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module RSpec
  module Core
    # Provides `before`, `after` and `around` hooks as a means of
    # supporting common setup and teardown. This module is extended
    # onto {ExampleGroup}, making the methods available from any `describe`
    # or `context` block and included in {Configuration}, making them
    # available off of the configuration object to define global setup
    # or teardown logic.
    module Hooks
      # @api public
      #
      # @overload before(&block)
      # @overload before(scope, &block)
      # @param scope [Symbol] `:example`, `:context`, or `:suite` (defaults to `:example`)
      # @overload before(scope, conditions, &block)
      # @param scope [Symbol] `:example`, `:context`, or `:suite` (defaults to `:example`)
      # @param conditions [Hash]
      # constrains this hook to examples matching these conditions e.g.
      # `before(:example, :ui => true) { ... }` will only run with examples or
      # groups declared with `:ui => true`.
      # @overload before(conditions, &block)
      # @param conditions [Hash]
      # constrains this hook to examples matching these conditions e.g.
      # `before(:example, :ui => true) { ... }` will only run with examples or
      # groups declared with `:ui => true`.
      #
      # @see #after
      # @see #around
      # @see ExampleGroup
      # @see SharedContext
      # @see SharedExampleGroup
      # @see Configuration
      #
      # Declare a block of code to be run before each example (using `:example`)
      # or once before any example (using `:context`). These are usually declared
      # directly in the {ExampleGroup} to which they apply, but they can also
      # be shared across multiple groups.
      #
      # You can also use `before(:suite)` to run a block of code before any
      # example groups are run. This should be declared in {RSpec.configure}
      #
      # Instance variables declared in `before(:example)` or `before(:context)` are
      # accessible within each example.
      #
      # ### Order
      #
      # `before` hooks are stored in three scopes, which are run in order:
      # `:suite`, `:context`, and `:example`. They can also be declared in several
      # different places: `RSpec.configure`, a parent group, the current group.
      # They are run in the following order:
      #
      # before(:suite) # declared in RSpec.configure
      # before(:context) # declared in RSpec.configure
      # before(:context) # declared in a parent group
      # before(:context) # declared in the current group
      # before(:example) # declared in RSpec.configure
      # before(:example) # declared in a parent group
      # before(:example) # declared in the current group
      #
      # If more than one `before` is declared within any one scope, they are run
      # in the order in which they are declared.
      #
      # ### Conditions
      #
      # When you add a conditions hash to `before(:example)` or `before(:context)`,
      # RSpec will only apply that hook to groups or examples that match the
      # conditions. e.g.
      #
      # RSpec.configure do |config|
      # config.before(:example, :authorized => true) do
      # log_in_as :authorized_user
      # end
      # end
      #
      # describe Something, :authorized => true do
      # # the before hook will run in before each example in this group
      # end
      #
      # describe SomethingElse do
      # it "does something", :authorized => true do
      # # the before hook will run before this example
      # end
      #
      # it "does something else" do
      # # the hook will not run before this example
      # end
      # end
      #
      # ### Warning: `before(:suite, :with => :conditions)`
      #
      # The conditions hash is used to match against specific examples. Since
      # `before(:suite)` is not run in relation to any specific example or
      # group, conditions passed along with `:suite` are effectively ignored.
      #
      # ### Exceptions
      #
      # When an exception is raised in a `before` block, RSpec skips any
      # subsequent `before` blocks and the example, but runs all of the
      # `after(:example)` and `after(:context)` hooks.
      #
      # ### Warning: implicit before blocks
      #
      # `before` hooks can also be declared in shared contexts which get
      # included implicitly either by you or by extension libraries. Since
      # RSpec runs these in the order in which they are declared within each
      # scope, load order matters, and can lead to confusing results when one
      # before block depends on state that is prepared in another before block
      # that gets run later.
      #
      # ### Warning: `before(:context)`
      #
      # It is very tempting to use `before(:context)` to speed things up, but we
      # recommend that you avoid this as there are a number of gotchas, as well
      # as things that simply don't work.
      #
      # #### context
      #
      # `before(:context)` is run in an example that is generated to provide group
      # context for the block.
      #
      # #### instance variables
      #
      # Instance variables declared in `before(:context)` are shared across all the
      # examples in the group. This means that each example can change the
      # state of a shared object, resulting in an ordering dependency that can
      # make it difficult to reason about failures.
      #
      # #### unsupported rspec constructs
      #
      # RSpec has several constructs that reset state between each example
      # automatically. These are not intended for use from within `before(:context)`:
      #
      # * `let` declarations
      # * `subject` declarations
      # * Any mocking, stubbing or test double declaration
      #
      # ### other frameworks
      #
      # Mock object frameworks and database transaction managers (like
      # ActiveRecord) are typically designed around the idea of setting up
      # before an example, running that one example, and then tearing down.
      # This means that mocks and stubs can (sometimes) be declared in
      # `before(:context)`, but get torn down before the first real example is ever
      # run.
      #
      # You _can_ create database-backed model objects in a `before(:context)` in
      # rspec-rails, but it will not be wrapped in a transaction for you, so
      # you are on your own to clean up in an `after(:context)` block.
      #
      # @example before(:example) declared in an {ExampleGroup}
      #
      # describe Thing do
      # before(:example) do
      # @thing = Thing.new
      # end
      #
      # it "does something" do
      # # here you can access @thing
      # end
      # end
      #
      # @example before(:context) declared in an {ExampleGroup}
      #
      # describe Parser do
      # before(:context) do
      # File.open(file_to_parse, 'w') do |f|
      # f.write <<-CONTENT
      # stuff in the file
      # CONTENT
      # end
      # end
      #
      # it "parses the file" do
      # Parser.parse(file_to_parse)
      # end
      #
      # after(:context) do
      # File.delete(file_to_parse)
      # end
      # end
      #
      # @note The `:example` and `:context` scopes are also available as
      # `:each` and `:all`, respectively. Use whichever you prefer.
      def before(*args, &block)
        hooks.register :append, :before, *args, &block
      end

