,
    build_train_valid_test_data_iterators,
)


class Llama2Wrapper(nn.Module):
    def __init__(self, cache_dir):
        super().__init__()
        initialize_model_parallel(1)
        cache_dir = Path(cache_dir)
        checkpoints = sorted(cache_dir.glob("*.pth"))
        assert (
            len(checkpoints) == 1
        ), "Currently, only llama2 unsharded models implemented"
        with open(cache_dir / "params.json", "r") as f:
            params = json.loads(f.read())
            params["vocab_size"] = 32000

        self.model = llama.Transformer(
            llama.ModelArgs(max_seq_len=4096, max_batch_size=1, **params)
        )
        self.model.load_state_dict(torch.load(checkpoints[0]), strict=False)

    def forward(self, input_ids, position_ids=None, attention_mask=None, labels=None):
        if labels is not None:
            warnings.warn("Llama2 does not compute loss")
        logits = self.model(input_ids, 0)
        loss = torch.tensor(0.0).to(logits.device, logits.dtype)
        return {"logits": logits, "loss": loss}


def is_meta_llama2_path(path: Optional[Path]) -> bool:
    return path is not None and len(list(path.glob("*.pth"))) > 0


def hf_provider(
    name: str, cache_dir: Optional[Path], device: str, size: int = 7, bf16: bool = False
):
    print("Getting huggingface model...")
    extra_kwargs = {}
    if bf16:
        extra_kwargs = {"torch_dtype": torch.bfloat16}
    if name == "falcon":
        model = AutoModelForCausalLM.from_pretrained(
            f"tiiuae/falcon-{size}b",
            cache_dir=cache_dir,
            trust_remote_code=True,
            **extra_kwargs,
        )
    elif name == "llama":
        try:
            model = LlamaForCausalLM.from_pretrained(cache_dir, **extra_kwargs)
        except OSError:
            print(
                f"Cache dir {cache_dir} does not look like a huggingface "
                "checkpoint, assuming cache_dir instead"
            )
            model = LlamaForCausalLM.from_pretrained(
                f"decapoda-research/llama-{size}b-hf",
                cache_dir=cache_dir,
                **extra_kwargs,
            )
    elif name == "llama2" and is_meta_llama2_path(cache_dir):
        print(
            f"baseline path {cache_dir} does not look like a huggingface, "
            "assuming it's raw llama2 weights instead"
        )
        model = Llama2Wrapper(cache_dir)
    elif name == "llama2":
        model = LlamaForCausalLM.from_pretrained(cache_dir, **extra_kwargs)
    elif name == "mistral":
        assert size == 7, "Mistral only supports 7B model"
        try:
            model = MistralForCausalLM.from_pretrained(cache_dir, **extra_kwargs)
        except OSError:
            print(
                f"Cache dir {cache_dir} does not look like a huggingface "
                "checkpoint, assuming cache_dir instead"
            )
            model = MistralForCausalLM.from_pretrained(
                f"mistralai/Mistral-{size}B-v0.1", cache_dir=cache_dir, **extra_kwargs
            )
    elif name == "gemma":
        model = GemmaForCausalLM.from_pretrained(cache_dir, **extra_kwargs)
    else:
        raise KeyError(f"Model {name} not implemented")
    return model.eval().requires_grad_(False).to(device)


def hf_our_provider(name: str, data_dir: Path, device: str, size: int = 7):
    if name in {"llama", "llama2"}:
        model = LlamaForCausalLM.from_pretrained(data_dir)
    else:
        raise NotImplementedError("Testing custom checkpoints supported for llama")
    return model.eval().requires_grad_(False).to(device)


def hf_forward(model, batch):
    device = next(param.device for param in model.parameters())
    batch = [tensor.to(device) for tensor in batch]
    tokens, labels, loss_mask, attention_mask, position_ids = batch
    output = model(input_ids=tokens, position_ids=position_ids, labels=tokens)
    return output["logits"], output["loss"]


def mega_provider(name: str):
    print("Getting megatron model...")
    model, _, _ = _setup_model_and_optimizer(model_provider, name, args=get_args())
    assert (
        len(model) == 1
    ), "correctness verification only supported with unsharded models"
    model = model[0].eval().requires_grad_(False)
    return model


