import torch
import torch.nn as nn
from torch.amp import autocast
from transformers import AutoModelForCausalLM, PreTrainedModel, PretrainedConfig
from transformers.models.llama.modeling_llama import LlamaAttention
from peft import LoraConfig, get_peft_model
import os
from typing import Optional, Tuple

hf_token = os.getenv("HF_TOKEN")

class CustomTransformerConfig(PretrainedConfig):
    def __init__(self, vocab_size=128256, hidden_size=4096, num_layers=32, num_heads=32, prediction_chunk=256, dropout=0,
                 max_position_embeddings=4096, masking_type="bidirectional", **kwargs):
        super().__init__(**kwargs)
        self.vocab_size = vocab_size
        self.hidden_size = hidden_size
        self.num_layers = num_layers
        self.num_heads = num_heads
        self.dropout = dropout
        self.prediction_chunk = prediction_chunk
        self.max_position_embeddings = max_position_embeddings
        self.input_size = prediction_chunk
        self.masking_type = masking_type

class CustomTransformerModel(PreTrainedModel):
    config_class = CustomTransformerConfig

    def __init__(self, config):
        super().__init__(config)
        self.llama = AutoModelForCausalLM.from_pretrained("meta-llama/Llama-3.2-3B", torch_dtype=torch.float16, device_map="auto", token=hf_token)
        self.llama.resize_token_embeddings(config.vocab_size)

        for param in self.llama.parameters():
            param.requires_grad = False
        for param in self.llama.lm_head.parameters():
            param.requires_grad = True

        lora_config = LoraConfig(
            r=512, lora_alpha=512, lora_dropout=0.0,
            target_modules=["q_proj", "v_proj", "k_proj", "o_proj"],
            bias="none", task_type=None
        )

        self.llama = get_peft_model(self.llama, lora_config)
        self.llama.print_trainable_parameters()

    def forward(self, input_ids, labels=None, **kwargs):
        batch_size, seq_len = input_ids.shape
        assert seq_len == self.config.prediction_chunk, f"Expected input length {self.config.prediction_chunk}, got {seq_len}"

        # Build attention mask
        device = input_ids.device

        masking_type = getattr(self.config, "masking_type", "bidirectional")
        if masking_type == 'bidirectional':
            base_mask = torch.ones(seq_len, seq_len, dtype=torch.bool, device=device)
        elif masking_type == 'bidirectional_masked':
            base_mask = torch.ones(seq_len, seq_len, dtype=torch.bool, device=device)
            base_mask.fill_diagonal_(False)
        elif masking_type == 'unidirectional':
            base_mask = torch.tril(torch.ones(seq_len, seq_len, dtype=torch.bool, device=device))
        else:
            raise ValueError(f"Unknown masking type: {self.config.masking_type}")

        attention_mask = base_mask.unsqueeze(0).unsqueeze(1).expand(batch_size, 1, seq_len, seq_len).clone()
        attention_mask = attention_mask.to(dtype=torch.float32)  # required for SDPA and Flash attention


        with autocast("cuda", dtype=torch.float16):
            outputs = self.llama(
                input_ids,
                attention_mask=attention_mask,
                output_hidden_states=True,
                use_cache=False,
                **kwargs
            )

        logits = outputs.logits[:, :, :self.config.vocab_size].view(batch_size, seq_len, self.config.vocab_size)

        loss = None
        if labels is not None:
            assert labels.shape == (batch_size, seq_len), f"Labels shape mismatch: expected ({batch_size}, {seq_len}), got {labels.shape}"
            loss_fct = nn.CrossEntropyLoss()
            loss = loss_fct(logits.view(-1, self.config.vocab_size), labels.view(-1))

        return {"loss": loss, "logits": logits} if loss is not None else {"logits": logits}

def disable_dropout(model):
    for name, module in model.named_modules():
        if isinstance(module, nn.Dropout):
            setattr(model, name, nn.Identity())
    return model