# This is adapted from the GPT-Neox library
import os
import struct
from functools import lru_cache
from itertools import accumulate
from pathlib import Path

import numpy as np
from torch.utils.data import Dataset

dtypes = {1: np.uint8, 2: np.int8, 3: np.int16, 4: np.int32, 5: np.int64, 6: np.float32, 7: np.float64, 8: np.uint16}


def code(dtype):
    for k in dtypes:
        if dtypes[k] == dtype:
            return k
    raise ValueError(dtype)


def index_file_path(prefix_path):
    return prefix_path + ".idx"


def data_file_path(prefix_path):
    return prefix_path + ".bin"


def _warmup_mmap_file(path):
    with open(path, "rb") as stream:
        while stream.read(100 * 1024 * 1024):
            pass


class MMapIndexedDataset(Dataset):
    class Index:
        _HDR_MAGIC = b"MMIDIDX\x00\x00"

        @classmethod
        def writer(cls, path, dtype):
            class _Writer:
                def __enter__(self):
                    self._file = open(path, "wb")  # noqa: SIM115

                    # Write Magic string so we can check the file format then opening it again.
                    self._file.write(cls._HDR_MAGIC)
                    # Write version number
                    # Little endian unsigned 64 Bit integer
                    self._file.write(struct.pack("<Q", 1))
                    # Little endian unsigned 8 Bit integer
                    self._file.write(struct.pack("<B", code(dtype)))

                    return self

                @staticmethod
                def _get_pointers(sizes):
                    pointers = np.zeros(len(sizes), dtype=np.int64)
                    sizes = np.array(sizes, dtype=np.int64)

                    np.cumsum(sizes[:-1], out=pointers[1:])
                    pointers = pointers * dtype().itemsize
                    return pointers

                def write(self, sizes, doc_idx):
                    pointers = self._get_pointers(sizes)

                    # Little endian unsigned 64 Bit integer
                    self._file.write(struct.pack("<Q", len(sizes)))
                    # Little endian unsigned 64 Bit integer
                    self._file.write(struct.pack("<Q", len(doc_idx)))

                    sizes = np.array(sizes, dtype=np.int32)
                    self._file.write(sizes.tobytes(order="C"))
                    del sizes

                    pointers = np.array(pointers, dtype=np.int64)
                    self._file.write(pointers.tobytes(order="C"))
                    del pointers

                    doc_idx = np.array(doc_idx, dtype=np.int64)
                    self._file.write(doc_idx.tobytes(order="C"))

                def __exit__(self, exc_type, exc_val, exc_tb):
                    self._file.close()

            return _Writer()

        def __init__(self, path, skip_warmup=False):
            with open(path, "rb") as stream:
                magic_test = stream.read(9)
                assert magic_test == self._HDR_MAGIC, (
                    "Index file doesn't match expected format. " "Make sure that --dataset-impl is configured properly."
                )
                # Little endian unsigned 64 Bit integer
                version = struct.unpack("<Q", stream.read(8))
                assert version == (1,)

                # Little endian unsigned 8 Bit integer
                (dtype_code,) = struct.unpack("<B", stream.read(1))
                self._dtype = dtypes[dtype_code]
                self._dtype_size = self._dtype().itemsize

                self._len = struct.unpack("<Q", stream.read(8))[0]
                self._doc_count = struct.unpack("<Q", stream.read(8))[0]
                offset = stream.tell()

            if not skip_warmup:
                print("    warming up index mmap file...")
                _warmup_mmap_file(path)

            self._bin_buffer_mmap = np.memmap(path, mode="r", order="C")
            self._bin_buffer = memoryview(self._bin_buffer_mmap)
            print("    reading sizes...")
            self._sizes = np.frombuffer(self._bin_buffer, dtype=np.int32, count=self._len, offset=offset)
            print("    reading pointers...")
            self._pointers = np.frombuffer(
                self._bin_buffer, dtype=np.int64, count=self._len, offset=offset + self._sizes.nbytes
            )
            print("    reading document index...")
            self._doc_idx = np.frombuffer(
                self._bin_buffer,
                dtype=np.int64,
                count=self._doc_count,
                offset=offset + self._sizes.nbytes + self._pointers.nbytes,
            )

        def __del__(self):
            self._bin_buffer_mmap._mmap.close()
            del self._bin_buffer_mmap

        @property
        def dtype(self):
            return self._dtype

        @property
        def sizes(self):
            return self._sizes

        @property
        def doc_idx(self):
            return self._doc_idx

        @lru_cache(maxsize=8)  # noqa: B019
        def __getitem__(self, i):
            return self._pointers[i], self._sizes[i]

        def __len__(self):
            return self._len

    def __init__(self, path, skip_warmup=False):
        super().__init__()

        self._path = None
        self._index = None
        self._bin_buffer = None

        self._do_init(path, skip_warmup)

    def __getstate__(self):
        return self._path

    def __setstate__(self, state):
        self._do_init(state)

    def _do_init(self, path, skip_warmup):
        self._path = path
        self._index = self.Index(index_file_path(self._path), skip_warmup)

        if not skip_warmup:
            print("    warming up data mmap file...")
            _warmup_mmap_file(data_file_path(self._path))
        print("    creating numpy buffer of mmap...")
        self._bin_buffer_mmap = np.memmap(data_file_path(self._path), mode="r", order="C")
        print("    creating memory view of numpy buffer...")
        self._bin_buffer = memoryview(self._bin_buffer_mmap)

    def __del__(self):
        self._bin_buffer_mmap._mmap.close()
        del self._bin_buffer_mmap
        del self._index

