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"""Dataset is currently unstable. APIs subject to change without notice."""

import pyarrow as pa
from pyarrow.fs import _normalize_path, _MockFileSystem
from pyarrow.util import _stringify_path, _is_path_like

from pyarrow._dataset import (  # noqa
    CsvFileFormat,
    Expression,
    Dataset,
    DatasetFactory,
    DirectoryPartitioning,
    FileFormat,
    FileFragment,
    FileSystemDataset,
    FileSystemDatasetFactory,
    FileSystemFactoryOptions,
    Fragment,
    HivePartitioning,
    IpcFileFormat,
    ParquetDatasetFactory,
    ParquetFactoryOptions,
    ParquetFileFormat,
    ParquetFileFragment,
    ParquetReadOptions,
    Partitioning,
    PartitioningFactory,
    RowGroupInfo,
    Scanner,
    ScanTask,
    UnionDataset,
    UnionDatasetFactory
)


def field(name):
    """Reference a named column of the dataset.

    Stores only the field's name. Type and other information is known only when
    the expression is bound to a dataset having an explicit scheme.

    Parameters
    ----------
    name : string
        The name of the field the expression references to.

    Returns
    -------
    field_expr : Expression
    """
    return Expression._field(name)


def scalar(value):
    """Expression representing a scalar value.

    Parameters
    ----------
    value : bool, int, float or string
        Python value of the scalar. Note that only a subset of types are
        currently supported.

    Returns
    -------
    scalar_expr : Expression
    """
    return Expression._scalar(value)


def partitioning(schema=None, field_names=None, flavor=None):
    """
    Specify a partitioning scheme.

    The supported schemes include:

    - "DirectoryPartitioning": this scheme expects one segment in the file path
      for each field in the specified schema (all fields are required to be
      present). For example given schema<year:int16, month:int8> the path
      "/2009/11" would be parsed to ("year"_ == 2009 and "month"_ == 11).
    - "HivePartitioning": a scheme for "/$key=$value/" nested directories as
      found in Apache Hive. This is a multi-level, directory based partitioning
      scheme. Data is partitioned by static values of a particular column in
      the schema. Partition keys are represented in the form $key=$value in
      directory names. Field order is ignored, as are missing or unrecognized
      field names.
      For example, given schema<year:int16, month:int8, day:int8>, a possible
      path would be "/year=2009/month=11/day=15" (but the field order does not
      need to match).

    Parameters
    ----------
    schema : pyarrow.Schema, default None
        The schema that describes the partitions present in the file path.
        If not specified, and `field_names` and/or `flavor` are specified,
        the schema will be inferred from the file path (and a
        PartitioningFactory is returned).
    field_names :  list of str, default None
        A list of strings (field names). If specified, the schema's types are
        inferred from the file paths (only valid for DirectoryPartitioning).
    flavor : str, default None
        The default is DirectoryPartitioning. Specify ``flavor="hive"`` for
        a HivePartitioning.

    Returns
    -------
    Partitioning or PartitioningFactory

    Examples
    --------

    Specify the Schema for paths like "/2009/June":

    >>> partitioning(pa.schema([("year", pa.int16()), ("month", pa.string())]))

    or let the types be inferred by only specifying the field names:

    >>> partitioning(field_names=["year", "month"])

    For paths like "/2009/June", the year will be inferred as int32 while month
    will be inferred as string.

    Create a Hive scheme for a path like "/year=2009/month=11":

    >>> partitioning(
    ...     pa.schema([("year", pa.int16()), ("month", pa.int8())]),
    ...     flavor="hive")

    A Hive scheme can also be discovered from the directory structure (and
    types will be inferred):

    >>> partitioning(flavor="hive")

    """
    if flavor is None:
        # default flavor
        if schema is not None:
            if field_names is not None:
                raise ValueError(
                    "Cannot specify both 'schema' and 'field_names'")
            return DirectoryPartitioning(schema)
        elif field_names is not None:
            if isinstance(field_names, list):
                return DirectoryPartitioning.discover(field_names)
            else:
                raise ValueError(
                    "Expected list of field names, got {}".format(
                        type(field_names)))
        else:
            raise ValueError(
                "For the default directory flavor, need to specify "
                "a Schema or a list of field names")
    elif flavor == 'hive':
        if field_names is not None:
            raise ValueError("Cannot specify 'field_names' for flavor 'hive'")
        elif schema is not None:
            if isinstance(schema, pa.Schema):
                return HivePartitioning(schema)
            else:
                raise ValueError(
                    "Expected Schema for 'schema', got {}".format(
                        type(schema)))
        else:
            return HivePartitioning.discover()
    else:
        raise ValueError("Unsupported flavor")


def _ensure_partitioning(scheme):
    """
    Validate input and return a Partitioning(Factory).

