Implement backend

[sovadim]

Description

The goal of the initial backend version is to add and delete nodes and relations between them.

Design

Nodes

There are 2 types of nodes: index nodes and skill nodes.

What info do nodes contain?

Index node

• Id
• Status: Enum (passed / failed / in progress / not reached / disabled)
• Level: Enum (A1, A2, A3)
• Sub-nodes: List
• Dependent nodes: List

Skill node

• Id
• Status: Enum (passed / failed / in progress / not reached / disabled)
• Level: Enum (A1, A2, A3)
• Sub-nodes: List
• Dependent nodes: List
• Questions: List
• Criterias: List

Both node types can be taken from one API endpoint. The index nodes will just have null values in fields that they don't have.

NB: Nodes contain graph edges as lists of ids of other nodes