require 'active_support/concern'
require 'active_support/descendants_tracker'
require 'active_support/core_ext/array/wrap'
require 'active_support/core_ext/class/attribute'
require 'active_support/core_ext/kernel/reporting'
require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/object/inclusion'

module ActiveSupport
  # \Callbacks are code hooks that are run at key points in an object's lifecycle.
  # The typical use case is to have a base class define a set of callbacks relevant
  # to the other functionality it supplies, so that subclasses can install callbacks
  # that enhance or modify the base functionality without needing to override
  # or redefine methods of the base class.
  #
  # Mixing in this module allows you to define the events in the object's lifecycle
  # that will support callbacks (via +ClassMethods.define_callbacks+), set the instance
  # methods, procs, or callback objects to be called (via +ClassMethods.set_callback+),
  # and run the installed callbacks at the appropriate times (via +run_callbacks+).
  #
  # Three kinds of callbacks are supported: before callbacks, run before a certain event;
  # after callbacks, run after the event; and around callbacks, blocks that surround the
  # event, triggering it when they yield. Callback code can be contained in instance
  # methods, procs or lambdas, or callback objects that respond to certain predetermined
  # methods. See +ClassMethods.set_callback+ for details.
  #
  # ==== Example
  #
  #   class Record
  #     include ActiveSupport::Callbacks
  #     define_callbacks :save
  #
  #     def save
  #       run_callbacks :save do
  #         puts "- save"
  #       end
  #     end
  #   end
  #
  #   class PersonRecord < Record
  #     set_callback :save, :before, :saving_message
  #     def saving_message
  #       puts "saving..."
  #     end
  #
  #     set_callback :save, :after do |object|
  #       puts "saved"
  #     end
  #   end
  #
  #   person = PersonRecord.new
  #   person.save
  #
  # Output:
  #   saving...
  #   - save
  #   saved
  #
  module Callbacks
    extend Concern

    included do
      extend ActiveSupport::DescendantsTracker
    end

    # Runs the callbacks for the given event.
    #
    # Calls the before and around callbacks in the order they were set, yields
    # the block (if given one), and then runs the after callbacks in reverse order.
    # Optionally accepts a key, which will be used to compile an optimized callback
    # method for each key. See +ClassMethods.define_callbacks+ for more information.
    #
    # If the callback chain was halted, returns +false+. Otherwise returns the result
    # of the block, or +true+ if no block is given.
    #
    #   run_callbacks :save do
    #     save
    #   end
    #
    def run_callbacks(kind, *args, &block)
      send("_run_#{kind}_callbacks", *args, &block)
    end

    private

    # A hook invoked everytime a before callback is halted.
    # This can be overriden in AS::Callback implementors in order
    # to provide better debugging/logging.
    def halted_callback_hook(filter)
    end

    class Callback #:nodoc:#
      @@_callback_sequence = 0

      attr_accessor :chain, :filter, :kind, :options, :per_key, :klass, :raw_filter

      def initialize(chain, filter, kind, options, klass)
        @chain, @kind, @klass = chain, kind, klass
        normalize_options!(options)

        @per_key              = options.delete(:per_key)
        @raw_filter, @options = filter, options
        @filter               = _compile_filter(filter)
        @compiled_options     = _compile_options(options)
        @callback_id          = next_id

        _compile_per_key_options
      end

      def clone(chain, klass)
        obj                  = super()
        obj.chain            = chain
        obj.klass            = klass
        obj.per_key          = @per_key.dup
        obj.options          = @options.dup
        obj.per_key[:if]     = @per_key[:if].dup
        obj.per_key[:unless] = @per_key[:unless].dup
        obj.options[:if]     = @options[:if].dup
        obj.options[:unless] = @options[:unless].dup
        obj
      end

      def normalize_options!(options)
        options[:if] = Array.wrap(options[:if])
        options[:unless] = Array.wrap(options[:unless])

        options[:per_key] ||= {}
        options[:per_key][:if] = Array.wrap(options[:per_key][:if])
        options[:per_key][:unless] = Array.wrap(options[:per_key][:unless])
      end

      def name
        chain.name
      end

      def next_id
        @@_callback_sequence += 1
      end

      def matches?(_kind, _filter)
        @kind == _kind && @filter == _filter
      end

      def _update_filter(filter_options, new_options)
        filter_options[:if].push(new_options[:unless]) if new_options.key?(:unless)
        filter_options[:unless].push(new_options[:if]) if new_options.key?(:if)
      end

      def recompile!(_options, _per_key)
        _update_filter(self.options, _options)
        _update_filter(self.per_key, _per_key)

        @callback_id      = next_id
        @filter           = _compile_filter(@raw_filter)
        @compiled_options = _compile_options(@options)
                            _compile_per_key_options
      end

      def _compile_per_key_options
        key_options  = _compile_options(@per_key)

        @klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
          def _one_time_conditions_valid_#{@callback_id}?
            true if #{key_options}
          end
        RUBY_EVAL
      end

      # This will supply contents for before and around filters, and no
      # contents for after filters (for the forward pass).
      def start(key=nil, object=nil)
        return if key && !object.send("_one_time_conditions_valid_#{@callback_id}?")

