# frozen_string_literal: true

require 'yaml'

module Opendax
  # Loads config/app.yml and deep-merges an environment overlay when present.
  #
  # Overlay resolution (first match wins):
  #   1. OPENDAX_ENV=local|staging|production → config/app.{env}.yml
  #   2. If OPENDAX_ENV unset and config/app.local.yml exists → use local overlay
  #
  # Never commit real secrets to config/app.yml — use app.local.yml or app.production.yml.
  module ConfigLoader
    BASE_PATH = 'config/app.yml'

    module_function

    def load
      base = load_yaml_hash!(BASE_PATH, 'base config')
      overlay_path = resolve_overlay_path
      return base unless overlay_path && File.exist?(overlay_path)

      overlay = load_yaml_hash!(overlay_path, 'overlay config')
      deep_merge(base, overlay)
    end

    def load_yaml_hash!(path, label)
      data = YAML.load_file(path)
      return data if data.is_a?(Hash)

      raise TypeError,
            "#{label} #{path} must be a YAML mapping (Hash), got #{data.class}. " \
            'Check syntax — quote values that contain colons (e.g. database passwords).'
    end

    def resolve_overlay_path
      env = ENV['OPENDAX_ENV'].to_s.strip
      if env.empty?
        return 'config/app.local.yml' if File.exist?('config/app.local.yml')

        return nil
      end

      "config/app.#{env}.yml"
    end

    def active_overlay
      path = resolve_overlay_path
      path if path && File.exist?(path)
    end

    def deep_merge(base, overlay)
      unless base.is_a?(Hash) && overlay.is_a?(Hash)
        raise TypeError,
              "deep_merge expects Hash + Hash, got #{base.class} + #{overlay.class}"
      end

      base.merge(overlay) do |key, old_val, new_val|
        if old_val.is_a?(Hash) && new_val.is_a?(Hash)
          deep_merge(old_val, new_val)
        elsif old_val.is_a?(Hash) && !new_val.is_a?(Hash)
          raise TypeError,
                "Config type mismatch at #{key}: base has Hash but overlay has " \
                "#{new_val.class}. Quote scalar values in app.staging.yml (passwords with ':' need quotes)."
        else
          new_val
        end
      end
    end
  end
end