require 'set'
require File.dirname(__FILE__) + '/core_ext/module/attribute_accessors'
require File.dirname(__FILE__) + '/core_ext/load_error'
require File.dirname(__FILE__) + '/core_ext/kernel'

module Dependencies #:nodoc:
  extend self

  # Should we turn on Ruby warnings on the first load of dependent files?
  mattr_accessor :warnings_on_first_load
  self.warnings_on_first_load = false

  # All files ever loaded.
  mattr_accessor :history
  self.history = Set.new

  # All files currently loaded.
  mattr_accessor :loaded
  self.loaded = Set.new

  # Should we load files or require them?
  mattr_accessor :mechanism
  self.mechanism = :load

  # The set of directories from which we may autoload files
  mattr_accessor :autoload_paths
  self.autoload_paths = []

  mattr_accessor :autoloaded_constants
  self.autoloaded_constants = []
  
  def load?
    mechanism == :load
  end

  def depend_on(file_name, swallow_load_errors = false)
    path = search_for_autoload_file(file_name)
    require_or_load(path || file_name)
  rescue LoadError
    raise unless swallow_load_errors
  end

  def associate_with(file_name)
    depend_on(file_name, true)
  end

  def clear
    loaded.clear
    remove_autoloaded_constants!
  end

  def require_or_load(file_name, const_path = nil)
    file_name = $1 if file_name =~ /^(.*)\.rb$/
    expanded = File.expand_path(file_name)
    return if loaded.include?(expanded)

    # Record that we've seen this file *before* loading it to avoid an
    # infinite loop with mutual dependencies.
    loaded << expanded

    if load?
      begin
        # Enable warnings iff this file has not been loaded before and
        # warnings_on_first_load is set.
        load_args = ["#{file_name}.rb"]
        load_args << const_path unless const_path.nil?
        
        if !warnings_on_first_load or history.include?(expanded)
          load_file(*load_args)
        else
          enable_warnings { load_file(*load_args) }
        end
      rescue
        loaded.delete expanded
        raise
      end
    else
      require file_name
    end

    # Record history *after* loading so first load gets warnings.
    history << expanded
  end
  
  # Is the provided constant path defined?
  def qualified_const_defined?(path)
    raise NameError, "#{path.inspect} is not a valid constant name!" unless
      /^(::)?([A-Z]\w*)(::[A-Z]\w*)*$/ =~ path
    Object.module_eval("defined?(#{path})", __FILE__, __LINE__)
  end
  
  # Given +path+ return an array of constant paths which would cause Dependencies
  # to attempt to load +path+.
  def autoloadable_constants_for_path(path)
    path = $1 if path =~ /\A(.*)\.rb\Z/
    expanded_path = File.expand_path(path)
    autoload_paths.collect do |root|
      expanded_root = File.expand_path root
      next unless expanded_path.starts_with? expanded_root
      
      nesting = expanded_path[(expanded_root.size)..-1]
      nesting = nesting[1..-1] if nesting && nesting[0] == ?/
      next if nesting.blank?
      
      nesting.camelize
    end.compact.uniq
  end
  
  # Search for a file in the autoload_paths matching the provided suffix.
  def search_for_autoload_file(path_suffix)
    path_suffix = path_suffix + '.rb' unless path_suffix.ends_with? '.rb'
    autoload_paths.each do |root|
      path = File.join(root, path_suffix)
      return path if File.file? path
    end
    nil # Gee, I sure wish we had first_match ;-)
  end
  
  # Does the provided path_suffix correspond to an autoloadable module?
  def autoloadable_module?(path_suffix)
    autoload_paths.any? do |autoload_path|
      File.directory? File.join(autoload_path, path_suffix)
    end
  end
  
  # Load the file at the provided path. +const_paths+ is a set of qualified
  # constant names. When loading the file, Dependencies will watch for the
  # addition of these constants. Each that is defined will be marked as
  # autoloaded, and will be removed when Dependencies.clear is next called.
  # 
  # If the second parameter is left off, then Dependencies will construct a set
  # of names that the file at +path+ may define. See
  # +autoloadable_constants_for_path+ for more details.
  def load_file(path, const_paths = autoloadable_constants_for_path(path))
    const_paths = [const_paths].compact unless const_paths.is_a? Array
    undefined_before = const_paths.reject(&method(:qualified_const_defined?))
    
    load path
    
    autoloaded_constants.concat const_paths.select(&method(:qualified_const_defined?))
    autoloaded_constants.uniq!
  end
  
  # Return the constant path for the provided parent and constant name.
  def qualified_name_for(mod, name)
    mod_name = to_constant_name mod
    (%w(Object Kernel).include? mod_name) ? name.to_s : "#{mod_name}::#{name}"
  end
  
