// See the file "COPYING" in the main distribution directory for copyright.

#include "zeek/script_opt/UsageAnalyzer.h"

#include "zeek/EventRegistry.h"
#include "zeek/module_util.h"
#include "zeek/script_opt/IDOptInfo.h"

namespace zeek::detail {

// The names of identifiers that correspond to events not-previously-known
// before their declaration in the scripts.
std::unordered_set<std::string> script_events;

void register_new_event(const IDPtr& id) { script_events.insert(id->Name()); }

UsageAnalyzer::UsageAnalyzer(std::vector<FuncInfo>& funcs) {
    // First, prune the script events to only those that were never
    // registered in a non-script context.
    auto script_events_orig = script_events;
    script_events.clear();

    for ( auto& ev : script_events_orig )
        if ( ! event_registry->NotOnlyRegisteredFromScript(ev) )
            script_events.insert(ev);

    // Setting a scope cues ID::Traverse to delve into function values.
    current_scope = global_scope();

    FindSeeds(reachables);
    FullyExpandReachables();

    // At this point, we've done the complete reachability analysis.
    // Report out on unreachables.  We do this in two steps: first,
    // unreachable events/hooks, and then unreachable functions.  We
    // split the two because we don't want to ding a function as being
    // unreachable if there's an (unreachable) event-or-hook that calls
    // it, since presumably the real problem is the latter being an
    // orphan, rather than the function.

    auto& globals = global_scope()->Vars();

    for ( auto& gpair : globals ) {
        auto id = gpair.second.get();
        auto& t = id->GetType();

        if ( t->Tag() != TYPE_FUNC )
            continue;

        if ( t->AsFuncType()->Flavor() == FUNC_FLAVOR_FUNCTION )
            continue;

        if ( reachables.count(id) > 0 )
            continue;

        auto flavor = t->AsFuncType()->FlavorString();
        auto loc = id->GetLocationInfo();

        id->Warn(util::fmt("handler for non-existing %s cannot be invoked", flavor.c_str()));

        // Don't ding any functions that are reachable via this
        // identifier.  This will also suppress flagging other events
        // and hooks, depending on order-of-traversal.  That seems
        // fine, as the key is to find the root of such issues.
        reachables.insert(id);
        Expand(id);
    }

    // Now make a second pass, focusing solely on functions.
    for ( auto& gpair : globals ) {
        auto& id = gpair.second;

        if ( reachables.count(id.get()) > 0 )
            continue;

        auto f = GetFuncIfAny(id);
        if ( ! f )
            continue;

        auto loc = id->GetLocationInfo();

        id->Warn("non-exported function does not have any callers");

        // Unlike for events/hooks above, we don't add the function to
        // the reachables.  This is because an orphan function is a
        // somewhat more significant potential error than an orphan
        // event handler or hook, as the latter can arise from simple
        // typos (because there will be a declaration elsewhere that
        // they're supposed to match), whereas orphan functions in
        // general will not.
    }
}

// Find all identifiers in attributes for seeding.
//
// General motivation: Dinging functions referenced from &default or &expire_func
// on tables or &default on record types is confusing when really the containing
// table/type is unused. Any IDs references from attributes are therefore
// implicitly used as seeds.
class AttrExprIdsCollector : public TraversalCallback {
public:
    TraversalCode PreAttr(const Attr* attr) override {
        ++attr_depth;
        return TC_CONTINUE;
    }

    TraversalCode PostAttr(const Attr* attr) override {
        --attr_depth;
        return TC_CONTINUE;
    }

    TraversalCode PreType(const Type* t) override {
        if ( analyzed_types.count(t) > 0 )
            return TC_ABORTSTMT;

        analyzed_types.insert(t);
        return TC_CONTINUE;
    }

    TraversalCode PreID(const ID* id) override {
        if ( ids.count(id) > 0 )
            return TC_ABORTSTMT;

        if ( attr_depth > 0 )
            ids.insert(id);

        id->GetType()->Traverse(this);

        if ( auto& attrs = id->GetAttrs() )
            attrs->Traverse(this);

        return TC_CONTINUE;
    }

    int attr_depth = 0;                   // Are we in an attribute?
    std::set<const detail::ID*> ids;      // List of IDs found in attributes.
    std::set<const Type*> analyzed_types; // Endless recursion avoidance.
};