    It passes None through if no partitioning scheme is defiend.
    """
    if scheme is None:
        pass
    elif isinstance(scheme, str):
        scheme = partitioning(flavor=scheme)
    elif isinstance(scheme, list):
        scheme = partitioning(field_names=scheme)
    elif isinstance(scheme, (Partitioning, PartitioningFactory)):
        pass
    else:
        ValueError("Expected Partitioning or PartitioningFactory, got {}"
                   .format(type(scheme)))
    return scheme


def _ensure_format(obj):
    if isinstance(obj, FileFormat):
        return obj
    elif obj == "parquet":
        return ParquetFileFormat()
    elif obj in {"ipc", "arrow", "feather"}:
        return IpcFileFormat()
    elif obj == "csv":
        return CsvFileFormat()
    else:
        raise ValueError("format '{}' is not supported".format(obj))


def _ensure_filesystem(fs_or_uri):
    from pyarrow.fs import (
        FileSystem, LocalFileSystem, SubTreeFileSystem, FileType
    )

    if isinstance(fs_or_uri, str):
        # instantiate the file system from an uri, if the uri has a path
        # component then it will be treated as a path prefix
        filesystem, prefix = FileSystem.from_uri(fs_or_uri)
        is_local = isinstance(filesystem, LocalFileSystem)
        prefix = _normalize_path(filesystem, prefix)
        if prefix:
            # validate that the prefix is pointing to a directory
            prefix_info = filesystem.get_file_info([prefix])[0]
            if prefix_info.type != FileType.Directory:
                raise ValueError(
                    "The path component of the filesystem URI must point to a "
                    "directory but it has a type: `{}`. The path component "
                    "is `{}` and the given filesystem URI is `{}`".format(
                        prefix_info.type.name, prefix_info.path, fs_or_uri
                    )
                )
            filesystem = SubTreeFileSystem(prefix, filesystem)
        return filesystem, is_local
    elif isinstance(fs_or_uri, (LocalFileSystem, _MockFileSystem)):
        return fs_or_uri, True
    elif isinstance(fs_or_uri, FileSystem):
        return fs_or_uri, False
    else:
        raise TypeError(
            '`filesystem` argument must be a FileSystem instance or a valid '
            'file system URI'
        )


def _ensure_multiple_sources(paths, filesystem=None):
    """
    Treat a list of paths as files belonging to a single file system

    If the file system is local then also validates that all paths
    are referencing existing *files* otherwise any non-file paths will be
    silently skipped (for example on a remote filesystem).

    Parameters
    ----------
    paths : list of path-like
        Note that URIs are not allowed.
    filesystem : FileSystem or str, optional
        If an URI is passed, then its path component will act as a prefix for
        the file paths.

    Returns
    -------
    (FileSystem, list of str)
        File system object and a list of normalized paths.

    Raises
    ------
    TypeError
        If the passed filesystem has wrong type.
    IOError
        If the file system is local and a referenced path is not available or
        not a file.
    """
    from pyarrow.fs import LocalFileSystem, FileType

    if filesystem is None:
        # fall back to local file system as the default
        filesystem = LocalFileSystem()

    # construct a filesystem if it is a valid URI
    filesystem, is_local = _ensure_filesystem(filesystem)

    # allow normalizing irregular paths such as Windows local paths
    paths = [_normalize_path(filesystem, _stringify_path(p)) for p in paths]