      alias_method :append_before, :before

      # Adds `block` to the front of the list of `before` blocks in the same
      # scope (`:example`, `:context`, or `:suite`).
      #
      # See {#before} for scoping semantics.
      def prepend_before(*args, &block)
        hooks.register :prepend, :before, *args, &block
      end

      # @api public
      # @overload after(&block)
      # @overload after(scope, &block)
      # @param scope [Symbol] `:example`, `:context`, or `:suite` (defaults to `:example`)
      # @overload after(scope, conditions, &block)
      # @param scope [Symbol] `:example`, `:context`, or `:suite` (defaults to `:example`)
      # @param conditions [Hash]
      # constrains this hook to examples matching these conditions e.g.
      # `after(:example, :ui => true) { ... }` will only run with examples or
      # groups declared with `:ui => true`.
      # @overload after(conditions, &block)
      # @param conditions [Hash]
      # constrains this hook to examples matching these conditions e.g.
      # `after(:example, :ui => true) { ... }` will only run with examples or
      # groups declared with `:ui => true`.
      #
      # @see #before
      # @see #around
      # @see ExampleGroup
      # @see SharedContext
      # @see SharedExampleGroup
      # @see Configuration
      #
      # Declare a block of code to be run after each example (using `:example`) or
      # once after all examples n the context (using `:context`). See {#before} for
      # more information about ordering.
      #
      # ### Exceptions
      #
      # `after` hooks are guaranteed to run even when there are exceptions in
      # `before` hooks or examples. When an exception is raised in an after
      # block, the exception is captured for later reporting, and subsequent
      # `after` blocks are run.
      #
      # ### Order
      #
      # `after` hooks are stored in three scopes, which are run in order:
      # `:example`, `:context`, and `:suite`. They can also be declared in several
      # different places: `RSpec.configure`, a parent group, the current group.
      # They are run in the following order:
      #
      # after(:example) # declared in the current group
      # after(:example) # declared in a parent group
      # after(:example) # declared in RSpec.configure
      # after(:context) # declared in the current group
      # after(:context) # declared in a parent group
      # after(:context) # declared in RSpec.configure
      # after(:suite) # declared in RSpec.configure
      #
      # This is the reverse of the order in which `before` hooks are run.
      # Similarly, if more than one `after` is declared within any one scope,
      # they are run in reverse order of that in which they are declared.
      #
      # @note The `:example` and `:context` scopes are also available as
      # `:each` and `:all`, respectively. Use whichever you prefer.
      def after(*args, &block)
        hooks.register :prepend, :after, *args, &block
      end

      alias_method :prepend_after, :after

      # Adds `block` to the back of the list of `after` blocks in the same
      # scope (`:example`, `:context`, or `:suite`).
      #
      # See {#after} for scoping semantics.
      def append_after(*args, &block)
        hooks.register :append, :after, *args, &block
      end

