Re-work completions: extend engine wrapper to handle prefixes.

This commit contains the bulk og the material changes for which the
previous commits established the basis.

1) Add a general framework for detecting query prefixes in search URLs,
adding them to query sent to the completion engine, and stripping them
from the resulting suggestions.  This allows the user to have a
search engine...

   j: http://www.google.com/search?q=javascript+%s Javascript

and have the prefix "javascript" included (automatically) in queries
sent to completion engines, which results in substantially better
suggestions.

2) Re-work completion for Google Maps in a simpler form.

1 files changed, 47 insertions, 19 deletions

diff --git a/background_scripts/completion_search.coffee b/background_scripts/completion_search.coffee
index b3ae88d4..09261ff6 100644
--- a/background_scripts/completion_search.coffee
+++ b/background_scripts/completion_search.coffee
@@ -1,12 +1,38 @@
 
-class EngineWrapper
+# This is a wrapper class for completion engines.  It handles the case where a custom search engine includes a
+# prefix query term (or terms).  For example:
+#
+#   http://www.google.com/search?q=javascript+%s
+#
+# In this case, we get better suggestions if we include the term "javascript" in queries sent to the
+# completion engine.  This wrapper handles adding such prefixes to completion-engine queries and removing them
+# from the resulting suggestions.
+class EnginePrefixWrapper
   constructor: (@searchUrl, @engine) ->
 
   getUrl: (queryTerms) ->
+    # This tests whether @searchUrl contains something of the form "...=abc+def+%s...", from which we extract
+    # a prefix of the form "abc def ".
+    if /\=.+\+%s/.test @searchUrl
+      terms = @searchUrl.replace /\+%s.*/, ""
+      terms = terms.replace /.*=/, ""
+      terms = terms.replace /\+/g, " "
+
+      queryTerms = [ terms.split(" ")..., queryTerms... ]
+      prefix = "#{terms} "
+
+      @postprocessSuggestions =
+        (suggestions) ->
+          for suggestion in suggestions
+            continue unless suggestion.startsWith prefix
+            suggestion[prefix.length..]
+
     @engine.getUrl queryTerms
 
   parse: (xhr) ->
-    @engine.parse xhr
+    @postprocessSuggestions @engine.parse xhr
+
+  postprocessSuggestions: (suggestions) -> suggestions
 
 CompletionSearch =
   debug: false
@@ -74,22 +100,23 @@ CompletionSearch =
 
     # If the user appears to be typing a continuation of the characters of the most recent query, then we can
     # sometimes re-use the previous suggestions.
-    if @mostRecentQuery? and @mostRecentSuggestions?
-      reusePreviousSuggestions = do =>
-        # Verify that the previous query is a prefix of the current query.
-        return false unless 0 == query.indexOf @mostRecentQuery.toLowerCase()
-        # Verify that every previous suggestion contains the text of the new query.
-        # Note: @mostRecentSuggestions may also be empty, in which case we drop though. The effect is that
-        # previous queries with no suggestions suppress subsequent no-hope HTTP requests as the user continues
-        # to type.
-        for suggestion in @mostRecentSuggestions
-          return false unless 0 <= suggestion.indexOf query
-        # Ok. Re-use the suggestion.
-        true
-
-      if reusePreviousSuggestions
-        console.log "reuse previous query:", @mostRecentQuery, @mostRecentSuggestions.length if @debug
-        return callback @completionCache.set completionCacheKey, @mostRecentSuggestions
+    if @mostRecentQuery? and @mostRecentSuggestions? and @mostRecentSearchUrl?
+      if searchUrl == @mostRecentSearchUrl
+        reusePreviousSuggestions = do =>
+          # Verify that the previous query is a prefix of the current query.
+          return false unless 0 == query.indexOf @mostRecentQuery.toLowerCase()
+          # Verify that every previous suggestion contains the text of the new query.
+          # Note: @mostRecentSuggestions may also be empty, in which case we drop though. The effect is that
+          # previous queries with no suggestions suppress subsequent no-hope HTTP requests as the user continues
+          # to type.
+          for suggestion in @mostRecentSuggestions
+            return false unless 0 <= suggestion.indexOf query
+          # Ok. Re-use the suggestion.
+          true
+
+        if reusePreviousSuggestions
+          console.log "reuse previous query:", @mostRecentQuery, @mostRecentSuggestions.length if @debug
+          return callback @completionCache.set completionCacheKey, @mostRecentSuggestions
 
     # That's all of the caches we can try.  Bail if the caller is only requesting synchronous results.  We
     # signal that we haven't found a match by returning null.
@@ -102,7 +129,7 @@ CompletionSearch =
 
         # Elide duplicate requests. First fetch the suggestions...
         @inTransit[completionCacheKey] ?= new AsyncDataFetcher (callback) =>
-          engine = new EngineWrapper searchUrl, @lookupEngine searchUrl
+          engine = new EnginePrefixWrapper searchUrl, @lookupEngine searchUrl
           url = engine.getUrl queryTerms
 
           @get searchUrl, url, (xhr = null) =>
@@ -128,6 +155,7 @@ CompletionSearch =
 
         # ... then use the suggestions.
         @inTransit[completionCacheKey].use (suggestions) =>
+          @mostRecentSearchUrl = searchUrl
           @mostRecentQuery = query
           @mostRecentSuggestions = suggestions
           callback @completionCache.set completionCacheKey, suggestions