defmodule Microwaveprop.FormatPropertyTest do
  use ExUnit.Case, async: true
  use ExUnitProperties

  alias Microwaveprop.Format

  # Any finite non-negative number is legitimate input for distance_km/1.
  # StreamData floats default to the full representable range — we keep
  # that but reject negatives since negative distances are meaningless
  # (the algorithm callers always pass an already-absolute km value).
  defp non_negative_number do
    one_of([
      integer(0..1_000_000_000),
      map(float(min: 0.0), fn f -> f end),
      map(integer(0..1_000_000), &(&1 * 1.0))
    ])
  end

  describe "distance_km/1" do
    property "returns a binary for nil" do
      # Not really a property, just pinned for discoverability alongside
      # the numeric properties.
      assert Format.distance_km(nil) == "—"
    end

    property "always returns a non-empty binary for any non-negative number" do
      check all(n <- non_negative_number()) do
        result = Format.distance_km(n)
        assert is_binary(result)
        assert result != ""
      end
    end

    property "output contains both `mi` and `km` units" do
      check all(n <- non_negative_number()) do
        result = Format.distance_km(n)
        assert result =~ "mi"
        assert result =~ "km"
      end
    end

    property "accepts Decimal input without crashing" do
      check all(n <- integer(0..10_000)) do
        decimal = Decimal.new(n)
        assert is_binary(Format.distance_km(decimal))
      end
    end

    property "accepts negative distances without crashing" do
      # Not a valid input at the call site, but we don't want arbitrary
      # numeric data (e.g. a sign slip in a caller) to crash the view.
      check all(n <- float(min: -1.0e6, max: -0.01)) do
        assert is_binary(Format.distance_km(n))
      end
    end
  end
end