def mega_forward(model, batch):
    tokens, labels, loss_mask, attention_mask, position_ids = batch
    assert torch.all(loss_mask)
    # we need to do two forward passes to get both the logits and the loss
    _, logits = out = model(tokens, position_ids, attention_mask, labels=labels)
    loss, _ = loss_func(model.training, batch, out)
    return logits, loss


def verify_step(our_forward, our_model, base_forward, base_model, batch):
    our_logits, our_loss = our_forward(our_model, batch)
    base_logits, base_loss = base_forward(base_model, batch)
    assert (
        our_logits.size() == base_logits.size()
    ), f"ours={our_logits.size()}, true={base_logits.size()}"
    our_logits = our_logits.cpu()
    base_logits = base_logits.cpu()
    abs_error = torch.abs(our_logits - base_logits)
    print(
        "Max absoulute error in the logits:",
        f"max={torch.max(abs_error):.6f}, avg={torch.mean(abs_error):.6f}",
    )
    assert our_loss.size() == base_loss.size()
    our_loss = our_loss.cpu()
    base_loss = base_loss.cpu()
    loss_error = torch.abs(our_loss - base_loss)
    print(
        f"Abs loss error: {loss_error:.6f} "
        f"Our loss: {our_loss:.3f}, theirs: {base_loss:.3f}"
    )


def is_megatron_path(path):
    path = Path(path) if isinstance(path, str) else path
    return (path / "latest_checkpointed_iteration.txt").exists()


def main():
    # Misc initializations
    print("Starting megatron vs huggingface verification")
    args = get_args()
    set_jit_fusion_options(args)

    # Determine if the provided weight is a megatron checkpoint or huggingface checkpoint
    print("Loading our model!")
    if is_megatron_path(args.load):
        our_model = mega_provider(args.model_name)
        our_forward = mega_forward
    else:
        print(
            "NOTE: The given path does not look like a megatron checkpoint, "
            f"assuming it's a huggingface checkpoint instead (path={args.load})"
        )
        our_model = hf_our_provider(
            args.model_name, args.load, "cuda:0"
        )
        our_forward = hf_forward
        args.iteration = 0

    # Load baseline model
    print("Loading baseline model!")
    base_model = hf_provider(
        args.model_name, args.cache_dir, args.baseline_device, size=args.model_size
    )
    base_forward = hf_forward

    # Load dataset iterator
    print("Loading dataset!")
    data_iterator, _, _ = build_train_valid_test_data_iterators(data_provider, args)

    # Now we can start the verifications
    for iteration in range(0, 10):
        print(f"Iteration {iteration}...")
        update_num_microbatches(args.consumed_train_samples)
        args.curr_iteration = iteration
        verify_step(
            our_forward, our_model, base_forward, base_model, get_batch(data_iterator)
        )


def extra_extra_args(parser):
    parser = extra_args(parser)
    group = parser.add_argument_group(title="huggingface")
    group.add_argument(
        "--huggingface_cache",
        type=Path,
        default=None,
        dest="cache_dir",
        help=(
            "If falcon, optional: path to huggingface cache. "
            "If llama2, optional: either the huggingface cache path, or "
            "the raw weight directory given by meta. "
            "If llama, optional: either the path to converted huggingface weights "
            "(use convert_llama_weights_to_hf.py) or the huggingface cache dir."
        ),
    )
    group.add_argument(
        "--huggingface_device",
        default="cuda:1",
        dest="baseline_device",
        help="Device to use for the baseline model",
    )
    group.add_argument("--model_size", type=int, default=7)
    return parser


if __name__ == "__main__":
    defaults = {
        "micro_batch_size": 1,
        "use_checkpoint_args": True,
        "train_iters": 10,
        "lr": 1.0,
    }
    # if not is_megatron_path(parse_args(extra_extra_args).load):
    #     defaults.update(
    #         {
    #             "encoder_num_layers": 1,
    #             "hidden_size": 1,
    #             "num_attention_heads": 1,
    #             "seq_length": 2048,
    #             "max_position_embeddings": 2048,
    #         }
    #     )
    initialize_megatron(extra_extra_args, args_defaults=defaults)
    main()