  # Load the constant named +const_name+ which is missing from +from_mod+. If
  # it is not possible to laod the constant into from_mod, try its parent module
  # using const_missing.
  def load_missing_constant(from_mod, const_name)
    qualified_name = qualified_name_for from_mod, const_name
    path_suffix = qualified_name.underscore
    name_error = NameError.new("uninitialized constant #{qualified_name}")
    
    file_path = search_for_autoload_file(path_suffix)
    if file_path && ! loaded.include?(File.expand_path(file_path)) # We found a matching file to load
      require_or_load file_path, qualified_name
      raise LoadError, "Expected #{file_path} to define #{qualified_name}" unless from_mod.const_defined?(const_name)
      return from_mod.const_get(const_name)
    elsif autoloadable_module? path_suffix # Create modules for directories
      mod = Module.new
      from_mod.const_set const_name, mod
      autoloaded_constants << qualified_name
      return mod
    elsif (parent = from_mod.parent) && parent != from_mod &&
          ! from_mod.parents.any? { |p| p.const_defined?(const_name) }
      # If our parents do not have a constant named +const_name+ then we are free
      # to attempt to load upwards. If they do have such a constant, then this
      # const_missing must be due to from_mod::const_name, which should not
      # return constants from from_mod's parents.
      begin
        return parent.const_missing(const_name)
      rescue NameError => e
        raise unless e.missing_name? qualified_name_for(parent, const_name)
        raise name_error
      end
    else
      raise name_error
    end
  end
  
  # Remove the constants that have been autoloaded.
  def remove_autoloaded_constants!
    until autoloaded_constants.empty?
      const = autoloaded_constants.shift
      next unless qualified_const_defined? const
      names = const.split('::')
      if names.size == 1 || names.first.empty? # It's under Object
        parent = Object
      else
        parent = (names[0..-2] * '::').constantize
      end
      parent.send :remove_const, names.last
      true
    end
  end
  
  # Determine if the given constant has been automatically loaded.
  def autoloaded?(desc)
    name = to_constant_name desc
    return false unless qualified_const_defined? name
    return autoloaded_constants.include?(name)
  end
  
  class LoadingModule
    # Old style environment.rb referenced this method directly.  Please note, it doesn't
    # actualy *do* anything any more.
    def self.root(*args)
      if defined?(RAILS_DEFAULT_LOGGER)
        RAILS_DEFAULT_LOGGER.warn "Your environment.rb uses the old syntax, it may not continue to work in future releases."
        RAILS_DEFAULT_LOGGER.warn "For upgrade instructions please see: http://manuals.rubyonrails.com/read/book/19"
      end
    end
  end

protected
  
  # Convert the provided const desc to a qualified constant name (as a string).
  # A module, class, symbol, or string may be provided.
  def to_constant_name(desc)
    name = case desc
      when String then desc.starts_with?('::') ? desc[2..-1] : desc
      when Symbol then desc.to_s
      when Module then desc.name
      else raise TypeError, "Not a valid constant descriptor: #{desc.inspect}"
    end
  end
  
end

Object.send(:define_method, :require_or_load)     { |file_name| Dependencies.require_or_load(file_name) } unless Object.respond_to?(:require_or_load)
Object.send(:define_method, :require_dependency)  { |file_name| Dependencies.depend_on(file_name) }       unless Object.respond_to?(:require_dependency)
Object.send(:define_method, :require_association) { |file_name| Dependencies.associate_with(file_name) }  unless Object.respond_to?(:require_association)

class Module #:nodoc:
  # Rename the original handler so we can chain it to the new one
  alias :rails_original_const_missing :const_missing
  
  # Use const_missing to autoload associations so we don't have to
  # require_association when using single-table inheritance.
  def const_missing(class_id)
    Dependencies.load_missing_constant self, class_id
  end
end

class Class
  def const_missing(class_id)
    if [Object, Kernel].include?(self) || parent == self
      super
    else
      begin
        parent.send :const_missing, class_id
      rescue NameError => e
        # Make sure that the name we are missing is the one that caused the error
        parent_qualified_name = Dependencies.qualified_name_for parent, class_id
        raise unless e.missing_name? parent_qualified_name
        qualified_name = Dependencies.qualified_name_for self, class_id
        raise NameError.new("uninitialized constant #{qualified_name}").copy_blame!(e)
      end
    end
  end
end

class Object #:nodoc:
  def load(file, *extras)
    super(file, *extras)
  rescue Object => exception
    exception.blame_file! file
    raise
  end

  def require(file, *extras)
    super(file, *extras)
  rescue Object => exception
    exception.blame_file! file
    raise
  end
end

# Add file-blaming to exceptions
class Exception #:nodoc:
  def blame_file!(file)
    (@blamed_files ||= []).unshift file
  end

  def blamed_files
    @blamed_files ||= []
  end

  def describe_blame
    return nil if blamed_files.empty?
    "This error occurred while loading the following files:\n   #{blamed_files.join "\n   "}"
  end

  def copy_blame!(exc)
    @blamed_files = exc.blamed_files.clone
    self
  end
end