require 'json'
require_relative 'alba/version'
require_relative 'alba/errors'
require_relative 'alba/resource'
require_relative 'alba/deprecation'

require_relative 'alba/railtie' if defined?(Rails::Railtie)

# Core module
module Alba
  class << self
    attr_reader :backend, :encoder

    # Getter for inflector, a module responsible for inflecting strings
    attr_reader :inflector

    # Set the backend, which actually serializes object into JSON
    #
    # @param backend [#to_sym, nil] the name of the backend
    #   Possible values are `oj`, `active_support`, `default`, `json` and nil
    # @return [Proc] the proc to encode object into JSON
    # @raise [Alba::UnsupportedBackend] if backend is not supported
    def backend=(backend)
      @backend = backend&.to_sym
      set_encoder_from_backend
    end

    # Set encoder, a Proc object that accepts an object and generates JSON from it
    # Set backend as `:custom` which indicates no preset encoder is used
    #
    # @param encoder [Proc]
    # @raise [ArgumentError] if given encoder is not a Proc or its arity is not one
    def encoder=(encoder)
      raise ArgumentError, 'Encoder must be a Proc accepting one argument' unless encoder.is_a?(Proc) && encoder.arity == 1

      @encoder = encoder
      @backend = :custom
    end

    # Serialize the object with inline definitions
    #
    # @param object [Object] the object to be serialized
    # @param root_key [Symbol, nil, true]
    # @param block [Block] resource block
    # @return [String] serialized JSON string
    # @raise [ArgumentError] if block is absent or `with` argument's type is wrong
    def serialize(object, root_key: nil, &block)
      klass = block ? resource_class(&block) : infer_resource_class(object.class.name)

      resource = klass.new(object)
      resource.serialize(root_key: root_key)
    end

    # Enable inference for key and resource name
    #
    # @param with [Symbol, Class, Module] inflector
    #   When it's a Symbol, it sets inflector with given name
    #   When it's a Class or a Module, it sets given object to inflector
    # @deprecated Use {#inflector=} instead
    def enable_inference!(with:)
      Alba::Deprecation.warn('Alba.enable_inference! is deprecated. Use `Alba.inflector=` instead.')
      @inflector = inflector_from(with)
      @inferring = true
    end

    # Disable inference for key and resource name
    #
    # @deprecated Use {#inflector=} instead
    def disable_inference!
      Alba::Deprecation.warn('Alba.disable_inference! is deprecated. Use `Alba.inflector = nil` instead.')
      @inferring = false
      @inflector = nil
    end

    # @deprecated Use {#inflector} instead
    # @return [Boolean] whether inference is enabled or not
    def inferring
      Alba::Deprecation.warn('Alba.inferring is deprecated. Use `Alba.inflector` instead.')
      @inferring
    end

    # Set an inflector
    #
    # @param inflector [Symbol, Class, Module] inflector
    #   When it's a Symbol, it accepts `:default`, `:active_support` or `:dry`
    #   When it's a Class or a Module, it should have some methods, see {Alba::DefaultInflector}
    def inflector=(inflector)
      @inflector = inflector_from(inflector)
    end

    # @param block [Block] resource body
    # @return [Class<Alba::Resource>] resource class
    def resource_class(&block)
      klass = Class.new
      klass.include(Alba::Resource)
      klass.class_eval(&block) if block
      klass
    end

    # @param name [String] a String Alba infers resource name with
    # @param nesting [String, nil] namespace Alba tries to find resource class in
    # @return [Class<Alba::Resource>] resource class
    def infer_resource_class(name, nesting: nil)
      raise Alba::Error, 'Inference is disabled so Alba cannot infer resource name. Set inflector before use.' unless Alba.inflector

      const_parent = nesting.nil? ? Object : Object.const_get(nesting)
      const_parent.const_get("#{inflector.classify(name)}Resource")
    end

    # Reset config variables
    # Useful for test cleanup
    def reset!
      @encoder = default_encoder
      @_on_error = :raise
      @_on_nil = nil
    end

    private

    def inflector_from(name_or_module)
      case name_or_module
      when nil then nil
      when :default, :active_support
        require_relative 'alba/default_inflector'
        Alba::DefaultInflector
      when :dry
        require 'dry/inflector'
        Dry::Inflector.new
      else
        validate_inflector(name_or_module)
      end
    end

    def set_encoder_from_backend
      @encoder = case @backend
                 when :oj, :oj_strict then try_oj
                 when :oj_rails then try_oj(mode: :rails)
                 when :oj_default then try_oj(mode: :default)
                 when :active_support then try_active_support
                 when nil, :default, :json then default_encoder
                 else
                   raise Alba::UnsupportedBackend, "Unsupported backend, #{backend}"
                 end
    end

    def try_oj(mode: :strict)
      require 'oj'
      case mode
      when :default
        ->(hash) { Oj.dump(hash) }
      else
        ->(hash) { Oj.dump(hash, mode: mode) }
      end
    rescue LoadError
      Kernel.warn '`Oj` is not installed, falling back to default JSON encoder.'
      default_encoder
    end

    def try_active_support
      require 'active_support/json'
      ->(hash) { ActiveSupport::JSON.encode(hash) }
    rescue LoadError
      Kernel.warn '`ActiveSupport` is not installed, falling back to default JSON encoder.'
      default_encoder
    end

    def default_encoder
      lambda do |hash|
        JSON.generate(hash)
      end
    end

    def validate_inflector(inflector)
      unless %i[camelize camelize_lower dasherize classify].all? { |m| inflector.respond_to?(m) }
        raise Alba::Error, "Given inflector, #{inflector.inspect} is not valid. It must implement `camelize`, `camelize_lower`, `dasherize` and `classify`."
      end

      inflector
    end
  end

  reset!
end