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

# Core module
module Alba
  # Base class for Errors
  class Error < StandardError; end

  # Error class for backend which is not supported
  class UnsupportedBackend < Error; end

  # Error class for type which is not supported
  class UnsupportedType < Error; end

  class << self
    attr_reader :backend, :encoder, :inferring, :_on_error, :transforming_root_key

    # Accessor for inflector, a module responsible for incflecting strings
    attr_accessor :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 key [Symbol, nil, true] DEPRECATED, use root_key instead
    # @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, key: nil, root_key: nil, &block)
      warn '`key` option to `serialize` method is deprecated, use `root_key` instead.' if key
      klass = block ? resource_class(&block) : infer_resource_class(object.class.name)

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

    # Enable inference for key and resource name
    def enable_inference!
      begin
        require 'active_support/inflector'
      rescue LoadError
        raise ::Alba::Error, 'To enable inference, please install `ActiveSupport` gem.'
      end
      @inferring = true
    end

    # Disable inference for key and resource name
    def disable_inference!
      @inferring = false
    end

    # Set error handler
    #
    # @param [Symbol] handler
    # @param [Block]
    # @raise [ArgumentError] if both handler and block params exist
    # @raise [ArgumentError] if both handler and block params don't exist
    # @return [void]
    def on_error(handler = nil, &block)
      raise ArgumentError, 'You cannot specify error handler with both Symbol and block' if handler && block
      raise ArgumentError, 'You must specify error handler with either Symbol or block' unless handler || block

      @_on_error = handler || block
    end

    # Enable root key transformation
    def enable_root_key_transformation!
      @transforming_root_key = true
    end

    # Disable root key transformation
    def disable_root_key_transformation!
      @transforming_root_key = false
    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)
      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)
      enable_inference!
      const_parent = nesting.nil? ? Object : Object.const_get(nesting)
      const_parent.const_get("#{ActiveSupport::Inflector.classify(name)}Resource")
    end

    private

    def set_encoder_from_backend
      @encoder = case @backend
                 when :oj, :oj_strict then try_oj
                 when :oj_rails then try_oj(mode: :rails)
                 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'
      ->(hash) { Oj.dump(hash, mode: mode) }
    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.dump(hash)
      end
    end
  end

  @encoder = default_encoder
  @_on_error = :raise
  @transforming_root_key = false # TODO: This will be true since 2.0
end