import json, random, math, os
from pathlib import Path
from datasets import (
    BuilderConfig, DatasetInfo, DownloadManager, GeneratorBasedBuilder,
    SplitGenerator, Split, Features, Image, Value
)
from huggingface_hub import hf_hub_url

_REPO_ID = "infosys/OpenHumnoidActuatedFaceData"
_IMAGES_PER_SHARD = 10_000            # how many files you put in each tar
_TAR_TPL = "images-{start:05d}-{end:05d}.tar"  # file-name pattern


class ImageSubsetConfig(BuilderConfig):
    def __init__(self, name, sample_size=None, **kw):
        super().__init__(name=name, version="1.0.2",
                         description=kw.get("description", ""))
        self.sample_size = sample_size


class MyImageDataset(GeneratorBasedBuilder):
    BUILDER_CONFIGS = [
        ImageSubsetConfig("full",  sample_size=None,
                          description="Entire dataset (≈100 GB)"),
        ImageSubsetConfig("small", sample_size=20_000,
                          description="20 K random images"),
    ]
    DEFAULT_CONFIG_NAME = "small"

    # ------------------------------------------------------------------ #
    # 1. Schema                                                          #
    # ------------------------------------------------------------------ #
    def _info(self):
        return DatasetInfo(
            description="Humanoid face images + 16 servo angles.",
            features=Features(
                {
                    "image": Image(),              # PIL.Image is fine
                    "actuated_angle":
                        {str(i): Value("int32") for i in range(16)},
                }
            ),
        )

    # ------------------------------------------------------------------ #
    # 2. Download                                                         #
    # ------------------------------------------------------------------ #
    def _split_generators(self, dl_manager: DownloadManager):
        # ---- 2-a: load metadata -------------------------------------- #
        meta_url = hf_hub_url(_REPO_ID, "metadata.json", repo_type="dataset")
        meta_path = dl_manager.download(meta_url)
        with open(meta_path, encoding="utf-8") as f:
            metadata = json.load(f)

        all_names = sorted(metadata)
        selected = (                           # sampling logic
            sorted(random.sample(all_names, self.config.sample_size))
            if self.config.sample_size else all_names
        )
        selected_set = set(selected)

        # ---- 2-b: figure out which shards we need -------------------- #
        max_idx = len(all_names) - 1
        n_shards = math.floor(max_idx / _IMAGES_PER_SHARD) + 1
        shard_files = [
            _TAR_TPL.format(start=s*_IMAGES_PER_SHARD,
                            end=min((s+1)*_IMAGES_PER_SHARD-1, max_idx))
            for s in range(n_shards)
        ]

        # ---- 2-c: download (and extract) each tar -------------------- #
        tar_urls   = [hf_hub_url(_REPO_ID, f, repo_type="dataset")
                      for f in shard_files]
        local_tars = dl_manager.download(tar_urls)          # .tar paths

        #   we’ll stream from the tar, so no extract() needed

        return [
            SplitGenerator(
                name=Split.TRAIN,
                gen_kwargs={
                    "tar_paths": local_tars,
                    "metadata": metadata,
                    "want": selected_set,
                },
            )
        ]

    # ------------------------------------------------------------------ #
    # 3. Generate                                                         #
    # ------------------------------------------------------------------ #
    def _generate_examples(self, tar_paths, metadata, want):
        """Stream over each tar and yield only requested files."""
        idx = 0
        for tar_path in tar_paths:
            # iterate without extraction
            for inner_path, fobj in \
                    self._iter_archive_fast(tar_path):      # helper below
                fname = Path(inner_path).name               # strip tar prefix
                if fname not in want:
                    continue

                angles = metadata[fname]
                yield idx, {
                    "image": {"bytes": fobj.read(), "path": fname},
                    "actuated_angle":
                        {str(i): int(angles.get(str(i), 0)) for i in range(16)}
                }
                idx += 1

    # Small wrapper so we don’t import datasets.utils.file_utils directly
    @staticmethod
    def _iter_archive_fast(tar_path):
        import tarfile
        with tarfile.open(tar_path) as tar:
            for member in tar:
                if member.isfile():
                    f = tar.extractfile(member)
                    yield member.name, f