      # @api public
      # @overload around(&block)
      # @overload around(scope, &block)
      # @param scope [Symbol] `:example` (defaults to `:example`)
      # present for syntax parity with `before` and `after`, but
      # `:example`/`:each` is the only supported value.
      # @overload around(scope, conditions, &block)
      # @param scope [Symbol] `:example` (defaults to `:example`)
      # present for syntax parity with `before` and `after`, but
      # `:example`/`:each` is the only supported value.
      # @param conditions [Hash]
      # constrains this hook to examples matching these conditions e.g.
      # `around(:example, :ui => true) { ... }` will only run with examples or
      # groups declared with `:ui => true`.
      # @overload around(conditions, &block)
      # @param conditions [Hash]
      # constrains this hook to examples matching these conditions e.g.
      # `around(:example, :ui => true) { ... }` will only run with examples or
      # groups declared with `:ui => true`.
      #
      # @yield [Example] the example to run
      #
      # @note the syntax of `around` is similar to that of `before` and `after`
      # but the semantics are quite different. `before` and `after` hooks are
      # run in the context of of the examples with which they are associated,
      # whereas `around` hooks are actually responsible for running the
      # examples. Consequently, `around` hooks do not have direct access to
      # resources that are made available within the examples and their
      # associated `before` and `after` hooks.
      #
      # @note `:example`/`:each` is the only supported scope.
      #
      # Declare a block of code, parts of which will be run before and parts
      # after the example. It is your responsibility to run the example:
      #
      # around(:example) do |ex|
      # # do some stuff before
      # ex.run
      # # do some stuff after
      # end
      #
      # The yielded example aliases `run` with `call`, which lets you treat it
      # like a `Proc`. This is especially handy when working with libaries
      # that manage their own setup and teardown using a block or proc syntax,
      # e.g.
      #
      # around(:example) {|ex| Database.transaction(&ex)}
      # around(:example) {|ex| FakeFS(&ex)}
      #
      def around(*args, &block)
        hooks.register :prepend, :around, *args, &block
      end

      # @private
      # Holds the various registered hooks.
      def hooks
        @hooks ||= HookCollections.new(self,
          :around => { :example => AroundHookCollection.new },
          :before => { :example => HookCollection.new, :context => HookCollection.new, :suite => HookCollection.new },
          :after => { :example => HookCollection.new, :context => HookCollection.new, :suite => HookCollection.new }
        )
      end

    private

      # @private
      class Hook
        attr_reader :block, :options

        def initialize(block, options)
          @block = block
          @options = options
        end

        def options_apply?(example_or_group)
          example_or_group.all_apply?(options)
        end
      end

      # @private
      class BeforeHook < Hook
        def run(example)
          example.instance_exec(example, &block)
        end
      end

      # @private
      class AfterHook < Hook
        def run(example)
          example.instance_exec_with_rescue("in an after hook", &block)
        end
      end

      # @private
      class AfterContextHook < Hook
        def run(example)
          example.instance_exec(example, &block)
        rescue Exception => e
          # TODO: come up with a better solution for this.
          RSpec.configuration.reporter.message <<-EOS

An error occurred in an `after(:context)` hook.
#{e.class}: #{e.message}
occurred at #{e.backtrace.first}

EOS
        end
      end

      # @private
      AroundHook = Hook

      # @private
      class BaseHookCollection
        Array.public_instance_methods(false).each do |name|
          define_method(name) { |*a, &b| hooks.__send__(name, *a, &b) }
        end

        attr_reader :hooks
        protected :hooks

        alias append push
        alias prepend unshift

        def initialize(hooks=[])
          @hooks = hooks
        end
      end

      # @private
      class HookCollection < BaseHookCollection
        def for(example_or_group)
          self.class.
            new(hooks.select {|hook| hook.options_apply?(example_or_group)}).
            with(example_or_group)
        end

        def with(example)
          @example = example
          self
        end

        def run
          hooks.each {|h| h.run(@example)}
        end
      end

      # @private
      class AroundHookCollection < BaseHookCollection
        def for(example, initial_procsy=nil)
          self.class.new(hooks.select {|hook| hook.options_apply?(example)}).
            with(example, initial_procsy)
        end

        def with(example, initial_procsy)
          @example = example
          @initial_procsy = initial_procsy
          self
        end

        def run
          hooks.inject(@initial_procsy) do |procsy, around_hook|
            procsy.wrap do
              @example.instance_exec(procsy, &around_hook.block)
            end
          end.call
        end
      end

