# `Mailglass.TemplateEngine`
[🔗](https://github.com/szTheory/mailglass/blob/v1.0.0/lib/mailglass/template_engine.ex#L1)

Behaviour for mailglass template engines.

The default implementation is `Mailglass.TemplateEngine.HEEx`, which renders
function components compiled by the Phoenix tag engine at build time.

To use MJML as an alternate rendering path, add `{:mjml, "~> 5.3"}` to your
deps and configure:

    config :mailglass, renderer: [engine: Mailglass.TemplateEngine.MJML]

See AUTHOR-05 in REQUIREMENTS.md. The MJML implementation ships separately
after the v0.1 release.

## Callbacks

- `compile/2` — compile a template source string to an intermediate form.
  For HEEx, templates are compiled at build time by the Phoenix tag engine;
  this callback exists for API symmetry and returns `{:ok, :heex_native}`.
- `render/3` — render the compiled form with assigns to HTML iodata.

# `compile`

```elixir
@callback compile(source :: String.t(), opts :: keyword()) ::
  {:ok, term()} | {:error, Mailglass.TemplateError.t()}
```

Compile a template source string. Returns an opaque compiled form.

# `render`

```elixir
@callback render(compiled :: term(), assigns :: map(), opts :: keyword()) ::
  {:ok, iodata()} | {:error, Mailglass.TemplateError.t()}
```

Render a compiled template with assigns. Returns HTML iodata.

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