pragma solidity ^0.4.24;

// ----------------------------------------------------------------------------
// Safe maths
// ----------------------------------------------------------------------------
contract SafeMath {
   function safeAdd(uint a, uint b) public pure returns (uint c) {
       c = a + b;
       require(c >= a);
   }
   function safeSub(uint a, uint b) public pure returns (uint c) {
       require(b <= a);
       c = a - b;
   }
   function safeMul(uint a, uint b) public pure returns (uint c) {
       c = a * b;
       require(a == 0 || c / a == b);
   }
   function safeDiv(uint a, uint b) public pure returns (uint c) {
       require(b > 0);
       c = a / b;
   }
}

// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
// ----------------------------------------------------------------------------
contract ERC20Interface {
   function totalSupply() public constant returns (uint);
   function balanceOf(address tokenOwner) public constant returns (uint balance);
   function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
   function transfer(address to, uint tokens) public returns (bool success);
   function burn(uint _tokens) public returns (bool success);
   function approve(address spender, uint tokens) public returns (bool success);
   function transferFrom(address from, address to, uint tokens) public returns (bool success);

   event Transfer(address indexed from, address indexed to, uint tokens);
   event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

// ----------------------------------------------------------------------------
// Contract function to receive approval and execute function in one call
//
// Borrowed from MiniMeToken
// ----------------------------------------------------------------------------
contract ApproveAndCallFallBack {
   function receiveApproval(address from, uint256 tokens, address token, bytes data) public;
}

// ----------------------------------------------------------------------------
// Owned contract
// ----------------------------------------------------------------------------
contract Owned {
   address public owner;
   address public newOwner;

   event OwnershipTransferred(address indexed _from, address indexed _to);

   constructor() public {
       owner = msg.sender;
   }

   modifier onlyOwner {
       require(msg.sender == owner);
       _;
   }

   function transferOwnership(address _newOwner) public onlyOwner {
       newOwner = _newOwner;
   }
   function acceptOwnership() public {
       require(msg.sender == newOwner);
       emit OwnershipTransferred(owner, newOwner);
       owner = newOwner;
       newOwner = address(0);
   }
}

// ----------------------------------------------------------------------------
// ERC20 Token, with the addition of symbol, name and decimals and assisted
// token transfers
// ----------------------------------------------------------------------------
contract USDSVToken is ERC20Interface, Owned, SafeMath {
   string public symbol;
   string public  name;
   uint8 public decimals;
   uint public _totalSupply;

   mapping(address => uint) balances;
   mapping(address => mapping(address => uint)) allowed;

   // ------------------------------------------------------------------------
   // Constructor
   // ------------------------------------------------------------------------
   constructor() public {
       symbol = "USDSV";
       name = "USD Satoshi Vision Token";
       decimals = 18;
       _totalSupply = 1000000000000000000000000000;
       balances[msg.sender] = _totalSupply;
       emit Transfer(address(0), msg.sender, _totalSupply);
   }

   // ------------------------------------------------------------------------
   // Total supply
   // ------------------------------------------------------------------------
   function totalSupply() public constant returns (uint) {
       return _totalSupply  - balances[address(0)];
   }

   // ------------------------------------------------------------------------
   // Get the token balance for account tokenOwner
   // ------------------------------------------------------------------------
   function balanceOf(address tokenOwner) public constant returns (uint balance) {
       return balances[tokenOwner];
   }

   // ------------------------------------------------------------------------
   // Transfer the balance from token owner's account to to account
   // - Owner's account must have sufficient balance to transfer
   // - 0 value transfers are allowed
   // ------------------------------------------------------------------------
   function transfer(address to, uint tokens) public returns (bool success) {
       balances[msg.sender] = safeSub(balances[msg.sender], tokens);
       balances[to] = safeAdd(balances[to], tokens);
       emit Transfer(msg.sender, to, tokens);
       return true;
   }
   
   // ------------------------------------------------------------------------
   // Burn the balance from token owner's account to to account
   // 
   // 
   // ------------------------------------------------------------------------
   function burn(uint tokens) public returns (bool success) {
       require(msg.sender == owner);
       balances[msg.sender] = safeSub(balances[msg.sender], tokens);
       _totalSupply = safeSub(_totalSupply, tokens);
       return true;
   }
   

   // ------------------------------------------------------------------------
   // Token owner can approve for spender to transferFrom(...) tokens
   // from the token owner's account
   //
   // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
   // recommends that there are no checks for the approval double-spend attack
   // as this should be implemented in user interfaces 
   // ------------------------------------------------------------------------
   function approve(address spender, uint _tokens) public returns (bool success) {
       require(_tokens > 0);
       require(_tokens <= balances[msg.sender]);
       allowed[msg.sender][spender] = _tokens;
       emit Approval(msg.sender, spender, _tokens);
       return true;
   }

   // ------------------------------------------------------------------------
   // Transfer tokens from the from account to the to account
   // 
   // The calling account must already have sufficient tokens approve(...)-d
   // for spending from the from account and
   // - From account must have sufficient balance to transfer
   // - Spender must have sufficient allowance to transfer
   // - 0 value transfers are allowed
   // ------------------------------------------------------------------------
   function transferFrom(address from, address to, uint tokens) public returns (bool success) {
       balances[from] = safeSub(balances[from], tokens);
       allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
       balances[to] = safeAdd(balances[to], tokens);
       emit Transfer(from, to, tokens);
       return true;
   }

   // ------------------------------------------------------------------------
   // Returns the amount of tokens approved by the owner that can be
   // transferred to the spender's account
   // ------------------------------------------------------------------------
   function allowance(address tokenOwner, address spender) public constant returns (uint remaining) {
       return allowed[tokenOwner][spender];
   }

   // ------------------------------------------------------------------------
   // Token owner can approve for spender to transferFrom(...) tokens
   // from the token owner's account. The spender contract function
   // receiveApproval(...) is then executed
   // ------------------------------------------------------------------------
   function approveAndCall(address spender, uint tokens, bytes data) public returns (bool success) {
       allowed[msg.sender][spender] = tokens;
       emit Approval(msg.sender, spender, tokens);
       ApproveAndCallFallBack(spender).receiveApproval(msg.sender, tokens, this, data);
       return true;
   }

   // ------------------------------------------------------------------------
   // Don't accept ETH
   // ------------------------------------------------------------------------
   function () public payable {
       revert();
   }

   // ------------------------------------------------------------------------
   // Owner can transfer out any accidentally sent ERC20 tokens
   // ------------------------------------------------------------------------
   function transferAnyERC20Token(address tokenAddress, uint tokens) public onlyOwner returns (bool success) {
       return ERC20Interface(tokenAddress).transfer(owner, tokens);
   }
}