      # @private
      class GroupHookCollection < BaseHookCollection
        def for(group)
          @group = group
          self
        end

        def run
          hooks.shift.run(@group) until hooks.empty?
        end
      end

      # @private
      class HookCollections
        def initialize(owner, data)
          @owner = owner
          @data = data
        end

        def [](key)
          @data[key]
        end

        def register_globals(host, globals)
          process(host, globals, :before, :example)
          process(host, globals, :after, :example)
          process(host, globals, :around, :example)

          process(host, globals, :before, :context)
          process(host, globals, :after, :context)
        end

        def around_example_hooks_for(example, initial_procsy=nil)
          AroundHookCollection.new(FlatMap.flat_map(@owner.parent_groups) do |a|
            a.hooks[:around][:example]
          end).for(example, initial_procsy)
        end

        def register(prepend_or_append, hook, *args, &block)
          scope, options = scope_and_options_from(*args)
          self[hook][scope].__send__(prepend_or_append, HOOK_TYPES[hook][scope].new(block, options))
        end

        # @private
        #
        # Runs all of the blocks stored with the hook in the context of the
        # example. If no example is provided, just calls the hook directly.
        def run(hook, scope, example_or_group, initial_procsy=nil)
          return if RSpec.configuration.dry_run?
          find_hook(hook, scope, example_or_group, initial_procsy).run
        end

        SCOPES = [:example, :context, :suite]

        SCOPE_ALIASES = { :each => :example, :all => :context }

        HOOK_TYPES = {
          :before => Hash.new { BeforeHook },
          :after => Hash.new { AfterHook },
          :around => Hash.new { AroundHook }
        }

        HOOK_TYPES[:after][:context] = AfterContextHook

      private

        def process(host, globals, position, scope)
          globals[position][scope].each do |hook|
            next unless scope == :example || hook.options_apply?(host)
            next if host.parent_groups.any? {|a| a.hooks[position][scope].include?(hook)}
            self[position][scope] << hook
          end
        end

        def scope_and_options_from(*args)
          return extract_scope_from(args), Metadata.build_hash_from(args)
        end

        def extract_scope_from(args)
          if known_scope?(args.first)
            normalized_scope_for(args.shift)
          elsif args.any? { |a| a.is_a?(Symbol) }
            error_message = "You must explicitly give a scope (#{SCOPES.join(", ")}) or scope alias (#{SCOPE_ALIASES.keys.join(", ")}) when using symbols as metadata for a hook."
            raise ArgumentError.new error_message
          else
            :example
          end
        end

        # @api private
        def known_scope?(scope)
          SCOPES.include?(scope) || SCOPE_ALIASES.keys.include?(scope)
        end

        # @api private
        def normalized_scope_for(scope)
          SCOPE_ALIASES[scope] || scope
        end

        def find_hook(hook, scope, example_or_group, initial_procsy)
          case [hook, scope]
          when [:before, :context]
            before_context_hooks_for(example_or_group)
          when [:after, :context]
            after_context_hooks_for(example_or_group)
          when [:around, :example]
            around_example_hooks_for(example_or_group, initial_procsy)
          when [:before, :example]
            before_example_hooks_for(example_or_group)
          when [:after, :example]
            after_example_hooks_for(example_or_group)
          when [:before, :suite], [:after, :suite]
            self[hook][:suite].with(example_or_group)
          end
        end

        def before_context_hooks_for(group)
          GroupHookCollection.new(self[:before][:context]).for(group)
        end

        def after_context_hooks_for(group)
          GroupHookCollection.new(self[:after][:context]).for(group)
        end

        def before_example_hooks_for(example)
          HookCollection.new(FlatMap.flat_map(@owner.parent_groups.reverse) do |a|
            a.hooks[:before][:example]
          end).for(example)
        end

        def after_example_hooks_for(example)
          HookCollection.new(FlatMap.flat_map(@owner.parent_groups) do |a|
            a.hooks[:after][:example]
          end).for(example)
        end
      end
    end
  end
end
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