Account Has Code - Basic EOS oracle for checking if an account has code on it.

acchascode.cpp

#include <eosiolib/eosio.hpp>
#include <eosiolib/singleton.hpp>

using namespace eosio;

class acchascode : contract {
private:

    // @abi table trustees
    struct Trustee {
        account_name account;

        account_name primary_key() const { return account; }
        EOSLIB_SERIALIZE( Trustee, (account) )
    };

    // @abi table accounts
    struct Account {
        account_name account;

        account_name primary_key() const { return account; }
        EOSLIB_SERIALIZE( Account, (account) )
    };

    typedef multi_index<N(trustees), Trustee> Trustees;
    typedef singleton<N(accounts), Account> Accounts;

public:
    using contract::contract;
    acchascode( name self ) : contract(self){}

    // @abi action
    void trustee(account_name account){
        require_auth(_self);
        Trustees trustees(_self, _self);
        auto exists = trustees.find(account);
        if(exists != trustees.end()) trustees.erase(exists);
        else trustees.emplace(_self, [&](auto& record){
            record.account = account;
        });
    }

    // @abi action
    void add(account_name account, account_name trustee){
        require_auth(trustee);

        Trustees trustees(_self, _self);
        eosio_assert(trustees.find(trustee) != trustees.end(), "Trustee is not a trusted oracle seeder");

        if(Accounts(_self, account).exists()) Accounts(_self, account).remove();
        else Accounts(_self, account).set(Account{account}, _self);
    }

};

EOSIO_ABI( acchascode, (trustee)(add) )