defmodule Translecto do
    @moduledoc """
      Translecto is a minimal translation library for Ecto to allow for translations at
      the database level.

      It takes a fairly simplistic approach to supporting this. The general idea is that
      your model has fields that it wishes to be translatable, these fields reference
      translation models (or model) which contain the translatable terms grouped
      by `:translate_id` and `:locale_id`.

      The `:translate_id` is the logical grouping of translatable data. While the
      `:locale_id` is the value (FK, string, integer, etc.) that distinguishes the specific
      translation for the given locale.

      Locale
      ------

      The locale is used to specify a specific localised translation. A locale may be a
      model which contains the different locales, or it may be another type that will be
      stored with the translation itself. Locales can apply globally or they may be
      different per translation. A globally applied locale can be specified in the config
      file by doing the following:

        config :translecto,
            locale: [schema: { :model, Model.Locale }, db: { :table, :locales }]

      The `:schema` field indicates the locale type that is applied to schemas, while the
      `:db` field indicates the locale type that is applied to the database (migration)
      files. For more info on the type of input see `Translecto.Schema.Translation.translation/1`
      and `Translecto.Migration.translation/1`.

      Translations
      ------------

      A translation is the model representing translated data. Multiple models may be used
      to store translations (possibly per context) or a single model can be used. To create
      a translation model you create a translation table and schema accordingly.

        defmodule Repo.Migrations.CreateItem.Content.Translations do
            use Ecto.Migration
            import Translecto.Migration

            def change do
                create table(:item_content_translations, primary_key: false) do
                    translation

                    add :name, :string,
                        null: false

                    add :description, :string,
                        null: false

                    timestamps
                end
            end
        end

        defmodule Item.Content.Translation do
            use Ecto.Schema
            use Translecto.Schema.Translation

            schema "food_diet_list" do
                translation
                field :name, :string
                field :description, :string
                timestamps
            end

            def changeset(struct, params \\\\ %{}) do
                struct
                |> translation_changeset(params)
                |> cast(params, [:name, :description])
                |> validate_required([:name, :description])
            end
        end

      Translatables
      -------------

      A translatable is a field that has translatable data. It references a group of rows
      from a translation model (by `:translate_id`), only needing the `:locale_id` to
      indicate the relevant localisation.

        defmodule Repo.Migrations.CreateItem do
            use Ecto.Migration
            import Translecto.Migration

            def change do
                create table(:items) do
                    translate :content,
                        null: false

                    \# ... other fields

                    timestamps
                end
            end
        end

        defmodule Item do
            use Ecto.Schema
            use Translecto.Schema.Translatable

            schema "items" do
                translatable :content, Item.Content.Translation
                \# ... other fields
                timestamps
            end

            def changeset(struct, params \\\\ %{}) do
                struct
                |> translatable_changeset(params, [:content])
                |> validate_required([:content])
                \# |> constraints/validations for other fields
            end
        end

      Insertion
      ---------

      To insert stuff you simply insert the translation data into the translation model
      using the correct grouping (`:translate_id`, `:locale_id`).

        content = Repo.insert! Item.Content.Translation.changeset(%Item.Content.Translation{}, %{ locale_id: 1, name: "1_1_name", description: "1_1_desc" })
        Repo.insert! Item.Content.Translation.changeset(%Item.Content.Translation{}, %{ translate_id: content.translate_id, locale_id: 2, name: "1_2_name", description: "1_2_desc" })

        Repo.insert! Item.changeset(%Item{}, %{ content: content.translate_id })


      Querying
      --------

      To simplify querying of translatable fields, the from query syntax has been
      extended to introduce a `:locale` field, and a `:translate` field. The `:locale`
      or `:locales` field specifies the current `:locale_id` or list of `:locale_id`'s,
      while the `:translate` or `:must_translate` field maps a model's translatable
      field to a new name.

        from item in Item,
            locale: 1,
            translate: content in item.content,
            select: { content.name, content.description }

      For more info on the type of fields see `Translecto.Query.from/2`.
    """
end