from pathlib import Path
import sys
import typing
import torch
import torchinfo
import ignite.engine
import ignite.metrics
from ignite.engine import Engine, Events
from ignite.handlers.tqdm_logger import ProgressBar
from dataset import PoetryDataLoader
from model import Rnn
from predict import generate_random_poetry
import settings

sys.path.append(str(Path(__file__).resolve().parent.parent.parent))
import gpu_utils


class Trainer:
    """核心训练器"""

    device: torch.device
    data_loader: PoetryDataLoader
    model: Rnn

    trainer: Engine
    pbar: ProgressBar

    def __init__(self):
        # 创建训练设备，模型和数据加载器。
        self.device = gpu_utils.get_gpu_device()
        self.data_loader = PoetryDataLoader(batch_size=settings.N_BATCH_SIZE)
        self.model = Rnn(self.data_loader.get_vocab_size()).to(self.device)
        # 展示模型结构。批次为指定批次数量，最大诗歌长度，同时输入一定是int32
        torchinfo.summary(self.model, 
                          (settings.N_BATCH_SIZE, settings.POETRY_MAX_LEN),
                          dtypes=[torch.int32,])
        
        # 优化器和损失函数
        optimizer = torch.optim.Adam(self.model.parameters(), eps=1e-7)
        criterion = torch.nn.CrossEntropyLoss()
        # 创建训练器
        self.trainer = ignite.engine.create_supervised_trainer(
            self.model, optimizer, criterion, self.device,
            # 由于PyTorch的交叉熵函数总是要求概率在dim=1，所以要调换一下维度才能传入。
            model_transform=lambda output: self.__adjust_for_loss(output))
        # 将训练器关联到进度条
        self.pbar = ProgressBar(persist=True)
        self.pbar.attach(self.trainer, output_transform=lambda loss: {"loss": loss})
        # 每次epoch后，作诗一首看看结果
        self.trainer.add_event_handler(
            Events.EPOCH_COMPLETED,
            lambda: print(generate_random_poetry(self.data_loader.get_tokenizer(), self.model, self.device))
        )

    def __adjust_for_loss(self, output: torch.Tensor) -> torch.Tensor:
        return output.permute(0, 2, 1)

    def train_model(self):
        # 训练模型
        self.trainer.run(self.data_loader.loader, max_epochs=settings.N_EPOCH)

    def save_model(self):
        # 确保保存模型的文件夹存在。
        settings.SAVED_MODEL_PATH.parent.mkdir(parents=True, exist_ok=True)
        # 仅保存模型参数
        torch.save(self.model.state_dict(), settings.SAVED_MODEL_PATH)
        print(f'Model was saved into: {settings.SAVED_MODEL_PATH}')


def main():
    trainer = Trainer()
    trainer.train_model()
    trainer.save_model()


if __name__ == "__main__":
    gpu_utils.print_gpu_availability()
    main()