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      1 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "chrome/browser/history/visit_tracker.h"
      6 
      7 #include "base/stl_util.h"
      8 
      9 namespace history {
     10 
     11 // When the list gets longer than 'MaxItems', CleanupTransitionList will resize
     12 // the list down to 'ResizeTo' size. This is so we only do few block moves of
     13 // the data rather than constantly shuffle stuff around in the vector.
     14 static const size_t kMaxItemsInTransitionList = 96;
     15 static const size_t kResizeBigTransitionListTo = 64;
     16 COMPILE_ASSERT(kResizeBigTransitionListTo < kMaxItemsInTransitionList,
     17                max_items_must_be_larger_than_resize_to);
     18 
     19 VisitTracker::VisitTracker() {
     20 }
     21 
     22 VisitTracker::~VisitTracker() {
     23   STLDeleteContainerPairSecondPointers(contexts_.begin(), contexts_.end());
     24 }
     25 
     26 // This function is potentially slow because it may do up to two brute-force
     27 // searches of the transitions list. This transitions list is kept to a
     28 // relatively small number by CleanupTransitionList so it shouldn't be a big
     29 // deal. However, if this ends up being noticable for performance, we may want
     30 // to optimize lookup.
     31 VisitID VisitTracker::GetLastVisit(ContextID context_id,
     32                                    int32 page_id,
     33                                    const GURL& referrer) {
     34   if (referrer.is_empty() || !context_id)
     35     return 0;
     36 
     37   ContextList::iterator i = contexts_.find(context_id);
     38   if (i == contexts_.end())
     39     return 0;  // We don't have any entries for this context.
     40   TransitionList& transitions = *i->second;
     41 
     42   // Recall that a page ID is associated with a single session history entry.
     43   // In the case of automatically loaded iframes, many visits/URLs can have the
     44   // same page ID.
     45   //
     46   // We search backwards, starting at the current page ID, for the referring
     47   // URL. This won't always be correct. For example, if a render process has
     48   // the same page open in two different tabs, or even in two different frames,
     49   // we can get confused about which was which. We can have the renderer
     50   // report more precise referrer information in the future, but this is a
     51   // hard problem and doesn't affect much in terms of real-world issues.
     52   //
     53   // We assume that the page IDs are increasing over time, so larger IDs than
     54   // the current input ID happened in the future (this will occur if the user
     55   // goes back). We can ignore future transitions because if you navigate, go
     56   // back, and navigate some more, we'd like to have one node with two out
     57   // edges in our visit graph.
     58   for (int i = static_cast<int>(transitions.size()) - 1; i >= 0; i--) {
     59     if (transitions[i].page_id <= page_id && transitions[i].url == referrer) {
     60       // Found it.
     61       return transitions[i].visit_id;
     62     }
     63   }
     64 
     65   // We can't find the referrer.
     66   return 0;
     67 }
     68 
     69 void VisitTracker::AddVisit(ContextID context_id,
     70                             int32 page_id,
     71                             const GURL& url,
     72                             VisitID visit_id) {
     73   TransitionList* transitions = contexts_[context_id];
     74   if (!transitions) {
     75     transitions = new TransitionList;
     76     contexts_[context_id] = transitions;
     77   }
     78 
     79   Transition t;
     80   t.url = url;
     81   t.page_id = page_id;
     82   t.visit_id = visit_id;
     83   transitions->push_back(t);
     84 
     85   CleanupTransitionList(transitions);
     86 }
     87 
     88 void VisitTracker::ClearCachedDataForContextID(ContextID context_id) {
     89   ContextList::iterator i = contexts_.find(context_id);
     90   if (i == contexts_.end())
     91     return;  // We don't have any entries for this context.
     92 
     93   delete i->second;
     94   contexts_.erase(i);
     95 }
     96 
     97 
     98 void VisitTracker::CleanupTransitionList(TransitionList* transitions) {
     99   if (transitions->size() <= kMaxItemsInTransitionList)
    100     return;  // Nothing to do.
    101 
    102   transitions->erase(transitions->begin(),
    103                      transitions->begin() + kResizeBigTransitionListTo);
    104 }
    105 
    106 }  // namespace history
    107