Examples
#############

This example demonstrates how to use common functionality of the ``PyFDB``. 
The section contains examples for all methods of the ``FDB`` object.

In general ``PyFDB`` is used to refer to the Python API of the ``FDB``, whereas
``FDB`` is used to refer to the underlying C++ class or the created Python instance.


.. _mars_selection_label:
MARS Selections
***************
One main concept of interacting with the ``FDB`` is a MARS selection. A
selection is a dictionary-like object describing the ranges or sets
coordinates, which point to multiple elements or sub-datacubes within a
datacube, see `Datacube Spec <https://github.com/ecmwf/datacube-spec>`__.

The recommended way of interacting with the ``FDB`` is to use a dictionary,
describing a MARS selection. The following example shows how to create a MARS
selection with it:

.. code-block:: python

    mars_selection = {
        "key-1": ["value-2", "value-4", "value-5"],     # String values
        "key-2": ["0.1", 0.2, "0.5"],                   # Mixed types
        "key-3": [0.1, 0.2, 0.5],                       # Float values
        "key-4": [1, 2, 0.5],                           # Integer and float values
        "key-5": 1,                                     # Single int value
        "key-6": [1 + 0.5 * x for x in range(2)],       # List of float value generated by a list expression
    }

.. note::

    The type of a MarsSelection is ``Mapping[str, str | int | float | Collection[str | int | float]]`` which can be given to
    the FDB object of the PyFDB module.

    Some of the methods accepts wildcard selection, e.g. :ref:`listing
    <list_label>`. For those it's possible to hand the wildcard selection
    directly:

MARS Identifier
***************
There is also the concept of a MARS identifier. Those are strict subsets of the MARS selections and 
differ by only allowing singular values.

.. code-block:: python

    mars_identifier = {
        "key-1": "value-1",     # String values
        "key-2": 2,     # String values
        # ...
    }

For further information about the individual MARS data types, see the `Datacube Spec <https://github.com/ecmwf/datacube-spec>`__.


PyFDB Initalisation
*******************

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    fdb = pyfdb.FDB()

If no configuration is supplied ``FDB`` falls back to derive the configuration
location from a predefined set of locations. You can supply a custom location
by specifying the ``FDB_HOME`` environment variable. If you want to set the
location of the configuration file only, use the ``FDB5_CONFIG_FILE``
environment variable. There is a plethora of different configuration options,
if in doubt, refer to the official ``FDB`` documentation at `ReadTheDocs
<https://fields-database.readthedocs.io/en/latest/>`__.

.. clear-namespace

You can also pass (dynamically) created custom configurations as parameters to
the ``FDB`` constructor. Those can be supplied as a ``Path`` pointing to the
location of the configuration file, as a ``str`` which is the ``yaml``
representation of the configuration or as a ``Dict[str, Any]`` as shown below. 

.. code-block:: python

    config = {
        "type":"local",
        "engine":"toc",
        "schema":"/path/to/fdb_schema",
        "spaces":[
            {
                "handler":"Default",
                "roots":[
                    {"path": "/path/to/root"}
                ]
            }
        ],
    }
    fdb = pyfdb.FDB(config=config, user_config={})

.. clear-namespace

For convenience, the ``FDB`` instance implements the ``Python`` context manager interface:

.. code-block:: python

    with pyfdb.FDB() as fdb:
        # Use fdb in here
        pass

On exiting the context, :ref:`flush_label` is called to guarantee any potential
:ref:`archive_label` operation has been synced. This can lead to non-intended
sync behaviors, see :ref:`archive_label` for further information.

The different methods of the ``FDB`` class can be leverage for different
use-cases. Below we listed examples of the most common method class display
different ways of using the Python API.