void UsageAnalyzer::FindSeeds(IDSet& seeds) const {
    AttrExprIdsCollector attr_ids_collector;
    for ( auto& gpair : global_scope()->Vars() ) {
        auto& id = gpair.second;

        if ( id->GetAttr(ATTR_IS_USED) || id->GetAttr(ATTR_DEPRECATED) ) {
            seeds.insert(id.get());
            continue;
        }

        auto f = GetFuncIfAny(id);

        if ( f && id->GetType<FuncType>()->Flavor() == FUNC_FLAVOR_EVENT ) {
            if ( script_events.count(f->Name()) == 0 )
                seeds.insert(id.get());

            continue;
        }

        // If the global is exported, or has global scope, we assume
        // it's meant to be used, even if the current scripts don't
        // use it.
        if ( id->IsExport() || id->ModuleName() == "GLOBAL" )
            seeds.insert(id.get());
        else
            // ...otherwise, find all IDs referenced from attribute expressions
            // found through this identifier.
            id->Traverse(&attr_ids_collector);
    }

    seeds.insert(attr_ids_collector.ids.begin(), attr_ids_collector.ids.end());
}

const Func* UsageAnalyzer::GetFuncIfAny(const ID* id) const {
    auto& t = id->GetType();
    if ( t->Tag() != TYPE_FUNC )
        return nullptr;

    auto fv = cast_intrusive<FuncVal>(id->GetVal());
    if ( ! fv )
        return nullptr;

    auto func = fv->Get();
    return func->GetKind() == Func::SCRIPT_FUNC ? func : nullptr;
}

void UsageAnalyzer::FullyExpandReachables() {
    // We use the following structure to avoid having to copy
    // the initial set of reachables, which can be quite large.
    if ( ExpandReachables(reachables) ) {
        auto r = new_reachables;
        reachables.insert(r.begin(), r.end());

        while ( ExpandReachables(r) ) {
            r = new_reachables;
            reachables.insert(r.begin(), r.end());
        }
    }
}

bool UsageAnalyzer::ExpandReachables(const IDSet& curr_r) {
    new_reachables.clear();

    for ( auto r : curr_r )
        Expand(r);

    return ! new_reachables.empty();
}

void UsageAnalyzer::Expand(const ID* id) {
    // A subtle problem arises for exported globals that refer to functions
    // that themselves generate events.  Because for identifiers we don't
    // traverse their values (since there's no Traverse infrastructure for
    // Val classes), we can see those identifiers initially in a seeding
    // context, where we can't associate them with their functions; and
    // then again when actually analyzing that function.
    //
    // It might be tempting to special-case the seeding phase, but that
    // gets hard if the global doesn't directly refer to the function,
    // but instead ultimately incorporates a type with an attribute that
    // uses the function.  So instead we allow re-visiting of identifiers
    // and just suppress them once-per-analysis traversal (to save a bunch
    // of computation).
    analyzed_IDs.clear();

    id->Traverse(this);
}

TraversalCode UsageAnalyzer::PreID(const ID* id) {
    if ( analyzed_IDs.count(id) > 0 )
        // No need to repeat the analysis.
        return TC_ABORTSTMT;

    // Mark so that we avoid redundant re-traversal.
    analyzed_IDs.insert(id);

    auto f = GetFuncIfAny(id);

    if ( f && reachables.count(id) == 0 )
        // Haven't seen this function before.
        new_reachables.insert(id);

    id->GetType()->Traverse(this);

    auto& attrs = id->GetAttrs();
    if ( attrs )
        attrs->Traverse(this);

    // Initialization expressions can have function calls or lambdas that
    // themselves link to other identifiers.
    for ( auto& ie : id->GetOptInfo()->GetInitExprs() )
        if ( ie )
            ie->Traverse(this);

    return TC_CONTINUE;
}

TraversalCode UsageAnalyzer::PreType(const Type* t) {
    if ( analyzed_types.count(t) > 0 )
        return TC_ABORTSTMT;

    // Save processing by avoiding a re-traversal of this type.
    analyzed_types.insert(t);
    return TC_CONTINUE;
}

} // namespace zeek::detail
