Design Specifications
=====================

This section contains detailed design specifications for system components following Sphinx-Needs methodology.

.. toctree::
   :maxdepth: 2
   :caption: Design Documents:

   spec_high_level_architecture
   spec_config_manager_json
   spec_config_webpage
   spec_web_server
   spec_distance_sensor
   spec_led_controller
   spec_display
   spec_startup_test
   spec_netif_tunnel
   spec_developer_docs
   spec_dev_environment
   spec_known_limitations

Overview
--------

Design specifications define **how** the system implements requirements. They are:

* **Traceable** - Each design spec links to parent requirements
* **Detailed** - Include architecture, data structures, APIs, and algorithms
* **Testable** - Provide basis for implementation and verification
* **Versioned** - Tracked in Git alongside code

Design Hierarchy
----------------

Design specifications are organized by scope:

1. **High-Level Architecture** (``SPEC_ARCH_*``) - System-wide design decisions

   * Layered architecture and component organization
   * Threading model and memory management
   * Build system and QEMU integration
   * Network architecture (WiFi, HTTP)
   * Performance targets and development workflow

2. **Component-Specific Designs** - Detailed component specifications

   * ``SPEC_CFG_JSON_*`` - Configuration Manager (JSON-based system)
   * ``SPEC_WEB_*`` - Web Server HTTP interface and REST API
   * Additional component designs to be added as needed

Each design specification uses Sphinx-Needs ``:spec:`` directive and links to parent requirements using ``:links:`` attribute.

Document Standards
------------------

All design documents follow this structure:

* **Metadata**: Version, date, author, requirements coverage
* **Architecture**: High-level design decisions and patterns
* **Data Structures**: Internal data layouts and formats
* **API Design**: Public interfaces and contracts
* **Implementation**: Detailed algorithms and approaches
* **Traceability**: Requirement coverage matrix

Design vs. Code
---------------

Design documents are **separate from code** to avoid bloat:

* **Design docs** (``docs/12_design/``): Architecture, algorithms, rationale
* **Code comments**: Implementation notes, requirement IDs
* **API docs** (Doxygen): Function signatures, parameter descriptions

This separation enables:

* Professional documentation tooling (Sphinx-Needs traceability matrices)
* Design review without code complexity
* Version control for design decisions
* Scalability for large projects

Traceability Chain
------------------

The complete traceability chain:

.. code-block:: text

   Requirements (docs/11_requirements/)
        ↓ :links: attribute
   Design Specs (docs/12_design/)
        ↓ @file comments with REQ/SPEC IDs
   Implementation (main/, components/)
        ↓ test suite references
   Tests (to be added)

See the **Traceability** section for visualizations of the complete chain.