Social Network and Chat project example (Erlang)

This is a skeleton of a backend for a social network and chat for mobile applications.
It's purposed for:

• to show Erlang developers, that storing code modules in separate sub-directories is a good;
• show no-Erlang developers, that Erlang can be used in writing complex applications;
• to show Erlang code structural patterns in action;

It is a simplified skeleton of a real-world chat and social network application. Many export functions and modules, which can tell something about its business logic were removed.

Code organization

/include for all headers, which are used in many modules. Although some Erlang programmers like to keep their headers files in src it is not recommended. In big projects src is used for sources and include is used for headers. Don't mess them out.
/src is used for source code. Here all modules are stored in subdirectories (like packages in Java/Python). Although some Erlang programmers throw their source code modules to src, like a trash - it is not recommended. Divide and rule.
/test is used for test code. Here test/unit contains unit tests, test/functional are functional tests based on common test framework, and test/full is full integration tests with emulation sending packages to handlers. Although some Erlang programmers mess out test code and production code - it is not recommended: test is for tests, src is for production code.

Patterns

Application is covered in src/main/sn_test_app.erl. It is small and simple.
Otp Process (gen_server) is covered in src/daemons/sn_conf_holder. Although it is only a template, created by Idea, without any real code.
Supervisor (static) is covered in src/main/sn_top_sup and src/sn_daemons_sup.
Interface is covered in src/business/auth/. There sn_auth_intf is and interface module with implementations in the same packages. Interface implementations nearly always should be in the same package or subpackages. The only exception is to expose an interface for outside usage in a library (like gen_server or cowboy_websocket behaviors).
Manager can be frequently meet all other the project. You can check src/business/friends/sn_friends_mngr as an example.
Logic is also frequently used nearly everywhere. As an example of masking logic pattern you can see src/business/friends/invite/sn_contacts_logics.erl. It contains an implementation of functions re-exported by a manager. These are the majority of logic modules in this project. Another logic pattern is shared code - it can be seen in src/business/auth/sn_auth_logic.erl. It shares common functions, which are called from interface implementations.