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require 'extlib/assertions'
require 'extlib/class'
require 'extlib/object'
require 'extlib/local_object_space'
module Extlib
#
# TODO: Write more documentation!
#
# Overview
# ========
#
# The Hook module is a very simple set of AOP helpers. Basically, it
# allows the developer to specify a method or block that should run
# before or after another method.
#
# Usage
# =====
#
# Halting The Hook Stack
#
# Inheritance
#
# Other Goodies
#
# Please bring up any issues regarding Hooks with carllerche on IRC
#
module Hook
def self.included(base)
base.extend(ClassMethods)
base.const_set("CLASS_HOOKS", {}) unless base.const_defined?("CLASS_HOOKS")
base.const_set("INSTANCE_HOOKS", {}) unless base.const_defined?("INSTANCE_HOOKS")
base.class_eval do
class << self
def method_added(name)
process_method_added(name, :instance)
super
end
def singleton_method_added(name)
process_method_added(name, :class)
super
end
end
end
end
module ClassMethods
extend Extlib::LocalObjectSpace
include Extlib::Assertions
# Inject code that executes before the target class method.
#
# @param target_method<Symbol> the name of the class method to inject before
# @param method_sym<Symbol> the name of the method to run before the
# target_method
# @param block<Block> the code to run before the target_method
#
# @note
# Either method_sym or block is required.
# -
# @api public
def before_class_method(target_method, method_sym = nil, &block)
install_hook :before, target_method, method_sym, :class, &block
end
#
# Inject code that executes after the target class method.
#
# @param target_method<Symbol> the name of the class method to inject after
# @param method_sym<Symbol> the name of the method to run after the target_method
# @param block<Block> the code to run after the target_method
#
# @note
# Either method_sym or block is required.
# -
# @api public
def after_class_method(target_method, method_sym = nil, &block)
install_hook :after, target_method, method_sym, :class, &block
end
#
# Inject code that executes before the target instance method.
#
# @param target_method<Symbol> the name of the instance method to inject before
# @param method_sym<Symbol> the name of the method to run before the
# target_method
# @param block<Block> the code to run before the target_method
#
# @note
# Either method_sym or block is required.
# -
# @api public
def before(target_method, method_sym = nil, &block)
install_hook :before, target_method, method_sym, :instance, &block
end
#
# Inject code that executes after the target instance method.
#
# @param target_method<Symbol> the name of the instance method to inject after
# @param method_sym<Symbol> the name of the method to run after the
# target_method
# @param block<Block> the code to run after the target_method
#
# @note
# Either method_sym or block is required.
# -
# @api public
def after(target_method, method_sym = nil, &block)
install_hook :after, target_method, method_sym, :instance, &block
end
# Register a class method as hookable. Registering a method means that
# before hooks will be run immediately before the method is invoked and
# after hooks will be called immediately after the method is invoked.
#
# @param hookable_method<Symbol> The name of the class method that should
# be hookable
# -
# @api public
def register_class_hooks(*hooks)
hooks.each { |hook| register_hook(hook, :class) }
end
# Register aninstance method as hookable. Registering a method means that
# before hooks will be run immediately before the method is invoked and
# after hooks will be called immediately after the method is invoked.
#
# @param hookable_method<Symbol> The name of the instance method that should
# be hookable
# -
# @api public
def register_instance_hooks(*hooks)
hooks.each { |hook| register_hook(hook, :instance) }
end
# Not yet implemented
def reset_hook!(target_method, scope)
raise NotImplementedError
end
# --- Alright kids... the rest is internal stuff ---
# Returns the correct HOOKS Hash depending on whether we are
# working with class methods or instance methods
def hooks_with_scope(scope)
case scope
when :class then class_hooks
when :instance then instance_hooks
else raise ArgumentError, 'You need to pass :class or :instance as scope'
end
end
def class_hooks
self.const_get("CLASS_HOOKS")
end
def instance_hooks
self.const_get("INSTANCE_HOOKS")
end
# Registers a method as hookable. Registering hooks involves the following
# process
#
# * Create a blank entry in the HOOK Hash for the method.
# * Define the methods that execute the before and after hook stack.
# These methods will be no-ops at first, but everytime a new hook is
# defined, the methods will be redefined to incorporate the new hook.
# * Redefine the method that is to be hookable so that the hook stacks
# are invoked approprietly.
def register_hook(target_method, scope)
if scope == :instance && !method_defined?(target_method)
raise ArgumentError, "#{target_method} instance method does not exist"
elsif scope == :class && !respond_to?(target_method)
raise ArgumentError, "#{target_method} class method does not exist"
end
hooks = hooks_with_scope(scope)
if hooks[target_method].nil?
