package_installer.rb in rconf-0.6.30

- old
+ new
@@ -22,17 +22,33 @@
     # packages(String|Array):: Package name or Packages list
     # opts[:abort_on_failure](String):: Optional, abort configuration
     #   and display given error message if install fails when set
     # opts[:report](TrueClass|FalseClass):: Whether to report installation
     #
+    # === Block
+    # If a block is given it will get called with no argument prior to the
+    # packages being installed. If the block returns true then installation
+    # will proceed otherwise it won't. Use the block to check whether 
+    # installation is required or whether the packages are already installed.
+    # If no block is given then installation will always occur.
+    #
     # === Return
     # true:: Always return true
-    def install(packages, opts=nil)
+    def install(packages, opts=nil, &install_check)
       packages = [ packages ].flatten
       report = opts && opts.delete(:report)
-      report_check("Installing the following packages:\n#{packages.join(' ')}\nThis could take a while") if report
-      Platform.dispatch(packages, opts) { :install }
-      report_success if report
+      must_install = true
+      if install_check
+        report_check("Checking for #{packages.join(', ')}") if report
+        must_install = install_check.call
+        report_result(must_install) if report
+      end
+      if must_install
+        report_check("Installing #{packages.join(', ')}") if report
+        Platform.dispatch(packages, opts) { :install }
+        report_success if report
+      end
+      true
     end
 
     protected
 
     # Install debian packages