defmodule Moar.Tuple do
# @related [test](/test/tuple_test.exs)
@moduledoc "Tuple-related functions."
@doc """
Converts a list of tuples to a single tuple whose first element is the first element of each tuple in
the list (which must all be the same), and whose second element is a list containing the second elements
of each tuple in the list.
Raises if the list contains tuples whose first elements are not all the same.
```elixir
iex> Moar.Tuple.from_list!([{:ok, :a}, {:ok, :b}])
{:ok, [:a, :b]}
iex> Moar.Tuple.from_list!([{:a, 1}, {:a, 2}, {:a, 3}])
{:a, [1, 2, 3]}
iex> Moar.Tuple.from_list!([{:a, 1}, {:b, 2}, {:a, 3}])
** (RuntimeError) Expected all items in the list to have have the same first element, but got: [:a, :b]
```
"""
@spec from_list!([any()]) :: {any(), [any()]}
def from_list!(list) do
{keys, values} = Enum.unzip(list)
case Enum.uniq(keys) do
[key] -> {key, values}
keys -> raise "Expected all items in the list to have have the same first element, but got: #{inspect(keys)}"
end
end
@doc """
Reduces a list of tuples to map where values are consolidated by the first element of each input tuple.
```elixir
iex> Moar.Tuple.reduce([{:ok, 1}, {:ok, 2}])
%{ok: [1, 2]}
iex> Moar.Tuple.reduce([{:ok, 1}, {:ok, 2}, {:error, 3}, {:ok, 4}])
%{ok: [1, 2, 4], error: [3]}
```
"""
@spec reduce([any()]) :: map()
def reduce(list) do
Enum.reduce(list, %{}, fn {k, v}, acc ->
Map.update(acc, k, [v], fn list -> [v | list] end)
end)
|> Map.new(fn {k, v} -> {k, Enum.reverse(v)} end)
end
end