import os
import torch
from datasets import load_dataset
from transformers import (
    AutoTokenizer,
    AutoModelForCausalLM,
    TrainingArguments,
)
from peft import (
    LoraConfig,
    get_peft_model,
    prepare_model_for_kbit_training,
)
from trl import SFTTrainer

# ----------------------------
# Environment safety (Windows)
# ----------------------------
os.environ["TORCHDYNAMO_DISABLE"] = "1"

# ----------------------------
# Model configuration
# ----------------------------
MODEL_NAME = "Qwen/Qwen2.5-7B-Instruct"

print(f"=== Starting fine-tuning script {MODEL_NAME} ===")

print(f"{80 * '_'}\n[1/7] Loading tokenizer...")
tokenizer = AutoTokenizer.from_pretrained(
    MODEL_NAME,
    trust_remote_code=True
)

# Ensure padding is defined
tokenizer.pad_token = tokenizer.eos_token
tokenizer.model_max_length = 1024

print("Tokenizer loaded and configured.")

print(f"{80 * '_'}\n[2/7] Loading model in 4-bit mode (QLoRA)...")
model = AutoModelForCausalLM.from_pretrained(
    MODEL_NAME,
    load_in_4bit=True,
    device_map="auto",
    torch_dtype=torch.float16,  # weights in fp16, gradients fp32
    trust_remote_code=True,
)
print("Model loaded.")

print(f"{80 * '_'}\n[3/7] Preparing model for k-bit training...")
model = prepare_model_for_kbit_training(model)

# Fix future PyTorch checkpointing behavior
model.gradient_checkpointing_enable(
    gradient_checkpointing_kwargs={"use_reentrant": False}
)

print("Model prepared for k-bit training.")

# ----------------------------
# LoRA configuration
# ----------------------------
print(f"{80 * '_'}\n[4/7] Configuring LoRA adapters...")
lora_config = LoraConfig(
    r=16,
    lora_alpha=32,
    lora_dropout=0.05,
    bias="none",
    task_type="CAUSAL_LM",
    target_modules=[
        "q_proj",
        "k_proj",
        "v_proj",
        "o_proj",
        "gate_proj",
        "up_proj",
        "down_proj",
    ],
)

model = get_peft_model(model, lora_config)
model.print_trainable_parameters()
print("LoRA adapters attached.")

# ----------------------------
# Dataset loading
# ----------------------------
print(f"{80 * '_'}\n[5/7] Loading dataset from JSON file...")
dataset = load_dataset(
    "json",
    data_files="traductions.json"
)

print(f"Dataset loaded with {len(dataset['train'])} samples.")

print("Formatting dataset for Ukrainian → French translation...")

def format_prompt(example):
    prompt = (
        "Translate the following Ukrainian text into French.\n\n"
        f"Ukrainian: {example['text']}\n"
        f"French: {example['translation']}"
    )
    return {"text": prompt}

dataset = dataset.map(
    format_prompt,
    remove_columns=dataset["train"].column_names
)

print("Dataset formatting completed.")

# ----------------------------
# Training arguments (AMP OFF)
# ----------------------------
print(f"{80 * '_'}\n[6/7] Initializing training arguments...")
training_args = TrainingArguments(
    output_dir="./qwen2.5-7b-uk-fr-lora",
    per_device_train_batch_size=1,
    gradient_accumulation_steps=8,
    learning_rate=2e-4,
    num_train_epochs=2,  # 2 epochs usually enough for translation
    fp16=False,
    bf16=False,
    logging_steps=10,
    save_steps=500,
    save_total_limit=2,
    optim="paged_adamw_32bit",
    report_to="none",
)

print("Training arguments ready.")

# ----------------------------
# Trainer
# ----------------------------
print("Initializing SFTTrainer...")
trainer = SFTTrainer(
    model=model,
    train_dataset=dataset["train"],
    processing_class=tokenizer,
    args=training_args,
)
print("Trainer initialized.")

# ----------------------------
# Train
# ----------------------------
print(f"{80 * '_'}\n[7/7] Starting training...")
trainer.train(resume_from_checkpoint=True)
print("Training completed successfully.")

# ----------------------------
# Save LoRA adapter
# ----------------------------
print("Saving LoRA adapter and tokenizer...")
trainer.model.save_pretrained("./qwen2.5-7b-uk-fr-lora")
tokenizer.save_pretrained("./qwen2.5-7b-uk-fr-lora")

print("=== Fine-tuning finished ===")
print("LoRA adapter saved in ./qwen2.5-7b-uk-fr-lora")