    # validate that all of the paths are pointing to existing *files*
    # possible improvement is to group the file_infos by type and raise for
    # multiple paths per error category
    if is_local:
        for info in filesystem.get_file_info(paths):
            file_type = info.type
            if file_type == FileType.File:
                continue
            elif file_type == FileType.NotFound:
                raise FileNotFoundError(info.path)
            elif file_type == FileType.Directory:
                raise IsADirectoryError(
                    'Path {} points to a directory, but only file paths are '
                    'supported. To construct a nested or union dataset pass '
                    'a list of dataset objects instead.'.format(info.path)
                )
            else:
                raise IOError(
                    'Path {} exists but its type is unknown (could be a '
                    'special file such as a Unix socket or character device, '
                    'or Windows NUL / CON / ...)'.format(info.path)
                )

    return filesystem, paths


def _ensure_single_source(path, filesystem=None):
    """
    Treat path as either a recursively traversable directory or a single file.

    Parameters
    ----------
    path : path-like
    filesystem : FileSystem or str, optional
        If an URI is passed, then its path component will act as a prefix for
        the file paths.

   Returns
    -------
    (FileSystem, list of str or fs.Selector)
        File system object and either a single item list pointing to a file or
        an fs.Selector object pointing to a directory.

    Raises
    ------
    TypeError
        If the passed filesystem has wrong type.
    FileNotFoundError
        If the referenced file or directory doesn't exist.
    """
    from pyarrow.fs import FileSystem, LocalFileSystem, FileType, FileSelector

    path = _stringify_path(path)

    # if filesystem is not given try to automatically determine one
    # first check if the file exists as a local (relative) file path
    # if not then try to parse the path as an URI
    file_info = None
    if filesystem is None:
        filesystem = LocalFileSystem()
        try:
            file_info = filesystem.get_file_info([path])[0]
        except OSError:
            file_info = None
            exists_locally = False
        else:
            exists_locally = (file_info.type != FileType.NotFound)

        # if the file or directory doesn't exists locally, then assume that
        # the path is an URI describing the file system as well
        if not exists_locally:
            try:
                filesystem, path = FileSystem.from_uri(path)
            except ValueError as e:
                # ARROW-8213: neither an URI nor a locally existing path,
                # so assume that local path was given and propagate a nicer
                # file not found error instead of a more confusing scheme
                # parsing error
                if "empty scheme" not in str(e):
                    raise
            else:
                # unset file_info to query it again from the new filesystem
                file_info = None

    # construct a filesystem if it is a valid URI
    filesystem, _ = _ensure_filesystem(filesystem)

    # ensure that the path is normalized before passing to dataset discovery
    path = _normalize_path(filesystem, path)

    # retrieve the file descriptor
    if file_info is None:
        file_info = filesystem.get_file_info([path])[0]

    # depending on the path type either return with a recursive
    # directory selector or as a list containing a single file
    if file_info.type == FileType.Directory:
        paths_or_selector = FileSelector(path, recursive=True)
    elif file_info.type == FileType.File:
        paths_or_selector = [path]
    else:
        raise FileNotFoundError(path)

    return filesystem, paths_or_selector


def _filesystem_dataset(source, schema=None, filesystem=None,
                        partitioning=None, format=None,
                        partition_base_dir=None, exclude_invalid_files=None,
                        selector_ignore_prefixes=None):
    """
    Create a FileSystemDataset which can be used to build a Dataset.

    Parameters are documented in the dataset function.

    Returns
    -------
    FileSystemDataset
    """
    format = _ensure_format(format or 'parquet')
    partitioning = _ensure_partitioning(partitioning)

    if isinstance(source, (list, tuple)):
        fs, paths_or_selector = _ensure_multiple_sources(source, filesystem)
    else:
        fs, paths_or_selector = _ensure_single_source(source, filesystem)

    options = FileSystemFactoryOptions(
        partitioning=partitioning,
        partition_base_dir=partition_base_dir,
        exclude_invalid_files=exclude_invalid_files,
        selector_ignore_prefixes=selector_ignore_prefixes
    )
    factory = FileSystemDatasetFactory(fs, paths_or_selector, format, options)

    return factory.finish(schema)


def _union_dataset(children, schema=None, **kwargs):
    if any(v is not None for v in kwargs.values()):
        raise ValueError(
            "When passing a list of Datasets, you cannot pass any additional "
            "arguments"
        )

    if schema is None:
        # unify the children datasets' schemas
        schema = pa.unify_schemas([child.schema for child in children])

    # create datasets with the requested schema
    children = [child.replace_schema(schema) for child in children]

    return UnionDataset(schema, children)


def parquet_dataset(metadata_path, schema=None, filesystem=None, format=None,
                    partitioning=None, partition_base_dir=None):
    """
    Create a FileSystemDataset from a `_metadata` file created via
    `pyarrrow.parquet.write_metadata`.

