import math
import multiprocessing
import os
from datetime import timedelta
from functools import partial
from itertools import chain

import torch
import torch.distributed as dist
from accelerate import Accelerator
from accelerate.logging import get_logger
from accelerate.state import AcceleratorState
from accelerate.utils import InitProcessGroupKwargs
from datasets import load_dataset
from lion_pytorch import Lion
from torch.distributed.algorithms._checkpoint.checkpoint_wrapper import (
    CheckpointImpl,
    apply_activation_checkpointing,
    checkpoint_wrapper,
)
from torch.distributed.fsdp import (
    BackwardPrefetch,
    FullyShardedDataParallel,
    MixedPrecision,
    ShardingStrategy,
)
from torch.distributed.fsdp.wrap import transformer_auto_wrap_policy
from torch.nn import LayerNorm
from torch.optim import AdamW
from torch.utils.data import DataLoader
from tqdm import tqdm
from transformers import (
    AutoTokenizer,
    default_data_collator,
    get_cosine_schedule_with_warmup,
    get_linear_schedule_with_warmup,
    set_seed,
)

from gen1.adam import StableAdamWUnfused
from gen1.model import Gen1, SpaceTimeUnet

# state = AcceleratorState()


logger = get_logger(__name__, log_level="INFO")

class CFG:
    BATCH_SIZE = 1
    GRADIENT_ACCUMULATE_EVERY: int = 1
    SEED: int = 42
    LEARNING_RATE: float = 1e-4 #3e-4 # 1e-4 for lion
    WEIGHT_DECAY: float = 0.1
    SEQ_LEN: int = 8192
    NUM_CPU: int = multiprocessing.cpu_count()
    USE_DEEPSPEED: bool = True
    USE_FSDP: bool = True
    USE_PRETOKENIZED: bool = True
    USE_ACTIVATION_CHECKPOINTING: bool = True
    RESUME_FROM_CHECKPOINT: str = False
    CHECKPOINTING_STEPS: int = 1000
    OUTPUT_DIR: str = 'checkpoints/' # Folder
    ENTITY_NAME: str = "gen1"
    LOGGING_STEPS: int = 100


# helpers


def print_num_params(model, accelerator: Accelerator):
    # n_params = sum(p.numel() for p in model.parameters() if p.requires_grad)
    n_params = sum(p.numel() for p in model.parameters() if p.requires_grad)
    accelerator.print(f"Number of parameters in model: {n_params}")


# activation checkpointing


def activation_checkpointing(
    model: torch.nn.Module,
    offload_to_cpu: bool = False,
    accelerator: Accelerator = None,
):
    """
    Apply activation checkpointing to a model.

    Args:
        model (Module): The model to which to apply activation checkpointing.
        offload_to_cpu (bool, optional): Whether to offload the activations to CPU. Defaults to False.
        accelerator (Accelerator, optional): The Accelerate library accelerator. Defaults to None.
    """
    if accelerator is not None:
        accelerator.print("Using activation checkpointing")
    def check_fn(submodule):
        return isinstance(submodule, SpaceTimeUnet)
    non_reentrant_wrapper = partial(
        checkpoint_wrapper,
        offload_to_cpu=offload_to_cpu,
        checkpoint_impl=CheckpointImpl.NO_REENTRANT,
    )
    apply_activation_checkpointing(
        model, checkpoint_wrapper_fn=non_reentrant_wrapper, check_fn=check_fn
    )


# FSDP


def fsdp(
    model: torch.nn.Module,
    auto_wrap: bool = False,
    mp: str = "fp32",
    shard_strat: str = "NO_SHARD",
):
    """
    This function wraps a given PyTorch model with the FullyShardedDataParallel (FSDP) wrapper to enable efficient data parallelism and model sharding.

    Args:
        model (torch.nn.Module): The original PyTorch model to be wrapped with FSDP.
        auto_wrap (bool, optional): If True, it enables automatic wrapping of the model's layers according to the transformer_auto_wrap_policy. Default is False.
        mp (str, optional): The mixed precision mode to be used. Can be 'bf16' for BFloat16, 'fp16' for Float16 or 'fp32' for Float32 precision. Default is 'fp32'.
        shard_strat (str, optional): The sharding strategy to be used. Can be 'SHARD_GRAD' for sharding at gradient computation, 'FULL_SHARD' for full model sharding or 'NO_SHARD' for no sharding. Default is 'NO_SHARD'.

