defmodule Growth do
  @moduledoc """
  Follow up child growth from 0 to 19 years, calculating z-scores for the following measurements:

  * weight between ages 0 and 10 years
  * height between ages 0 and 19 years
  * body mass index (bmi) between ages 0 and 19 years
  * head circumference between ages 0 and 5 years
  * arm circumference between ages 3 months and 5 years
  * subscapular skinfold between ages 3 months and 5 years
  * triceps skinfold between ages 3 months and 5 years
  """

  alias __MODULE__.Calc.Age
  alias __MODULE__.Calc.BMI

  @type gender :: :male | :female

  @type measure :: number() | nil

  @type opts :: [
          date_of_measurement: Date.t(),
          weight: measure(),
          height: measure(),
          arm_circumference: measure(),
          head_circumference: measure(),
          subscapular_skinfold: measure(),
          triceps_skinfold: measure()
        ]

  @type t :: %__MODULE__{
          name: String.t(),
          gender: gender(),
          date_of_birth: Date.t(),
          date_of_measurement: Date.t(),
          age_in_days: pos_integer(),
          age_in_weeks: pos_integer(),
          age_in_months: pos_integer(),
          weight: measure(),
          height: measure(),
          arm_circumference: measure(),
          head_circumference: measure(),
          subscapular_skinfold: measure(),
          triceps_skinfold: measure(),
          bmi: measure(),
          results: list()
        }

  @enforce_keys [:name, :gender, :date_of_birth]
  defstruct [
    :name,
    :gender,
    :date_of_birth,
    :date_of_measurement,
    :age_in_days,
    :age_in_weeks,
    :age_in_months,
    :weight,
    :height,
    :arm_circumference,
    :head_circumference,
    :subscapular_skinfold,
    :triceps_skinfold,
    :bmi,
    :results
  ]

  @valid_measures [
    :date_of_measurement,
    :weight,
    :height,
    :arm_circumference,
    :head_circumference,
    :subscapular_skinfold,
    :triceps_skinfold
  ]

  @doc """
  Create a new growth measurement for a children with name, gender, date of birth, and the following optional arguments:

  * `:date_of_measurement`: date when the measures were collected, defaults to today.
  * `:weight`: weight in kilograms, defaults to `nil`.
  * `:height`: height in centimeters, defaults to `nil`.
  * `:arm_circumference`: arm circumference in centimeters, defaults to `nil`.
  * `:head_circumference`: head circumference in centimeters, defaults to `nil`.
  * `:subscapular_skinfold`: subscapular skinfold in milimeters, defaults to `nil`.
  * `:triceps_skinfold`: triceps skinfold in milimeters, defaults to `nil`.

  """
  @spec new(String.t(), gender(), Date.t(), opts()) :: t()
  def new(name, gender, date_of_birth, opts \\ []) do
    default_opts()
    |> Enum.reduce(
      %__MODULE__{
        name: name,
        gender: gender,
        date_of_birth: date_of_birth
      },
      fn {key, default_value}, measurement ->
        opts
        |> Keyword.get(key, default_value)
        |> then(&Map.put(measurement, key, &1))
      end
    )
    |> with_age_in_days()
    |> with_age_in_weeks()
    |> with_age_in_months()
    |> with_bmi()
  end

  for precision <- [:day, :week, :month] do
    @doc """
    Add age with given precision in growth measurement.
    """
    @spec unquote(:"with_age_in_#{precision}s")(t()) :: t()

    def unquote(:"with_age_in_#{precision}s")(
          %__MODULE__{date_of_birth: date_of_birth, date_of_measurement: date_of_measurement} =
            growth
        )
        when not is_nil(date_of_birth) and not is_nil(date_of_measurement) do
      age = Age.calculate(unquote(precision), date_of_birth, date_of_measurement)
      Map.put(growth, unquote(:"age_in_#{precision}s"), age)
    end

    def unquote(:"with_age_in_#{precision}s")(%__MODULE__{date_of_birth: date_of_birth} = growth)
        when not is_nil(date_of_birth) do
      unquote(:"with_age_in_#{precision}s")(%{growth | date_of_measurement: Date.utc_today()})
    end

    def unquote(:"with_age_in_#{precision}s")(growth) do
      growth
    end
  end

  def with_bmi(%__MODULE__{weight: weight, height: height} = growth)
      when is_number(weight) and is_number(height) do
    %{growth | bmi: BMI.calculate(:metric, weight, height)}
  end

  def with_bmi(growth) do
    growth
  end

  defp default_opts do
    Enum.map(@valid_measures, fn
      :date_of_measurement = key ->
        {key, Date.utc_today()}

      key ->
        {key, nil}
    end)
  end
end