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
      #
      # Note that filtered config `:context` hooks can still be applied
      # to individual examples that have matching metadata. Just like
      # Ruby's object model is that every object has a singleton class
      # which has only a single instance, RSpec's model is that every
      # example has a singleton example group containing just the one
      # example.
      #
      # ### 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.
      # @note The `:scope` alias is only supported for hooks registered on
      #       `RSpec.configuration` since they exist independently of any
      #       example or example group.
      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.
      # @note The `:scope` alias is only supported for hooks registered on
      #       `RSpec.configuration` since they exist independently of any
      #       example or example group.
      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, FilterableItemRepository::UpdateOptimized)
      end

    private

      # @private
      class Hook
        attr_reader :block, :options

        def initialize(block, options)
          @block = block
          @options = 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
      class AroundHook < Hook
        def execute_with(example, procsy)
          example.instance_exec(procsy, &block)
          return if procsy.executed?
          Pending.mark_skipped!(example,
                                "#{hook_description} did not execute the example")
        end

        if Proc.method_defined?(:source_location)
          def hook_description
            "around hook at #{Metadata.relative_path(block.source_location.join(':'))}"
          end
        else
          def hook_description
            "around hook"
          end
        end
      end

      # @private
      #
      # This provides the primary API used by other parts of rspec-core. By hiding all
      # implementation details behind this facade, it's allowed us to heavily optimize
      # this, so that, for example, hook collection objects are only instantiated when
      # a hook is added. This allows us to avoid many object allocations for the common
      # case of a group having no hooks.
      #
      # This is only possible because this interface provides a "tell, don't ask"-style
      # API, so that callers _tell_ this class what to do with the hooks, rather than
      # asking this class for a list of hooks, and then doing something with them.
      class HookCollections
        def initialize(owner, filterable_item_repo_class)
          @owner                      = owner
          @filterable_item_repo_class = filterable_item_repo_class
          @before_example_hooks       = nil
          @after_example_hooks        = nil
          @before_context_hooks       = nil
          @after_context_hooks        = nil
          @around_example_hooks       = nil
        end

        def register_globals(host, globals)
          parent_groups = host.parent_groups

          process(host, parent_groups, globals, :before, :example, &:options)
          process(host, parent_groups, globals, :after,  :example, &:options)
          process(host, parent_groups, globals, :around, :example, &:options)

          process(host, parent_groups, globals, :before, :context, &:options)
          process(host, parent_groups, globals, :after,  :context, &:options)
        end

        def register_global_singleton_context_hooks(example, globals)
          parent_groups = example.example_group.parent_groups

          process(example, parent_groups, globals, :before, :context) { {} }
          process(example, parent_groups, globals, :after,  :context) { {} }
        end

        def register(prepend_or_append, position, *args, &block)
          scope, options = scope_and_options_from(*args)

          if scope == :suite
            # TODO: consider making this an error in RSpec 4. For SemVer reasons,
            # we are only warning in RSpec 3.
            RSpec.warn_with "WARNING: `#{position}(:suite)` hooks are only supported on " \
                            "the RSpec configuration object. This " \
                            "`#{position}(:suite)` hook, registered on an example " \
                            "group, will be ignored."
            return
          end

          hook = HOOK_TYPES[position][scope].new(block, options)
          ensure_hooks_initialized_for(position, scope).__send__(prepend_or_append, hook, 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(position, scope, example_or_group)
          return if RSpec.configuration.dry_run?

          if scope == :context
            run_owned_hooks_for(position, :context, example_or_group)
          else
            case position
            when :before then run_example_hooks_for(example_or_group, :before, :reverse_each)
            when :after  then run_example_hooks_for(example_or_group, :after,  :each)
            when :around then run_around_example_hooks_for(example_or_group) { yield }
            end
          end
        end

        SCOPES = [:example, :context]

