defmodule DaProductApp.BatchNumber do
  use Ecto.Schema
  import Ecto.Changeset
  import Ecto.Query

  @primary_key {:id, :id, autogenerate: true}
  
  schema "batch_numbers" do
    field :merchant_id, :string
    field :batch_number, :string
    field :date, :date
    field :transaction_count, :integer, default: 0
    field :last_used_at, :utc_datetime

    timestamps()
  end

  @doc false
  def changeset(batch_number, attrs) do
    batch_number
    |> cast(attrs, [:merchant_id, :batch_number, :date, :transaction_count, :last_used_at])
    |> validate_required([:merchant_id, :batch_number, :date])
    |> unique_constraint([:merchant_id, :date], name: :unique_merchant_date)
  end

  @doc """
  Gets or creates a batch number for a merchant on a specific date.
  Returns a 6-digit zero-padded batch number string.
  """
  def get_or_create_batch_number(merchant_id, date \\ Date.utc_today()) do
    case DaProductApp.Repo.get_by(__MODULE__, merchant_id: merchant_id, date: date) do
      nil ->
        # Create new batch number starting with 000001
        batch_number = "000001"
        attrs = %{
          merchant_id: merchant_id,
          batch_number: batch_number,
          date: date,
          transaction_count: 1,
          last_used_at: DateTime.utc_now()
        }
        
        case DaProductApp.Repo.insert(changeset(%__MODULE__{}, attrs)) do
          {:ok, batch_record} -> {:ok, batch_record.batch_number}
          {:error, _changeset} -> 
            # Handle race condition - try to get existing record
            case DaProductApp.Repo.get_by(__MODULE__, merchant_id: merchant_id, date: date) do
              nil -> {:error, "Failed to create batch number"}
              existing -> increment_batch_number(existing)
            end
        end
        
      existing_batch ->
        increment_batch_number(existing_batch)
    end
  end

  defp increment_batch_number(batch_record) do
    new_count = batch_record.transaction_count + 1
    new_batch_number = String.pad_leading("#{new_count}", 6, "0")
    
    changeset = changeset(batch_record, %{
      batch_number: new_batch_number,
      transaction_count: new_count,
      last_used_at: DateTime.utc_now()
    })
    
    case DaProductApp.Repo.update(changeset) do
      {:ok, updated_batch} -> {:ok, updated_batch.batch_number}
      {:error, _changeset} -> {:error, "Failed to update batch number"}
    end
  end
end