component-system/lib/components_elixir/inventory/storage_location.ex

defmodule ComponentsElixir.Inventory.StorageLocation do
  @moduledoc """
  Schema for storage locations with hierarchical organization.

  Storage locations can be nested (shelf -> drawer -> box) and each
  has a unique QR code for quick scanning and identification.
  """
  use Ecto.Schema
  import Ecto.Changeset
  import Ecto.Query

  alias ComponentsElixir.Inventory.{StorageLocation, Component}

  schema "storage_locations" do
    field :name, :string
    field :description, :string
    field :apriltag_id, :integer
    field :is_active, :boolean, default: true

    # Computed/virtual fields - not stored in database
    field :level, :integer, virtual: true
    field :path, :string, virtual: true

    # Only parent relationship is stored
    belongs_to :parent, StorageLocation
    has_many :children, StorageLocation, foreign_key: :parent_id
    has_many :components, Component

    timestamps()
  end

    @doc false
  def changeset(storage_location, attrs) do
    storage_location
    |> cast(attrs, [:name, :description, :parent_id, :is_active, :apriltag_id])
    |> validate_required([:name])
    |> validate_length(:name, min: 1, max: 100)
    |> validate_length(:description, max: 500)
    |> validate_apriltag_id()
    |> foreign_key_constraint(:parent_id)
    |> validate_no_circular_reference()
    |> put_apriltag_id()
  end

  # Prevent circular references (location being its own ancestor)
  defp validate_no_circular_reference(changeset) do
    case get_change(changeset, :parent_id) do
      nil -> changeset
      parent_id ->
        location_id = changeset.data.id
        if location_id && would_create_cycle?(location_id, parent_id) do
          add_error(changeset, :parent_id, "cannot be a descendant of this location")
        else
          changeset
        end
    end
  end

  defp would_create_cycle?(location_id, parent_id) do
    # Check if parent_id is the same as location_id or any of its descendants
    location_id == parent_id or
    (parent_id && is_descendant_of?(parent_id, location_id))
  end

  defp is_descendant_of?(potential_descendant, ancestor_id) do
    case ComponentsElixir.Repo.get(StorageLocation, potential_descendant) do
      nil -> false
      %{parent_id: nil} -> false
      %{parent_id: ^ancestor_id} -> true
      %{parent_id: parent_id} -> is_descendant_of?(parent_id, ancestor_id)
    end
  end

  @doc """
  Returns the full hierarchical path as a human-readable string.
  """
  def full_path(storage_location) do
    storage_location.path
    |> String.split("/")
    |> Enum.join(" → ")
  end

  @doc """
  Returns the AprilTag format for this storage location.
  Returns the AprilTag ID that corresponds to this location.
  """
  def apriltag_format(storage_location) do
    storage_location.apriltag_id
  end

  # Private functions for changeset processing

  defp validate_apriltag_id(changeset) do
    changeset
    |> validate_number(:apriltag_id, greater_than_or_equal_to: 0, less_than_or_equal_to: 586)
    |> unique_constraint(:apriltag_id, message: "AprilTag ID is already in use")
  end

  defp put_apriltag_id(changeset) do
    case get_field(changeset, :apriltag_id) do
      nil -> put_change(changeset, :apriltag_id, get_next_available_apriltag_id())
      _ -> changeset
    end
  end

  # Compute the hierarchy level based on parent chain
  def compute_level(%StorageLocation{parent_id: nil}), do: 0
  def compute_level(%StorageLocation{parent: %StorageLocation{} = parent}) do
    compute_level(parent) + 1
  end
  def compute_level(%StorageLocation{parent_id: parent_id}) when not is_nil(parent_id) do
    # Parent not loaded, fetch it
    parent = ComponentsElixir.Inventory.get_storage_location!(parent_id)
    compute_level(parent) + 1
  end

  # Compute the full path based on parent chain
  def compute_path(%StorageLocation{name: name, parent_id: nil}), do: name
  def compute_path(%StorageLocation{name: name, parent: %StorageLocation{} = parent}) do
    "#{compute_path(parent)}/#{name}"
  end
  def compute_path(%StorageLocation{name: name, parent_id: parent_id}) when not is_nil(parent_id) do
    # Parent not loaded, fetch it
    parent = ComponentsElixir.Inventory.get_storage_location!(parent_id)
    "#{compute_path(parent)}/#{name}"
  end

  defp get_next_available_apriltag_id do
    # Get all used AprilTag IDs
    used_ids = ComponentsElixir.Repo.all(
      from sl in ComponentsElixir.Inventory.StorageLocation,
      where: not is_nil(sl.apriltag_id),
      select: sl.apriltag_id
    )

    # Find the first available ID (0-586)
    0..586
    |> Enum.find(&(&1 not in used_ids))
    |> case do
      nil ->
        # All IDs are used - this should be handled at the application level
        raise "All AprilTag IDs are in use"
      id -> id
    end
  end
end