hooks[target_method] = {
# We need to keep track of which class in the Inheritance chain the
# method was declared hookable in. Every time a child declares a new
# hook for the method, the hook stack invocations need to be redefined
# in the original Class. See #define_hook_stack_execution_methods
:before => [], :after => [], :in => self
}
define_hook_stack_execution_methods(target_method, scope)
define_advised_method(target_method, scope)
end
end
# Is the method registered as a hookable in the given scope.
def registered_as_hook?(target_method, scope)
! hooks_with_scope(scope)[target_method].nil?
end
# Generates names for the various utility methods. We need to do this because
# the various utility methods should not end in = so, while we're at it, we
# might as well get rid of all punctuation.
def hook_method_name(target_method, prefix, suffix)
target_method = target_method.to_s
case target_method[-1,1]
when '?' then "#{prefix}_#{target_method[0..-2]}_ques_#{suffix}"
when '!' then "#{prefix}_#{target_method[0..-2]}_bang_#{suffix}"
when '=' then "#{prefix}_#{target_method[0..-2]}_eq_#{suffix}"
# I add a _nan_ suffix here so that we don't ever encounter
# any naming conflicts.
else "#{prefix}_#{target_method[0..-1]}_nan_#{suffix}"
end
end
# This will need to be refactored
def process_method_added(method_name, scope)
hooks_with_scope(scope).each do |target_method, hooks|
if hooks[:before].any? { |hook| hook[:name] == method_name }
define_hook_stack_execution_methods(target_method, scope)
end
if hooks[:after].any? { |hook| hook[:name] == method_name }
define_hook_stack_execution_methods(target_method, scope)
end
end
end
# Defines two methods. One method executes the before hook stack. The other executes
# the after hook stack. This method will be called many times during the Class definition
# process. It should be called for each hook that is defined. It will also be called
# when a hook is redefined (to make sure that the arity hasn't changed).
def define_hook_stack_execution_methods(target_method, scope)
unless registered_as_hook?(target_method, scope)
raise ArgumentError, "#{target_method} has not be registered as a hookable #{scope} method"
end
hooks = hooks_with_scope(scope)
before_hooks = hooks[target_method][:before]
before_hooks = before_hooks.map{ |info| inline_call(info, scope) }.join("\n")
after_hooks = hooks[target_method][:after]
after_hooks = after_hooks.map{ |info| inline_call(info, scope) }.join("\n")
before_hook_name = hook_method_name(target_method, 'execute_before', 'hook_stack')
after_hook_name = hook_method_name(target_method, 'execute_after', 'hook_stack')
hooks[target_method][:in].class_eval <<-RUBY, __FILE__, __LINE__ + 1
#{scope == :class ? 'class << self' : ''}
private
remove_method :#{before_hook_name} if instance_methods(false).any? { |m| m.to_sym == :#{before_hook_name} }
def #{before_hook_name}(*args)
#{before_hooks}
end
remove_method :#{after_hook_name} if instance_methods(false).any? { |m| m.to_sym == :#{after_hook_name} }
def #{after_hook_name}(*args)
