5 files changed, 80 insertions, 16 deletions

diff --git a/lib/dsl.rb b/lib/dsl.rb
index caed790..b9062e5 100644
--- a/lib/dsl.rb
+++ b/lib/dsl.rb
@@ -25,7 +25,7 @@ module RCM
 
     def initialize(reset)
       DSL.reset! if reset
-      @id = "dsl[#{@@rcm_counter += 1}]"
+      @id = "dsl(#{@@rcm_counter += 1})"
       @conds_met = true
       @scheduled = []
       yield self if block_given?
diff --git a/lib/dslkeywords/file.rb b/lib/dslkeywords/file.rb
index 501b7c8..e83906e 100644
--- a/lib/dslkeywords/file.rb
+++ b/lib/dslkeywords/file.rb
@@ -1,13 +1,32 @@
+require 'digest'
 require 'erb'
 require 'fileutils'
 
 require_relative 'resource'
 
 module RCM
+  # Backup the file on change
+  module FileBackup
+    def backup!(path)
+      return unless ::File.exist?(path)
+
+      backup_dir = "#{::File.dirname(path)}/.rcm"
+      Dir.mkdir(backup_dir) unless ::File.directory?(backup_dir)
+      checksum = Digest::SHA256.file(path).hexdigest
+      backup_path = "#{backup_dir}/#{::File.basename(path)}.#{checksum}"
+      return if ::File.exist?(backup_path)
+
+      info("Backing up #{path} -> #{backup_path}")
+      ::File.rename(path, backup_path)
+    end
+  end
+
   # Managing files
   class File < Resource
     attr_reader :path
 
+    include FileBackup
+
     def initialize(path)
       super(path)
       @path = path
@@ -25,6 +44,7 @@ module RCM
     def ensure_line(line) = @ensure_line = line
 
     def evaluate!
+      return unless super
       return evaluate_ensure_line! unless @ensure_line.nil?
 
       write_content!(real_content)
@@ -44,9 +64,10 @@ module RCM
     def write_content!(text)
       create_parent_directory!
       debug text if option :debug
-      info "Creating file #{@path}"
+      info "Managing file #{@path}"
       tmp_path = "#{@path}.tmp"
       ::File.write(tmp_path, text)
+      backup!(@path)
       ::File.rename(tmp_path, @path)
     end
 
diff --git a/lib/dslkeywords/keyword.rb b/lib/dslkeywords/keyword.rb
index 2696e41..2dfff91 100644
--- a/lib/dslkeywords/keyword.rb
+++ b/lib/dslkeywords/keyword.rb
@@ -9,7 +9,7 @@ module RCM
     include Options
     include Log
 
-    def initialize(name) = @id = "#{self.class.to_s.sub('RCM::', '').downcase}['#{name}']"
+    def initialize(name) = @id = "#{self.class.to_s.sub('RCM::', '').downcase}('#{name}')"
     def to_s = @id
   end
 end
diff --git a/lib/dslkeywords/notify.rb b/lib/dslkeywords/notify.rb
index 602d216..e1d8a3d 100644
--- a/lib/dslkeywords/notify.rb
+++ b/lib/dslkeywords/notify.rb
@@ -15,7 +15,11 @@ module RCM
       @message = msg unless msg.nil?
     end
 
-    def evaluate! = puts "#{id} => #{@message}"
+    def evaluate!
+      return unless super
+
+      puts "#{id} => #{@message}"
+    end
   end
 
   # Add notify keyword to the DSL
diff --git a/lib/dslkeywords/resource.rb b/lib/dslkeywords/resource.rb
index c9098d4..f665a50 100644
--- a/lib/dslkeywords/resource.rb
+++ b/lib/dslkeywords/resource.rb
@@ -7,41 +7,80 @@ module RCM
   module ResourceDependencies
     def initialize(...)
       super(...)
+      @depends_on = Set.new
       @valid_resources = Set.new
       ObjectSpace.each_object(Class).each do |klass|
         @valid_resources << klass.to_s.sub('RCM::', '').downcase.to_sym if klass < Resource
       end
     end
 
-    # Only to have the resourcename[id] syntax available in the DSL
-    class SyntaxSugar
-      def initialize(name) = @name = name
-      def [](other) = "#{@name}['#{other}']"
-    end
-
     class NoSuchResourceType < StandardError; end
 
-    def method_missing(method_name)
+    def method_missing(method_name, *args)
       raise NoSuchResourceType, "No such resource type: #{method_name}" unless @valid_resources.include?(method_name)
 
-      SyntaxSugar.new(method_name)
+      args.map { |arg| "#{method_name}('#{arg}')" }
     end
 
     def respond_to_missing? = true
 
     def depends_on(*others)
-      @dependencies = {} if @dependencies.nil?
-      others.each do |other|
+      return @depends_on if others.empty?
+
+      others.flatten.each do |other|
         info "Registered dependency on #{other}"
-        @dependencies[other] = {}
+        @depends_on << other
       end
     end
 
-    def dependencies = @dependencies.nil ? [] : @dependencies
+    def depends_on?(*others) = others.flatten.none? { |other| !@depends_on&.include?(other) }
+  end
+
+  # To resolve dependencies
+  module DependencyEvaluator
+    attr_reader :evaluated
+
+    class DependencyLoop < StandardError; end
+    class UnresolvedDependency < StandardError; end
+
+    def evaluate!
+      return false if @evaluated
+
+      raise DependencyLoop, "Dependency loop detected for #{id}" if @loop_detection
+
+      @loop_detection = true
+
+      # Try to evaluate all dependencies recursively.
+      @depends_on.each.map { Resource.find(_1) }.each(&:evaluate!)
+
+      # Raise an exception when there are still unresolved dependencies.
+      unresolved = @depends_on.each.map { Resource.find(_1) }.reject(&:evaluated)
+      raise UnresolvedDependency, "Unresolved dependencies: #{unresolved.map(&:id)}" if unresolved.count.positive?
+
+      @loop_detection = false
+      @evaluated = true
+    end
   end
 
   # A resource is something concrete to be managed, e.g. a file, or a CRON job.
   class Resource < Keyword
+    include DependencyEvaluator
     include ResourceDependencies
+
+    class NoSuchResourceObject < StandardError; end
+
+    # TODO: Detect duplicate resource definition
+
+    @@resource_find_cache = {}
+
+    def self.find(id)
+      return @@resource_find_cache[id] if @@resource_find_cache.key?(id)
+
+      klass = Object.const_get("RCM::#{id.split('(').first.capitalize}")
+      resource = ObjectSpace.each_object(klass).find { _1.id == id }
+      raise NoSuchResourceObject, "Unable to find resource #{id}" if resource.nil?
+
+      @@resource_find_cache[id] = resource
+    end
   end
 end