defmodule Ecto.Adapters.Mnesia.Source do
  @moduledoc false

  defstruct table: nil,
            schema: nil,
            loaded: nil,
            default: nil,
            match_all: nil,
            autogenerate_id: nil,
            index: %{},
            source_field: %{},
            schema_erl_prefix: nil,
            record_name: nil,
            attributes: [],
            extra_key: nil,
            erl_vars: %{}

  @type t :: %__MODULE__{}

  @doc """
  Returns source structure

  If type is `:query`, some additional fields are be pre-computed for query
  """
  def new(params, type \\ :insert)

  def new({table, schema, _prefix}, type) do
    new(%{source: table, schema: schema}, type)
  end

  def new(%{source: table, schema: schema} = meta, type) do
    table = String.to_atom(table)
    schema = schema
    record_name = record_name(schema)
    keys = schema.__schema__(:primary_key)
    loaded = schema.__schema__(:loaded)

    %__MODULE__{
      table: table,
      schema: schema,
      record_name: record_name,
      loaded: loaded,
      autogenerate_id: meta[:autogenerate_id]
    }
    |> build_extra_key(keys)
    |> build_attributes()
    |> build_index()
    |> build_default()
    |> build_match_all()
    |> build_source_field()
    |> build_query_optims(type)
  end

  def new(%{schema: schema} = meta, type) do
    new(Map.put(meta, :source, schema.__schema__(:source)), type)
  end

  @doc false
  def attributes(%{attributes: attributes}) do
    attributes
  end

  @doc false
  def fields(%{schema: schema}) do
    schema.__schema__(:fields)
  end

  @doc false
  @spec uniques(t(), Keyword.t()) :: [{atom(), term()}]
  def uniques(%{schema: schema}, params) do
    keys = schema.__schema__(:primary_key)

    keys
    |> Enum.reduce([], fn key, acc ->
      case Keyword.fetch(params, key) do
        {:ok, value} -> [{key, value} | acc]
        :error -> acc
      end
    end)
  end

  @doc false
  def qlc_attributes_pattern(%{erl_vars: erl_vars} = source) do
    Enum.map(source.attributes, &{:var, 1, erl_vars[&1]})
  end

  @doc false
  def to_erl_var(%{erl_vars: erl_vars} = source, attribute) do
    Map.get_lazy(erl_vars, attribute, fn ->
      String.to_atom(source.schema_erl_prefix <> "_" <> to_string(attribute))
    end)
  end

  ###
  ### Priv
  ###
  defp build_query_optims(%{schema: schema, attributes: attributes} = source, :query) do
    {p, refix} = schema |> to_string() |> String.split_at(1)
    prefix = String.capitalize(p) <> refix

    erl_vars =
      Enum.reduce(attributes, %{}, fn attr, acc ->
        Map.put(acc, attr, String.to_atom(prefix <> "_" <> to_string(attr)))
      end)

    %{source | schema_erl_prefix: prefix, erl_vars: erl_vars}
  end

  defp build_query_optims(source, _), do: source

  defp record_name(schema) do
    if function_exported?(schema, :__record_name__, 0) do
      apply(schema, :__record_name__, [])
    else
      schema
    end
  end

  defp build_extra_key(source, []), do: source

  defp build_extra_key(source, [_]), do: source

  defp build_extra_key(source, keys) do
    extra_key =
      keys
      |> Enum.map(&source.schema.__schema__(:field_source, &1))
      |> Enum.with_index()
      |> Enum.reduce(%{}, fn {key, i}, acc ->
        Map.put(acc, key, i)
      end)

    %{source | extra_key: extra_key}
  end

  defp build_attributes(%{schema: schema, extra_key: nil} = source),
    do: %{source | attributes: schema_sources(schema)}

  defp build_attributes(%{schema: schema} = source),
    do: %{source | attributes: [:__key__ | schema_sources(schema)]}

  defp build_index(%{attributes: attributes} = source) do
    index =
      attributes
      |> Enum.with_index()
      |> Enum.reduce(%{}, fn {a, i}, acc -> Map.put(acc, a, i + 1) end)

    %{source | index: index}
  end

  defp build_source_field(%{schema: schema} = source) do
    map =
      schema
      |> apply(:__schema__, [:fields])
      |> Enum.reduce(%{}, &Map.put(&2, schema.__schema__(:field_source, &1), &1))

    %{source | source_field: map}
  end

  defp build_default(%{attributes: attributes, record_name: record_name} = source) do
    default =
      nil
      |> Tuple.duplicate(length(attributes))
      |> Tuple.insert_at(0, record_name)
      |> maybe_default_extra_key(source)

    %{source | default: default}
  end

  defp build_match_all(%{attributes: attributes, record_name: record_name} = source) do
    pattern =
      :_
      |> Tuple.duplicate(length(attributes))
      |> Tuple.insert_at(0, record_name)

    %{source | match_all: pattern}
  end

  defp maybe_default_extra_key(record, %{extra_key: nil}), do: record

  defp maybe_default_extra_key(record, %{extra_key: extra_key}) do
    put_elem(record, 1, Tuple.duplicate(nil, Enum.count(extra_key)))
  end

  defp schema_sources(schema) do
    schema
    |> apply(:__schema__, [:fields])
    |> Enum.map(&schema.__schema__(:field_source, &1))
  end
end