#include "source/common/stats/stat_merger.h"

#include <algorithm>

namespace Envoy {

namespace Stats {

  // By the time a parent exits, all its contributions to accumulated gauges

  // should be zero. But depending on the timing of the stat-merger

  // communication shutdown and other shutdown activities on the parent, the

  // gauges may not all be zero yet. So simply erase all the parent

  // contributions.

StatName StatMerger::DynamicContext::makeDynamicStatName(const std::string& name,

  // Name has embedded dynamic segments; we'll need to join together the

  // static/dynamic StatName segments.

      // Handle start of dynamic span. We note that we are in a dynamic

      // span by adding to dynamic_segments, which should of course be

      // non-empty.

        // Handle start==end (a one-segment span).

        // Handle start<end, so we save the first segment in dynamic_segments.

      // Handle that we are not in dynamic mode; we are just allocating

      // a symbolic segment.

      // Handle the next dynamic segment.

        // Handle that this dynamic segment is the last one, and we're flipping

        // back to symbolic mode.

void StatMerger::mergeCounters(const Protobuf::Map<std::string, uint64_t>& counter_deltas,

void StatMerger::mergeGauges(const Protobuf::Map<std::string, uint64_t>& gauges,

    // Merging gauges via RPC from the parent has 3 cases; case 1 and 3b are the

    // most common.

    //

    // 1. Child thinks gauge is Accumulate : data is combined in

    //    gauge_ref.add() below.

    // 2. Child thinks gauge is NeverImport: we skip this loop entry via

    //    'continue'.

    // 3. Child has not yet initialized gauge yet -- this merge is the

    //    first time the child learns of the gauge. It's possible the child

    //    will think the gauge is NeverImport due to a code change. But for

    //    now we will leave the gauge in the child process as

    //    import_mode==Uninitialized, and accumulate the parent value in

    //    gauge_ref.add(). Gauges in this mode will be included in

    //    stats-sinks or the admin /stats calls, until the child initializes

    //    the gauge, in which case:

    // 3a. Child later initializes gauges as NeverImport: the parent value is

    //     cleared during the mergeImportMode call.

    // 3b. Child later initializes gauges as Accumulate: the parent value is

    //     retained.

    // TODO(snowp): Propagate tag values during hot restarts.

      // On the first iteration through the loop, the gauge will not be loaded into the scope

      // cache even though it might exist in another scope. Thus, we need to check again for

      // the import status to see if we should skip this gauge.

      //

      // TODO(mattklein123): There is a race condition here. It's technically possible that

      // between the time we created this stat, the stat might be created by the child as a

      // never import stat, making the below math invalid. A follow up solution is to take the

      // store lock starting from gaugeFromStatName() to the end of this function, but this will

      // require adding some type of mergeGauge() function to the scope and dealing with recursive

      // lock acquisition, etc. so we will leave this as a follow up. This race should be incredibly

      // rare.

void StatMerger::mergeStats(const Protobuf::Map<std::string, uint64_t>& counter_deltas,

                            const Protobuf::Map<std::string, uint64_t>& gauges,

} // namespace Stats

} // namespace Envoy