erDiagram
    USERS {
        UUID user_id PK
        string login
        string salt
        string hashed_password
        string role
        datetime created_at
    }

    SESSIONS {
        UUID session_id PK
        UUID user_id FK
        datetime expired_at
        string user_agent
    }

    STUDENTS {
        UUID student_id PK
        int tg_user_id
        string tg_username
        string gh_username
        datetime registered_at
    }

    TASKS {
        UUID task_id PK
        string name
        string system_instructions
        string ideas
        string gh_repo_url
        string level
        string tags
        bool is_draft
    }

    SUBMISSIONS {
        UUID submission_id PK
        UUID task_id FK
        UUID student_id FK
        string gh_repo_url
        string code_file_name
        string llm_grade
        string llm_feedback
        string llm_report
        datetime evaluated_at
        datetime created_at
    }

    COMPLAINTS {
        UUID complaint_id PK
        UUID task_id FK
        UUID student_id FK
        string student_request
        string teacher_response
        datetime created_at
    }

    USERS ||--o{ SESSIONS : has
    STUDENTS ||--o{ SUBMISSIONS : makes
    TASKS ||--o{ SUBMISSIONS : receives
    TASKS ||--o{ COMPLAINTS : receives
    STUDENTS ||--o{ COMPLAINTS : makes