# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.


# copied from fairseq/fairseq/data/indexed_dataset.py
# Removed IndexedRawTextDataset since it relied on Fairseq dictionary
# other slight modifications to remove fairseq dependencies
# Added document index to index file and made it accessible.
#    An empty sentence no longer separates documents.


# copied from Megatron
# Used for building mmap datasets.
from functools import lru_cache
import struct
import numpy as np
import shutil

__all__ = ["make_mmap_builder"]

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


def __best_fitting_dtype(vocab_size=None):
    if vocab_size is not None and vocab_size < 65500:
        return np.uint16
    else:
        return np.int32


def make_mmap_builder(out_file, vocab_size=None):
    return MMapIndexedDatasetBuilder(
        out_file, dtype=__best_fitting_dtype(vocab_size)
    )


def code(dtype):
    for k in dtypes.keys():
        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"


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

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

                    self._file.write(cls._HDR_MAGIC)
                    self._file.write(struct.pack("<Q", 1))
                    self._file.write(struct.pack("<B", code(dtype)))

                    return self

                @staticmethod
                def _get_pointers(sizes):
                    dtype_size = dtype().itemsize
                    address = 0
                    pointers = []

                    for size in sizes:
                        pointers.append(address)
                        address += size * dtype_size

                    return pointers

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

                    self._file.write(struct.pack("<Q", len(sizes)))
                    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 self._HDR_MAGIC == magic_test, (
                    "Index file doesn't match expected format. "
                    "Make sure that --dataset-impl is configured properly."
                )
                version = struct.unpack("<Q", stream.read(8))
                assert (1,) == version

                (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()

            self._bin_buffer_mmap = np.memmap(path, mode="r", order="C")
            self._bin_buffer = memoryview(self._bin_buffer_mmap)
            self._sizes = np.frombuffer(
                self._bin_buffer, dtype=np.int32, count=self._len, offset=offset
            )
            self._pointers = np.frombuffer(
                self._bin_buffer,
                dtype=np.int64,
                count=self._len,
                offset=offset + self._sizes.nbytes,
            )
            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)
        def __getitem__(self, i):
            return self._pointers[i], self._sizes[i]

        def __len__(self):
            return self._len


class MMapIndexedDatasetBuilder(object):
    def __init__(self, out_file, dtype=np.int64):
        self._data_file = open(out_file, "wb")
        self._dtype = dtype
        self._sizes = []
        self._doc_idx = [0]

    def add_item(self, tensor):
        np_array = np.array(tensor.numpy(), dtype=self._dtype)
        self._data_file.write(np_array.tobytes(order="C"))
        self._sizes.append(np_array.size)

    def end_document(self):
        self._doc_idx.append(len(self._sizes))

    def merge_file_(self, another_file):
        # Concatenate index
        index = MMapIndexedDataset.Index(index_file_path(another_file))
        assert index.dtype == self._dtype

        for size in index.sizes:
            self._sizes.append(size)

        # Concatenate data
        with open(data_file_path(another_file), "rb") as f:
            shutil.copyfileobj(f, self._data_file)

    def finalize(self, index_file):
        self._data_file.close()

        with MMapIndexedDataset.Index.writer(index_file, self._dtype) as index:
            index.write(self._sizes, self._doc_idx)