defmodule AshPostgres do
  @behaviour Ash.DataLayer

  defmacro __using__(opts) do
    quote bind_quoted: [repo: opts[:repo]] do
      @data_layer AshPostgres
      @repo repo

      unless repo do
        raise "You must pass the `repo` option to `use AshPostgres` for #{__MODULE__}"
      end

      unless repo.__adapter__() == Ecto.Adapters.Postgres do
        raise "Only Ecto.Adapters.Postgres is supported with AshPostgres for now"
      end

      def repo() do
        @repo
      end
    end
  end

  def repo(resource) do
    resource.repo()
  end

  import Ecto.Query, only: [from: 2]

  @impl true
  def limit(query, limit, _resource) do
    {:ok, from(row in query, limit: ^limit)}
  end

  @impl true
  def offset(query, offset, _resource) do
    {:ok, from(row in query, offset: ^offset)}
  end

  @impl true
  def run_query(query, resource) do
    {:ok, repo(resource).all(query)}
  end

  @impl true
  def resource_to_query(resource), do: Ecto.Queryable.to_query(resource)

  @impl true
  def create(resource, changeset, relationships) do
    repo = repo(resource)

    repo.transaction(fn ->
      changeset = cast_assocs(changeset, repo, resource, relationships)

      result =
        try do
          changeset
          |> repo.insert()
          |> case do
            {:ok, result} -> result
            {:error, changeset} -> repo.rollback(changeset)
          end
        rescue
          e ->
            repo.rollback(e)
        end

      case changeset do
        %{__after_action__: [_ | _] = after_action_hooks} ->
          Enum.each(after_action_hooks, fn hook ->
            case hook.(changeset, result, repo) do
              :ok -> :ok
              {:error, error} -> repo.rollback(error)
              :error -> repo.rollback(:error)
            end
          end)

          result

        _ ->
          result
      end
    end)
  end

  @impl true
  def sort(query, sort, _resource) do
    {:ok,
     from(row in query,
       order_by: ^sort
     )}
  end

  @impl true
  def filter(query, filter, resource) do
    Enum.reduce(filter, {:ok, query}, fn
      _, {:error, error} ->
        {:error, error}

      {key, value}, {:ok, query} ->
        do_filter(query, key, value, resource)
    end)
  end

  defp do_filter(
         query,
         :from_related,
         {records, %{cardinality: :many_to_many} = relationship},
         _resource
       ) do
    ids = Enum.map(records, &Map.get(&1, relationship.source_field))

    {:ok,
     from(row in query,
       join: join_row in ^relationship.through,
       on:
         field(join_row, ^relationship.destination_field_on_join_table) ==
           field(row, ^relationship.destination_field),
       where: field(join_row, ^relationship.source_field_on_join_table) in ^ids,
       select_merge: %{__related_id__: field(join_row, ^relationship.source_field_on_join_table)}
     )}
  end

  defp do_filter(query, :from_related, {records, relationship}, _resource) do
    ids = Enum.map(records, &Map.get(&1, relationship.source_field))

    {:ok,
     from(row in query,
       where: field(row, ^relationship.destination_field) in ^ids
     )}
  end

  # TODO This is a really dumb implementation of this.
  defp do_filter(query, key, value, resource) do
    cond do
      attr = Ash.attribute(resource, key) ->
        filter_attribute(query, attr, value, resource)

      rel = Ash.relationship(resource, key) ->
        filter_relationship(query, rel, value, resource)

      true ->
        {:error, "No such filter"}
    end
  end

  defp filter_attribute(query, attribute, value, _resource) do
    query =
      from(row in query,
        where: field(row, ^attribute.name) == ^value
      )

    {:ok, query}
  end

  # Only supports a single id for now
  defp filter_relationship(query, %{name: name}, id, _resource) do
    query =
      from(row in query,
        join: related in assoc(row, ^name),
        where: related.id == ^id
      )

    {:ok, query}
  end

  @impl true
  def can_query_async?(resource) do
    repo(resource).in_transaction?()
  end

  def cast_assocs(changeset, repo, resource, relationships) do
    Enum.reduce(relationships, changeset, fn {relationship, value}, changeset ->
      case Ash.relationship(resource, relationship) do
        %{type: :belongs_to, source_field: source_field} ->
          belongs_to_assoc_update(changeset, source_field, value)

        %{type: :has_one} = rel ->
          has_one_assoc_update(changeset, repo, rel, value)

        %{type: :has_many} = rel ->
          has_many_assoc_update(changeset, rel, value)

