# OrchidSymbiont
**Lazy Dependency Injection & Process Management for [Orchid](https://github.com/SynapticStrings/Orchid).**
OrchidSymbiont acts as a sidecar for your Orchid workflows. It allows individual steps to declare requirements for specific background services (GenServers). Symbiont ensures these services are **started on-demand (Just-In-Time)**, resolved, and injected directly into your step's execution context.
> **Why?** Perfect for steps requiring heavy resources (ML Models, Database Workers, Persistent Connections) that you don't want to keep running when the workflow is idle.
## Features
* **Lazy Loading**: Processes are only started when a Step actually needs them.
* **Automatic Registry**: Handles process registration, lookup, and idempotency (won't start twice).
* **Seamless Injection**: Injects process references(PID) directly into the step logic via a specialized Hook.
* **Blueprint Catalog**: Decouple service implementation from step definition.
* **Session Isolation (Multi-Tenancy)** *(New in 0.2.0)*: Run completely isolated sandboxes of your services for different tenants or concurrent workflows.
## Installation
Add to your `mix.exs`:
```elixir
def deps do
[
{:orchid, "~> 0.5"},
{:orchid_symbiont, "~> 0.2"}
]
end
```
Ensure `Application` is started in your supervision tree (handled automatically for the global default namespace).
## Usage
### 1. Register Symbionts (Global)
Tell Symbiont how to start your service.
```elixir
# Register a logical name to a GenServer spec
# :heavy_calculator maps to {MyCalculatorWorker, [init_arg: :foo]}
OrchidSymbiont.register(:heavy_calculator, {MyCalculatorWorker, [init_arg: :foo]})
```
### 2. Define Steps
Implement the `OrchidSymbiont.Step` behaviour. Note that we use `run_with_model/3` instead of the standard `run/2`.
```elixir
defmodule MyWorkflow.CalculateStep do
@behaviour OrchidSymbiont.Step
@impl true
def required, do: [:heavy_calculator]
@impl true
def run_with_model(input, handlers, _opts) do
# Get the resolved service reference
worker = handlers[:heavy_calculator]
result = OrchidSymbiont.call(worker, {:compute, input})
{:ok, result}
end
end
```
### 3. Run with Hook
Inject the `OrchidSymbiont.Hooks.Injector` into your recipe's step configuration.
```elixir
step_opts = [
# This hook activates the Symbiont logic
extra_hooks_stack: [OrchidSymbiont.Hooks.Injector]
]
# ... define steps and recipe ...
Orchid.run(recipe, inputs)
```
---
## 🚀 Advanced: Session Isolation (New in 0.2.0)
If you are building a SaaS application or need completely isolated environments for different workflows, you can use **Sessions**.
A Session creates a dedicated, dynamically named `Registry`, `DynamicSupervisor`, and `Catalog`. Processes running in `:session_a` cannot see or conflict with processes in `:session_b`, even if they share the same logical names!
### 1. Start a Session Runtime
You must start a Runtime for your specific session in your application's supervision tree (or dynamically):
```elixir
# Start an isolated environment for a specific project/tenant
children = [
{OrchidSymbiont.Runtime, session_id: "project_a_session"}
]
Supervisor.start_link(children, strategy: :one_for_one)
```
### 2. Register for a specific Session
You can register blueprints globally (without a session ID) or specifically for a session.
*Note: If a session cannot find a blueprint in its own catalog, it will smartly fall back to the global catalog!*
```elixir
# Register specifically for project_a_session
OrchidSymbiont.register("project_a_session", :heavy_calculator, {MyCustomWorker, []})
```
### 3. Run the Workflow in a Session
To tell the Symbiont Injector Hook to use a specific session, simply pass the `session_id` into the Orchid `WorkflowCtx` baggage:
```elixir
workflow_ctx = Orchid.WorkflowCtx.new()
|> Orchid.WorkflowCtx.put_baggage(:session_id, "project_a_session") # <-- Tell Symbiont to use this sandbox
Orchid.run(recipe, inputs, workflow_ctx: workflow_ctx)
```
That's it! Symbiont will now automatically resolve and start processes under the isolated `"project_a_session"` supervision tree.
---
## How it works
1. **Intercept**: The `OrchidSymbiont.Hooks.Injector` pauses the step execution.
2. **Check**: It reads the `required()` list from your step and looks for a `:session_id` in the workflow baggage.
3. **Resolve**:
* Uses the `Naming` module to route to the correct `Registry` and `Catalog` based on the session ID.
* Checks if the service is alive. If not, looks up the blueprint and starts it under the isolated `DynamicSupervisor`.
4. **Inject**: The `PID` is wrapped in a `Handler` struct and passed to `run_with_model`.
