defmodule Firebird.WasmModules.Algorithms do
  Module.register_attribute(__MODULE__, :wasm, accumulate: true)

  @moduledoc """
  Common algorithms compiled to WebAssembly.

  Demonstrates the Elixir-to-WASM compilation for algorithmic workloads.
  All functions use only the compilable subset of Elixir.
  """

  @wasm true
  def is_prime(n) do
    if n <= 1 do
      0
    else
      if n <= 3 do
        1
      else
        if rem(n, 2) == 0 do
          0
        else
          is_prime_check(n, 3)
        end
      end
    end
  end

  @wasm true
  def is_prime_check(n, i) do
    if i * i > n do
      1
    else
      if rem(n, i) == 0 do
        0
      else
        is_prime_check(n, i + 2)
      end
    end
  end

  @wasm true
  def count_primes(0), do: 0
  def count_primes(n), do: is_prime(n) + count_primes(n - 1)

  @wasm true
  def ackermann(0, n), do: n + 1
  def ackermann(m, 0), do: ackermann(m - 1, 1)
  def ackermann(m, n), do: ackermann(m - 1, ackermann(m, n - 1))

  @wasm true
  def binary_search_sqrt(n) do
    binary_search_sqrt_helper(n, 0, n)
  end

  @wasm true
  def binary_search_sqrt_helper(n, lo, hi) do
    if lo > hi do
      lo - 1
    else
      mid = div(lo + hi, 2)

      if mid * mid == n do
        mid
      else
        if mid * mid < n do
          binary_search_sqrt_helper(n, mid + 1, hi)
        else
          binary_search_sqrt_helper(n, lo, mid - 1)
        end
      end
    end
  end

  @wasm true
  def tribonacci(0), do: 0
  def tribonacci(1), do: 1
  def tribonacci(2), do: 1
  def tribonacci(n), do: tribonacci(n - 1) + tribonacci(n - 2) + tribonacci(n - 3)

  @wasm true
  def digital_root(n) do
    if n < 10 do
      n
    else
      digital_root(div(n, 10) + rem(n, 10))
    end
  end
end