        # options[0] is the compiled form of supplied conditions
        # options[1] is the "end" for the conditional
        #
        case @kind
        when :before
          # if condition    # before_save :filter_name, :if => :condition
          #   filter_name
          # end
          <<-RUBY_EVAL
            if !halted && #{@compiled_options}
              # This double assignment is to prevent warnings in 1.9.3 as
              # the `result` variable is not always used except if the
              # terminator code refers to it.
              result = result = #{@filter}
              halted = (#{chain.config[:terminator]})
              if halted
                halted_callback_hook(#{@raw_filter.inspect.inspect})
              end
            end
          RUBY_EVAL
        when :around
          # Compile around filters with conditions into proxy methods
          # that contain the conditions.
          #
          # For `around_save :filter_name, :if => :condition':
          #
          # def _conditional_callback_save_17
          #   if condition
          #     filter_name do
          #       yield self
          #     end
          #   else
          #     yield self
          #   end
          # end
          #
          name = "_conditional_callback_#{@kind}_#{next_id}"
          @klass.class_eval <<-RUBY_EVAL,  __FILE__, __LINE__ + 1
             def #{name}(halted)
              if #{@compiled_options} && !halted
                #{@filter} do
                  yield self
                end
              else
                yield self
              end
            end
          RUBY_EVAL
          "#{name}(halted) do"
        end
      end

      # This will supply contents for around and after filters, but not
      # before filters (for the backward pass).
      def end(key=nil, object=nil)
        return if key && !object.send("_one_time_conditions_valid_#{@callback_id}?")

        case @kind
        when :after
          # after_save :filter_name, :if => :condition
          <<-RUBY_EVAL
          if #{@compiled_options}
            #{@filter}
          end
          RUBY_EVAL
        when :around
          <<-RUBY_EVAL
            value
          end
          RUBY_EVAL
        end
      end

      private

      # Options support the same options as filters themselves (and support
      # symbols, string, procs, and objects), so compile a conditional
      # expression based on the options
      def _compile_options(options)
        conditions = ["true"]

        unless options[:if].empty?
          conditions << Array.wrap(_compile_filter(options[:if]))
        end

        unless options[:unless].empty?
          conditions << Array.wrap(_compile_filter(options[:unless])).map {|f| "!#{f}"}
        end

        conditions.flatten.join(" && ")
      end

      # Filters support:
      #
      #   Arrays::  Used in conditions. This is used to specify
      #             multiple conditions. Used internally to
      #             merge conditions from skip_* filters
      #   Symbols:: A method to call
      #   Strings:: Some content to evaluate
      #   Procs::   A proc to call with the object
      #   Objects:: An object with a before_foo method on it to call
      #
      # All of these objects are compiled into methods and handled
      # the same after this point:
      #
      #   Arrays::  Merged together into a single filter
      #   Symbols:: Already methods
      #   Strings:: class_eval'ed into methods
      #   Procs::   define_method'ed into methods
      #   Objects::
      #     a method is created that calls the before_foo method
      #     on the object.
      #
      def _compile_filter(filter)
        method_name = "_callback_#{@kind}_#{next_id}"
        case filter
        when Array
          filter.map {|f| _compile_filter(f)}
        when Symbol
          filter
        when String
          "(#{filter})"
        when Proc
          @klass.send(:define_method, method_name, &filter)
          return method_name if filter.arity <= 0

          method_name << (filter.arity == 1 ? "(self)" : " self, Proc.new ")
        else
          @klass.send(:define_method, "#{method_name}_object") { filter }

          _normalize_legacy_filter(kind, filter)
          scopes = Array.wrap(chain.config[:scope])
          method_to_call = scopes.map{ |s| s.is_a?(Symbol) ? send(s) : s }.join("_")

          @klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
            def #{method_name}(&blk)
              #{method_name}_object.send(:#{method_to_call}, self, &blk)
            end
          RUBY_EVAL

          method_name
        end
      end

      def _normalize_legacy_filter(kind, filter)
        if !filter.respond_to?(kind) && filter.respond_to?(:filter)
          filter.singleton_class.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
            def #{kind}(context, &block) filter(context, &block) end
          RUBY_EVAL
        elsif filter.respond_to?(:before) && filter.respond_to?(:after) && kind == :around
          def filter.around(context)
            should_continue = before(context)
            yield if should_continue
            after(context)
          end
        end
      end
    end

    # An Array with a compile method
    class CallbackChain < Array #:nodoc:#
      attr_reader :name, :config

      def initialize(name, config)
        @name = name
        @config = {
          :terminator => "false",
          :rescuable => false,
          :scope => [ :kind ]
        }.merge(config)
      end