Orca Robotics

00001 #ifndef ORCALOG_FILEBREADCRUMBS_H
00002 #define ORCALOG_FILEBREADCRUMBS_H
00003 
00004 #include <sstream>
00005 #include <fstream>
00006 #include <vector>
00007 #include <IceUtil/IceUtil.h>
00008 #include <orcalog/utils.h>
00009 
00010 namespace orcalog {
00011 namespace detail {
00012 
00014 enum SeekResult {
00015     SeekOK,
00016     SeekQueryInFuture,
00017     SeekQueryBeforeStart
00018 };
00020 
00021 //
00022 // @brief Class to leave a trail of bread-crumbs when moving sequentially through a 
00023 //        file, so we can rewind.
00024 //        Assumes that we start from the start and place a crumb at every point to which
00025 //        we might later want to rewind.
00026 //
00027 // @author Alex Brooks
00028 //
00029 template<typename IndexType>
00030 class FileBreadCrumbs
00031 {
00032 public: 
00033 
00034     // As you move through the file, call this to leave a trail
00035     // of bread-crumbs so that rewind is possible.
00036     // 'pos' can be read with 'tellg()' (STL book p.634)
00037     void placeCrumb( const std::ios::pos_type &pos, const IndexType &t );
00038 
00039     // Tries to find the first marker after (or at) the query.
00040     // Returns:
00041     //   SeekOK: valid answer returned in 'pos'.
00042     //   SeekQueryInFuture : there was no marker at or after the query (ie the query is in the future).
00043     SeekResult getCrumbAtOrAfter( const IndexType &t, std::ios::pos_type &pos );
00044 
00045     // Tries to find the marker exactly at the query.
00046     // Returns:
00047     //   true:  found
00048     //   false: not found
00049     bool getCrumbAt( const IndexType &t, std::ios::pos_type &pos );
00050 
00051     // Tries to find the last marker before the query.
00052     // Returns:
00053     //   SeekOK: valid answer returned in 'pos'.
00054     //   SeekQueryBeforeStart : there was no marker before the query (ie the query is before the start).
00055     SeekResult getCrumbBefore( const IndexType &t, std::ios::pos_type &pos );
00056 
00057     const IndexType &latest() const { return maxIndex_; }
00058 
00059 private: 
00060 
00061     bool haveCrumbAt( const IndexType &t );
00062 
00063     std::map<IndexType,std::ios::pos_type> crumbs_;
00064     typedef typename std::map<IndexType,std::ios::pos_type>::const_iterator ConstCrumbsIterator;
00065 
00066     IndexType maxIndex_;
00067 };
00068 
00071 
00072 template<typename IndexType>
00073 bool
00074 FileBreadCrumbs<IndexType>::haveCrumbAt( const IndexType &index )
00075 {
00076     ConstCrumbsIterator it =
00077         crumbs_.find( index );
00078     return !(it == crumbs_.end());
00079 }
00080 
00081 template<typename IndexType>
00082 void
00083 FileBreadCrumbs<IndexType>::placeCrumb( const std::ios::pos_type &pos,
00084                                               const IndexType &index )
00085 {
00086     if ( crumbs_.size() == 0 )
00087     {
00088         // First crumb -- add it and make this the maxIndex_
00089         maxIndex_ = index;
00090         crumbs_[index] = pos;
00091     }
00092     else
00093     {
00094         // Already have at least one crumb.
00095         // Add this one if it's new.
00096         if ( index > maxIndex_    ||
00097              !haveCrumbAt(index) )
00098         {
00099             crumbs_[index] = pos;
00100             if ( index > maxIndex_ )
00101                 maxIndex_ = index;
00102         }
00103     }
00104 }
00105 
00106 template<typename IndexType>
00107 SeekResult
00108 FileBreadCrumbs<IndexType>::getCrumbAtOrAfter( const IndexType &index,
00109                                                      std::ios::pos_type &pos )
00110 {
00111     ConstCrumbsIterator it = crumbs_.lower_bound( index );
00112     if ( it == crumbs_.end() )
00113     {
00114         return SeekQueryInFuture;
00115     }
00116     else
00117     {
00118         pos = it->second;
00119         return SeekOK;
00120     }
00121 }
00122 
00123 template<typename IndexType>
00124 bool
00125 FileBreadCrumbs<IndexType>::getCrumbAt( const IndexType &index,
00126                                         std::ios::pos_type &pos )
00127 {
00128     ConstCrumbsIterator it = crumbs_.find( index );
00129     if ( it == crumbs_.end() )
00130     {
00131         return false;
00132     }
00133     else
00134     {
00135         pos = it->second;
00136         return true;
00137     }
00138 }
00139 
00140 template<typename IndexType>
00141 SeekResult 
00142 FileBreadCrumbs<IndexType>::getCrumbBefore( const IndexType &index,
00143                                             std::ios::pos_type &pos )
00144 {
00145     // Find the first crumb after the specified index
00146     ConstCrumbsIterator it = crumbs_.lower_bound( index );
00147 
00148     if ( it == crumbs_.begin() )
00149     {
00150         return SeekQueryBeforeStart;
00151     }
00152     else
00153     {
00154         it--;
00155         pos = it->second;
00156         return SeekOK;
00157     }
00158 }
00159 
00161 
00162 inline std::string toString( SeekResult &r )
00163 {
00164     std::stringstream ss;
00165     switch (r)
00166     {
00167     case SeekOK:
00168         ss << "SeekOK";
00169         break;
00170     case SeekQueryInFuture:
00171         ss << "SeekQueryInFuture";
00172         break;
00173     case SeekQueryBeforeStart:
00174         ss << "SeekQueryBeforeStart";
00175         break;
00176     default:
00177         ss << "Unknown SeekResult";
00178         break;
00179     }
00180     return ss.str();
00181 }
00182 
00183 } // end namespace orcalog
00184 } // end namespace detail
00185 
00186 #endif
filebreadcrumbs.h