    Parameters
    ----------
    metadata_path : path,
        Path pointing to a single file parquet metadata file
    schema : Schema, optional
        Optionally provide the Schema for the Dataset, in which case it will
        not be inferred from the source.
    filesystem : FileSystem or URI string, default None
        If a single path is given as source and filesystem is None, then the
        filesystem will be inferred from the path.
        If an URI string is passed, then a filesystem object is constructed
        using the URI's optional path component as a directory prefix. See the
        examples below.
        Note that the URIs on Windows must follow 'file:///C:...' or
        'file:/C:...' patterns.
    format : ParquetFileFormat
        An instance of a ParquetFileFormat if special options needs to be
        passed.
    partitioning : Partitioning, PartitioningFactory, str, list of str
        The partitioning scheme specified with the ``partitioning()``
        function. A flavor string can be used as shortcut, and with a list of
        field names a DirectionaryPartitioning will be inferred.
    partition_base_dir : str, optional
        For the purposes of applying the partitioning, paths will be
        stripped of the partition_base_dir. Files not matching the
        partition_base_dir prefix will be skipped for partitioning discovery.
        The ignored files will still be part of the Dataset, but will not
        have partition information.

    Returns
    -------
    FileSystemDataset
    """
    from pyarrow.fs import LocalFileSystem

    if format is None:
        format = ParquetFileFormat()
    elif not isinstance(format, ParquetFileFormat):
        raise ValueError("format argument must be a ParquetFileFormat")

    if filesystem is None:
        filesystem = LocalFileSystem()
    else:
        filesystem, _ = _ensure_filesystem(filesystem)

    metadata_path = _normalize_path(filesystem, _stringify_path(metadata_path))
    options = ParquetFactoryOptions(
        partition_base_dir=partition_base_dir,
        partitioning=_ensure_partitioning(partitioning)
    )

    factory = ParquetDatasetFactory(
        metadata_path, filesystem, format, options=options)
    return factory.finish(schema)


def dataset(source, schema=None, format=None, filesystem=None,
            partitioning=None, partition_base_dir=None,
            exclude_invalid_files=None, ignore_prefixes=None):
    """
    Open a dataset.

    Datasets provides functionality to efficiently work with tabular,
    potentially larger than memory and multi-file dataset.

    - A unified interface for different sources, like Parquet and Feather
    - Discovery of sources (crawling directories, handle directory-based
      partitioned datasets, basic schema normalization)
    - Optimized reading with predicate pushdown (filtering rows), projection
      (selecting columns), parallel reading or fine-grained managing of tasks.

    Note that this is the high-level API, to have more control over the dataset
    construction use the low-level API classes (FileSystemDataset,
    FilesystemDatasetFactory, etc.)

