tiramisu/doc/api_value.md

# Manage values

## Values with options

### Simple option

Begin by creating a Config. This Config will contains two options:

- first one is an option where the user will set an unix path
- second one is an option that calculate the disk usage of the previous unix path

Let's import needed object:

```python
from asyncio import run
from shutil import disk_usage
from os.path import isdir
from tiramisu import FilenameOption, FloatOption, OptionDescription, Config, \
                     Calculation, Params, ParamValue, ParamOption, ParamSelfOption
```

Create a function that verify the path exists in current system:

```python
def valid_is_dir(path):
    # verify if path is a directory
    if not isdir(path):
        raise ValueError('this directory does not exist')
```

Use this function as a :doc:`validator` in a new option call `path`:

```python
filename = FilenameOption('path', 'Path', validators=[Calculation(valid_is_dir,
                                                      Params(ParamSelfOption()))])
```

Create a second function that calculate the disk usage:

```python
def calc_disk_usage(path, size='bytes'):
    # do not calc if path is None
    if path is None:
        return None
    if size == 'bytes':
        div = 1
    else:
        # bytes to gigabytes
        div = 1024 * 1024 * 1024
    return disk_usage(path).free / div
```

Add a new option call `usage` that use this function with first argument the option `path` created before:

```python
usage = FloatOption('usage', 'Disk usage', Calculation(calc_disk_usage,
                                                       Params(ParamOption(filename))))
```

Finally add those options in option description and a Config:

```python
disk = OptionDescription('disk', 'Verify disk usage', [filename, usage])
root = OptionDescription('root', 'root', [disk])
async def main():
    config = await Config(root)
    await config.property.read_write()
    return config

config = run(main())
```

#### Get and set a value

First of all, retrieve the values of both options:

```python
async def main():
    print(await config.option('disk.path').value.get())
    print(await config.option('disk.usage').value.get())

run(main())
```

returns:

```
None
None
```

Enter a value of the `path` option:

```python
async def main():
    await config.option('disk.path').value.set('/')
    print(await config.option('disk.path').value.get())
    print(await config.option('disk.usage').value.get())

run(main())
```

returns:

```
/
668520882176.0
```

When you enter a value it is validated:

```python
async def main():
    try:
        await config.option('disk.path').value.set('/unknown')
    except ValueError as err:
        print(err)

run(main())
```

returns:

```
"/unknown" is an invalid file name for "Path", this directory does not exist
```

#### Is value is valid?

To check is a value is valid:

```python
await config.option('disk.path').value.valid()
```

#### Display the default value

Even if the value is modify, you can display the default value with `default` method:

>>> config.option('disk.path').value.set('/')
>>> config.option('disk.usage').value.set(1.0)
>>> config.option('disk.usage').value.get()
1.0
>>> config.option('disk.usage').value.default()
668510105600.0

#### Return to the default value

If the value is modified, just `reset` it to retrieve the default value:

>>> config.option('disk.path').value.set('/')
>>> config.option('disk.path').value.get()
/
>>> config.option('disk.path').value.reset()
>>> config.option('disk.path').value.get()
None

#### The ownership of a value

Every option has an owner, that will indicate who changed the option's value last.

The default owner of every option is "default", and means that the value is the default one.

If you use a "reset" instruction to get back to the default value, the owner will get back
to "default" as well.

>>> config.option('disk.path').value.reset()
>>> config.option('disk.path').owner.isdefault()
True
>>> config.option('disk.path').owner.get()
default
>>> config.option('disk.path').value.set('/')
>>> config.option('disk.path').owner.isdefault()
False
>>> config.option('disk.path').owner.get()
user

All modified values have an owner. We can change at anytime this owner:

>>> config.option('disk.path').owner.set('itsme')
>>> config.option('disk.path').owner.get()
itsme

.. note::
    This will work only if the current owner isn't "default".

This new user will be keep until anyone change the value:

>>> config.option('disk.path').value.set('/')
>>> config.option('disk.path').owner.get()
user

This username is in fact the `config` user, which is `user` by default:

>>> config.owner.get()
user

This owner will be the owner that all the options in the config will get when their value is changed.

This explains why earlier, the owner became "user" when changing the option's value.

We can change this owner:

>>> config.owner.set('itsme')
>>> config.option('disk.path').value.set('/')
>>> config.option('disk.path').owner.get()
itsme

### Get choices from a Choice option

In the previous example, it's difficult to change the second argument of the `calc_disk_usage`.

For ease the change, add a `ChoiceOption` and replace the `size_type` and `disk` option:

.. literalinclude:: ../src/api_value_choice.py
   :lines: 26-31
   :linenos:

We set the default value to `bytes`, if not, the default value will be None.

:download:`download the config <../src/api_value_choice.py>`

At any time, we can get all de choices avalaible for an option:

>>> config.option('disk.size_type').value.list()
('bytes', 'giga bytes')

### Value in multi option

.. FIXME undefined

For multi option, just modify a little bit the previous example.
The user can, now, set multiple path.

