Vela is a tiny library providing easy management of validated cached state with some history.

Including use Vela in your module would turn the module into struct, setting field accordingly to the specification, passed as a parameter.

Vela allows the following configurable parameters per field:

• limit — length of the series to keep (default: 5)
• compare_by — comparator extraction function to extract the value, to be used for comparison, from the underlying terms (default: & &1)
• comparator — the function that accepts a series name and two values and returns the greater one to be used in Vela.δ/1 (default: &</2)
• threshold — if specified, the inserted value is checked to fit in δ ± threshold; whether it does not, it goes to errors (float() | nil, default: nil)
• validator — the function to be used to invalidate the accumulated values (default: fn _ -> true end)
• sorter — the function to be used to sort values within one serie, if none is given, it sorts in the natural order, FIFO, newest is the one to pop
• corrector — the function to be used to correct the values rejected by validator; the function should return {:ok, corrected_value} to enforce insertion into Vela, or :error if the value cannot be corrected and should be nevertheless rejected
• errors — number of errors to keep (default: 5)

Also, Vela accepts :__meta__ keyword parameter for the cases when the consumer needs the very custom meta to be passed to the struct.

Vela implements Access behaviour.

Usage

defmodule Vela.Test do
  use Vela,
    series1: [limit: 3, errors: 1], # no validation
    series2: [limit: 2, validator: Vela.Test]
    series3: [
          compare_by: &Vela.Test.comparator/1,
          validator: &Vela.Test.validator/2
    ]

  @behaviour Vela.Validator

  @impl Vela.Validator
  def valid?(_serie, value), do: value > 0

  @spec comparator(%{created_at :: DateTime.t()}) :: DateTime.t()
  def comparator(%{created_at: created_at}),
    do: created_at

  @spec validator(value :: t()) :: boolean()
  def validator(value),
    do: is_integer(value) and value > 300
end

In the example above, before any structure update attempt (via Access,) this valid?/2 function would be called.

If it returns true, the value gets inserted / updated, and the series behind is truncated if needed. It it returns false, the state is not updated, and the value is put into the map under __errors__ key of the struct. The length of errors is also configurable via errors: keyword parameter.