require 'ostruct'
require 'yaml'
require 'local_gem/version'

module LocalGem
  extend self
  def local_require(path) #:nodoc:
    Singleton.local_require(path)
  end

  def local_gem(*args) #:nodoc:
    Singleton.local_gem(*args)
  end

  def setup_config(config, &block) #:nodoc:
    Singleton.setup_config(config, &block)
  end

  module Singleton
    extend self
    attr_accessor :config, :config_file

    # Holds the mapping of local gems and their paths to load.
    def config
      @config ||= read_config
    end

    # Reads config from @config_file and returns a hash.
    # @config_file can be set via its accessor. Otherwise it defaults to a local local_gem.yml or
    # ~/.local_gem.yml.
    def read_config
      @config_file ||= ['local_gem.yml', File.join("~", ".local_gem.yml")].detect {|e| File.exists?(File.expand_path(e)) }
      @config_file ? YAML::load(File.new(File.expand_path(@config_file))) : {:gems=>{}}
    end

    # Takes either a hash or a block and initializes config().
    def setup_config(config=nil, &block)
      @config = config || ConfigStruct.block_to_hash(block)
    end

    # Loads the local gem if found or defaults to a normal gem call.
    def local_gem(*args)
      load_local_gem(args[0]) || gem(*args)
    end

    # Loads the local gem if found and then does a normal require on it.
    def local_require(lib)
      load_local_gem(lib)
      require(lib)
    end

    # Adds a given library's path (specified in config) to the beginning of $LOAD_PATH.
    def load_local_gem(library)
      if path = config[:gems][library]
        path = [path] unless path.is_a?(Array)
        path.map {|e| File.expand_path(e) }.each do |f|
          $:.unshift(f) unless $:.include?(f)
        end
        true
      else
        false
      end
    end
  end

  class ConfigStruct < OpenStruct
    # Converts the data within the given block to hash
    def self.block_to_hash(block=nil)
      config = self.new
      if block
        block.call(config)
        config.to_hash
      else
        {}
      end
    end

    def to_hash #:nodoc:
      @table
    end
  end
end