# Module: hardware_service

## Purpose

Collects a hardware fingerprint string from the host OS (CPU, GPU, memory, drive serial) for use in hardware-bound encryption key derivation.

## Public Interface

### Classes

#### `HardwareService` (cdef class)

| Method              | Signature                      | Description                                    |
|---------------------|--------------------------------|------------------------------------------------|
| `get_hardware_info` | `@staticmethod cdef str ()`    | Returns cached hardware fingerprint string     |

### Module-level State

| Name             | Type | Description                      |
|------------------|------|----------------------------------|
| `_CACHED_HW_INFO`| str  | Cached result (computed once)    |

## Internal Logic

### `get_hardware_info`

1. If cached (`_CACHED_HW_INFO is not None`), return cached value immediately
2. Detect OS via `os.name`:
   - **Windows (`nt`)**: PowerShell command querying WMI (Win32_Processor, Win32_VideoController, Win32_OperatingSystem, Disk serial)
   - **Linux/other**: shell commands (`lscpu`, `lspci`, `free`, block device serial)
3. Parse output lines → extract CPU, GPU, memory, drive serial
4. Format: `"CPU: {cpu}. GPU: {gpu}. Memory: {memory}. DriveSerial: {serial}"`
5. Cache result in `_CACHED_HW_INFO`

The function uses `subprocess.check_output(shell=True)` — platform-specific shell commands.

## Dependencies

- **Internal**: `constants` (for `log()`)
- **External**: `os`, `subprocess` (stdlib)

## Consumers

- `api_client` — `load_bytes()` and `check_resource()` call `HardwareService.get_hardware_info()`

## Data Models

None.

## Configuration

None. Hardware detection commands are hardcoded per platform.

## External Integrations

- **OS commands**: Windows PowerShell (Get-CimInstance, Get-Disk) or Linux shell (lscpu, lspci, free, /sys/block)

## Security

Produces a hardware fingerprint used to bind encryption keys to specific machines. The fingerprint includes drive serial number, which acts as a machine-unique identifier.

## Tests

No tests found.