ioquatix/build-environment

# Copyright, 2012, by Samuel G. D. Williams. <http://www.codeotaku.com>
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

require 'ostruct'

module Build
    class Environment
        Default = Struct.new(:value)
        Replace = Struct.new(:value)
        
        class Define < Struct.new(:klass, :block)
            def initialize(klass, &block)
                super klass, block
            end
            
            def to_s
                "#<#{klass} #{block ? block.source_location.join(':') : 'unknown'}>"
            end
        end
        
        def construct!(proxy, *arguments, &block)
            constructor = Constructor.new(self, proxy)
            
            if block_given?
                constructor.instance_exec(*arguments, &block)
            end
            
            return self
        end
        
        class Constructor
            def initialize(environment, proxy = nil)
                @environment = environment
                @proxy = proxy
            end
            
            def respond_to?(name, include_private = false)
                @environment.include?(name) || @proxy&.respond_to?(name, include_private) || super
            end
            
            def method_missing(name, *args, **options, &block)
                if options.empty?
                    if args.empty? and block_given?
                        @environment[name] = block
                        
                        return name
                    elsif !args.empty?
                        if args.count == 1
                            @environment[name] = args.first
                        else
                            @environment[name] = args
                        end
                        
                        return name
                    end
                end
                
                if @proxy
                    # This is a bit of a hack, but I'm not sure if there is a better way.
                    if options.empty?
                        @proxy.send(name, *args, &block)
                    else
                        @proxy.send(name, *args, **options, &block)
                    end
                else
                    super
                end
            end
            
            def respond_to(*args)
                super or @proxy&.respond_to(*args)
            end
            
            def [] key
                @environment[key]
            end
            
            def parent
                @environment.parent
            end
            
            def hash(**options)
                OpenStruct.new(options)
            end
            
            def default(name)
                @environment[name] = Default.new(@environment[name])
                
                return name
            end
            
            def replace(name)
                @environment[name] = Replace.new(@environment[name])
                
                return name
            end
            
            def append(name)
                @environment[name] = Array(@environment[name])
                
                return name
            end
            
            def define(klass, name, &block)
                @environment[name] = Define.new(klass, &block)
                
                return name
            end
        end
        
        # Flatten the list of environments.
        def self.combine(*environments)
            ordered = []
            
            environments.each do |environment|
                environment.flatten_to_array(ordered)
            end
            
            ordered.inject(nil) do |parent, environment|
                environment.dup(parent: parent)
            end
        end
        
        def merge(**options, &block)
            self.class.new(self, **options, &block)
        end
        
        # Convert the hierarchy of environments to an array where the parent comes before the child.
        def to_a
            flat = []
            
            flatten_to_array(flat)
            
            return flat
        end
        
        def flatten_to_array(array)
            if @parent
                @parent.flatten_to_array(array)
            end
            
            array << self
        end
    end
end