import os
import torch
from transformers import AutoTokenizer, AutoModelForCausalLM, Trainer, TrainingArguments, DataCollatorForLanguageModeling, TrainerCallback
from datasets import load_dataset
import matplotlib.pyplot as plt

# Set Hugging Face token (replace with your actual token)
os.environ["HF_TOKEN"] = "hf_XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"

# Recommended for download stability, if you had issues before
os.environ["HF_HUB_DOWNLOAD_TIMEOUT"] = "600" # 10 minutes timeout
os.environ["HF_HUB_ENABLE_HF_TRANSFER"] = "1" # Enable robust downloader

# Download model and tokenizer
model_name = "Salesforce/codegen-350M-multi"
local_model_path = "./codegen_model"

print(f"Attempting to download/load tokenizer from {model_name} to {local_model_path}...")
tokenizer = AutoTokenizer.from_pretrained(model_name, cache_dir=local_model_path)
print("Tokenizer loaded.")

print(f"Attempting to download/load model from {model_name} to {local_model_path}...")
# Removed torch_dtype=torch.float16 as it's typically for GPU and might not help on CPU
# and could even cause unexpected behavior on some CPU setups.
model = AutoModelForCausalLM.from_pretrained(model_name, cache_dir=local_model_path)
print("Model loaded.")

# Set padding token
tokenizer.pad_token = tokenizer.eos_token

# Move model to CPU
device = torch.device("cpu")
model.to(device)
print(f"Model moved to {device}.")

# Load custom dataset from JSONL file
dataset_file = "custom_dataset.jsonl"
print(f"Loading dataset from {dataset_file}...")
dataset = load_dataset('json', data_files=dataset_file, split='train')
print("Dataset loaded.")
print(f"Dataset size: {len(dataset)} examples.")
print(f"First example of dataset: {dataset[0]}") # Print first example to check data format

# Tokenize dataset
def tokenize_function(examples):
    inputs = [f"{prompt}\n{code}" for prompt, code in zip(examples["prompt"], examples["code"])]
    # --- REDUCED MAX_LENGTH TO SAVE MEMORY ---
    return tokenizer(inputs, truncation=True, padding="max_length", max_length=64) # Try 64 or even 32 if 128 is too much

print("Tokenizing dataset...")
tokenized_dataset = dataset.map(tokenize_function, batched=True, remove_columns=["prompt", "code"])
print("Dataset tokenized.")
print(f"First tokenized example: {tokenized_dataset[0]}")

# Data collator for language modeling
data_collator = DataCollatorForLanguageModeling(tokenizer=tokenizer, mlm=False)

# Define training arguments
training_args = TrainingArguments(
    output_dir="./finetuned_codegen",
    overwrite_output_dir=True,
    num_train_epochs=3,
    # --- AGGRESSIVELY REDUCED BATCH SIZE AND GRADIENT ACCUMULATION FOR CPU ---
    per_device_train_batch_size=1,
    gradient_accumulation_steps=1, # No accumulation, true batch size of 1
    save_steps=500,
    save_total_limit=2,
    logging_steps=10, # Log more frequently to see if it starts moving
    learning_rate=5e-5,
    fp16=False, # Keep False for CPU
    use_cpu=True, # Use this instead of no_cuda=True
    dataloader_pin_memory=False, # Disable pin_memory for CPU
    report_to="none", # Disable reporting to avoid potential hangs
    gradient_checkpointing=True, # Keep this, it helps with memory on CPU too
    max_grad_norm=1.0,
)

# Custom callback to store training loss
class LossCallback(TrainerCallback):
    def __init__(self):
        self.losses = []
        self.log_steps = []

    def on_log(self, args, state, control, logs=None, **kwargs):
        if logs and "loss" in logs:
            self.losses.append(logs["loss"])
            self.log_steps.append(state.global_step)
            print(f"Step {state.global_step}: Loss = {logs['loss']:.4f}")

loss_callback = LossCallback()

# Initialize Trainer
trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=tokenized_dataset,
    data_collator=data_collator,
    callbacks=[loss_callback],
)

# Start fine-tuning
print("Starting fine-tuning...")
print("WARNING: Training on CPU will be extremely slow. The 0% progress bar might take a very long time to update.")
print("Please monitor your system's RAM and CPU usage.")
trainer.train()
print("Fine-tuning finished.")

# Save fine-tuned model
model.save_pretrained("./finetuned_codegen")
tokenizer.save_pretrained("./finetuned_codegen")
print("Model fine-tuned and saved to ./finetuned_codegen.")

# Plot training loss
if loss_callback.losses:
    plt.figure(figsize=(10, 6))
    plt.plot(loss_callback.log_steps, loss_callback.losses, label="Training Loss")
    plt.xlabel("Steps")
    plt.ylabel("Loss")
    plt.title("Fine-Tuning Loss Curve")
    plt.legend()
    plt.grid(True)
    plot_path = "./finetuned_codegen/loss_plot.png"
    plt.savefig(plot_path)
    print(f"Loss plot saved to {plot_path}")
else:
    print("No training losses recorded to plot.")
plt.show()

print("Fine-tuning script finished execution.")