.. _archive_label:

Archive
***********

**Archive binary data into the underlying FDB.**

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    with pyfdb.FDB(fdb_config_path) as fdb:
        filename = data_path / "x138-300.grib"

        fdb.archive(filename.read_bytes())
        # On exit of this scope fdb is flushed

In this scenario a ``GRIB`` file is archived to the configured ``FDB``. The FDB
reads metadata from the given ``GRIB`` file and saves this, if no optional
``identifier`` is supplied. If we set an ``identifier``, there are no
consistency checks taking place and our data is saved with the metadata given
from the supplied ``identifier``. This enables us to store arbitrary binary data 
under the given key, as shown below:

.. code-block:: python

   identifier = {
        "class": "rd",
        "expver": "zzzz",
        "stream": "oper",
        "date": "20191110",
        "time": "0000",
        "domain": "g",
        "type": "an",
        "levtype": "pl",
        "step": "0",
        "levelist": "300",
        "param": "138",
   }

   with pyfdb.FDB(fdb_config_path) as fdb:
       fdb.archive(b"test-binary-data", identifier=identifier)
       # On exit of this scope fdb is flushed

The ``flush`` command guarantees that the archived data has been flushed to the
``FDB``. In combination with using the context manager of the ``FDB`` object,
the syncing may behave differently from what the user expects. Take a look at
the following code, utilizing the archive method:

.. skip: start

.. Sybil can't skip code blocks in the default version. Therefore we need an example here

>> fdb = pyfdb.FDB()
>> for step in range(240):
>>    with fdb:
>>        fdb.archive(...)
>>        fdb.archvie(...)

.. skip: end

This would call the ``exit`` function of the ``FDB`` after each iteration of
the step loop, therefore causing a ``flush`` of the archived data. Compare the before-mentioned call 
with the following:

.. skip: start

.. Sybil can't skip code blocks in the default version. Therefore we need an example here

>> fdb = pyfdb.FDB()
>> for step in range(240):
>>    fdb.archive(...)
>>    fdb.archvie(...)
>>    fdb.flush()

.. skip: end

Both of these examples achieve the same result in the normal, successful
execution case. However, in the case with a manual call to flush() if an
exception is thrown interrupting the execution when some archive() calls
have succeed and some have not then none of this data will become visible to
the user. When using the context manager, flush() will be implicitly called
when leaving the scope including when an exception is thrown, making partial
output visible to the user. Which of these outcomes is most desirable
depends on the workflow.

.. clear-namespace

.. _flush_label:

Flush
***********

**Flush all buffers and close all data handles of the underlying FDB into a consistent DB state.**

.. invisible-code-block: python

   import pyfdb

.. tip::

   It's always safe to call ``flush``.

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    filename = data_path / "x138-300.grib"

    fdb.archive(open(filename, "rb").read())
    fdb.flush()

The ``flush`` command guarantees that the :ref:`archived <archive_label>` data
has been flushed to the ``FDB``. It's always safe to call ``flush``. You can
either call the method explicitly or by using the context manager capabilities
of the ``FDB``. See :ref:`archive_label`.

.. clear-namespace

.. _retrieve_label:

Retrieving
***********

**Retrieve data which is specified by a MARS selection.**

.. invisible-code-block: python

   import pyfdb

To Memory
=========

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    selection = {
        "type": "an",
        "class": "ea",
        "domain": "g",
        "expver": "0001",
        "stream": "oper",
        "date": "20200101",
        "levtype": "sfc",
        "step": "0",
        "param": ["167", "165", "166"],
        "time": "1800",
    }

    with fdb.retrieve(selection) as data_handle:
        data_handle.read(4) # == b"GRIB"
        # data_handle.readall() # As an alternative to read all messages

The code above shows how to retrieve a MARS selection given as a dictionary.
The retrieved ``data_handle`` has to be opened before being read and closed
afterwards. If you are interested in reading the entire ``data_handle``, you
could use the ``readall`` method. 

.. tip::

    For the ``readall`` method there is no need to ``open`` or ``close`` the
    ``data_handle`` after the call to ``readall``.

