// File: contracts/library/ERC20.sol

pragma solidity ^0.4.24;

interface ERC20 {

    function totalSupply() public view returns (uint);
    function balanceOf(address owner) public view returns (uint);
    function allowance(address owner, address spender) public view returns (uint);
    function transfer(address to, uint value) public returns (bool);
    function transferFrom(address from, address to, uint value) public returns (bool);
    function approve(address spender, uint value) public returns (bool);

}

// File: contracts/library/Ownable.sol

pragma solidity ^0.4.24;

contract Ownable {

    address public owner;

    modifier onlyOwner {
        require(isOwner(msg.sender));
        _;
    }

    function Ownable() public {
        owner = msg.sender;
    }

    function transferOwnership(address _newOwner) public onlyOwner {
        owner = _newOwner;
    }

    function isOwner(address _address) public view returns (bool) {
        return owner == _address;
    }
}

// File: contracts/library/SafeMath.sol

pragma solidity ^0.4.24;

library SafeMath {

    function mul(uint a, uint b) internal pure returns (uint) {
        uint c = a * b;
        assert(a == 0 || c / a == b);
        return c;
    }

    function div(uint a, uint b) internal pure returns (uint) {
        assert(b > 0);
        uint c = a / b;
        assert(a == b * c + a % b);
        return c;
    }

    function sub(uint a, uint b) internal pure returns (uint) {
        assert(b <= a);
        return a - b;
    }

    function add(uint a, uint b) internal pure returns (uint) {
        uint c = a + b;
        assert(c >= a);
        return c;
    }

    function max64(uint64 a, uint64 b) internal pure returns (uint64) {
        return a >= b ? a : b;
    }

    function min64(uint64 a, uint64 b) internal pure returns (uint64) {
        return a < b ? a : b;
    }

    function max256(uint a, uint b) internal pure returns (uint) {
        return a >= b ? a : b;
    }

    function min256(uint a, uint b) internal pure returns (uint) {
        return a < b ? a : b;
    }
}

// File: contracts/library/Pausable.sol

pragma solidity ^0.4.24;


/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is Ownable {
  event Pause();
  event Unpause();

  bool public paused = false;


  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {
    require(!paused);
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {
    require(paused);
    _;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() onlyOwner whenNotPaused public {
    paused = true;
    emit Pause();
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() onlyOwner whenPaused public {
    paused = false;
    emit Unpause();
  }
}

// File: contracts/library/Whitelist.sol

pragma solidity ^0.4.24;



/**
 * @title Whitelist
 * @dev The Whitelist contract has a whitelist of addresses, and provides basic authorization control functions.
 * @dev This simplifies the implementation of "user permissions".
 */
contract Whitelist is Ownable {
  mapping(address => bool) public whitelist;

  event WhitelistedAddressAdded(address addr);
  event WhitelistedAddressRemoved(address addr);

  /**
   * @dev Throws if called by any account that's not whitelisted.
   */
  modifier onlyWhitelisted() {
    require(whitelist[msg.sender]);
    _;
  }

  /**
   * @dev add an address to the whitelist
   * @param addr address
   * @return true if the address was added to the whitelist, false if the address was already in the whitelist
   */
  function addAddressToWhitelist(address addr) onlyOwner public returns(bool success) {
    if (!whitelist[addr]) {
      whitelist[addr] = true;
      emit WhitelistedAddressAdded(addr);
      success = true;
    }
  }

  /**
   * @dev add addresses to the whitelist
   * @param addrs addresses
   * @return true if at least one address was added to the whitelist,
   * false if all addresses were already in the whitelist
   */
  function addAddressesToWhitelist(address[] addrs) onlyOwner public returns(bool success) {
    for (uint256 i = 0; i < addrs.length; i++) {
      if (addAddressToWhitelist(addrs[i])) {
        success = true;
      }
    }
  }

  /**
   * @dev remove an address from the whitelist
   * @param addr address
   * @return true if the address was removed from the whitelist,
   * false if the address wasn't in the whitelist in the first place
   */
  function removeAddressFromWhitelist(address addr) onlyOwner public returns(bool success) {
    if (whitelist[addr]) {
      whitelist[addr] = false;
      emit WhitelistedAddressRemoved(addr);
      success = true;
    }
  }

  /**
   * @dev remove addresses from the whitelist
   * @param addrs addresses
   * @return true if at least one address was removed from the whitelist,
   * false if all addresses weren't in the whitelist in the first place
   */
  function removeAddressesFromWhitelist(address[] addrs) onlyOwner public returns(bool success) {
    for (uint256 i = 0; i < addrs.length; i++) {
      if (removeAddressFromWhitelist(addrs[i])) {
        success = true;
      }
    }
  }

