defmodule StrainTest do
  use ExUnit.Case

  defp is_odd?(n), do: rem(n, 2) == 1
  defp is_even?(n), do: rem(n, 2) == 0

  describe "keep" do
    # @tag :pending
    test "on empty list returns empty list" do
      assert Strain.keep([], fn _ -> true end) == []
    end

    # @tag :pending
    test "keep everything" do
      assert Strain.keep([1, 3, 5], fn _ -> true end) == [1, 3, 5]
    end

    # @tag :pending
    test "keep nothing" do
      assert Strain.keep([1, 3, 5], fn _ -> false end) == []
    end

    # @tag :pending
    test "keep first and last" do
      assert Strain.keep([1, 2, 3], &is_odd?/1) == [1, 3]
    end

    # @tag :pending
    test "keep neither first nor last" do
      assert Strain.keep([1, 2, 3], &is_even?/1) == [2]
    end

    # @tag :pending
    test "keep strings" do
      words = ~w(apple zebra banana zombies cherimoya zelot)
      assert Strain.keep(words, &String.starts_with?(&1, "z")) == ~w(zebra zombies zelot)
    end

    # @tag :pending
    test "keep lists" do
      rows = [
        [1, 2, 3],
        [5, 5, 5],
        [5, 1, 2],
        [2, 1, 2],
        [1, 5, 2],
        [2, 2, 1],
        [1, 2, 5]
      ]

      assert Strain.keep(rows, fn row -> 5 in row end) == [
               [5, 5, 5],
               [5, 1, 2],
               [1, 5, 2],
               [1, 2, 5]
             ]
    end
  end

  describe "discard" do
    # @tag :pending
    test "on empty list returns empty list" do
      assert Strain.discard([], fn _ -> true end) == []
    end

    # @tag :pending
    test "discard everything" do
      assert Strain.discard([1, 3, 5], fn _ -> true end) == []
    end

    # @tag :pending
    test "discard nothing" do
      assert Strain.discard([1, 3, 5], fn _ -> false end) == [1, 3, 5]
    end

    # @tag :pending
    test "discard first and last" do
      assert Strain.discard([1, 2, 3], &is_odd?/1) == [2]
    end

    # @tag :pending
    test "discard neither first nor last" do
      assert Strain.discard([1, 2, 3], &is_even?/1) == [1, 3]
    end

    # @tag :pending
    test "discard strings" do
      words = ~w(apple zebra banana zombies cherimoya zelot)
      assert Strain.discard(words, &String.starts_with?(&1, "z")) == ~w(apple banana cherimoya)
    end

    # @tag :pending
    test "discard arrays" do
      rows = [
        [1, 2, 3],
        [5, 5, 5],
        [5, 1, 2],
        [2, 1, 2],
        [1, 5, 2],
        [2, 2, 1],
        [1, 2, 5]
      ]

      assert Strain.discard(rows, fn row -> 5 in row end) == [[1, 2, 3], [2, 1, 2], [2, 2, 1]]
    end
  end
end