    Raises:
        ValueError: If the provided mp (mixed precision mode) is not 'bf16', 'fp16' or 'fp32'.
        ValueError: If the provided shard_strat (sharding strategy) is not 'SHARD_GRAD', 'FULL_SHARD' or 'NO_SHARD'.

    Returns:
        torch.nn.Module: The input model wrapped with FSDP.
    """
    if auto_wrap:
        gen1_auto_wrap_policy = partial(
            transformer_auto_wrap_policy,
            transformer_layer_cls={
                SpaceTimeUnet,
            },
        )
    else:
        gen1_auto_wrap_policy = None

    if mp == "bf16":
        mp_fsdp = MixedPrecision(
            param_dtype=torch.bfloat16,
            # Gradient communication precision.
            reduce_dtype=torch.bfloat16,
            # Buffer precision.
            buffer_dtype=torch.bfloat16,
        )
    elif mp == "fp16":
        mp_fsdp = MixedPrecision(
            param_dtype=torch.float16,
            # Gradient communication precision.
            reduce_dtype=torch.float16,
            # Buffer precision.
            buffer_dtype=torch.float16,
        )
    elif mp == "fp32":
        mp_fsdp = MixedPrecision(
            param_dtype=torch.float32,
            # Gradient communication precision.
            reduce_dtype=torch.float32,
            # Buffer precision.
            buffer_dtype=torch.float32,
        )
    else:
        raise ValueError(
            "Invalid scheduler_type. Expected 'bf16', 'fp16' or 'fp32', got: {}".format(
                mp
            )
        )

    if shard_strat == "SHARD_GRAD":
        sharding_strat_fsdp = ShardingStrategy.SHARD_GRAD_OP 
    elif shard_strat == "FULL_SHARD":
        sharding_strat_fsdp = ShardingStrategy.FULL_SHARD
    elif shard_strat == "NO_SHARD":
        sharding_strat_fsdp = ShardingStrategy.NO_SHARD
    else:
        raise ValueError(
            "Invalid scheduler_type. Expected 'SHARD_GRAD', 'FULL_SHARD' or 'NO_SHARD', got: {}".format(
                shard_strat
            )
        )

    model = FullyShardedDataParallel(
        model,
        auto_wrap_policy=gen1_auto_wrap_policy,
        mixed_precision=mp_fsdp,
        backward_prefetch=BackwardPrefetch.BACKWARD_PRE,
        sharding_strategy=sharding_strat_fsdp,
        forward_prefetch=True,
        use_orig_params=True,
    )

    return model


# learning rate scheduler


def get_lr_scheduler_with_warmup(
    optimizer: torch.optim.Optimizer,
    scheduler_type: str,
    num_warmup_steps: int,
    max_train_steps: int,
    grad_accumulate_every: int = 1,
    accelerator: Accelerator = None,
):
    """
    Get a learning rate scheduler with warmup.

    Args:
        optimizer (Optimizer): The optimizer for which to create the learning rate scheduler.
        scheduler_type (str): The type of learning rate scheduler to create, either "linear" or "cosine".
        num_warmup_steps (int): The number of warmup steps for the learning rate scheduler.
        max_train_steps (int): The maximum number of training steps.
        grad_accumulate_every (int, optional): The gradient accumulation factor. Defaults to 1.
        accelerator (Accelerator, optional): The Accelerate library accelerator. Defaults to None.

    Returns:
        The learning rate scheduler with warmup.

