"""
Prepare Dataset Module

Load and preprocess training data for fine-tuning.
Converts JSONL files to Hugging Face Dataset format.

Example usage:
    from src.training.prepare_dataset import prepare_dataset

    train_dataset, val_dataset = prepare_dataset(
        train_path="data/training/train.jsonl",
        val_path="data/training/validation.jsonl",
    )
"""

import json
from pathlib import Path
from typing import Optional, Tuple

from loguru import logger

try:
    from datasets import Dataset, DatasetDict
    HF_DATASETS_AVAILABLE = True
except ImportError:
    HF_DATASETS_AVAILABLE = False
    logger.warning("datasets library not available")

try:
    from transformers import AutoTokenizer
    TRANSFORMERS_AVAILABLE = True
except ImportError:
    TRANSFORMERS_AVAILABLE = False
    logger.warning("transformers library not available")


def load_jsonl(path: str | Path) -> list[dict]:
    """Load data from JSONL file."""
    data = []
    with open(path, "r", encoding="utf-8") as f:
        for line in f:
            if line.strip():
                data.append(json.loads(line))
    return data


def format_chat_template(
    messages: list[dict],
    tokenizer,
    add_generation_prompt: bool = False,
) -> str:
    """
    Format messages using the tokenizer's chat template.

    Args:
        messages: List of message dicts with 'role' and 'content'
        tokenizer: HuggingFace tokenizer
        add_generation_prompt: Whether to add generation prompt at end

    Returns:
        Formatted string
    """
    if hasattr(tokenizer, "apply_chat_template"):
        return tokenizer.apply_chat_template(
            messages,
            tokenize=False,
            add_generation_prompt=add_generation_prompt,
        )
    else:
        # Fallback to ChatML format
        formatted = ""
        for msg in messages:
            role = msg["role"]
            content = msg["content"]
            if role == "system":
                formatted += f"<|im_start|>system\n{content}<|im_end|>\n"
            elif role == "user":
                formatted += f"<|im_start|>user\n{content}<|im_end|>\n"
            elif role == "assistant":
                formatted += f"<|im_start|>assistant\n{content}<|im_end|>\n"
        return formatted


def prepare_dataset(
    train_path: str | Path,
    val_path: Optional[str | Path] = None,
    tokenizer_name: str = "Qwen/Qwen3-4B-Instruct",
    max_length: int = 2048,
    add_eos_token: bool = True,
) -> Tuple:
    """
    Prepare training and validation datasets.

    Args:
        train_path: Path to training JSONL file
        val_path: Path to validation JSONL file (optional)
        tokenizer_name: Name of tokenizer to use for formatting
        max_length: Maximum sequence length
        add_eos_token: Whether to add EOS token

    Returns:
        Tuple of (train_dataset, val_dataset) or (train_dataset, None)
    """
    if not HF_DATASETS_AVAILABLE:
        raise ImportError("datasets library required. Run: pip install datasets")

    if not TRANSFORMERS_AVAILABLE:
        raise ImportError("transformers library required. Run: pip install transformers")

    logger.info(f"Loading tokenizer: {tokenizer_name}")
    tokenizer = AutoTokenizer.from_pretrained(tokenizer_name, trust_remote_code=True)

    # Ensure padding token is set
    if tokenizer.pad_token is None:
        tokenizer.pad_token = tokenizer.eos_token

    # Load training data
    logger.info(f"Loading training data from: {train_path}")
    train_data = load_jsonl(train_path)
    logger.info(f"Loaded {len(train_data)} training examples")

    # Format training examples
    train_formatted = []
    for example in train_data:
        messages = example["messages"]
        text = format_chat_template(messages, tokenizer)
        if add_eos_token and not text.endswith(tokenizer.eos_token):
            text += tokenizer.eos_token
        train_formatted.append({"text": text})

    train_dataset = Dataset.from_list(train_formatted)

    # Load validation data if provided
    val_dataset = None
    if val_path:
        logger.info(f"Loading validation data from: {val_path}")
        val_data = load_jsonl(val_path)
        logger.info(f"Loaded {len(val_data)} validation examples")

        val_formatted = []
        for example in val_data:
            messages = example["messages"]
            text = format_chat_template(messages, tokenizer)
            if add_eos_token and not text.endswith(tokenizer.eos_token):
                text += tokenizer.eos_token
            val_formatted.append({"text": text})

        val_dataset = Dataset.from_list(val_formatted)

    logger.info("Dataset preparation complete")
    return train_dataset, val_dataset


def prepare_dataset_dict(
    train_path: str | Path,
    val_path: str | Path,
    tokenizer_name: str = "Qwen/Qwen3-4B-Instruct",
    max_length: int = 2048,
) -> DatasetDict:
    """
    Prepare a DatasetDict with train and validation splits.

