Introduction
============

Actions and dependencies
------------------------

In *ActionTree*, you create a dependency graph of actions to be executed and then call the :func:`.execute` function on its root.

For example, let's say you want to generate three files, and then concatenate them into a fourth file.

First, import :mod:`.ActionTree`

.. BEGIN SECTION introduction_actions.py

>>> from ActionTree import Action, execute

Then create your specialized :class:`.Action` classes:

>>> class CreateFile(Action):
...     def __init__(self, name):
...         super(CreateFile, self).__init__("create {}".format(name))
...         self.__name = name
...
...     def do_execute(self, dependency_statuses):
...         with open(self.__name, "w") as f:
...             f.write("This is {}\n".format(self.__name))


>>> class ConcatFiles(Action):
...     def __init__(self, files, name):
...         super(ConcatFiles, self).__init__("concat")
...         self.__files = files
...         self.__name = name
...
...     def do_execute(self, dependency_statuses):
...         with open(self.__name, "w") as output:
...             for file in self.__files:
...                 with open(file) as input:
...                     output.write(input.read())

.. END SECTION introduction_actions.py

.. We have to import these classes to make them picklable in doctests

.. doctest::
    :hide:

    >>> from introduction_actions import CreateFile, ConcatFiles

Create an actions dependency graph:

>>> concat = ConcatFiles(["first", "second", "third"], "fourth")
>>> concat.add_dependency(CreateFile("first"))
>>> concat.add_dependency(CreateFile("second"))
>>> concat.add_dependency(CreateFile("third"))

And :func:`.execute` it:

>>> execute(concat).is_success
True

The actions have been executed successfully:

>>> def cat(name):
...     with open(name) as f:
...         print(f.read(), end="")

>>> cat("first")
This is first

>>> cat("second")
This is second

>>> cat("third")
This is third

>>> cat("fourth")
This is first
This is second
This is third

You have no guaranty about the order of execution of the ``CreateFile`` actions,
but you are sure that they are all finished before the ``ConcatFiles`` action starts.
If your system has several CPUs, the ``CreateFile`` actions have been executed concurrently.

Preview
-------

If you just want to know what *would* be done, you can use :meth:`.Action.get_possible_execution_order`:

>>> [a.label for a in concat.get_possible_execution_order()]
['create first', 'create second', 'create third', 'concat']

As said earlier, you have no guaranty about the order of the first three actions,
so :meth:`~.Action.get_possible_execution_order` returns *one* possible order.

Stock actions
-------------

ActionTree ships with some :mod:`~.ActionTree.stock` actions for common tasks,
including running subprocesses and basic operations on files and directories.

Say you want to compile :ref:`two C++ files <source_files>` and link them:

.. BEGIN SECTION stock_link.py

>>> from ActionTree import execute
>>> from ActionTree.stock import CreateDirectory, CallSubprocess

>>> make_build_dir = CreateDirectory("_build")

>>> compile_a = CallSubprocess(["g++", "-c", "a.cpp", "-o", "_build/a.o"], label="g++ -c a.cpp")
>>> compile_a.add_dependency(make_build_dir)

>>> compile_b = CallSubprocess(["g++", "-c", "b.cpp", "-o", "_build/b.o"], label="g++ -c b.cpp")
>>> compile_b.add_dependency(make_build_dir)

>>> link = CallSubprocess(["g++", "-o", "_build/test", "_build/a.o", "_build/b.o"], label="g++ -o test")
>>> link.add_dependency(compile_a)
>>> link.add_dependency(compile_b)

.. END SECTION stock_link.py

>>> link_report = execute(link)