Search completion; reuse previous query.

2 files changed, 28 insertions, 1 deletions

diff --git a/background_scripts/completion_engines.coffee b/background_scripts/completion_engines.coffee
index 85062c49..425ff47e 100644
--- a/background_scripts/completion_engines.coffee
+++ b/background_scripts/completion_engines.coffee
@@ -176,7 +176,7 @@ CompletionEngines =
     # to generate a key.  We mix in some junk generated by pwgen. A key clash might be possible, but
     # vanishingly unlikely.
     junk = "//Zi?ei5;o//"
-    completionCacheKey = searchUrl + junk + queryTerms.join junk
+    completionCacheKey = searchUrl + junk + queryTerms.map((s) -> s.toLowerCase()).join junk
     @completionCache ?= new SimpleCache 60 * 60 * 1000, 2000 # One hour, 2000 entries.
     if @completionCache.has completionCacheKey
       # We add a short delay, even for a cache hit.  This avoids an ugly flicker when the additional
@@ -186,6 +186,21 @@ CompletionEngines =
         callback @completionCache.get completionCacheKey
       return
 
+    if @mostRecentQuery? and @mostRecentSuggestions?
+      # If the user appears to be typing a continuation of the characters in all of the most recent query,
+      # then we can re-use the results of the previous query.
+      reusePreviousSuggestions = do (query) =>
+        query = queryTerms.join(" ").toLowerCase()
+        return false unless 0 == query.indexOf @mostRecentQuery.toLowerCase()
+        previousSuggestions = @mostRecentSuggestions.map (s) -> s.toLowerCase()
+        return false unless query.length <= Utils.longestCommonPrefix previousSuggestions
+        true
+
+      if reusePreviousSuggestions
+        console.log "reuse previous query", @mostRecentQuery if @debug
+        @mostRecentQuery = queryTerms.join " "
+        return callback @completionCache.set completionCacheKey, @mostRecentSuggestions
+
     fetchSuggestions = (engine, callback) =>
       url = engine.getUrl queryTerms
       query = queryTerms.join(" ").toLowerCase()
@@ -227,6 +242,8 @@ CompletionEngines =
         queue = @inTransit[completionCacheKey] = []
         engine = @lookupEngine searchUrl
         fetchSuggestions engine, (suggestions) =>
+          @mostRecentQuery = queryTerms.join " "
+          @mostRecentSuggestions = suggestions
           @completionCache.set completionCacheKey, suggestions unless engine.doNotCache
           callback suggestions
           delete @inTransit[completionCacheKey]
diff --git a/lib/utils.coffee b/lib/utils.coffee
index 16adc305..a1ed23c2 100644
--- a/lib/utils.coffee
+++ b/lib/utils.coffee
@@ -184,6 +184,16 @@ Utils =
       return true if re.test string
     false
 
+  # Calculate the length of the longest shared prefix of a list of strings.
+  longestCommonPrefix: (strings) ->
+    return 0 unless 0 < strings.length
+    strings.sort (a,b) -> a.length - b.length
+    [ shortest, strings... ] = strings
+    for ch, index in shortest.split ""
+      for str in strings
+        return index if ch != str[index]
+    return shortest.length
+
   # Convenience wrapper for setTimeout (with the arguments around the other way).
   setTimeout: (ms, func) -> setTimeout func, ms