.. clear-namespace

To File
=========

Another use-case, which is often needed, is saving certain ``GRIB`` data in a
file on your local machine. The following code is showing how to achieve this:

.. code-block:: python

    import shutil

    fdb = pyfdb.FDB(fdb_config_path)

    # Specify selection here
    # --------------------
    selection = {
        "type": "an",
        "class": "ea",
        "domain": "g",
        "expver": "0001",
        "stream": "oper",
        "date": "20200101",
        "levtype": "sfc",
        "step": "0",
        "param": ["167", "165", "166"],
        "time": "1800",
    }

    filename = test_case_tmp / 'output.grib'

    with open(filename, 'wb') as out:
        with fdb.retrieve(selection) as data_handle:
            out.write(data_handle.readall())

The example above, as a first step, reads all data in memory and writes the
data to the specified file afterwards. In case the data of the selection is
to large to fit in memory, we can leverage the ``shutil`` functions read the content
buffered and write the individual chunks in a single file onto disk:

.. invisible-code-block: python

   import pyfdb
   import tempfile
   import shutil

.. code-block:: python

    with tempfile.TemporaryFile() as out:
        with fdb.retrieve(selection) as data_handle:
            assert data_handle
            shutil.copyfileobj(data_handle, out)

Depending on the implementation this ``shutil`` uses the ``read`` method or the
``readinto`` method. The first is copying a specific buffer, one at a time till
the entire data handle is depleted. The latter, leverages a ``memoryview`` to make it a zero-copy
function.

.. clear-namespace

.. _list_label:

List
****

**List data present at the underlying fdb archive and which can be retrieved.**

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    selection = {
            "type": "an",
            "class": "ea"
        }

    list_iterator = fdb.list(selection, level=1)
    elements = list(list_iterator)

    for el in elements:
        print(el)

    assert len(elements) == 32

The code above shows an example of listing the contents of the ``FDB`` for a given selection.
The selection is describing a ``MarsSelection`` (A MARS request without the verb).

.. note::

   A ``MarsSelection`` doesn't need to be fully specified. In the example above
   you can see that many of the MARS keys aren't specified. In case of ``list``, the given keys
   are treated as a selector, meaning that all data which matches those keys is returned. For
   every key, which isn't explicitly stated, all found data is returned.

   We recommend to use lists of values at all given times, as seen in :ref:`mars_selection_label`.


``level=1`` refers to the schema level of the ``FDB``. A given ``Rule`` in a
``FDB`` schema could look like:

.. code-block::

    [ class, expver, stream, date, time, domain?
      ^^^^^^^^^^^^^^^ Level 1 ^^^^^^^^^^^^^^^^^^
      [ type, levtype
        ^^ Level 2 ^^
              [ step, levelist?, param ]]
                ^^^^^^^ Level 3 ^^^^^^^
    ]

Depending on the given ``level`` different outputs are to be expected:

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    selection = {
        "type": "an",
        "class": "ea",
        "domain": "g",
        "expver": "0001",
        "stream": "oper",
        "date": "20200101",
        "levtype": "sfc",
        "step": "0",
        "time": "1800",
    }
    list_iterator = fdb.list(selection) # level == 3
    elements = list(list_iterator)
    print(elements[0])

::

    {class=ea,expver=0001,stream=oper,date=20200101,time=1800,domain=g}
    {type=an,levtype=sfc}
    {step=0,param=131},
    TocFieldLocation[uri=URI[scheme=file,name=/<path-to-db_store>/ea:0001:oper:20200101:1800:g/an:sfc.20251118.151917.<?>.375861178007828.data],offset=10732,length=10732,remapKey={}],
    length=10732,
    timestamp=1763479157

    {class=ea,expver=0001,stream=oper,date=20200101,time=1800,domain=g}
    {type=an,levtype=sfc}
    {step=0,param=132},
    TocFieldLocation[uri=URI[scheme=file,name=/<path-to-db_store>/db_store/ea:0001:oper:20200101:1800:g/an:sfc.20251118.151917.<?>.375861178007828.data],offset=21464,length=10732,remapKey={}],
    length=10732,
    timestamp=1763479157