    Parameters
    ----------
    source : path, list of paths, dataset, list of datasets or URI
        Path pointing to a single file:
            Open a FileSystemDataset from a single file.
        Path pointing to a directory:
            The directory gets discovered recursively according to a
            partitioning scheme if given.
        List of file paths:
            Create a FileSystemDataset from explicitly given files. The files
            must be located on the same filesystem given by the filesystem
            parameter.
            Note that in contrary of construction from a single file, passing
            URIs as paths is not allowed.
        List of datasets:
            A nested UnionDataset gets constructed, it allows arbitrary
            composition of other datasets.
            Note that additional keyword arguments are not allowed.
    schema : Schema, optional
        Optionally provide the Schema for the Dataset, in which case it will
        not be inferred from the source.
    format : FileFormat or str
        Currently "parquet" and "ipc"/"arrow"/"feather" are supported. For
        Feather, only version 2 files are supported.
    filesystem : FileSystem or URI string, default None
        If a single path is given as source and filesystem is None, then the
        filesystem will be inferred from the path.
        If an URI string is passed, then a filesystem object is constructed
        using the URI's optional path component as a directory prefix. See the
        examples below.
        Note that the URIs on Windows must follow 'file:///C:...' or
        'file:/C:...' patterns.
    partitioning : Partitioning, PartitioningFactory, str, list of str
        The partitioning scheme specified with the ``partitioning()``
        function. A flavor string can be used as shortcut, and with a list of
        field names a DirectionaryPartitioning will be inferred.
    partition_base_dir : str, optional
        For the purposes of applying the partitioning, paths will be
        stripped of the partition_base_dir. Files not matching the
        partition_base_dir prefix will be skipped for partitioning discovery.
        The ignored files will still be part of the Dataset, but will not
        have partition information.
    exclude_invalid_files : bool, optional (default True)
        If True, invalid files will be excluded (file format specific check).
        This will incur IO for each files in a serial and single threaded
        fashion. Disabling this feature will skip the IO, but unsupported
        files may be present in the Dataset (resulting in an error at scan
        time).
    ignore_prefixes : list, optional
        Files matching one of those prefixes will be ignored by the
        discovery process. This is matched to the basename of a path.
        By default this is ['.', '_'].
        Note that discovery happens only if a directory is passed as source.

    Returns
    -------
    dataset : Dataset
        Either a FileSystemDataset or a UnionDataset depending on the source
        parameter.

    Examples
    --------
    Opening a single file:

    >>> dataset("path/to/file.parquet", format="parquet")

    Opening a single file with an explicit schema:

    >>> dataset("path/to/file.parquet", schema=myschema, format="parquet")

    Opening a dataset for a single directory:

    >>> dataset("path/to/nyc-taxi/", format="parquet")
    >>> dataset("s3://mybucket/nyc-taxi/", format="parquet")

    Opening a dataset from a list of relatives local paths:

    >>> dataset([
    ...     "part0/data.parquet",
    ...     "part1/data.parquet",
    ...     "part3/data.parquet",
    ... ], format='parquet')

    With filesystem provided:

    >>> paths = [
    ...     'part0/data.parquet',
    ...     'part1/data.parquet',
    ...     'part3/data.parquet',
    ... ]
    >>> dataset(paths, filesystem='file:///directory/prefix, format='parquet')

    Which is equivalent with:

    >>> fs = SubTreeFileSystem("/directory/prefix", LocalFileSystem())
    >>> dataset(paths, filesystem=fs, format='parquet')

    With a remote filesystem URI:

    >>> paths = [
    ...     'nested/directory/part0/data.parquet',
    ...     'nested/directory/part1/data.parquet',
    ...     'nested/directory/part3/data.parquet',
    ... ]
    >>> dataset(paths, filesystem='s3://bucket/', format='parquet')

    Similarly to the local example, the directory prefix may be included in the
    filesystem URI:

    >>> dataset(paths, filesystem='s3://bucket/nested/directory',
    ...         format='parquet')

    Construction of a nested dataset:

    >>> dataset([
    ...     dataset("s3://old-taxi-data", format="parquet"),
    ...     dataset("local/path/to/data", format="ipc")
    ... ])
    """
    # collect the keyword arguments for later reuse
    kwargs = dict(
        schema=schema,
        filesystem=filesystem,
        partitioning=partitioning,
        format=format,
        partition_base_dir=partition_base_dir,
        exclude_invalid_files=exclude_invalid_files,
        selector_ignore_prefixes=ignore_prefixes
    )

    # TODO(kszucs): support InMemoryDataset for a table input
    if _is_path_like(source):
        return _filesystem_dataset(source, **kwargs)
    elif isinstance(source, (tuple, list)):
        if all(_is_path_like(elem) for elem in source):
            return _filesystem_dataset(source, **kwargs)
        elif all(isinstance(elem, Dataset) for elem in source):
            return _union_dataset(source, **kwargs)
        else:
            unique_types = set(type(elem).__name__ for elem in source)
            type_names = ', '.join('{}'.format(t) for t in unique_types)
            raise TypeError(
                'Expected a list of path-like or dataset objects. The given '
                'list contains the following types: {}'.format(type_names)
            )
    else:
        raise TypeError(
            'Expected a path-like, list of path-likes or a list of Datasets '
            'instead of the given type: {}'.format(type(source).__name__)
        )
