From a1328211b04c7574c58497c909fc7889f29ea49a Mon Sep 17 00:00:00 2001
From: Sam Lown <me@samlown.com>
Date: Mon, 11 Jun 2012 20:48:36 +0200
Subject: [PATCH] Working on migration

---
 lib/couchrest/model/designs/design.rb | 87 +++++++++++++++++++++------
 1 file changed, 68 insertions(+), 19 deletions(-)

diff --git a/lib/couchrest/model/designs/design.rb b/lib/couchrest/model/designs/design.rb
index c6f9ee88..de332842 100644
--- a/lib/couchrest/model/designs/design.rb
+++ b/lib/couchrest/model/designs/design.rb
@@ -67,45 +67,94 @@ def sync!(db = nil)
         #  3. Wait until the view returns a result
         #  4. Copy over the original design doc
         #
-        # A status will be returned according to which method was used in
-        # the migration, if at all. The symbols are:
+        # If a block is provided, it will be called with the result of the migration:
         #
         #  * :no_change - Nothing performed as there are no changes.
         #  * :created   - Add a new design doc as non existed
         #  * :migrated  - Migrated the existing design doc.
         #
+        # This can be used for progressivly printing the results of the migration.
         #
-        def migrate!(db = nil)
-          doc = load_from_database(db)
+        # After completion, either a "cleanup" Proc object will be provided to finalize
+        # the process and copy the document into place, or simply nil if no cleanup is
+        # required. For example:
+        #
+        #     print "Synchronising Cat model designs: "
+        #     callback = Cat.design_doc.migrate do |res|
+        #       puts res.to_s
+        #     end
+        #     if callback
+        #       puts "Cleaning up."
+        #       callback.call
+        #     end
+        #
+        def migrate(db = nil, &block)
+          doc     = load_from_database(db)
+          cleanup = nil
 
           if !doc
             # no need to migrate, just save it
-            db.save_doc(to_hash)
-            :created
+            new_doc = to_hash.dup
+            db.save_doc(new_doc)
+
+            result = :created
           else doc['couchrest-hash'] != checksum
-            # Migration required
-            doc.merge!(to_hash)
-            doc['_id'] = self['_id']+"_#{Time.now.to_i}"
-            db.save_doc(doc)
+            id = self['_id'] + "_migration"
+
+            # Delete current migration if there is one
+            old_migration = db.get(id)
+            db.delete_doc(old_migration) if old_migration
+
+            # Save new design doc
+            new_doc = doc.merge(to_hash)
+            new_doc['_id'] = id
+            new_doc.delete('_rev')
+            db.save_doc(new_doc)
+
+            # Proc definition to copy the migration doc over the original
+            cleanup = Proc.new do
+              db.copy_doc(new_doc, doc)
+              db.delete_doc(new_doc)
+              self
+            end
 
+            result = :migrated
+          else
+            # Already up to date
+            result = :no_change
+          end
+
+          if new_doc && !new_doc['views'].empty?
             # Create a view query and send
-            name = doc['views'].keys.first
-            view = doc['views'][name]
+            name = new_doc['views'].keys.first
+            view = new_doc['views'][name]
             params = {:limit => 1}
-            params[:reduce => false] if view['reduce']
+            params[:reduce] = false if view['reduce']
             db.view(name, params)
+          end
 
-            # When that finishes, copy the design doc back
-            db.copy_doc(doc['_id'], self['_id'])
+          # Provide the result in block
+          yield result if block_given?
+
+          cleanup
+        end
 
-            :migrated
+        # Perform a single migration and inmediatly request a cleanup operation:
+        #
+        #     print "Synchronising Cat model designs: "
+        #     Cat.design_doc.migrate! do |res|
+        #       puts res.to_s
+        #     end
+        #
+        def migrate!(db = nil, &block)
+          callback = migrate(db, &block)
+          if callback.is_a?(Proc)
+            callback.call
           else
-            # Already up to date
-            :no_change
+            callback
           end
         end
 
-
         def checksum
           sum = self['couchrest-hash']
           if sum && (@_original_hash == to_hash)