    {class=ea,expver=0001,stream=oper,date=20200101,time=1800,domain=g}
    {type=an,levtype=sfc}
    {step=0,param=167},
    TocFieldLocation[uri=URI[scheme=file,name=/<path-to-db_store>/db_store/ea:0001:oper:20200101:1800:g/an:sfc.20251118.151917.<?>.375861178007828.data],offset=0,length=10732,remapKey={}],
    length=10732,
    timestamp=1763479157

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)
    selection = {
        "type": "an",
        "class": "ea",
        "domain": "g",
        "expver": "0001",
        "stream": "oper",
        "date": "20200101",
        "levtype": "sfc",
        "step": "0",
        "time": "1800",
    }
    list_iterator = fdb.list(selection, level=2)
    elements = list(list_iterator)
    print(elements[0])

::

    {class=ea,expver=0001,stream=oper,date=20200101,time=1800,domain=g}
    {type=an,levtype=sfc},
    length=0,
    timestamp=0

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)
    selection = {
        "type": "an",
        "class": "ea",
        "domain": "g",
        "expver": "0001",
        "stream": "oper",
        "date": "20200101",
        "levtype": "sfc",
        "step": "0",
        "time": "1800",
    }
    list_iterator = fdb.list(selection, level=1)
    elements = list(list_iterator)
    print(elements[0])

:: 

    {class=ea,expver=0001,stream=oper,date=20200101,time=1800,domain=g},
    length=0,
    timestamp=0

For each level the returned iterator of ``ListElement`` is restricting the elements to the corresponding
level of the underlying FDB. ``level=1`` returns elements, which key only contains MARS keys of level 1,
``level=2`` returns elements, which key contains MARS keys of level 2 and ``level=3`` returns elements
which key contain all MARS keys and the corresponding ``DataHandle`` pointing to the location of the
file on disk.

You can use this directly to read the message represented by the ``ListElement``, e.g.:

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    list_iterator = fdb.list(selection, level=3)
    selection = {
            "type": "an",
            "class": "ea",
            "domain": "g",
            "expver": "0001",
            "stream": "oper",
            "date": "20200101",
            "levtype": "sfc",
            "step": "0",
            "param": ["167", "131", "132"],
            "time": "1800",
    }

    for el in list_iterator:
        data_handle = el.data_handle
        data_handle.open()
        assert data_handle.read(4) == b"GRIB"
        data_handle.close()

.. clear-namespace

.. _inspect_label:
   
Inspect
*******

**Inspects the content of the underlying FDB and returns a generator of list elements
describing which field was part of the MARS selection.**

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    identifier = {
        "type": "an",
        "class": "ea",
        "domain": "g",
        "expver": "0001",
        "stream": "oper",
        "date": "20200101",
        "levtype": "sfc",
        "step": "0",
        "param": "131",
        "time": "1800",
    }

    inspect_iterator = fdb.inspect(identifier)
    elements = list(inspect_iterator)

    # Because the identifier needs to be fully specified, there
    # should be only a single element returned
    assert len(elements) == 1

    for el in elements:
        with el.data_handle as data_handle:
            assert data_handle.read(4) == b"GRIB"

The code above shows how to inspect certain elements stored in the ``FDB``. This call is similar to
a ``list`` call with ``level=3``, although the internals are quite different. The functionality is
designed to list a vast amount of individual fields. 

Similar to the :ref:`list <list_label>` command, each ``ListElement`` returned, contains a ``DataHandle`` which can
be used to directly access the data associated with the element, see the example of ``list``.

.. note::

   Due to the internals of the ``FDB`` only a fully specified MARS selection
   with singular values (also called Identifier) is accepted. If a list is given
   for a key, e.g. ``param=131/132``, the second value is silently dropped.

.. clear-namespace

.. _status_label:

Status
*******

**List the status of all FDB entries with their control identifiers, e.g., whether a certain database was locked for retrieval.**

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    selection = {
        "type": "an",
        "class": "ea",
        "domain": "g",
    }

    status_iterator = fdb.status(selection)
    elements = list(status_iterator)

    len(elements) # == 32

The output of such a command can look like the above and is the same output you get from the
call to `control <control_label>` when setting certain ``ControlIdentifiers`` for elements of the ``FDB``.

