track reverse dependencies (#16, #32, #35)

1 files changed, 24 insertions, 4 deletions

diff --git a/html/js/git-deps-data.coffee b/html/js/git-deps-data.coffee
index ae3816f..9034b18 100644
--- a/html/js/git-deps-data.coffee
+++ b/html/js/git-deps-data.coffee
@@ -10,12 +10,20 @@ links = []
 # same node twice.
 node_index = {}
 
-# Constraints will be added to try to keep siblings at the same y
-# position.  For this we need to track siblings, which we do by
-# mapping each parent to an array of its siblings in this hash.
-# It also enables us to deduplicate links across multiple XHRs.
+# Track dependencies in a hash of hashes which maps parents to
+# children to booleans.  Constraints will be added to try to keep
+# siblings at the same y position.  For this we need to track
+# siblings, which we do by mapping each parent to an array of its
+# siblings in this hash.  It also enables us to deduplicate links
+# across multiple XHRs.
 deps = {}
 
+# Track dependences in reverse in a hash of hashes which maps children
+# to parents to booleans.  This allows us to highlight parents when
+# the mouse hovers over a child, and know when we can safely remove
+# a commit due to its sole parent being deleted.
+rdeps = {}
+
 # Returns 1 iff a node was added, otherwise 0.
 add_node = (commit) ->
     if commit.sha1 of node_index
@@ -38,6 +46,16 @@ add_dependency = (parent_sha1, child_sha1) ->
     add_link parent_sha1, child_sha1
     return 1
 
+# Returns 1 iff a reverse dependency was added, otherwise 0.
+add_rev_dependency = (child_sha1, parent_sha1) ->
+    rdeps[child_sha1] = {}  unless child_sha1 of rdeps
+
+    # We've already got this link, presumably
+    # from a previous XHR.
+    return 0 if parent_sha1 of rdeps[child_sha1]
+    rdeps[child_sha1][parent_sha1] = true
+    return 1
+
 add_link = (parent_sha1, child_sha1) ->
     pi = node_index[parent_sha1]
     ci = node_index[child_sha1]
@@ -58,6 +76,7 @@ add_data = (data) ->
 
     for dep in data.dependencies
         new_deps += add_dependency(dep.parent, dep.child)
+        add_rev_dependency(dep.child, dep.parent)
 
     if new_nodes > 0 or new_deps > 0
         return [
@@ -82,6 +101,7 @@ module.exports =
     links: links
     node_index: node_index
     deps: deps
+    rdeps: rdeps
 
     # Functions
     add: add_data