dynalab-core/docs/API.md

# DynaLab Core API

`Core` is the Python interface for running a DynaLab Core instance, inspecting
signals and their current values, recording incoming data, playing recordings,
and creating derived signals. Connectors provide realtime data to a running
core using the [DynaLab protocol](Protocol.md).

> [!WARNING]
> DynaLab Core is in alpha. Its public API may change between releases.

## Quick Start

Create a configuration, construct the core, then start it. Always stop the core
when the application exits so its server and worker threads are shut down.

```python
from dynalab_core import Core
from dynalab_core.config import CoreConfig

core = Core(CoreConfig(host="127.0.0.1", port=58763))

try:
    core.start()
    core.wait()  # Blocks until stop() is called or a timeout expires.
finally:
    core.stop()
```

`Core` does not currently implement the context-manager protocol. Use
`try`/`finally` when the core may be started.

## Configuration

`CoreConfig` is defined in `dynalab_core.config`.

```python
from dynalab_core.config import CoreConfig

config = CoreConfig(
    host="127.0.0.1",  # Default
    port=58763,         # Default; must be in the range 0 through 65535
)
```

| Field | Type | Default | Description |
| --- | --- | --- | --- |
| `host` | `str` | `"127.0.0.1"` | Address on which the core server listens. |
| `port` | `int` | `58763` | TCP port on which the core server listens. |

`CoreConfig.bind_str() -> str` returns the configured address in
`"host:port"` form.

## Lifecycle

### `Core(config: CoreConfig)`

Creates a core and starts its internal input worker. The network server is not
started until `start()` is called.

### `start() -> None`

Starts the configured server and begins accepting connector connections. This
method returns after the server start sequence completes.

Call `start()` once per `Core` instance. Calling it in any state other than the
initial state raises `CoreError` with code `"invalid_state"`. Server startup
failures, such as an address already in use, raise `JsonServerError` while
retaining the underlying exception as their cause.

### `wait(timeout: float | None = None) -> None`

Blocks until `stop()` is called or until `timeout` seconds have elapsed. Omit
`timeout` to wait indefinitely. This is useful for keeping a command-line
application alive without a busy loop.

### `stop() -> bool`

Stops the server, disconnects connectors, signals the input worker to stop, and
stops the playback engine and all bound derive units. It also releases any call
currently blocked in `wait()`.

Returns `True` when the server, connector registry, derive registry, and input
worker stop within their allowed timeouts, or `False` when shutdown is
incomplete.

Call this during application shutdown, including when startup or runtime work
raises an exception. A stopped core cannot be started again.

## Modes

Core operates in one of two modes:

| Mode | Signal source | Available operation |
| --- | --- | --- |
| `"realtime"` | Connected connectors | Recording |
| `"playback"` | A loaded recording | Playback |

The initial mode is `"realtime"`. Connected endpoints remain connected in
playback mode, but their incoming values are not routed into Core.

`CoreMode` is defined in `dynalab_core.types` as the literal union of these two
strings.

### `set_mode(mode: CoreMode) -> None`

Changes the active mode and clears all cached live values. `mode` must be
`"realtime"` or `"playback"`; any other value raises `CoreError` with code
`"invalid_mode"`.

The mode cannot be changed while a recording is active. Attempting to do so
raises `CoreError` with code `"recording_active"`.

> [!IMPORTANT]
> Changing mode does not automatically pause active playback. Call `pause()`
> before switching from playback to realtime mode.

### `get_mode() -> CoreMode`

Returns the active mode as either `"realtime"` or `"playback"`.

## Signals

Signals are registered by connectors during their protocol handshake. A signal
is described by `SignalDescriptor` from
`dynalab_core.protocols.packets.handshake`.

```python
from uuid import UUID

from dynalab_core.protocols.packets.handshake import SignalDescriptor

signal = SignalDescriptor(
    id=UUID("2d60a378-f37c-4c37-867b-c68f5116598b"),
    name="Engine RPM",
    type="number",
    min_value=0.0,
    max_value=6000.0,
    unit="rpm",
    timeout_ms=2_000,
)
```

| Field | Type | Default | Description |
| --- | --- | --- | --- |
| `id` | `UUID` | Required | Stable, unique signal identifier. |
| `name` | `str` | Required | Human-readable signal name. |
| `type` | `"number"` or `"binary"` | Required | Signal value category. Values are represented as `float` by the current data API. |
| `min_value` | `float \| None` | `None` | Optional lower bound. |
| `max_value` | `float \| None` | `None` | Optional upper bound. |
| `unit` | `str \| None` | `None` | Optional display unit. |
| `timeout_ms` | `int` | `2000` | How long a received value remains live. |
| `origin` | `"source"` or `"derived"` | `"source"` | Whether a connector or a derive unit produces the signal. |

### `get_signal_descriptor(signal_id: UUID) -> SignalDescriptor | None`

Returns the descriptor for `signal_id`, including a derived-signal output, or
`None` when no matching signal is available. In realtime mode, source
descriptors come from connected connectors. In playback mode, they come from
the loaded recording. Use a UUID, not its string representation.

