currency.hpp

#include <eosiolib/eosio.hpp>
#include <eosiolib/asset.hpp>
#include <eosiolib/multi_index.hpp>

namespace eosio {
   using std::string;
   using std::array;

   /**
    *  This contract enables the creation, issuance, and transfering of many different tokens.
    *
    */
   class currency {
      public:
         currency( account_name contract = current_receiver() )
         :_contract(contract) 
         { }

         struct create {
            account_name           issuer;
            asset                  maximum_supply;
           // array<char,32>         issuer_agreement_hash;
            uint8_t                issuer_can_freeze     = true;
            uint8_t                issuer_can_recall     = true;
            uint8_t                issuer_can_whitelist  = true;

            /*(issuer_agreement_hash)*/
            EOSLIB_SERIALIZE( create, (issuer)(maximum_supply)(issuer_can_freeze)(issuer_can_recall)(issuer_can_whitelist) )
         };

         struct transfer  
         {
            account_name from;
            account_name to;
            asset        quantity;
            string       memo;

            EOSLIB_SERIALIZE( transfer, (from)(to)(quantity)(memo) )
         };

         struct issue {
            account_name to;
            asset        quantity;
            string       memo;

            EOSLIB_SERIALIZE( issue, (to)(quantity)(memo) )
         };

         struct fee_schedule {
            auto primary_key() const { return 0; }

            array<extended_asset,7> fee_per_length;
            EOSLIB_SERIALIZE( fee_schedule, (fee_per_length) )
         };

         struct account {
            asset    balance;
            bool     frozen    = false;
            bool     whitelist = true;

            uint64_t primary_key() const { return balance.symbol; }

            EOSLIB_SERIALIZE( account, (balance)(frozen)(whitelist) )
         };

         struct currency_stats {
            asset          supply;
            asset          max_supply;
            account_name   issuer;
            bool           can_freeze    = true;
            bool           can_recall    = true;
            bool           can_whitelist = true;
            bool           is_frozen     = false;
            bool           is_whitelist  = false;

            uint64_t primary_key() const { return supply.symbol.name(); }

            EOSLIB_SERIALIZE( currency_stats, (supply)(max_supply)(issuer)(can_freeze)(can_recall)(can_whitelist)(is_frozen)(is_whitelist) )
         };

         typedef eosio::multi_index<N(accounts), account> accounts;
         typedef eosio::multi_index<N(stat), currency_stats> stats;


         asset get_balance( account_name owner, symbol_name symbol )const {
            accounts t( _contract, owner );
            return t.get(symbol).balance;
         }

         asset get_supply( symbol_name symbol )const {
            accounts t( _contract, symbol );
            return t.get(symbol).balance;
         }

         static void inline_transfer( account_name from, account_name to, extended_asset amount, string memo = string(), permission_name perm = N(active) ) {
            action act( permission_level( from, perm ), amount.contract, N(transfer), transfer{from,to,amount,memo} );
            act.send();
         }

         void inline_transfer( account_name from, account_name to, asset amount, string memo = string(), permission_name perm = N(active) ) {
            action act( permission_level( from, perm ), _contract, N(transfer), transfer{from,to,amount,memo} );
            act.send();
         }


         bool apply( account_name contract, action_name act ) {
            if( contract != _contract ) 
               return false;

            switch( act ) {
               case N(issue):
                  print( "issue\n");
                 on( unpack_action<issue>() );
                 return true;
               case N(transfer):
                  print( "transfer\n");
                 on( unpack_action<transfer>() );
                 return true;
               case N(create):
                  print( "create\n");
                 on( unpack_action<create>() );
                 return true;
            }
            return false;
         }

          /**
           * This is factored out so it can be used as a building block 
           */
          void create_currency( const create& c ) {
             auto sym = c.maximum_supply.symbol;
          //   eosio_assert( sym.is_valid(), "invalid symbol name" );

             stats statstable( _contract, sym.name() );
             auto existing = statstable.find( sym.name() );
             eosio_assert( existing == statstable.end(), "token with symbol already exists" );

             statstable.emplace( c.issuer, [&]( auto& s ) {
                s.supply.symbol = c.maximum_supply.symbol;
                s.max_supply    = c.maximum_supply;
                s.issuer        = c.issuer;
                s.can_freeze    = c.issuer_can_freeze;
                s.can_recall    = c.issuer_can_recall;
                s.can_whitelist = c.issuer_can_whitelist;
             });
          }

          void issue_currency( const issue& i ) {
             auto sym = i.quantity.symbol.name();
             stats statstable( _contract, sym );
             const auto& st = statstable.get( sym );

             statstable.modify( st, 0, [&]( auto& s ) {
                s.supply.amount += i.quantity.amount;
                eosio_assert( s.supply.amount >= 0, "underflow" );
             });

             add_balance( st.issuer, i.quantity, st, st.issuer );
          }

      private:
          void sub_balance( account_name owner, asset value, const currency_stats& st ) {
             accounts from_acnts( _contract, owner );

             const auto& from = from_acnts.get( value.symbol );
             eosio_assert( from.balance.amount >= value.amount, "overdrawn balance" );

             if( has_auth( owner ) ) {
                eosio_assert( !st.can_freeze || !from.frozen, "account is frozen by issuer" );
                eosio_assert( !st.is_whitelist || from.whitelist, "account is not white listed" );
             } else if( has_auth( st.issuer ) ) {
                eosio_assert( st.can_recall, "issuer may not recall token" );
             } else {
                eosio_assert( false, "insufficient authority" );
             }

             from_acnts.modify( from, owner, [&]( auto& a ) {
                 a.balance.amount -= value.amount;
             });
          }

          void add_balance( account_name owner, asset value, const currency_stats& st, account_name ram_payer )
          {
             accounts to_acnts( _contract, owner );
             auto to    = to_acnts.find( value.symbol );
             if( to == to_acnts.end() ) {
                eosio_assert( !st.is_whitelist, "can only transfer to white listed accounts" );
                to_acnts.emplace( ram_payer, [&]( auto& a ){
                  a.balance = value;
                });
             } else {
                eosio_assert( !st.is_whitelist || to->whitelist, "receiver requires whitelist by issuer" );
                to_acnts.modify( to, 0, [&]( auto& a ) {
                  a.balance.amount += value.amount;
                });
             }
          }


          void on( const create& c ) {
             require_auth( c.issuer );
             create_currency( c );

             /*
             auto fee = get_fee_schedule()[c.maximum_supply.name_length()];
             if( fee.amount > 0 ) {
                inline_transfer( c.issuer, _contract, fee, "symbol registration fee" );
             }
             */
          }

          void on( const issue& i ) {
             auto sym = i.quantity.symbol.name();
             stats statstable( _contract, sym );
             const auto& st = statstable.get( sym );

             require_auth( st.issuer );
             eosio_assert( i.quantity.amount > 0, "cannot transfer negative quantity" );

             statstable.modify( st, 0, [&]( auto& s ) {
                s.supply.amount += i.quantity.amount;
             });

             add_balance( st.issuer, i.quantity, st, st.issuer );

             if( i.to != st.issuer )
             {
                inline_transfer( st.issuer, i.to, i.quantity, i.memo );
             }
          }

          void on( const transfer& t ) {
             auto sym = t.quantity.symbol.name();
             stats statstable( _contract, sym );
             const auto& st = statstable.get( sym );

             require_recipient( t.to );

             eosio_assert( t.quantity.amount > 0, "cannot transfer negative quantity" );
             sub_balance( t.from, t.quantity, st );
             add_balance( t.to, t.quantity, st, t.from );
          }


      private:
         account_name _contract;
   };

}