#{after_hooks}
end
#{scope == :class ? 'end' : ''}
RUBY
end
# Returns ruby code that will invoke the hook. It checks the arity of the hook method
# and passes arguments accordingly.
def inline_call(method_info, scope)
Extlib::Hook::ClassMethods.hook_scopes << method_info[:from]
name = method_info[:name]
if scope == :instance
args = method_defined?(name) && instance_method(name).arity != 0 ? '*args' : ''
%(#{name}(#{args}) if self.class <= Extlib::Hook::ClassMethods.object_by_id(#{method_info[:from].object_id}))
else
args = respond_to?(name) && method(name).arity != 0 ? '*args' : ''
%(#{name}(#{args}) if self <= Extlib::Hook::ClassMethods.object_by_id(#{method_info[:from].object_id}))
end
end
def define_advised_method(target_method, scope)
args = args_for(method_with_scope(target_method, scope))
renamed_target = hook_method_name(target_method, 'hookable_', 'before_advised')
source = <<-EOD
def #{target_method}(#{args})
retval = nil
catch(:halt) do
#{hook_method_name(target_method, 'execute_before', 'hook_stack')}(#{args})
retval = #{renamed_target}(#{args})
#{hook_method_name(target_method, 'execute_after', 'hook_stack')}(retval, #{args})
retval
end
end
EOD
if scope == :instance && !instance_methods(false).any? { |m| m.to_sym == target_method }
send(:alias_method, renamed_target, target_method)
proxy_module = Module.new
proxy_module.class_eval(source, __FILE__, __LINE__)
self.send(:include, proxy_module)
else
source = %{alias_method :#{renamed_target}, :#{target_method}\n#{source}}
source = %{class << self\n#{source}\nend} if scope == :class
class_eval(source, __FILE__, __LINE__)
end
end
# --- Add a hook ---
def install_hook(type, target_method, method_sym, scope, &block)
assert_kind_of 'target_method', target_method, Symbol
assert_kind_of 'method_sym', method_sym, Symbol unless method_sym.nil?
assert_kind_of 'scope', scope, Symbol
if !block_given? and method_sym.nil?
raise ArgumentError, "You need to pass 2 arguments to \"#{type}\"."
end
if method_sym.to_s[-1,1] == '='
raise ArgumentError, "Methods ending in = cannot be hooks"
end
unless [ :class, :instance ].include?(scope)
raise ArgumentError, 'You need to pass :class or :instance as scope'
end
if registered_as_hook?(target_method, scope)
hooks = hooks_with_scope(scope)
#if this hook is previously declared in a sibling or cousin we must move the :in class
#to the common ancestor to get both hooks to run.
if !(hooks[target_method][:in] <=> self)
before_hook_name = hook_method_name(target_method, 'execute_before', 'hook_stack')
after_hook_name = hook_method_name(target_method, 'execute_after', 'hook_stack')
hooks[target_method][:in].class_eval <<-RUBY, __FILE__, __LINE__ + 1
remove_method :#{before_hook_name} if instance_methods(false).any? { |m| m.to_sym == :#{before_hook_name} }
def #{before_hook_name}(*args)
super
end
remove_method :#{after_hook_name} if instance_methods(false).any? { |m| m.to_sym == :#{before_hook_name} }
def #{after_hook_name}(*args)
super
end
RUBY
while !(hooks[target_method][:in] <=> self) do
hooks[target_method][:in] = hooks[target_method][:in].superclass
end
define_hook_stack_execution_methods(target_method, scope)
hooks[target_method][:in].class_eval{define_advised_method(target_method, scope)}
end
else
register_hook(target_method, scope)
hooks = hooks_with_scope(scope)
end
#if we were passed a block, create a method out of it.
if block
method_sym = "__hooks_#{type}_#{quote_method(target_method)}_#{hooks[target_method][type].length}".to_sym
if scope == :class
meta_class.instance_eval do
define_method(method_sym, &block)
end
else
define_method(method_sym, &block)
end
end
# Adds method to the stack an redefines the hook invocation method
hooks[target_method][type] << { :name => method_sym, :from => self }
define_hook_stack_execution_methods(target_method, scope)
end
# --- Helpers ---
def args_for(method)
if method.arity == 0
"&block"
elsif method.arity > 0
"_" << (1 .. method.arity).to_a.join(", _") << ", &block"
elsif (method.arity + 1) < 0
"_" << (1 .. (method.arity).abs - 1).to_a.join(", _") << ", *args, &block"
else
"*args, &block"
end
end
def method_with_scope(name, scope)
case scope
when :class then method(name)
when :instance then instance_method(name)
else raise ArgumentError, 'You need to pass :class or :instance as scope'
end
end
def quote_method(name)
name.to_s.gsub(/\?$/, '_q_').gsub(/!$/, '_b_').gsub(/=$/, '_eq_')
end
end
end
end