        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

      protected

        EMPTY_HOOK_ARRAY = [].freeze

        def matching_hooks_for(position, scope, example_or_group)
          repository = hooks_for(position, scope) { return EMPTY_HOOK_ARRAY }

          # It would be nice to not have to switch on type here, but
          # we don't want to define `ExampleGroup#metadata` because then
          # `metadata` from within an individual example would return the
          # group's metadata but the user would probably expect it to be
          # the example's metadata.
          metadata = case example_or_group
                     when ExampleGroup then example_or_group.class.metadata
                     else example_or_group.metadata
                     end

          repository.items_for(metadata)
        end

        def all_hooks_for(position, scope)
          hooks_for(position, scope) { return EMPTY_HOOK_ARRAY }.items_and_filters.map(&:first)
        end

        def run_owned_hooks_for(position, scope, example_or_group)
          matching_hooks_for(position, scope, example_or_group).each do |hook|
            hook.run(example_or_group)
          end
        end

        def processable_hooks_for(position, scope, host)
          if scope == :example
            all_hooks_for(position, scope)
          else
            matching_hooks_for(position, scope, host)
          end
        end

      private

        def hooks_for(position, scope)
          if position == :before
            scope == :example ? @before_example_hooks : @before_context_hooks
          elsif position == :after
            scope == :example ? @after_example_hooks : @after_context_hooks
          else # around
            @around_example_hooks
          end || yield
        end

        def ensure_hooks_initialized_for(position, scope)
          if position == :before
            if scope == :example
              @before_example_hooks ||= @filterable_item_repo_class.new(:all?)
            else
              @before_context_hooks ||= @filterable_item_repo_class.new(:all?)
            end
          elsif position == :after
            if scope == :example
              @after_example_hooks ||= @filterable_item_repo_class.new(:all?)
            else
              @after_context_hooks ||= @filterable_item_repo_class.new(:all?)
            end
          else # around
            @around_example_hooks ||= @filterable_item_repo_class.new(:all?)
          end
        end

        def process(host, parent_groups, globals, position, scope)
          hooks_to_process = globals.processable_hooks_for(position, scope, host)
          return if hooks_to_process.empty?

          hooks_to_process -= FlatMap.flat_map(parent_groups) do |group|
            group.hooks.all_hooks_for(position, scope)
          end
          return if hooks_to_process.empty?

          repository = ensure_hooks_initialized_for(position, scope)
          hooks_to_process.each { |hook| repository.append hook, (yield hook) }
        end

        def scope_and_options_from(*args)
          return :suite if args.first == :suite
          scope = extract_scope_from(args)
          meta  = Metadata.build_hash_from(args, :warn_about_example_group_filtering)
          return scope, meta
        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

        def known_scope?(scope)
          SCOPES.include?(scope) || SCOPE_ALIASES.keys.include?(scope)
        end

        def normalized_scope_for(scope)
          SCOPE_ALIASES[scope] || scope
        end

        def run_example_hooks_for(example, position, each_method)
          owner_parent_groups.__send__(each_method) do |group|
            group.hooks.run_owned_hooks_for(position, :example, example)
          end
        end

        def run_around_example_hooks_for(example)
          hooks = FlatMap.flat_map(owner_parent_groups) do |group|
            group.hooks.matching_hooks_for(:around, :example, example)
          end

          return yield if hooks.empty? # exit early to avoid the extra allocation cost of `Example::Procsy`

          initial_procsy = Example::Procsy.new(example) { yield }
          hooks.inject(initial_procsy) do |procsy, around_hook|
            procsy.wrap { around_hook.execute_with(example, procsy) }
          end.call
        end

        if respond_to?(:singleton_class) && singleton_class.ancestors.include?(singleton_class)
          def owner_parent_groups
            @owner.parent_groups
          end
        else # Ruby < 2.1 (see https://bugs.ruby-lang.org/issues/8035)
          def owner_parent_groups
            @owner_parent_groups ||= [@owner] + @owner.parent_groups
          end
        end
      end
    end
  end
end