    Args:
        train_path: Path to training JSONL
        val_path: Path to validation JSONL
        tokenizer_name: Tokenizer name
        max_length: Maximum sequence length

    Returns:
        DatasetDict with 'train' and 'validation' keys
    """
    train_dataset, val_dataset = prepare_dataset(
        train_path=train_path,
        val_path=val_path,
        tokenizer_name=tokenizer_name,
        max_length=max_length,
    )

    return DatasetDict({
        "train": train_dataset,
        "validation": val_dataset,
    })


def tokenize_dataset(
    dataset: Dataset,
    tokenizer,
    max_length: int = 2048,
    num_proc: int = 4,
) -> Dataset:
    """
    Tokenize a dataset for training.

    Args:
        dataset: Dataset with 'text' column
        tokenizer: HuggingFace tokenizer
        max_length: Maximum sequence length
        num_proc: Number of processes for parallel tokenization

    Returns:
        Tokenized dataset
    """
    def tokenize_function(examples):
        return tokenizer(
            examples["text"],
            truncation=True,
            max_length=max_length,
            padding=False,
            return_tensors=None,
        )

    tokenized = dataset.map(
        tokenize_function,
        batched=True,
        num_proc=num_proc,
        remove_columns=dataset.column_names,
        desc="Tokenizing",
    )

    return tokenized


def push_dataset_to_hub(
    dataset_dict: DatasetDict,
    repo_id: str,
    private: bool = True,
    token: Optional[str] = None,
) -> None:
    """
    Push dataset to Hugging Face Hub.

    Args:
        dataset_dict: DatasetDict to push
        repo_id: Repository ID on HF Hub
        private: Whether repo should be private
        token: HF token (uses HF_TOKEN env var if not provided)
    """
    import os
    token = token or os.environ.get("HF_TOKEN")

    logger.info(f"Pushing dataset to: {repo_id}")
    dataset_dict.push_to_hub(
        repo_id,
        private=private,
        token=token,
    )
    logger.info("Dataset pushed successfully")


def main():
    """CLI entry point for testing dataset preparation."""
    import argparse

    parser = argparse.ArgumentParser(
        description="Prepare training datasets for fine-tuning",
        formatter_class=argparse.RawDescriptionHelpFormatter,
        epilog="""
Examples:
    python prepare_dataset.py data/training/train.jsonl --val data/training/validation.jsonl
    python prepare_dataset.py data/training/train.jsonl --push-to-hub username/dataset-name
        """,
    )

    parser.add_argument("train", help="Path to training JSONL file")
    parser.add_argument("--val", help="Path to validation JSONL file")
    parser.add_argument(
        "--tokenizer",
        default="Qwen/Qwen3-4B-Instruct",
        help="Tokenizer name (default: Qwen/Qwen3-4B-Instruct)",
    )
    parser.add_argument(
        "--max-length",
        type=int,
        default=2048,
        help="Maximum sequence length (default: 2048)",
    )
    parser.add_argument(
        "--push-to-hub",
        help="Push dataset to HF Hub with this repo ID",
    )
    parser.add_argument(
        "--private",
        action="store_true",
        default=True,
        help="Make HF repo private (default: True)",
    )

    args = parser.parse_args()

    # Prepare dataset
    if args.val:
        dataset_dict = prepare_dataset_dict(
            train_path=args.train,
            val_path=args.val,
            tokenizer_name=args.tokenizer,
            max_length=args.max_length,
        )
        print(f"\nDataset prepared:")
        print(f"  Train: {len(dataset_dict['train'])} examples")
        print(f"  Validation: {len(dataset_dict['validation'])} examples")

        # Show sample
        print("\nSample training example:")
        print(dataset_dict["train"][0]["text"][:500] + "...")

        # Push to hub if requested
        if args.push_to_hub:
            push_dataset_to_hub(
                dataset_dict,
                args.push_to_hub,
                private=args.private,
            )
    else:
        train_dataset, _ = prepare_dataset(
            train_path=args.train,
            tokenizer_name=args.tokenizer,
            max_length=args.max_length,
        )
        print(f"\nDataset prepared: {len(train_dataset)} examples")
        print("\nSample:")
        print(train_dataset[0]["text"][:500] + "...")


if __name__ == "__main__":
    main()