::

    ControlElement(
        control_identifiers=[WIPE], 
        key={'class': ['ea'], 'date': ['20200104'], 'domain': ['g'], 'expver': ['0001'], 'stream': ['oper'], 'time': ['2100']},
        location=/<some-path>/db_store/ea:0001:oper:20200104:2100:g
    )


You can see that the ``ControlIdentifier`` for ``WIPE`` is active for the given entry of the ``FDB``.

.. tip::
   Use the ``control`` functionality of FDB to switch certain properties of ``FDB`` elements.
   Refer to the :ref:`control_label` section for further information.

.. _wipe_label:

Wipe
*******

**Wipe data from the database**

.. invisible-code-block: python

   import pyfdb

Delete FDB databases and the data therein contained. Use the passed
selection to identify the database to delete. This is equivalent to a UNIX rm command.
This function deletes either whole databases, or whole indexes within databases

.. tip::

   You should check the elements of a deletion before running it with the ``doit`` flag.
   Double check that the dry-run, which is active per default, really returns the elements you are
   expecting.

A potential deletion operation could look like this:

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    elements = list(fdb.wipe({"class": "ea"}))
    len(elements) > 0

    # NOTE: Double check that the returned elements are those you want to delete
    for element in elements:
        print(element)
    

    # Do the actual deletion with the `doit=True` flag
    wipe_iterator = fdb.wipe({"class": "ea"}, doit=True)
    wiped_elements = list(wipe_iterator)

    for element in wiped_elements:
        print(element)

.. clear-namespace

.. _purge_label:

Purge
*******
**Remove duplicate data from the database.**

.. invisible-code-block: python

   import pyfdb

Purge duplicate entries from the database and remove the associated data if the data is owned and not adopted.
Data in the ``FDB`` is immutable. It is masked, but not removed, when overwritten with new data using the same key.
Masked data can no longer be accessed. Indexes and data files that only contains masked data may be removed.

If an index refers to data that is not owned by the FDB (in particular data which has been adopted from an
existing ``FDB``), this data will not be removed.

.. tip::

   It's always advised to check the elements of a deletion before running it with the ``doit`` flag.
   Double check that the dry-run, which is active per default, really returns the elements you are
   expecting.

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    elements = list(fdb.purge({"class": "ea"}))
    len(elements) > 0

    # NOTE: Double check that the returned elements are those you want to delete
    for element in elements:
        print(element)

    # Do the actual deletion with the `doit=True` flag
    purge_iterator = fdb.purge({"class": "ea"}, doit=True)
    purge_elements = list(purge_iterator)

    for element in purge_elements:
        print(element)

.. clear-namespace

.. _stats_label:

Stats
*******
**Print information about FDB databases, aggregating the information over all the databases visited into a final summary.**

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    selection = {
            "type": "an",
            "class": "ea",
            "domain": "g",
            "expver": "0001",
            "stream": "oper",
            "date": "20200101",
            "levtype": "sfc",
            "step": "0",
            "param": ["167", "165", "166"],
            "time": "1800",
        }

    elements = list(fdb.stats(selection))

    for el in elements:
        print(el)

The example above shows how to use the ``stats`` function to get an overview over the statistics a given MARS selection
has. For every database and every index the selection touches, it aggregates statistics and shows the result in a table.
The ``StatsElement`` s returned from the call are Python string resembling individual lines of the output generated by
the underlying ``FDB``. A potential call of the example above could lead to the following output:

::

    Index Statistics:
    Fields                          : 3
    Size of fields                  : 32,196 (31.4414 Kbytes)
    Reacheable fields               : 3
    Reachable size                  : 32,196 (31.4414 Kbytes)