First of all, we have to modification in this option:

- add multi attribute to True
- the function use in validation valid a single value, so each value in the list must be validate separatly, for that we add whole attribute to False in `ParamSelfOption` object

.. literalinclude:: ../src/api_value_multi.py
   :lines: 23-25
   :linenos:

Secondly, the function calc_disk_usage must return a list:

.. literalinclude:: ../src/api_value_multi.py
   :lines: 11-26
   :linenos:

Finally `usage` option is also a multi:

.. literalinclude:: ../src/api_value_multi.py
   :lines: 27-30
   :linenos:

:download:`download the config <../src/api_value_multi.py>`

#### Get or set a multi value

Since the options are multi, the default value is a list:

>>> config.option('disk.path').value.get()
[]
>>> config.option('disk.usage').value.get()
[]

A multi option waiting for a list:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.path').value.get()
['/', '/tmp']
>>> config.option('disk.usage').value.get()
[668499898368.0, 8279277568.0]

#### The ownership of multi option

There is no difference in behavior between a simple option and a multi option:

>>> config.option('disk.path').value.reset()
>>> config.option('disk.path').owner.isdefault()
True
>>> config.option('disk.path').owner.get()
default
>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.path').owner.get()
user

### Leadership

In previous example, we cannot define different `size_type` for each path. If you want do this, you need a leadership.

In this case, each time we add a path, we can change an associate `size_type`.

As each value of followers are isolate, the function `calc_disk_usage` will receive only one path and one size.

So let's change this function:

.. literalinclude:: ../src/api_value_leader.py
   :lines: 12-18
   :linenos:

Secondly the option `size_type` became a multi:

.. literalinclude:: ../src/api_value_leader.py
   :lines: 24-25
   :linenos:

Finally disk has to be a leadership:

.. literalinclude:: ../src/api_value_leader.py
   :lines: 30
   :linenos:

#### Get and set a leader

A leader is, in fact, a multi option:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.path').value.get()
['/', '/tmp']

There is two differences:

- we can get the leader length:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.path').value.len()
2

- we cannot reduce by assignation a leader:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> from tiramisu.error import LeadershipError
>>> try:
...     config.option('disk.path').value.set(['/'])
... except LeadershipError as err:
...     print(err)
cannot reduce length of the leader "Path"

We cannot reduce a leader because Tiramisu cannot determine which isolate follower we have to remove, this first one or the second one?

To reduce use the `pop` method:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.path').value.pop(1)
>>> config.option('disk.path').value.get()
['/']

#### Get and set a follower

As followers are isolate, we cannot get all the follower values:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> from tiramisu.error import APIError
>>> try:
...     config.option('disk.size_type').value.get()
... except APIError as err:
...     print(err)
index must be set with the follower option "Size type"

Index is mandatory:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.size_type', 0).value.get()
bytes
>>> config.option('disk.size_type', 1).value.get()
bytes

It's the same thing during the assignment:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.size_type', 0).value.set('giga bytes')

As the leader, follower has a length (in fact, this is the leader's length):

>>> config.option('disk.size_type').value.len()
2

#### The ownership of a leader and follower

There is no differences between a multi option and a leader option:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.path').owner.get()
user

For follower, it's different, always because followers are isolate:

>>> config.option('disk.size_type', 0).value.set('giga bytes')
>>> config.option('disk.size_type', 0).owner.isdefault()
False
>>> config.option('disk.size_type', 0).owner.get()
user
>>> config.option('disk.size_type', 1).owner.isdefault()
True
>>> config.option('disk.size_type', 1).owner.get()
default

## Values in option description

With an option description we can have directly a dict with all option's name and value:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.size_type', 0).value.set('giga bytes')
>>> config.option('disk').value.dict()
{'path': ['/', '/tmp'], 'size_type': ['giga bytes', 'bytes'], 'usage': [622.578239440918, 8279273472.0]}

An attribute fullpath permit to have fullpath of child option:

>>> config.option('disk').value.dict(fullpath=True)
{'disk.path': ['/', '/tmp'], 'disk.size_type': ['giga bytes', 'bytes'], 'disk.usage': [622.578239440918, 8279273472.0]}

## Values in config

###dict

With the `config` we can have directly a dict with all option's name and value:

>>> config.option('disk.path').value.set(['/', '/tmp'])
>>> config.option('disk.size_type', 0).value.set('giga bytes')
>>> config.value.dict()
{'disk.path': ['/', '/tmp'], 'disk.size_type': ['giga bytes', 'bytes'], 'disk.usage': [622.578239440918, 8279273472.0]}

If you don't wan't path but only the name:

>>> config.value.dict(flatten=True)
{'path': ['/', '/tmp'], 'size_type': ['giga bytes', 'bytes'], 'usage': [622.578239440918, 8279273472.0]}

### importation/exportation

In config, we can export full values:

>>> config.value.exportation()
[['disk.path', 'disk.size_type'], [None, [0]], [['/', '/tmp'], ['giga bytes']], ['user', ['user']]]

and reimport it later:

>>> export = config.value.exportation()
>>> config.value.importation(export)

.. note:: The exportation format is not stable and can be change later, please do not use importation otherwise than jointly with exportation.