    Raises:
        ValueError: If scheduler_type is not "linear" or "cosine".
    """
    NUM_WARMUP_STEPS = num_warmup_steps
    GRADIENT_ACCUMULATE_EVERY = grad_accumulate_every
    if accelerator is not None:
        accelerator.print(f"Using {scheduler_type} lr scheduler")
    if scheduler_type == "linear":
        return get_linear_schedule_with_warmup(
            optimizer=optimizer,
            num_warmup_steps=NUM_WARMUP_STEPS * GRADIENT_ACCUMULATE_EVERY,
            num_training_steps=max_train_steps * GRADIENT_ACCUMULATE_EVERY,
        )
    elif scheduler_type == "cosine":
        return get_cosine_schedule_with_warmup(
            optimizer=optimizer,
            num_warmup_steps=NUM_WARMUP_STEPS * GRADIENT_ACCUMULATE_EVERY,
            num_training_steps=max_train_steps * GRADIENT_ACCUMULATE_EVERY,
        )
    else:
        raise ValueError(
            "Invalid scheduler_type. Expected 'linear' or 'cosine', got: {}".format(
                scheduler_type
            )
        )


# optimizers


def decoupled_optimizer(
    model: torch.nn.Module,
    learning_rate: float,
    weight_decay: float,
    beta_1: float,
    beta_2: float,
    optimizer_type: str,
    use_fsdp: bool = True,
    accelerator: Accelerator = None,
):
    """
    Decouples the optimizer from the training process.

    This function sets up the optimizer for the model by creating two groups of parameters:
    one for weight decay and one without weight decay. Then, it initializes the optimizer
    with these two groups of parameters.

    Args:
        model (Module): The model whose parameters are optimized.
        learning_rate (float): The learning rate for the optimizer.
        weight_decay (float): The weight decay for the optimizer.
        beta_1 (float): The exponential decay rate for the 1st moment estimates.
        beta_2 (float): The exponential decay rate for the 2nd moment estimates.
        optimizer_type (str): The type of the optimizer. Can be 'lion', 'adamw', or 'stable_adamw'.
        use_fsdp (bool, optional): If True, the optimizer will work with fully sharded data parallelism. Defaults to True.
        accelerator (Accelerator, optional): The accelerator from HuggingFace's Accelerate library. Defaults to None.

    Returns:
        Optimizer: The initialized optimizer.

    Raises:
        ValueError: If the optimizer type is not 'lion', 'adamw' or 'stable_adamw'.
    """
    accelerator.print(f"Using {optimizer_type} optimizer")
    # Create an empty dictionary called param_dict to store the model's named parameters.
    param_dict = {}
    # Iterate over the model's named parameters and populate the param_dict with key-value pairs.
    for param_name, param in model.named_parameters():
        param_dict[param_name] = param

    # Separate the model's named modules into two groups: decay and no_decay.

    # Create an empty list to store the names of the LayerNorm and Embedding layer weights with no weight decay.
    no_decay = []

    if use_fsdp:
        exclude_module = "_fsdp_wrapped_module.token_emb"
    else:
        exclude_module = "token_emb"

    # Iterate through the named modules of the model.
    for module_name, module in model.named_modules():
        # Check if the current module is an instance of any of the desired types (LayerNorm or torch.nn.Embedding).
        for ndim in [LayerNorm, torch.nn.Embedding]:
            if isinstance(module, ndim):
                # If torch.nn.Embedding, append its name with a ".weight" suffix to the no_decay list.
                if module_name == exclude_module:
                    no_decay.append(f"{module_name}.weight")
                else:
                    # If the module is an instance of LayerNorm
                    no_decay.append(f"{module_name}.gamma")
                # Exit the inner loop since the desired module has been found.
                break

    # Create an empty list to store the names of the Linear layer weights with weight decay.
    decay = []

    # Iterate through the named modules of the model.
    for module_name, module in model.named_modules():
        # Check if the current module is an instance of the desired type (torch.nn.Linear).
        for ndim in [torch.nn.Linear]:
            if isinstance(module, ndim):
                # If the module is an instance of torch.nn.Linear, append its name with a ".weight" suffix to the decay list.
                decay.append(f"{module_name}.weight")
                # Exit the inner loop since the desired module has been found.
                break

    # Create two separate lists of model parameters: decay_param and no_decay_param.
    # The decay_param list contains the parameters that should have weight decay applied.
    # The no_decay_param list contains the parameters that should not have weight decay applied, excluding the 'to_logits.weight' parameter.

