# Adopted from https://github.com/guandeh17/Self-Forcing
# SPDX-License-Identifier: Apache-2.0
from torch.utils.data import Dataset
import numpy as np
import torch
import lmdb
import json
from pathlib import Path
from PIL import Image
import os
import datasets



class TextDataset(Dataset):
    def __init__(self, prompt_path, extended_prompt_path=None):
        with open(prompt_path, encoding="utf-8") as f:
            self.prompt_list = [line.rstrip() for line in f]

        if extended_prompt_path is not None:
            with open(extended_prompt_path, encoding="utf-8") as f:
                self.extended_prompt_list = [line.rstrip() for line in f]
            assert len(self.extended_prompt_list) == len(self.prompt_list)
        else:
            self.extended_prompt_list = None

    def __len__(self):
        return len(self.prompt_list)

    def __getitem__(self, idx):
        batch = {
            "prompts": self.prompt_list[idx],
            "idx": idx,
        }
        if self.extended_prompt_list is not None:
            batch["extended_prompts"] = self.extended_prompt_list[idx]
        return batch


class TwoTextDataset(Dataset):
    """Dataset that returns two text prompts per sample for prompt-switch training.

    The dataset behaves similarly to :class:`TextDataset` but instead of a single
    prompt, it provides *two* prompts – typically the first prompt is used for the
    first segment of the video, and the second prompt is used after a temporal
    switch during training.

    Args:
        prompt_path (str): Path to a text file containing the *first* prompt for
            each sample. One prompt per line.
        switch_prompt_path (str): Path to a text file containing the *second*
            prompt for each sample. Must have the **same number of lines** as
            ``prompt_path`` so that prompts are paired 1-to-1.
    """
    def __init__(self, prompt_path: str, switch_prompt_path: str):
        # Load the first-segment prompts.
        with open(prompt_path, encoding="utf-8") as f:
            self.prompt_list = [line.rstrip() for line in f]

        # Load the second-segment prompts.
        with open(switch_prompt_path, encoding="utf-8") as f:
            self.switch_prompt_list = [line.rstrip() for line in f]

        assert len(self.switch_prompt_list) == len(self.prompt_list), (
            "The two prompt files must contain the same number of lines so that "
            "each first-segment prompt is paired with exactly one second-segment prompt."
        )

    def __len__(self):
        return len(self.prompt_list)

    def __getitem__(self, idx):
        return {
            "prompts": self.prompt_list[idx],            # first-segment prompt
            "switch_prompts": self.switch_prompt_list[idx],  # second-segment prompt
            "idx": idx,
        }


class MultiTextDataset(Dataset):
    """Dataset for multi-segment prompts stored in a JSONL file.

    Each line is a JSON object, e.g.
        {"prompts": ["a cat", "a dog", "a bird"]}

    Args
    ----
    prompt_path : str
        Path to the JSONL file
    field       : str
        Name of the list-of-strings field, default "prompts"
    cache_dir   : str | None
        ``cache_dir`` passed to HF Datasets (optional)
    """

    def __init__(self, prompt_path: str, field: str = "prompts", cache_dir: str | None = None):
        self.ds = datasets.load_dataset(
            "json",
            data_files=prompt_path,
            split="train",
            cache_dir=cache_dir,
            streaming=False, 
        )

        assert len(self.ds) > 0, "JSONL is empty"
        assert field in self.ds.column_names, f"Missing field '{field}'"

        seg_len = len(self.ds[0][field])
        for i, ex in enumerate(self.ds):
            val = ex[field]
            assert isinstance(val, list), f"Line {i} field '{field}' is not a list"
            assert len(val) == seg_len,  f"Line {i} list length mismatch"

        self.field = field

    def __len__(self):
        return len(self.ds)

    def __getitem__(self, idx: int):
        return {
            "idx": idx,
            "prompts_list": self.ds[idx][self.field],  # List[str]
        }


def cycle(dl):
    while True:
        for data in dl:
            yield data