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

    # @lru_cache(maxsize=8)
    def __getitem__(self, idx):
        if isinstance(idx, int):
            ptr, size = self._index[idx]
            np_array = np.frombuffer(self._bin_buffer, dtype=self._index.dtype, count=size, offset=ptr)
            return np_array
        elif isinstance(idx, slice):
            start, stop, step = idx.indices(len(self))
            if step != 1:
                raise ValueError("Slices into indexed_dataset must be contiguous")
            ptr = self._index._pointers[start]
            sizes = self._index._sizes[idx]
            offsets = list(accumulate(sizes))
            total_size = sum(sizes)
            np_array = np.frombuffer(self._bin_buffer, dtype=self._index.dtype, count=total_size, offset=ptr)
            sents = np.split(np_array, offsets[:-1])
            return sents

    def get(self, idx, offset=0, length=None):
        """Retrieves a single item from the dataset with the option to only
        return a portion of the item.

        get(idx) is the same as [idx] but get() does not support slicing.
        """
        ptr, size = self._index[idx]
        if length is None:
            length = size - offset
        ptr += offset * np.dtype(self._index.dtype).itemsize
        np_array = np.frombuffer(self._bin_buffer, dtype=self._index.dtype, count=length, offset=ptr)
        return np_array

    @property
    def sizes(self):
        return self._index.sizes

    @property
    def doc_idx(self):
        return self._index.doc_idx

    def get_doc_idx(self):
        return self._index._doc_idx

    def set_doc_idx(self, doc_idx_):
        self._index._doc_idx = doc_idx_

    @property
    def supports_prefetch(self):
        return False

    @staticmethod
    def exists(path):
        return os.path.exists(index_file_path(path)) and os.path.exists(data_file_path(path))


class GPT2Dataset(Dataset):
    """Streamlined version of the GPT2Dataset in megatron."""

    def __init__(
        self, indexed_dataset: MMapIndexedDataset, doc_idx: np.memmap, sample_idx: np.memmap, shuffle_idx: np.memmap
    ):
        self.indexed_dataset = indexed_dataset
        self.doc_idx = doc_idx
        self.sample_idx = sample_idx
        self.shuffle_idx = shuffle_idx

        self.shuffle_idx_len = self.shuffle_idx.shape[0] - 1
        self.sample_idx_len = self.sample_idx.shape[0] - 1

        if self.shuffle_idx_len != self.sample_idx_len:
            print(f"WARNING: {self.shuffle_idx_len=} != {self.sample_idx_len=}")

    def __len__(self):
        return min(self.shuffle_idx_len, self.sample_idx_len)

    def __getitem__(self, idx: int) -> dict[str, np.ndarray]:
        # Get the shuffled index.
        idx = self.shuffle_idx[idx]
        # Start and end documents and offsets.
        doc_index_f = self.sample_idx[idx][0]
        doc_index_l = self.sample_idx[idx + 1][0]
        offset_f = self.sample_idx[idx][1]
        offset_l = self.sample_idx[idx + 1][1]
        # If we are within the same document, just extract the chunk.
        if doc_index_f == doc_index_l:
            sample = self.indexed_dataset.get(
                self.doc_idx[doc_index_f], offset=offset_f, length=offset_l - offset_f + 1
            )
        else:
            # Otherwise, get the rest of the initial document.
            sample_list = [self.indexed_dataset.get(self.doc_idx[doc_index_f], offset=offset_f)]
            # Loop over all in between documents and add the entire document.
            for i in range(doc_index_f + 1, doc_index_l):
                sample_list.append(self.indexed_dataset.get(self.doc_idx[i]))
            # And finally add the relevant portion of last document.
            sample_list.append(self.indexed_dataset.get(self.doc_idx[doc_index_l], length=offset_l + 1))
            sample = np.concatenate(sample_list)

        return {"text": np.array(sample, dtype=np.int64)}


def read_dataset(file_path: str | Path, prefix: str, document_path: str | Path = ".") -> GPT2Dataset:
    # e.g., pile_20B_tokenizer_text_document_train_indexmap_120ns_2048sl_1234s_doc_idx.npy
    # prefix: pile_20B_tokenizer_text_document_train_indexmap_120ns_2048sl_1234s

    file_path = Path(file_path)
    document_path = Path(document_path)

    doc_idx = np.load(file_path / f"{prefix}_doc_idx.npy", allow_pickle=True, mmap_mode="r")
    sample_idx = np.load(file_path / f"{prefix}_sample_idx.npy", allow_pickle=True, mmap_mode="r")
    shuffle_idx = np.load(file_path / f"{prefix}_shuffle_idx.npy", allow_pickle=True, mmap_mode="r")
    indexed_dataset = MMapIndexedDataset(str(document_path / "pile_20B_tokenizer_text_document"), skip_warmup=True)

    ds = GPT2Dataset(indexed_dataset=indexed_dataset, doc_idx=doc_idx, sample_idx=sample_idx, shuffle_idx=shuffle_idx)

    # check seqlen is correct
    print("Seq length ==", len(ds[0]["text"]))
    print("Num batches ==", len(ds) / 1024, "(should be 143k)")

    return ds