        %{type: :many_to_many} = rel ->
          many_to_many_assoc_update(changeset, rel, value, repo)

        _ ->
          changeset
      end
    end)
  end

  defp has_one_assoc_update(
         changeset,
         repo,
         %{
           destination: destination,
           destination_field: destination_field,
           source_field: source_field
         },
         identifier
       ) do
    Ecto.Changeset.prepare_changes(changeset, fn changeset ->
      value =
        case identifier do
          %{id: id} -> id
          nil -> nil
          _ -> raise "what"
        end

      query =
        from(row in destination,
          where:
            field(row, ^destination_field) == ^Ecto.Changeset.get_field(changeset, source_field)
        )

      repo.update_all(query, set: [{destination_field, value}])

      changeset
    end)
  end

  defp belongs_to_assoc_update(changeset, source_field, %{id: id}) do
    Ecto.Changeset.cast(changeset, %{source_field => id}, [source_field])
  end

  defp belongs_to_assoc_update(changeset, source_field, nil) do
    Ecto.Changeset.cast(changeset, %{source_field => nil}, [source_field])
  end

  defp has_many_assoc_update(
         changeset,
         %{
           destination: destination,
           destination_field: destination_field,
           source_field: source_field
         },
         values
       ) do
    ids = values |> Enum.map(&Map.get(&1, :id)) |> Enum.reject(&is_nil/1)

    add_after_action_hook(changeset, fn _changeset, result, repo ->
      field_value = Map.get(result, source_field)

      query =
        from(row in destination,
          where: row.id in ^ids
        )

      repo.update_all(query, set: [{destination_field, field_value}])

      :ok
    end)
  end

  defp many_to_many_assoc_update(
         changeset,
         %{
           through: through,
           source_field: source_field,
           source_field_on_join_table: source_field_on_join_table,
           destination_field_on_join_table: destination_field_on_join_table
         },
         values,
         repo
       ) do
    ids = values |> Enum.map(&Map.get(&1, :id)) |> Enum.reject(&is_nil/1)

    source_id =
      Ecto.Changeset.get_field(
        changeset,
        source_field
      )

    changeset
    |> Ecto.Changeset.prepare_changes(fn changeset ->
      delete_now_unrelated_ids(
        repo,
        source_id,
        through,
        source_field_on_join_table,
        destination_field_on_join_table,
        ids
      )

      changeset
    end)
    |> add_after_action_hook(fn _changeset, _result, repo ->
      upsert_join_table_rows(
        repo,
        source_id,
        through,
        values,
        source_field_on_join_table,
        destination_field_on_join_table
      )
    end)
  end

  defp delete_now_unrelated_ids(
         repo,
         source_id,
         through,
         source_field_on_join_table,
         destination_field_on_join_table,
         ids
       ) do
    query =
      from(join_row in through,
        where: field(join_row, ^destination_field_on_join_table) not in ^ids,
        where: field(join_row, ^source_field_on_join_table) == ^source_id
      )

    repo.delete_all(query)
  end

  defp upsert_join_table_rows(
         repo,
         source_id,
         through,
         values,
         source_field_on_join_table,
         destination_field_on_join_table
       ) do
    Enum.each(values, fn fields ->
      update_fields = Map.delete(fields, :id)

      cond do
        update_fields == %{} && is_nil(Map.get(fields, :id)) ->
          :ok

        is_bitstring(through) ->
          :ok

        true ->
          # TODO: This needs to be wired up properly
          # (fields/changes need to come from resource/relationship config)
          attributes =
            update_fields
            |> Map.put(source_field_on_join_table, source_id)
            |> Map.put(destination_field_on_join_table, Map.get(fields, :id))

          changeset =
            through
            |> struct()
            |> Ecto.Changeset.cast(attributes, Map.keys(attributes))

          repo.insert(changeset,
            on_conflict: :replace_all_except_primary_key,
            conflict_target: [source_field_on_join_table, destination_field_on_join_table]
          )

          :ok
      end
    end)
  end

  defp add_after_action_hook(changeset, hook) do
    changeset
    |> Map.put_new(:__after_action__, [])
    |> Map.update!(:__after_action__, fn list -> [hook | list] end)
  end

  # Copied from an older file, to be added as more functionality is added back in

      # @impl true
      # def update(%resource{} = record, _action, attributes, relationships, _params) do
      #   @repo.transaction(fn ->
      #     changeset =
      #       record
      #       |> Ecto.Changeset.cast(attributes, Map.keys(attributes))
      #       |> AshPostgres.DataLayer.cast_assocs(@repo, resource, relationships)