### `get_all_signal_descriptors() -> list[SignalDescriptor]`

Returns the source descriptors available in the current mode followed by the
descriptors from bound derive units. In realtime mode, source descriptors come
from connected connectors. In playback mode, they come from the loaded
recording; previously recorded derived descriptors are omitted because bound
derive units recalculate those values.

Connector membership is dynamic: a disconnected connector's signals are no
longer returned in realtime mode.

## Live Values

After a connector sends a value, Core retains its latest value until the
signal's `timeout_ms` has elapsed. A stale, unknown, or not-yet-received value
is represented by `None`.

### `get_live_value(signal_id: UUID) -> float | None`

Returns the latest non-stale value for one signal.

```python
rpm = core.get_live_value(signal_id)
if rpm is not None:
    print(f"Engine speed: {rpm:.0f} rpm")
```

### `get_all_live_values() -> dict[UUID, float]`

Returns a snapshot mapping signal IDs to their latest non-stale values. Signals
without a current value are omitted.

```python
for signal_id, value in core.get_all_live_values().items():
    print(signal_id, value)
```

Incoming data timestamps use the monotonic-nanosecond timebase. See
[Protocol timestamps](Protocol.md#timestamps) when implementing a connector.

## Recording

Recording captures incoming connector and derived values in an in-memory
buffer. Recording is only available in realtime mode.

### `start_recording() -> None`

Clears the current recording buffer, records a new UTC start timestamp, and
begins capturing subsequent values. Calling this method in playback mode raises
`CoreError` with code `"incorrect_mode"`; calling it while already recording
raises `CoreError` with code `"recording_active"`.

> [!IMPORTANT]
> Starting a recording discards any values captured by a previous recording.

### `stop_recording() -> None`

Stops capture, normalizes the recorded data, and creates a processing buffer
containing the completed recording and its signal manifest. Timestamps in the
completed recording are nanoseconds relative to its first sample.

Calling this method in playback mode raises `CoreError` with code
`"incorrect_mode"`; calling it when no recording is active raises `CoreError`
with code `"not_recording"`.

> [!IMPORTANT]
> Stopping a recording replaces the previous processing buffer. Persist or
> process it before stopping another recording.

### `get_recording_state() -> bool`

Returns `True` while a recording is active and `False` otherwise.

### `write(dir: str | Path, filename: str) -> None`

Writes the most recently completed recording to a DLPak archive. The `.dlpak`
extension is added to `filename` when it is not already present.

```python
from pathlib import Path

core.write(Path("recordings"), "dyno-run-001")
```

Complete a recording with `stop_recording()` before calling `write()`. If no
completed recording is available, the method raises `CoreError` with code
`"no_recording"`. Archive write failures raise `DLPakError` with code
`"write_failed"` and retain the underlying exception as their cause.

## Playback

Playback feeds a completed recording through the same live-value and derive
pipeline used for realtime data. Switch Core to playback mode and load data
before starting playback:

```python
from pathlib import Path

core.set_mode("playback")
core.load_playback_engine(Path("recordings/dyno-run-001.dlpak"))
core.play()
```

### `load_playback_engine(input: Path | None = None) -> None`

Loads playback data. Pass a DLPak archive path to load a saved recording, or
omit `input` to load the recording most recently completed by this `Core`
instance.

This method is only available in playback mode; otherwise it raises `CoreError`
with code `"invalid_mode"`. Omitting `input` before a recording has been
completed raises `CoreError` with code `"no_playback_data"`. A file that cannot
be read or validated raises `DLPakError` with code `"read_failed"`. Replacing
data while playback is active raises `PlaybackError` with code
`"already_playing"`.

Loading data does not start playback.

### `play() -> None`

Starts or resumes playback from the current position. Playback stops
automatically at the end of the recording and resets its position to the
beginning.

Calling this method outside playback mode raises `CoreError` with code
`"invalid_mode"`. Starting before data is loaded raises `PlaybackError` with
code `"no_data"`.

