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

#pragma once

#include <unordered_map>
#include <unordered_set>
#include <vector>

#include "zeek/Expr.h"
#include "zeek/script_opt/ObjMgr.h"

namespace zeek::detail {

// UseDefs track which variables (identifiers) are used at or subsequent
// to a given (reduced) Statement.  They allow us to determine unproductive
// variable assignments (both to warn the user, and to prune temporaries),
// and also accesses to globals (so we know which ones need to be synchronized
// across function calls).

class UseDefSet;
using UDs = std::shared_ptr<UseDefSet>;

class UseDefSet {
public:
    UseDefSet() {}
    UseDefSet(const UDs& uds) { Replicate(uds); }

    void Replicate(const UDs& from) { use_defs = from->use_defs; }

    bool HasID(const ID* id) { return use_defs.find(id) != use_defs.end(); }

    void Add(const ID* id) { use_defs.insert(id); }
    void Remove(const ID* id) { use_defs.erase(id); }

    const IDSet& IterateOver() const { return use_defs; }

    void Dump() const;
    void DumpNL() const {
        Dump();
        printf("\n");
    }

protected:
    IDSet use_defs;
};

class Reducer;

class UseDefs {
public:
    UseDefs(StmtPtr body, std::shared_ptr<Reducer> rc, FuncTypePtr ft);

    // Does a full pass over the function body's AST.  We can wind
    // up doing this multiple times because when we use use-defs to
    // prune AST nodes, that in turn can change other use-defs.
    void Analyze();

    // True if we've computed use-defs for the given statement.
    bool HasUsage(const Stmt* s) const { return use_defs_map.find(s) != use_defs_map.end(); }
    bool HasUsage(const StmtPtr& s) const { return HasUsage(s.get()); }

    // Returns the use-defs for the given statement.
    UDs GetUsage(const Stmt* s) const { return FindUsage(s); }
    UDs GetUsage(const StmtPtr& s) const { return FindUsage(s.get()); }

    // Removes assignments corresponding to unused temporaries.
    // In the process, reports on locals that are assigned
    // but never used.  Returns the body, which may have been
    // changed if the original first statement has been pruned.
    StmtPtr RemoveUnused();

    void Dump();

private:
    // Makes one pass over the statements, removing assignments
    // corresponding to temporaries (because those can be propagated).
    // "iter" is the iteration count of how often we've done such passes,
    // with the first pass being numbered 1.
    //
    // Returns true if something was removed, false if not.
    bool RemoveUnused(int iter);

    // For a given identifier defined at a given statement, returns
    // whether it is unused.  If "report" is true, also reports
    // this fact.
    bool CheckIfUnused(const Stmt* s, const ID* id, bool report);

    // Propagates use-defs (backwards) across statement s,
    // given its successor's UDs.
    //
    // succ_stmt is the successor statement to this statement.
    // We only care about it for potential assignment statements,
    // (see the "successor" map below).
    //
    // second_pass is true when we revisit a set of statements
    // to propagate additional UDs generated by loop confluence.
    // If true, it prevents some redundant bookkeeping from occurring.
    UDs PropagateUDs(const StmtPtr& s, UDs succ_UDs, const StmtPtr& succ_stmt, bool second_pass) {
        return PropagateUDs(s.get(), std::move(succ_UDs), succ_stmt.get(), second_pass);
    }
    UDs PropagateUDs(const Stmt* s, UDs succ_UDs, const Stmt* succ_stmt, bool second_pass);

    UDs FindUsage(const Stmt* s) const;
    UDs FindSuccUsage(const Stmt* s) const;

    // Returns a new use-def corresponding to the variables
    // referenced in e.
    UDs ExprUDs(const Expr* e);

    // Helper method that adds in an expression's use-defs (if any)
    // to an existing set of UDs.
    void AddInExprUDs(UDs uds, const Expr* e);

    // Add an ID into an existing set of UDs.
    void AddID(UDs uds, const ID* id) const;

    // Returns a new use-def corresponding to the given one, but
    // with the definition of "id" removed.
    UDs RemoveID(const ID* id, const UDs& uds);

    // Similar, but updates the UDs in place.
    void RemoveUDFrom(UDs uds, const ID* id);

    // Adds in the additional UDs to the main UDs.  Always creates
    // a new use_def and updates main_UDs to point to it.
    void FoldInUDs(UDs& main_UDs, const UDs& u1, const UDs& u2 = nullptr);

    // Adds in the given UDs to those already associated with s.
    void UpdateUDs(const Stmt* s, const UDs& uds);

    // Returns a new use-def corresponding to the union of 2 or 3 UDs.
    UDs UD_Union(const UDs& u1, const UDs& u2, const UDs& u3 = nullptr) const;

    // Associate a (shallow) copy of the given UDs with the given
    // statement.
    UDs UseUDs(const Stmt* s, UDs uds);

    // Sets the given statement's UDs to a new UD set corresponding
    // to the union of the given UDs and those associated with the
    // given expression.
    UDs CreateExprUDs(const Stmt* s, const Expr* e, const UDs& uds);

    // The given statement takes ownership of the given UDs.
    UDs CreateUDs(const Stmt* s, UDs uds);

    // Maps each statement to its associated use-def identifiers
    // (which could be nil).
    std::unordered_map<const Stmt*, UDs> use_defs_map;

    // The following tracks statements whose use-defs are
    // currently copies of some other statement's use-defs.
    std::unordered_set<const Stmt*> UDs_are_copies;

    // Track the statements we've processed.  This lets us dump
    // things out in order, even though the main map is unordered.
    std::vector<const Stmt*> stmts;

    // For a given expression statement, maps it to its successor
    // (the statement that will execute after it).  We need this
    // because we track UDs present at the *beginning* of
    // a statement, not at its end; those at the end are
    // the same as those at the beginning of the successor.
    std::unordered_map<const Stmt*, const Stmt*> successor;

    // Loop bodies have two successors, and it's important to
    // track both because sometimes a relevant UD will be present
    // in only one or the other.
    std::unordered_map<const Stmt*, const Stmt*> successor2;

    ObjMgr om;

    StmtPtr body;
    std::shared_ptr<Reducer> rc;
    FuncTypePtr ft;
};

} // namespace zeek::detail
