Fibonacci n-step number sequences

# title: Fibonacci n-step number sequences
# source: https://rosettacode.org/wiki/Fibonacci_n-step_number_sequences
# category: Rosetta Code
# difficulty: Intro
# summary: Generate Tribonacci and Tetranacci sequences by summing the previous n terms.
# tags: popular, math, sequences, iteration
# vibe: 0.2

def trailing_sum(values, count)
  total = 0
  index = values.length - count

  while index < values.length
    total = total + values[index]
    index = index + 1
  end

  total
end

def n_step_sequence(seed, count)
  values = []
  index = 0

  while index < seed.length && values.length < count
    values = values.push(seed[index])
    index = index + 1
  end

  while values.length < count
    values = values.push(trailing_sum(values, seed.length))
  end

  values
end

def run
  {
    tribonacci: n_step_sequence([0, 0, 1], 12),
    tetranacci: n_step_sequence([0, 0, 0, 1], 12)
  }
end