    # Create an empty list called decay_param to store the parameters with weight decay.
    decay_param = []

    if use_fsdp:
        exclude_param = "_fsdp_wrapped_module.to_logits.weight"
    else:
        exclude_param = "to_logits.weight"

    # Iterate over the decay list, which contains the names of the parameters with weight decay.
    for param in decay:
        # Check if the current parameter is not 'to_logits.weight'.
        # Append the corresponding parameter from param_dict to the decay_param list.

        if param != exclude_param:
            decay_param.append(param_dict[param])

    # Create an empty list called no_decay_param to store the parameters without weight decay.
    no_decay_param = []

    # Iterate over the no_decay list, which contains the names of the parameters without weight decay.
    for param in no_decay:
        try:
                
            # Append the corresponding parameter from param_dict to the no_decay_param list.
            no_decay_param.append(param_dict[param])
        except KeyError:
            # print(f"Parameter {param_name} does not exist in the model")
            pass

    # Create a list called grouped_params that contains two dictionaries.
    # The first dictionary has the decay_param list and the corresponding weight_decay value.
    # The second dictionary has the no_decay_param list and a weight_decay value of 0.0.
    grouped_params = [
        {"params": decay_param, "weight_decay": weight_decay},
        {"params": no_decay_param, "weight_decay": 0.0},
    ]

    # Create a variable called optimizer that stores an instance of the optimizer.
    if optimizer_type == "lion":
        optimizer = Lion(grouped_params, lr=learning_rate, betas=(beta_1, beta_2),)
    elif optimizer_type == "adamw":
        optimizer = AdamW(grouped_params, lr=learning_rate, betas=(beta_1, beta_2),)
    elif optimizer_type == "stable_adamw":
        optimizer = StableAdamWUnfused(
            grouped_params, lr=learning_rate, betas=(beta_1, beta_2),
        )
    # elif optimizer_type=="Adam8bit":
    #     optimizer = bnb.optim.Adam8bit(grouped_params, lr=learning_rate, betas=(beta_1, beta_2))
    # elif optimizer_type=="Lion8Bit":
    #     optimizer = bnb.optim.Lion8bit(grouped_params, lr=learning_rate, betas=(beta_1, beta_2))
    else:
        raise ValueError(
            "Invalid optimizer_type. Expected 'lion', 'adamw', 'deepspeed' or 'stable_adamw', got: {}".format(
                optimizer_type
            )
        )

    # Return the optimizer.
    return optimizer


# dataloaders


def build_dataloaders():
    """
    Build data loaders for training.

    This function performs the following steps:
    1. Load the tokenizer from the pretrained "EleutherAI/gpt-neox-20b" model.
    2. Load the "openwebtext" dataset.
    3. Tokenize the dataset, adding the end-of-sentence token to each text.
    4. Process the tokenized dataset into chunks of a specified block size.

    Returns:
        Dataset: The processed dataset ready for training.
    """
    tokenizer = AutoTokenizer.from_pretrained("EleutherAI/gpt-neox-20b")
    dataset = load_dataset("openwebtext", split="train")

    tokenized_dataset = dataset.map(
        lambda example: tokenizer([t + tokenizer.eos_token for t in example["text"]]),
        batched=True,
        num_proc=CFG.NUM_CPU,
        remove_columns=["text"],
    )

    block_size = CFG.SEQ_LEN

    # Main data processing function that will concatenate all texts from our dataset and generate chunks of block_size.
    def group_texts(examples):
        # Concatenate all texts.
        concatenated_examples = {k: list(chain(*examples[k])) for k in examples.keys()}
        total_length = len(concatenated_examples[list(examples.keys())[0]])
        # We drop the small remainder, we could add padding if the model supported it instead of this drop, you can
        # customize this part to your needs.
        if total_length >= block_size:
            total_length = (total_length // block_size) * block_size
        # Split by chunks of max_len.
        result = {
            k: [t[i : i + block_size] for i in range(0, total_length, block_size)]
            for k, t in concatenated_examples.items()
        }
        return result

