defmodule LangChain.Message.ContentPart do
  @moduledoc """
  Models a `ContentPart`. Some LLMs support combining text, images, and possibly
  other content as part of a single user message. A `ContentPart` represents a
  block, or part, of a message's content that is all of one type.

  ## Types

  - `:text` - The message part is text.
  - `:image_url` - The message part is a URL to an image.
  - `:image` - The message part is image data that is base64 encoded text.

  ## Fields

  - `:content` - Text content.
  - `:options` - Options that may be specific to the LLM for a particular
    message type. For example, Anthropic requires an image's `media_type` to be
    provided by the caller. This can be provided using `media: "image/png"`.

  """
  use Ecto.Schema
  import Ecto.Changeset
  require Logger
  alias __MODULE__
  alias LangChain.LangChainError

  @primary_key false
  embedded_schema do
    field :type, Ecto.Enum, values: [:text, :image_url, :image], default: :text
    field :content, :string
    field :options, :any, virtual: true
  end

  @type t :: %ContentPart{}

  @update_fields [:type, :content, :options]
  @create_fields @update_fields
  @required_fields [:type, :content]

  @doc """
  Build a new message and return an `:ok`/`:error` tuple with the result.
  """
  @spec new(attrs :: map()) :: {:ok, t()} | {:error, Ecto.Changeset.t()}
  def new(attrs \\ %{}) do
    %ContentPart{}
    |> cast(attrs, @create_fields)
    |> common_validations()
    |> apply_action(:insert)
  end

  @doc """
  Build a new message and return it or raise an error if invalid.

  ## Example

      ContentPart.new!(%{type: :text, content: "Greetings!"})

      ContentPart.new!(%{type: :image_url, content: "https://example.com/images/house.jpg"})
  """
  @spec new!(attrs :: map()) :: t() | no_return()
  def new!(attrs \\ %{}) do
    case new(attrs) do
      {:ok, message} ->
        message

      {:error, changeset} ->
        raise LangChainError, changeset
    end
  end

  @doc """
  Create a new ContentPart that contains text. Raises an exception if not valid.
  """
  @spec text!(String.t()) :: t() | no_return()
  def text!(content) do
    new!(%{type: :text, content: content})
  end

  @doc """
  Create a new ContentPart that contains an image encoded as base64 data. Raises
  an exception if not valid.

  ## Options

  - `:media` - Provide the "media type" for the image. Examples: "image/jpeg",
    "image/png", etc. ChatGPT does not require this but other LLMs may.
  """
  @spec image!(String.t(), Keyword.t()) :: t() | no_return()
  def image!(content, opts \\ []) do
    new!(%{type: :image, content: content, options: opts})
  end

  @doc """
  Create a new ContentPart that contains a URL to an image. Raises an exception if not valid.
  """
  @spec image_url!(String.t()) :: t() | no_return()
  def image_url!(content) do
    new!(%{type: :image_url, content: content})
  end

  @doc false
  def changeset(message, attrs) do
    message
    |> cast(attrs, @update_fields)
    |> common_validations()
  end

  defp common_validations(changeset) do
    changeset
    |> validate_required(@required_fields)
  end
end