# `Ltix.DeepLinking`
[🔗](https://github.com/DecoyLex/ltix/blob/main/lib/ltix/deep_linking.ex#L1)

Package content items into a signed response JWT for the platform.

When the platform sends an `LtiDeepLinkingRequest` launch, your tool
presents a selection UI and calls `build_response/3` with the chosen
items. The response JWT is then POSTed back to the platform's return URL.

Content items are built with these modules:

  * `Ltix.DeepLinking.ContentItem.LtiResourceLink` — an LTI activity
    the platform will link to
  * `Ltix.DeepLinking.ContentItem.Link` — an external URL
  * `Ltix.DeepLinking.ContentItem.File` — a downloadable file
  * `Ltix.DeepLinking.ContentItem.HtmlFragment` — inline HTML to embed
  * `Ltix.DeepLinking.ContentItem.Image` — an image for direct rendering

See the [Deep Linking](deep-linking.md) guide for the full workflow
and [Building Content Items](cookbooks/building-content-items.md) for
recipes.

# `build_response`

```elixir
@spec build_response(Ltix.LaunchContext.t(), list(), keyword()) ::
  {:ok, Ltix.DeepLinking.Response.t()} | {:error, Exception.t()}
```

Build a signed Deep Linking response JWT.

Takes a `LaunchContext` from an `LtiDeepLinkingRequest` launch, a list of
content items, and optional message/log fields. Returns a `Response` with
the signed JWT and the platform's return URL.

## Options

  * `:msg` — user-facing message to show on return
  * `:log` — log message for the platform
  * `:error_message` — user-facing error message
  * `:error_log` — error log message for the platform

## Errors

  * `Ltix.Errors.Invalid.InvalidMessageType` — context is not a deep
    linking launch
  * `Ltix.Errors.Invalid.ContentItemTypeNotAccepted` — item type not
    in `accept_types`
  * `Ltix.Errors.Invalid.ContentItemsExceedLimit` — multiple items
    when `accept_multiple` is `false`
  * `Ltix.Errors.Invalid.LineItemNotAccepted` — line item present
    when `accept_lineitem` is `false`

## Examples

    {:ok, link} = Ltix.DeepLinking.ContentItem.LtiResourceLink.new(
      url: "https://tool.example.com/activity/123",
      title: "Quiz 1"
    )

    {:ok, response} = Ltix.DeepLinking.build_response(context, [link],
      msg: "Selected 1 item"
    )

    # response.jwt — signed JWT to POST to response.return_url

See the [Deep Linking](deep-linking.md) guide for the full workflow.

---

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