    train_dataset = tokenized_dataset.map(
        group_texts, batched=True, num_proc=CFG.NUM_CPU,
    )

    return train_dataset

#switch to falconwebdataset
def build_pre_tokenized():
    d0 = load_dataset("conceptofmind/c4_0-to-20_neox_with_eos_8k", split="train[:10]")
    # d1 = load_dataset("conceptofmind/c4_21-to-40_neox_with_eos_8k", split="train")
    # d2 = load_dataset("conceptofmind/c4_41-to-60_neox_with_eos_8k", split="train")
    # d3 = load_dataset("conceptofmind/c4_61-to-80_neox_with_eos_8k", split="train")
    # d4 = load_dataset("conceptofmind/c4_81-to-100_neox_with_eos_8k", split="train")
    # train_dataset = concatenate_datasets([d0, d1, d2, d3, d4])
    return d0



def Train():
    # accelerator

    timeout = InitProcessGroupKwargs(timeout=timedelta(seconds=1_000_000))

    accelerator = Accelerator(
        gradient_accumulation_steps=CFG.GRADIENT_ACCUMULATE_EVERY,
        mixed_precision="fp16",
        log_with="wandb",
        kwargs_handlers=[timeout],
    )

    state = AcceleratorState()
    
    state.deepspeed_plugin.deepspeed_config['train_micro_batch_size_per_gpu'] = CFG.BATCH_SIZE #??????

    accelerator.init_trackers(
        project_name="gen1",
        config={
            "batch_size": CFG.BATCH_SIZE,
            "gradient_accumulate_every": CFG.GRADIENT_ACCUMULATE_EVERY,
            "learning_rate": CFG.LEARNING_RATE,
            "seq_len": CFG.SEQ_LEN,
        },
        # init_kwargs={"wandb": {"entity": CFG.ENTITY_NAME}},
    )

    accelerator.print(f"Total GPUS: {accelerator.num_processes}")

    # set seed

    set_seed(CFG.SEED)

    model = Gen1()

    print_num_params(model, accelerator)

    if CFG.USE_FSDP:
        model = fsdp(
            model,
            mp="fp16",
            shard_strat="SHARD_GRAD"
        )

    if CFG.USE_ACTIVATION_CHECKPOINTING:
        activation_checkpointing(model, accelerator)

    model = accelerator.prepare(model)

    # dataloaders

    if CFG.USE_PRETOKENIZED:
        train_dataset = build_pre_tokenized()
    else:
        train_dataset = build_dataloaders()

    train_loader = DataLoader(
        train_dataset, batch_size=CFG.BATCH_SIZE, collate_fn=default_data_collator,
    )


    # optimizer
    optim = decoupled_optimizer(
        model=model,
        learning_rate=CFG.LEARNING_RATE, 
        weight_decay=CFG.WEIGHT_DECAY, 
        beta_1=0.90, 
        beta_2=0.95, 
        optimizer_type='lion',  
        use_fsdp=True,
        accelerator=accelerator
    )

    # Determine number of training steps

    max_train_steps = math.ceil(len(train_loader) / CFG.GRADIENT_ACCUMULATE_EVERY)
    accelerator.print(f"Max train steps: {max_train_steps}")

    # lr scheduler

    NUM_WARMUP_STEPS = int(max_train_steps * 0.01)
    accelerator.print(f"Num warmup steps: {NUM_WARMUP_STEPS}")

    # if False: # if CFG.USE_DEEPSPEED:
    #     lr_scheduler = DummyScheduler(
    #         optim, 
    #         total_num_steps=max_train_steps * accelerator.num_processes, 
    #         warmup_num_steps=NUM_WARMUP_STEPS
    #     )
    # else:
    lr_scheduler = get_lr_scheduler_with_warmup(
        optimizer=optim,
        scheduler_type="cosine",
        num_warmup_steps=NUM_WARMUP_STEPS,
        max_train_steps=max_train_steps,
        grad_accumulate_every=CFG.GRADIENT_ACCUMULATE_EVERY,
    )

    # prepare

    optim, train_loader, lr_scheduler = accelerator.prepare(
        optim, train_loader, lr_scheduler
    )