    DB Statistics:
    Databases                       : 1
    TOC records                     : 2
    Size of TOC files               : 2,048 (2 Kbytes)
    Size of schemas files           : 228 (228 bytes)
    TOC records                     : 2
    Owned data files                : 1
    Size of owned data files        : 32,196 (31.4414 Kbytes)
    Index files                     : 1
    Size of index files             : 131,072 (128 Kbytes)
    Size of TOC files               : 2,048 (2 Kbytes)
    Total owned size                : 165,544 (161.664 Kbytes)
    Total size                      : 165,544 (161.664 Kbytes)

.. clear-namespace

.. _control_label:

Control
*******
**Enable certain features of FDB databases, e.g., disables or enables retrieving, list, etc.**

The example given below shows how the activation/deactivation of the wipe functionality of the ``FDB``
works for a certain selection. 

.. invisible-code-block: python

   import pyfdb
   import pytest

.. tip::
   Consume the iterator, returned by the ``control`` call, completely. Otherwise, the lock file
   won't be created.

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    selection = {
        "class": "ea",
        "domain": "g",
        "expver": "0001",
        "stream": "oper",
        "date": "20200101",
        "time": "1800",
    }

    print("Lock the database for wiping")
    control_iterator = fdb.control(selection, pyfdb.ControlAction.DISABLE, [pyfdb.ControlIdentifier.WIPE])
    elements = list(control_iterator)

    assert len(elements) == 1
    assert (fdb_config_path.parent / "db_store" / "ea:0001:oper:20200101:1800:g" / "wipe.lock").exists()

    print("Try Wipe")
    wipe_iterator = fdb.wipe(selection, doit=True)

    elements = []

    with pytest.raises(RuntimeError):
        for el in wipe_iterator:
            elements.append(el)

    assert len(elements) == 0

    print("Unlock the database for wiping")
    control_iterator = fdb.control(selection, pyfdb.ControlAction.ENABLE, [pyfdb.ControlIdentifier.WIPE])
    elements = list(control_iterator)

    assert len(elements) > 0
    assert not (fdb_config_path.parent / "db_store" / "ea:0001:oper:20200101:1800:g" / "wipe.lock").exists()

    print("Wipe")
    fdb.wipe(selection, doit=True)
    fdb.flush()

    print("Success")


After specifying the selection we want to target, this has to be a selection which contains keys of 
the first and second level of the schema, we can call the ``control`` function and specify the wished action:
in this case ``ControlIdentifier.WIPE`` and ``ControlAction.DISABLE``, which translate to wanting to disable
wiping for the specified database. We could specify multiple of the ``ControlIdentifier`` in a single call.

For each of the ``ControlIdentifier`` the underlying ``FDB`` will create a ``<control-identifier-name>.lock`` file, 
which resides inside the database specified by the MARS selection. If we decide to enable the action again, this
file gets deleted.

After disabling the action, a call to it results in an empty iterator being returned.

.. clear-namespace

.. _axes_label:

Axes
*******
**Return the 'axes' and their extent of a selection for a given level of the schema in an IndexAxis object.**

If a key is not specified the entire extent (all values) are returned.

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    selection = {
            "type": "an",
            "class": "ea",
            "domain": "g",
            "expver": "0001",
            "stream": "oper",
            # "date": "20200101", # Left out to show all values are returned
            "levtype": "sfc",
            "step": "0",
            "time": "1800",
        }

    print("---------- Level 3: ----------")
    index_axis = fdb.axes(selection)
    # len(index_axis.items()) == 11

    for k, v in index_axis.items():
        print(f"k={k} | v={v}")

    print("---------- Level 2: ----------")
    index_axis = fdb.axes(selection, level=2)
    #len(index_axis.items()) == 8

    for k, v in index_axis.items():
        print(f"k={k} | v={v}")

    print("---------- Level 1: ----------")
    index_axis = fdb.axes(selection, level=1)
    # len(index_axis.items()) == 6

    for k, v in index_axis.items():
        print(f"k={k} | v={v}")

The example above produces the following output:

::

