defmodule Corex.Form do
  @moduledoc """
  Helper functions to work with forms.

  Corex form components such as `Corex.Checkbox` and `Corex.Select` with classic form and with Phoenix form using the `Phoenix.Component.form/1` function.

  ## Examples

  ### Classic Form

  In a classic form, you can use the `name` attribute to identify the checkbox.
  The generated parameters will be as follows:  `/?terms=true`

  This works in Controller View and Live View

  ```heex
  <form id="my-form">
    <.checkbox name="terms" class="checkbox">
      <:label>I accept the terms</:label>
    </.checkbox>
    <button type="submit">Submit</button>
  </form>
  ```

  ### Phoenix Form

  In a Phoenix form, you can use the field attribute to identify the checkbox.
  The generated parameters will be as follows:  `/?terms=true`

  > #### Required {: .neutral}
  > You must use the `Corex.Form.get_form_id/1` function to get the form id and pass it to the form component.

  #### In a Controller

  ```heex
  <.form :let={f} for={@changeset} id={get_form_id(@changeset)}>
    <.checkbox field={f[:terms]} class="checkbox">
      <:label>I accept the terms</:label>
    </.checkbox>
    <button type="submit">Submit</button>
  </.form>
  ```

  #### In a Live View


  > #### Required {: .neutral}
  > - You must use the `Corex.Form.get_form_id/1` function to get the form id and pass it to the form component.
  > - You must enable the controlled mode. This allows the Live View to be the source of truth and the component to be in sync accordingly


  ```heex
  <.form for={@form} id={get_form_id(@form)}>
    <.checkbox field={@form[:terms]} controlled class="checkbox">
      <:label>I accept the terms</:label>
    </.checkbox>
    <button type="submit">Submit</button>
  </.form>
  ```
  """

  alias Phoenix.Component
  alias Phoenix.HTML.Form
  alias Ecto.Changeset

  @doc """
  Returns the form id.

  Accepts either:
    * an `Ecto.Changeset`
    * a `Phoenix.HTML.Form`

  ## Examples

  #### In a Controller

  ```heex
  <.form :let={f} for={@changeset} id={get_form_id(@changeset)}>
    <.checkbox field={f[:terms]} class="checkbox">
      <:label>I accept the terms</:label>
    </.checkbox>
    <button type="submit">Submit</button>
  </.form>
  ```

  #### In a Live View

  ```heex
  <.form for={@form} id={get_form_id(@form)}>
    <.checkbox field={@form[:terms]} controlled class="checkbox">
      <:label>I accept the terms</:label>
    </.checkbox>
    <button type="submit">Submit</button>
  </.form>
  ```
  """
  @spec get_form_id(Form.t() | Changeset.t()) :: binary()
  def get_form_id(%Form{id: id}) when is_binary(id), do: id

  def get_form_id(%Changeset{} = changeset) do
    changeset
    |> Component.to_form()
    |> Map.fetch!(:id)
  end

  def get_form_id(other) do
    raise ArgumentError,
          "expected Ecto.Changeset or Phoenix.HTML.Form, got: #{inspect(other)}"
  end
end