      #     result =
      #       case @repo.update(changeset) do
      #         {:ok, result} -> result
      #         {:error, changeset} -> @repo.rollback(changeset)
      #       end

      #     case changeset do
      #       %{__after_action__: [_ | _] = after_action_hooks} ->
      #         Enum.each(after_action_hooks, fn hook ->
      #           case hook.(changeset, result, @repo) do
      #             :ok -> :ok
      #             {:error, error} -> @repo.rollback(error)
      #             :error -> @repo.rollback(:error)
      #           end
      #         end)

      #         result

      #       _other ->
      #         result
      #     end
      #   end)
      # end

      # @impl true
      # def append_related(record, relationship, resource_identifiers) do
      #   @repo.transaction(fn ->
      #     AshPostgres.DataLayer.append_related(@repo, record, relationship, resource_identifiers)
      #   end)
      # end

      # @impl true
      # def delete_related(record, relationship, resource_identifiers) do
      #   @repo.transaction(fn ->
      #     AshPostgres.DataLayer.delete_related(@repo, record, relationship, resource_identifiers)
      #   end)
      # end

      # @impl true
      # def replace_related(record, relationship, resource_identifiers) do
      #   @repo.transaction(fn ->
      #     AshPostgres.DataLayer.replace_related(@repo, record, relationship, resource_identifiers)
      #   end)
      # end

      # @impl true
      # def delete(record, _action, _params) do
      #   @repo.delete(record)
      # end
    end
  end

  # @doc false
  # def replace_related(
  #       repo,
  #       record,
  #       %{
  #         type: :many_to_many,
  #         through: through,
  #         source_field: source_field,
  #         source_field_on_join_table: source_field_on_join_table,
  #         destination_field_on_join_table: destination_field_on_join_table
  #       },
  #       identifiers
  #     ) do
  #   ids = identifiers |> Enum.map(&Map.get(&1, :id)) |> Enum.reject(&is_nil/1)

  #   source_id = Map.get(record, source_field)

  #   delete_now_unrelated_ids(
  #     repo,
  #     source_id,
  #     through,
  #     source_field_on_join_table,
  #     destination_field_on_join_table,
  #     ids
  #   )

  #   upsert_join_table_rows(
  #     repo,
  #     source_id,
  #     through,
  #     identifiers,
  #     source_field_on_join_table,
  #     destination_field_on_join_table
  #   )

  #   record
  # end

  # def replace_related(
  #       repo,
  #       record,
  #       %{
  #         type: :has_many,
  #         source_field: source_field,
  #         destination: destination,
  #         destination_field: destination_field
  #       },
  #       identifiers
  #     ) do
  #   ids = identifiers |> Enum.map(&Map.get(&1, :id)) |> Enum.reject(&is_nil/1)

  #   field_value = Map.get(record, source_field)

  #   query =
  #     from(row in destination,
  #       where: row.id in ^ids
  #     )

  #   repo.update_all(query, set: [{destination_field, field_value}])

  #   record
  # end

  # def replace_related(
  #       repo,
  #       record,
  #       %{
  #         type: :belongs_to,
  #         source_field: source_field
  #       },
  #       identifier
  #     ) do
  #   value =
  #     case identifier do
  #       %{id: id} -> id
  #       nil -> nil
  #       _ -> raise "what do"
  #     end

  #   record
  #   |> Ecto.Changeset.cast(%{source_field => value}, [source_field])
  #   |> repo.update()
  #   |> case do
  #     {:ok, record} -> record
  #     {:error, error} -> repo.rollback(error)
  #   end
  # end

  # def replace_related(
  #       repo,
  #       record,
  #       %{
  #         type: :has_one,
  #         source_field: source_field,
  #         destination_field: destination_field,
  #         destination: destination
  #       },
  #       identifier
  #     ) do
  #   value =
  #     case identifier do
  #       %{id: id} -> id
  #       nil -> nil
  #       _ -> raise "what"
  #     end

  #   query =
  #     from(row in destination,
  #       where: field(row, ^destination_field) == ^Map.get(record, source_field)
  #     )

  #   repo.update_all(query, set: [{destination_field, value}])

  #   record
  # end

  # @doc false
  # def append_related(repo, record, %{type: :many_to_many} = relationship, identifiers) do
  #   source_id = Map.get(record, relationship.source_field)

  #   upsert_join_table_rows(
  #     repo,
  #     source_id,
  #     relationship.through,
  #     identifiers,
  #     relationship.source_field_on_join_table,
  #     relationship.destination_field_on_join_table
  #   )

