obstools/healthcheck-endpoint

# frozen_string_literal: true

module HealthcheckEndpoint
  class Resolver
    require 'rack'
    require 'securerandom'
    require 'json'

    PROBE_ENDPOINTS = %i[endpoint_startup endpoint_liveness endpoint_readiness].freeze
    CONTENT_TYPE = { 'Content-Type' => 'application/json' }.freeze
    ROOT_NAMESPACE = '/'

    def self.call(rack_env)
      new(rack_env).call
    end

    def initialize(rack_env)
      @request = ::Rack::Request.new(rack_env)
    end

    def call
      return unless probe_name

      [response_status, HealthcheckEndpoint::Resolver::CONTENT_TYPE, [response_jsonapi]]
    end

    private

    attr_reader :request

    def configuration
      HealthcheckEndpoint.configuration
    end

    def root_namespace
      @root_namespace ||= configuration.endpoints_namespace
    end

    def root_namespace?
      root_namespace.eql?(HealthcheckEndpoint::Resolver::ROOT_NAMESPACE)
    end

    HealthcheckEndpoint::Resolver::PROBE_ENDPOINTS.each do |method|
      define_method(method) do
        target_endpoint = configuration.public_send(method)
        root_namespace? ? target_endpoint : "#{root_namespace}#{target_endpoint}"
      end
    end

    def probe_name
      @probe_name ||=
        case request.path
        when endpoint_startup then :startup
        when endpoint_liveness then :liveness
        when endpoint_readiness then :readiness
        end
    end

    def probe_result
      @probe_result ||=
        configuration.public_send(:"services_#{probe_name}").each_with_object({}) do |service_name, response|
          response[service_name] = configuration.services[service_name].call
        end
    end

    def response_status
      configuration.public_send(
        probe_result.values.all? ? :"endpoint_#{probe_name}_status_success" : :"endpoint_#{probe_name}_status_failure"
      )
    end

    def response_jsonapi
      {
        data: {
          id: ::SecureRandom.uuid,
          type: "application-#{probe_name}-healthcheck", # TODO: it would be great to be able to configure this
          attributes: probe_result
        }
      }.to_json
    end
  end
end