from typing import Optional
from functools import partial
from contextlib import contextmanager
from pathlib import Path

import torch
from torch.utils.data import DataLoader

from accelerate import Accelerator
from transformers import CLIPTextModel
from diffusers import AutoencoderKL, UNet2DConditionModel, DPMSolverMultistepScheduler
from diffusers.loaders import AttnProcsLayers

from models.clip.tokenizer import MultiCLIPTokenizer
from training.functional import TrainingStrategy, TrainingCallbacks, save_samples


def lora_strategy_callbacks(
    accelerator: Accelerator,
    unet: UNet2DConditionModel,
    text_encoder: CLIPTextModel,
    tokenizer: MultiCLIPTokenizer,
    vae: AutoencoderKL,
    sample_scheduler: DPMSolverMultistepScheduler,
    train_dataloader: DataLoader,
    val_dataloader: Optional[DataLoader],
    sample_output_dir: Path,
    checkpoint_output_dir: Path,
    seed: int,
    lora_layers: AttnProcsLayers,
    max_grad_norm: float = 1.0,
    sample_batch_size: int = 1,
    sample_num_batches: int = 1,
    sample_num_steps: int = 20,
    sample_guidance_scale: float = 7.5,
    sample_image_size: Optional[int] = None,
):
    sample_output_dir.mkdir(parents=True, exist_ok=True)
    checkpoint_output_dir.mkdir(parents=True, exist_ok=True)

    save_samples_ = partial(
        save_samples,
        accelerator=accelerator,
        text_encoder=text_encoder,
        tokenizer=tokenizer,
        vae=vae,
        sample_scheduler=sample_scheduler,
        train_dataloader=train_dataloader,
        val_dataloader=val_dataloader,
        output_dir=sample_output_dir,
        seed=seed,
        batch_size=sample_batch_size,
        num_batches=sample_num_batches,
        num_steps=sample_num_steps,
        guidance_scale=sample_guidance_scale,
        image_size=sample_image_size,
    )

    def on_prepare():
        lora_layers.requires_grad_(True)

    def on_accum_model():
        return unet

    @contextmanager
    def on_train(epoch: int):
        tokenizer.train()
        yield

    @contextmanager
    def on_eval():
        tokenizer.eval()
        yield

    def on_before_optimize(lr: float, epoch: int):
        accelerator.clip_grad_norm_(lora_layers.parameters(), max_grad_norm)

    @torch.no_grad()
    def on_checkpoint(step, postfix):
        print(f"Saving checkpoint for step {step}...")

        unet_ = accelerator.unwrap_model(unet, False)
        unet_.save_attn_procs(
            checkpoint_output_dir / f"{step}_{postfix}",
            safe_serialization=True
        )
        del unet_

    @torch.no_grad()
    def on_sample(step):
        unet_ = accelerator.unwrap_model(unet, False)
        save_samples_(step=step, unet=unet_)
        del unet_

        if torch.cuda.is_available():
            torch.cuda.empty_cache()

    return TrainingCallbacks(
        on_prepare=on_prepare,
        on_accum_model=on_accum_model,
        on_train=on_train,
        on_eval=on_eval,
        on_before_optimize=on_before_optimize,
        on_checkpoint=on_checkpoint,
        on_sample=on_sample,
    )


def lora_prepare(
    accelerator: Accelerator,
    text_encoder: CLIPTextModel,
    unet: UNet2DConditionModel,
    optimizer: torch.optim.Optimizer,
    train_dataloader: DataLoader,
    val_dataloader: Optional[DataLoader],
    lr_scheduler: torch.optim.lr_scheduler._LRScheduler,
    lora_layers: AttnProcsLayers,
    **kwargs
):
    lora_layers, optimizer, train_dataloader, val_dataloader, lr_scheduler = accelerator.prepare(
        lora_layers, optimizer, train_dataloader, val_dataloader, lr_scheduler)

    return text_encoder, unet, optimizer, train_dataloader, val_dataloader, lr_scheduler, {"lora_layers": lora_layers}


lora_strategy = TrainingStrategy(
    callbacks=lora_strategy_callbacks,
    prepare=lora_prepare,
)