    # checkpoint scheduler

    accelerator.register_for_checkpointing(lr_scheduler)

    # I do not know why Huggingface recommends recalculation of max_train_steps

    max_train_steps = math.ceil(len(train_loader) / CFG.GRADIENT_ACCUMULATE_EVERY)
    accelerator.print(f"Max train steps recalculated: {max_train_steps}")

    # Total batch size for logging

    total_batch_size = (
        CFG.BATCH_SIZE * accelerator.num_processes * CFG.GRADIENT_ACCUMULATE_EVERY
    )
    accelerator.print(f"Total batch size: {total_batch_size}")

    # resume training

    progress_bar = tqdm(
        range(max_train_steps), disable=not accelerator.is_local_main_process
    )
    completed_steps = 0

    if CFG.RESUME_FROM_CHECKPOINT:
        if CFG.RESUME_FROM_CHECKPOINT is not None or CFG.RESUME_FROM_CHECKPOINT != "":
            accelerator.print(f"Resuming from checkpoint {CFG.RESUME_FROM_CHECKPOINT}")
            accelerator.load_state(CFG.RESUME_FROM_CHECKPOINT)
            path = os.path.basename(CFG.RESUME_FROM_CHECKPOINT)
        training_difference = os.path.splitext(path)[0]

        # need to multiply `gradient_accumulation_steps` to reflect real steps
        resume_step = (
            int(training_difference.replace("step_", ""))
            * CFG.GRADIENT_ACCUMULATE_EVERY
        )

    if CFG.RESUME_FROM_CHECKPOINT and resume_step is not None:
        train_loader = accelerator.skip_first_batches(train_loader, resume_step)
        completed_steps += resume_step
        progress_bar.update(resume_step)

    # training

    model.train()
    for step, batch in enumerate(train_loader):
        with accelerator.accumulate(model):
            inputs = batch["input_ids"].to(accelerator.device)
            loss = model(inputs, return_loss=True)
            accelerator.backward(loss)

            accelerator.log({"loss": loss.item()}, step=step)

            if accelerator.sync_gradients:
                accelerator.clip_grad_norm_(model.parameters(), 1.0)

            optim.step()
            lr_scheduler.step()
            optim.zero_grad()

        if accelerator.sync_gradients:
            progress_bar.update(1)
            completed_steps += 1

        if isinstance(CFG.CHECKPOINTING_STEPS, int):
            if completed_steps % CFG.CHECKPOINTING_STEPS == 0:
                output_dir = f"step_{completed_steps }"
                if CFG.OUTPUT_DIR is not None:
                    output_dir = os.path.join(CFG.OUTPUT_DIR, output_dir)
                accelerator.save_state(output_dir)

        if completed_steps >= max_train_steps:
            break

        #logging every CFG.LOGGING STEPS
        if CFG.LOGGING_STEPS > 0 and step % CFG.LOGGING_STEPS == 0:
            logger.info(
                f"Step: {completed_steps}/{max_train_steps}, Loss: {loss.item():.5f}"
            )

    # end training

    # accelerator.print(f"Training Finished")
    accelerator.end_training()

    # save final model

    # accelerator.print(f"Saving model to {CFG.OUTPUT_DIR}")
    if CFG.OUTPUT_DIR is not None:
        accelerator.wait_for_everyone()
        unwrapped_model = accelerator.unwrap_model(model)
        with accelerator.main_process_first():
            accelerator.save(
                unwrapped_model.state_dict(), f"{CFG.OUTPUT_DIR}/final/final_model.pt"
            )


def train():
    os.environ['MASTER_ADDR'] #'localhost'
    os.environ['MASTER_PORT'] #= '9994'
    
    # # [CRITICAL] Pay attention to this when scaling to multiple GPUs and clusters
    
    # # Pay attention to this, use "accelerate config"

    os.environ['RANK']       #= str(0) # Number of nodes (servers)
    os.environ['WORLD_SIZE'] # = str(torch.cuda.device_count())

    dist.init_process_group(backend='nccl') #init_method="env://")
    
    Train()

if __name__ == '__main__':
    train()