test_input = [ 
  199,
  200,
  208,
  210,
  200,
  207,
  240,
  269,
  260,
  263
]

# part 1 solution
solve = fn input ->
  input
  |> Stream.chunk_every(2, 1, :discard)
  |> Stream.map(fn [a,b] -> b - a end)
  |> Stream.filter(fn a -> a > 0 end)
  |> Enum.count()
end

# transform problem for part 2
window_sum = fn input ->
  input
    |> Stream.chunk_every(3, 1, :discard)
    |> Stream.map(&Enum.sum/1)
end

# verify solution for test input
if not(solve.(test_input) == 7) or not(solve.(test_input |> window_sum.()) == 5) do
  raise "solution doesn't solve test input"
end

# parse input from text data to solve
parse = fn input -> 
  input 
  |> Stream.map(&String.trim/1)
  |> Stream.reject(&(&1 == ""))
  |> Stream.map(&String.to_integer/1)
end


File.stream!("./day1.txt")
|> parse.()
|> then(fn i ->
    p1 = i |> solve.()
    p2 = i |> window_sum.() |> solve.()
    "p1: #{p1}\tp2: #{p2}"
  end)
|> IO.puts()