add extension points for GitAccess caching

lib/gollum/git_access.rb

@@ -42,13 +42,13 @@ module Gollum
       if sha?(ref)
         ref
       else
-        @ref_map[ref] ||= ref_to_sha!(ref)
+        get_cache(:ref, ref) { ref_to_sha!(ref) }
       end
     end
 
     def tree(ref)
       sha = ref_to_sha(ref)
-      @tree_map[sha] ||= tree!(sha)
+      get_cache(:tree, sha) { tree!(sha) }
     end
 
     def blob(sha)
@@ -57,21 +57,21 @@ module Gollum
 
     def commit(ref)
       if sha?(ref)
-        @commit_map[ref] ||= commit!(ref)
+        get_cache(:commit, ref) { commit!(ref) }
       else
-        if sha = @ref_map[ref]
+        if sha = get_cache(:ref, ref)
           commit(sha)
         else
           cm = commit!(ref)
-          @ref_map[ref]      = cm.id
+          set_cache(:ref,    ref,   cm.id)
-          @commit_map[cm.id] = cm
+          set_cache(:commit, cm.id, cm)
         end
       end
     end
 
     def commits(*shas)
       shas.flatten!
-      cached_commits = multi_get(:commit_map, shas)
+      cached_commits = multi_get(:commit, shas)
       missing_shas   = shas.select do |sha|
         !cached_commits.key?(sha)
       end
@@ -85,16 +85,6 @@ module Gollum
       shas.map { |sha| cached_commits[sha] }
     end
 
-    def multi_get(name, keys)
-      value = instance_variable_get("@#{name}")
-      keys.inject({}) do |memo, key|
-        if v = value[key]
-          memo[key] = v
-        end
-        memo
-      end
-    end
-
     def sha?(str)
       str =~ /^[0-9a-f]{40}$/
     end
@@ -119,6 +109,30 @@ module Gollum
       @repo.commit(sha)
     end
 
+    def get_cache(name, key)
+      cache = instance_variable_get("@#{name}_map")
+      value = cache[key]
+      if value.nil? && block_given?
+        set_cache(name, key, value = yield)
+      end
+      value
+    end
+
+    def set_cache(name, key, value)
+      cache      = instance_variable_get("@#{name}_map")
+      cache[key] = value
+    end
+
+    def multi_get(name, keys)
+      value = instance_variable_get("@#{name}_map")
+      keys.inject({}) do |memo, key|
+        if v = value[key]
+          memo[key] = v
+        end
+        memo
+      end
+    end
+
     # Parses a line of output from the `ls-tree` command.
     #
     # line - A String line of output: