# `Sig.NodeContext`
[🔗](https://github.com/peeeuzin/sig/blob/v0.1.0/lib/sig/node_context.ex#L1)

The data a node receives when it runs.

It is passed to `c:Sig.Node.run/1` (and as the second argument of
`c:Sig.Node.run/2`).

## Fields

  * `:params` - the deep merge of workflow, execution and node params, in
    that order (node params win). This is what nodes usually read.
  * `:context` - the deep merge of workflow and execution context.
  * `:results` - the results of the nodes that already completed in this
    execution, keyed by node name.
  * `:node_name` - the name of the node being run.
  * `:attempt` - the current attempt number, starting at `1`.
  * `:workflow_id` / `:execution_id` - IDs of the workflow and execution.
  * `:workflow_params`, `:execution_params`, `:node_params` - each level of
    params before merging.
  * `:workflow_context`, `:execution_context` - each level of context
    before merging.

All maps come from JSONB columns, so their keys are strings.

## Access

The struct implements `Access`, so `context[:results]` and
`context["results"]` work as well as `context.results`.

## Example

    def run(%Sig.NodeContext{} = context) do
      user = context.results["fetch_user"]
      amount = context.params["amount"]
      {:ok, %{"debited" => amount, "user_id" => user["id"], "attempt" => context.attempt}}
    end

# `t`

```elixir
@type t() :: %Sig.NodeContext{
  attempt: non_neg_integer(),
  context: map(),
  execution_context: map(),
  execution_id: String.t() | nil,
  execution_params: map(),
  node_name: String.t(),
  node_params: map(),
  params: map(),
  results: map(),
  workflow_context: map(),
  workflow_id: String.t() | nil,
  workflow_params: map()
}
```

The context passed to a node.

# `build`

```elixir
@spec build(map()) :: t()
```

Builds a `NodeContext`, computing the merged `:params` and `:context`.

Accepts a map with any of the struct fields except `:params` and
`:context`, which are derived. Missing maps default to `%{}` and `:attempt`
defaults to `1`.

## Examples

    iex> ctx = Sig.NodeContext.build(%{
    ...>   workflow_params: %{"currency" => "BRL", "amount" => 10},
    ...>   execution_params: %{"amount" => 20},
    ...>   node_params: %{"amount" => 30}
    ...> })
    iex> ctx.params
    %{"currency" => "BRL", "amount" => 30}

---

*Consult [api-reference.md](api-reference.md) for complete listing*