### `pause() -> None`

Pauses playback. A subsequent `play()` resumes from the current position.
Calling this method outside playback mode raises `CoreError` with code
`"invalid_mode"`. Calling it when playback is already paused has no effect.

### `seek(timestamp_ns: int) -> None`

Sets the playback position to `timestamp_ns`, measured in nanoseconds from the
recording's first sample. Samples after that timestamp are emitted when
playback starts or resumes. A negative timestamp raises `PlaybackError` with
code `"invalid_timestamp"`.

Calling this method outside playback mode raises `CoreError` with code
`"invalid_mode"`.

### `get_playback_state() -> bool`

Returns `True` while the playback engine is actively emitting data and `False`
while it is paused, has not started, or has reached the end of the recording.

## Derived Signals

A derive unit calculates a new value whenever one of its input signals receives
an update and all inputs have non-stale live values. Define the calculation as a
Python source string and bind it with `bind_derive_unit()`.

### `bind_derive_unit(function, input_signals, output_signal) -> UUID`

```python
from uuid import uuid4

from dynalab_core.protocols.packets.handshake import SignalDescriptor

processing_function = """
from dynalab_core.protocols.packets.data import ValueDescriptor
from dynalab_core.protocols.packets.handshake import SignalDescriptor

def add(left: ValueDescriptor, right: ValueDescriptor, output: SignalDescriptor) -> ValueDescriptor:
    return ValueDescriptor(
        signal_id=output.id,
        value=left.value + right.value,
        timestamp=left.timestamp,
    )
"""

output_signal = SignalDescriptor(
    id=uuid4(),
    name="Total",
    type="number",
    origin="derived",
)

unit_id = core.bind_derive_unit(
    processing_function,
    input_signals=[left_signal, right_signal],
    output_signal=output_signal,
)
```

`function` must define exactly one Python function. Its parameters must be:

1. Zero or more `ValueDescriptor` parameters, in the same order as
   `input_signals`.
2. One final `SignalDescriptor` parameter for `output_signal`.
3. A return annotation of `ValueDescriptor`.

The parameter annotations must use the imported `ValueDescriptor` and
`SignalDescriptor` classes shown above. The source string is executed with
`exec()`, so only bind code from trusted sources.

The returned UUID identifies the bound unit. Invalid source or function shape
raises `DeriveError`. Its code is `"invalid_source"` when the source cannot be
loaded or does not define exactly one function, and `"invalid_signature"` when
the function annotations or parameter order are invalid.

### `unbind_derive_unit(unit_id: UUID) -> None`

Stops and removes the derive unit identified by `unit_id`. Passing an unknown
or already unbound ID has no effect.

The returned ID is no longer valid after unbinding. Create and bind a new unit
to resume derived-value processing.

## Exceptions

All expected library exceptions are defined in `dynalab_core.errors` and derive
from `DynaLabError`. Exceptions are grouped by subsystem rather than by every
individual failure reason:

| Exception | Area | Codes |
| --- | --- | --- |
| `CoreError` | Core lifecycle, mode, and recording operations. | `invalid_state`, `invalid_mode`, `incorrect_mode`, `recording_active`, `not_recording`, `no_recording`, `no_playback_data` |
| `DLPakError` | Archive preparation, reading, and writing. | `no_data`, `no_manifest`, `read_failed`, `write_failed` |
| `DeriveError` | Derive source, signatures, arguments, and registration. | `invalid_source`, `invalid_signature`, `input_signal_mismatch`, `argument_mismatch`, `already_registered` |
| `PlaybackError` | Playback state and data. | `no_data`, `incomplete_data`, `already_playing`, `invalid_timestamp`, `stopped` |
| `ConnectorError` | Connector queues and registration. | `queue_full`, `already_registered` |
| `JsonServerError` | JSON server startup and timeouts. | `start_timeout`, `startup_failed` |

Every exception has a human-readable message and a stable, machine-readable
`code`. Catch a subsystem exception when the application can recover from that
area, or catch `DynaLabError` at the application's outer boundary:

```python
from dynalab_core.errors import CoreError, DynaLabError

try:
    core.start_recording()
except CoreError as error:
    if error.code == "incorrect_mode":
        core.set_mode("realtime")
        core.start_recording()

try:
    run_application()
except DynaLabError as error:
    print(f"DynaLab operation failed ({error.code}): {error}")
```

Wrapped operating-system, validation, and archive errors are available through
the standard `error.__cause__` attribute. Internal transport conditions such as
a peer disconnect or an invalid incoming frame are handled by the server and
logged instead of being raised from a background task to application code.