openapi: 3.0.4
info:
  title: VPN Core API
  version: 1.0.0

servers:
  - url: https://api.yourdomain.com/v1

components:
  schemas:

    UserCreateRequestDTO:
      type: object
      required:
        - username
      properties:
        username:
          type: string
          description: Unique username

    UserResponseDTO:
      type: object
      properties:
        id:
          type: string
          description: Internal user identifier

    ConfigMetaDTO:
      type: object
      properties:
        id:
          type: string
          description: Configuration file identifier
        name:
          type: string
          description: Configuration name

paths:

  /users:
    post:
      summary: Create user
      description: |
        Creates a user on first request.
        If a user with this username already exists —
        returns the existing user.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/UserCreateRequestDTO"
      responses:
        "201":
          description: User created
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/UserResponseDTO"
        "200":
          description: User already exists
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/UserResponseDTO"
        "400":
          description: Bad request

  /configs:
    post:
      summary: Upload binary configuration file
      description: |
        Uploads a binary configuration file
        associated with a user.
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              type: object
              required:
                - fileName
              properties:
                fileName:
                  type: string
                  description: Configuration file name
      responses:
        "201":
          description: File successfully uploaded
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/ConfigMetaDTO"
        "400":
          description: Invalid input

    get:
      summary: Get user configuration files
      description: Returns a list of all configuration files for the given user.
      parameters:
        - in: query
          name: userId
          required: true
          schema:
            type: string
          description: User identifier
      responses:
        "200":
          description: List of configuration files
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: "#/components/schemas/ConfigMetaDTO"
        "400":
          description: Bad request