  #   record
  # end

  # def append_related(
  #       repo,
  #       record,
  #       %{type: :has_many, destination: destination, destination_field: destination_field},
  #       identifiers
  #     ) do
  #   ids =
  #     identifiers
  #     |> Enum.map(&Map.get(&1, :id))
  #     |> Enum.reject(&is_nil/1)

  #   query =
  #     from(related in destination,
  #       where: related.id in ^ids,
  #       where: field(related, ^destination_field) != ^record.id
  #     )

  #   repo.update_all(query, set: [{destination_field, record.id}])
  # end

  # @doc false
  # def delete_related(repo, record, %{type: :many_to_many} = relationship, identifiers) do
  #   source_id = Map.get(record, relationship.source_field)

  #   ids =
  #     identifiers
  #     |> Enum.map(&Map.get(&1, :id))
  #     |> Enum.reject(&is_nil/1)

  #   delete_related_ids(
  #     repo,
  #     source_id,
  #     relationship.through,
  #     relationship.source_field_on_join_table,
  #     relationship.destination_field_on_join_table,
  #     ids
  #   )

  #   record
  # end

  # def delete_related(
  #       repo,
  #       record,
  #       %{type: :has_many, destination: destination, destination_field: destination_field},
  #       identifiers
  #     ) do
  #   ids =
  #     identifiers
  #     |> Enum.map(&Map.get(&1, :id))
  #     |> Enum.reject(&is_nil/1)

  #   query =
  #     from(related in destination,
  #       where: related.id in ^ids,
  #       where: field(related, ^destination_field) != ^record.id
  #     )

  #   # TODO: Validate the a delete_related action doesn't exist for has_many relationships
  #   # where the destination field is not nullable. That will only ever error.

  #   repo.update_all(query, set: [{destination_field, record.id}])
  # end

  # defp delete_related_ids(
  #        repo,
  #        source_id,
  #        through,
  #        source_field_on_join_table,
  #        destination_field_on_join_table,
  #        ids
  #      ) do
  #   query =
  #     from(join_row in through,
  #       where: field(join_row, ^destination_field_on_join_table) in ^ids,
  #       where: field(join_row, ^source_field_on_join_table) == ^source_id
  #     )

  #   repo.delete_all(query)
  # end

  # def add_through_schema_fields(repo, resource, includes) when is_list(includes) do
  #   Enum.flat_map(includes, fn {rel, further} ->
  #     case Ash.relationship(resource, rel) do
  #       %{type: :many_to_many, destination: destination} = relationship ->
  #         [
  #           {rel, &fetch_and_add_through_row(&1, repo, relationship)},
  #           {rel, add_through_schema_fields(repo, destination, further)}
  #         ]

  #       %{destination: destination} ->
  #         [
  #           {rel, add_through_schema_fields(repo, destination, further)}
  #         ]
  #     end
  #   end)
  # end

  # def add_through_schema_fields(_repo, _resource, includes), do: includes

  # defp fetch_and_add_through_row(source_ids, repo, relationship) do
  #   query =
  #     from(join_row in relationship.through,
  #       where:
  #         type(field(join_row, ^relationship.source_field_on_join_table), :binary_id) in ^source_ids,
  #       join: destination_row in ^relationship.destination,
  #       on:
  #         type(field(join_row, ^relationship.destination_field_on_join_table), :binary_id) ==
  #           field(destination_row, ^relationship.destination_field)
  #     )

  #   query
  #   |> add_select(relationship)
  #   |> repo.all()
  #   |> Enum.map(fn {destination_row, join_row} ->
  #     {Map.get(join_row, relationship.source_field_on_join_table),
  #      Map.put(destination_row, :__join_row__, join_row)}
  #   end)
  # end

  # defp add_select(query, relationship) do
  #   case relationship.through do
  #     string when is_bitstring(string) ->
  #       from([join_row, destination_row] in query,
  #         select:
  #           {destination_row,
  #            %{
  #              ^relationship.source_field_on_join_table =>
  #                type(field(join_row, ^relationship.source_field_on_join_table), :binary_id),
  #              ^relationship.destination_field_on_join_table =>
  #                type(field(join_row, ^relationship.destination_field_on_join_table), :binary_id)
  #            }}
  #       )

  #     module when is_atom(module) ->
  #       from([join_row, destination_row] in query,
  #         select: {destination_row, join_row}
  #       )
  #   end
  # end
end