Resolve some uses of {Ref} and {Fn::FindInMap} inside Boxen decls.

This is required if you want to e.g. use a different base AMI depending
on the target region.  It's nice to use the same syntax as CloudFormation
runtime.

ChangeLog

@@ -8,9 +8,11 @@ PENDING
     will write those files at startup.
 * Rename "lib/projinfo.js" to "lib/loadTemplate.js", since that's really
   the only thing that it does.
+* Resolve uses of {'Ref'} and {'Fn::FindInMap'} in Boxen declarations.
+  This is helpful if you need to use a different AMI in different regions.
+* Allow specifying --aws-id, --aws-secret and --aws-region on the command line.
 * Tweak how .awsbox.json declarations are upgraded into a Boxen, making it
   possible to disable this feature by setting Boxen.AWSBox = null;
-* Allow specifying --aws-id, --aws-secret and --aws-region on the command line.
 
 
 0.3.0 - 2013-06-25

lib/loadTemplate.js

@@ -212,6 +212,40 @@ function loadTemplate(projDir, opts, cb) {
         cb(null);
       },
 
+      // Resolve any CloudFormation function calls inside Boxen declarations.
+      // It's kinda yuck that we have to do this, but the Boxen need to be
+      // build before CloudFormation ever sees the template.
+      function resolveFunctionCallsInBoxenDefinitions(cb) {
+        // Do one pass to resolve "AWS::Region" and "AWS::StackName" refs.
+        traverse(cfg).forEach(function(obj) {
+          if (typeof obj === 'object') {
+            var keys = Object.keys(obj);
+            if (keys.length === 1 && keys[0] === 'Ref') {
+              if (obj['Ref'] === 'AWS::Region') {
+                this.update(opts.aws_region);
+              } else if (obj['Ref'] === 'AWS::StackName' && opts.name) {
+                this.update(opts.name);
+              }
+            }
+          }
+        });
+        // Now we can resolve any occurrances of Fn::FindInMap.
+        traverse(cfg).forEach(function(obj) {
+          if (typeof obj === 'object') {
+            var keys = Object.keys(obj);
+            if (keys.length === 1 && keys[0] === 'Fn::FindInMap') {
+              try {
+                var mapped = cfg.Mappings[obj['Fn::FindInMap'][0]];
+                mapped = mapped[obj['Fn::FindInMap'][1]];
+                mapped = mapped[obj['Fn::FindInMap'][2]];
+                this.update(mapped);
+              } catch (e) { };
+            }
+          }
+        });
+        return cb(null);
+      },
+
       // Apply any custom helper functions.
       // We traverse the entire document looking for single-key objects
       // whose key matches "Fn::AWSBoxen::<funcname>", then call the named