   ---------- Level 3: ----------
   k=class    | v=['ea']
   k=date     | v=['20200101', '20200102', '20200103', '20200104']
   k=domain   | v=['g']
   k=expver   | v=['0001']
   k=levelist | v=['']
   k=levtype  | v=['sfc']
   k=param    | v=['131', '132', '167']
   k=step     | v=['0']
   k=stream   | v=['oper']
   k=time     | v=['1800']
   k=type     | v=['an']

   ---------- Level 2: ----------
   k=class    | v=['ea']
   k=date     | v=['20200101', '20200102', '20200103', '20200104']
   k=domain   | v=['g']
   k=expver   | v=['0001']
   k=levtype  | v=['sfc']
   k=stream   | v=['oper']
   k=time     | v=['1800']
   k=type     | v=['an']

   ---------- Level 1: ----------
   k=class    | v=['ea']
   k=date     | v=['20200101', '20200102', '20200103', '20200104']
   k=domain   | v=['g']
   k=expver   | v=['0001']
   k=stream   | v=['oper']
   k=time     | v=['1800']

For each specified ``level``, the keys affected by the MARS selection at that level are returned. 
Optional keys in the ``FDB`` schema appear as empty lists. If a key is missing from the selection,
the key and all values stored in the ``FDB`` are returned (see the ``date`` key above).

In case you want to see the 'span' of all elements stored in an ``FDB`` you could use the following code:

.. warning::

   This following code is an expensive call (depending on the size of the ``FDB``).
   For testing purposes or locally configured ``FDB`` instances this is fine.

.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)
    index_axis: pyfdb.IndexAxis = fdb.axes({})

.. clear-namespace

.. _enabled_label:

Enabled
*******
**Check whether a specific control identifier is enabled.**

.. invisible-code-block: python

   import pyfdb

.. code-block:: python

    from pyfdb import ControlIdentifier

    fdb = pyfdb.FDB(fdb_config_path)

    assert fdb.enabled(ControlIdentifier.NONE) is True
    assert fdb.enabled(ControlIdentifier.LIST) is True
    assert fdb.enabled(ControlIdentifier.RETRIEVE) is True
    assert fdb.enabled(ControlIdentifier.ARCHIVE) is True
    assert fdb.enabled(ControlIdentifier.WIPE) is True
    assert fdb.enabled(ControlIdentifier.UNIQUEROOT) is True

The examples above show how a default ``FDB`` is configured, this is, all possible ``ControlAction`` s
are enabled by default.

Configuring the ``FDB`` to disallow writing via setting ``writable = False`` in the ``fdb_config.yaml``,
we end up with the following ``ControlIdentifier`` s:

.. code-block:: python

    import yaml
    from pyfdb import ControlIdentifier

    fdb_config = yaml.safe_load(fdb_config_path.read_text())
    fdb_config["writable"] = False

    fdb = pyfdb.FDB(fdb_config)

    assert fdb.enabled(ControlIdentifier.NONE) is True
    assert fdb.enabled(ControlIdentifier.LIST) is True
    assert fdb.enabled(ControlIdentifier.RETRIEVE) is True
    assert fdb.enabled(ControlIdentifier.ARCHIVE) is False
    assert fdb.enabled(ControlIdentifier.WIPE) is False
    assert fdb.enabled(ControlIdentifier.UNIQUEROOT) is True

The configuration changes accordingly, if we substitute ``writable = False`` with ``visitable = False``.

.. clear-namespace

.. _dirty_label:

Dirty
*************
**Return whether a flush of the FDB is needed, for example if data was archived since the last flush.**


.. code-block:: python

    fdb = pyfdb.FDB(fdb_config_path)

    filename = data_path / "x138-300.grib"

    fdb.archive(open(filename, "rb").read())
    fdb.dirty() # == True
    fdb.flush()
    fdb.dirty() # == False

The example above shows return value of the ``dirty`` command after an :ref:`archive <archive_label>` command results in ``True``. 
Flushing resets the internal status of the ``FDB`` and the call to ``dirty`` returns ``False`` afterwards.

.. clear-namespace