oak

# Copyright 2024 Clivern. All rights reserved.
# Use of this source code is governed by the MIT
# license that can be found in the LICENSE file.

defmodule Oak.Metric.Counter do
  @moduledoc """
  Represents a Counter metric.

  A Counter is a cumulative metric that represents a single monotonically
  increasing counter whose value can only increase or be reset to zero.
  """

  defstruct [:name, :help, :labels, :value]

  @doc """
  Creates a new Counter metric.
  """
  def new(name, help, labels \\ %{}) do
    %__MODULE__{
      name: name,
      help: help,
      labels: labels,
      value: 0
    }
  end

  @doc """
  Increments the counter by the given amount.
  """
  def inc(counter, amount \\ 1) when is_integer(amount) and amount >= 0 do
    %{counter | value: counter.value + amount}
  end

  @doc """
  Returns the current value of the counter.
  """
  def value(counter), do: counter.value

  @doc """
  Resets the counter to zero.
  """
  def reset(counter) do
    %{counter | value: 0}
  end

  @doc """
  Returns a string representation of the counter in Prometheus exposition format.
  """
  def to_string(counter) do
    labels_str =
      counter.labels
      |> Enum.map(fn {key, value} -> "#{key}=\"#{value}\"" end)
      |> Enum.join(",")

    labels_formatted = if labels_str == "", do: "", else: "{#{labels_str}}"

    "#{counter.name}#{labels_formatted} #{counter.value}"
  end
end