}

// File: contracts/Staking.sol

pragma solidity ^0.4.24;






/**
 * @title Staking and voting contract.
 * @author IoTeX Team
 *
 */
contract Staking is Pausable, Whitelist {
    using SafeMath for uint256;

    // Events to be emitted
    event BucketCreated(uint256 bucketIndex, bytes12 canName, uint256 amount, uint256 stakeDuration, bool nonDecay, bytes data);
    event BucketUpdated(uint256 bucketIndex, bytes12 canName, uint256 stakeDuration, uint256 stakeStartTime, bool nonDecay, address bucketOwner, bytes data);
    event BucketUnstake(uint256 bucketIndex, bytes12 canName, uint256 amount, bytes data);
    event BucketWithdraw(uint256 bucketIndex, bytes12 canName, uint256 amount, bytes data);
    // TODO add change owner event which is not covered by BucketUpdated event

    // IOTX used for staking
    ERC20 stakingToken;

    // Unit is epoch
    uint256 public constant minStakeDuration = 0;
    uint256 public constant maxStakeDuration = 350;
    uint256 public constant minStakeAmount = 100 * 10 ** 18;
    uint256 public constant unStakeDuration = 3;

    uint256 public constant maxBucketsPerAddr = 500;
    uint256 public constant secondsPerEpoch = 86400;

    // Core data structure to track staking/voting status
    struct Bucket {
        bytes12 canName;            // Candidate name, which maps to public keys by NameRegistration.sol
        uint256 stakedAmount;       // Number of tokens
        uint256 stakeDuration;      // Stake duration, unit: second since epoch
        uint256 stakeStartTime;     // Staking start time, unit: second since epoch
        bool nonDecay;              // Nondecay staking -- staking for N epochs consistently without decaying
        uint256 unstakeStartTime;   // unstake timestamp, unit: second since epoch
        address bucketOwner;        // Owner of this bucket, usually the one who created it but can be someone else
        uint256 createTime;         // bucket firstly create time
        uint256 prev;               // Prev non-zero bucket index
        uint256 next;               // Next non-zero bucket index
    }
    mapping(uint256 => Bucket) public buckets;
    uint256 bucketCount; // number of total buckets. used to track the last used index for the bucket

    // Map from owner address to array of bucket indexes.
    mapping(address => uint256[]) public stakeholders;

    /**
     * @dev Modifier that checks that this given bucket can be updated/deleted by msg.sender
     * @param _address address to transfer tokens from
     * @param _bucketIndex uint256 the index of the bucket
     */
    modifier canTouchBucket(address _address, uint256 _bucketIndex) {
        require(_address != address(0));
        require(buckets[_bucketIndex].bucketOwner == msg.sender, "sender is not the owner.");
        _;
    }

    /**
     * @dev Modifier that check if a duration meets requirement
     * @param _duration uint256 duration to check
     */
    modifier checkStakeDuration(uint256 _duration) {
        require(_duration >= minStakeDuration && _duration <= maxStakeDuration, "The stake duration is too small or large");
        require(_duration % 7 == 0, "The stake duration should be multiple of 7");
        _;
    }

    /**
     * @dev Constructor function
     * @param _stakingTokenAddr address The address of the token contract used for staking
     */
    constructor(address _stakingTokenAddr) public {
        stakingToken = ERC20(_stakingTokenAddr);
        // create one bucket to initialize the double linked list
        buckets[0] = Bucket("", 1, 0, block.timestamp, true, 0, msg.sender, block.timestamp, 0, 0);
        stakeholders[msg.sender].push(0);
        bucketCount = 1;
    }

    function getActiveBucketIdxImpl(uint256 _prevIndex, uint256 _limit) internal returns(uint256 count, uint256[] indexes) {
        require (_limit > 0 && _limit < 5000);
        Bucket memory bucket = buckets[_prevIndex];
        require(bucket.next > 0, "cannot find bucket based on input index.");

        indexes = new uint256[](_limit);
        uint256 i = 0;
        for (i = 0; i < _limit; i++) {
            while (bucket.next > 0 && buckets[bucket.next].unstakeStartTime > 0) { // unstaked.
                bucket = buckets[bucket.next]; // skip
            }
            if (bucket.next == 0) { // no new bucket
                break;
            }
            indexes[i] = bucket.next;
            bucket = buckets[bucket.next];
        }
        return (i, indexes);
    }

    function getActiveBucketIdx(uint256 _prevIndex, uint256 _limit) external view returns(uint256 count, uint256[] indexes) {
        return getActiveBucketIdxImpl(_prevIndex, _limit);
    }

    /**
     * @dev Get active buckets for a range of indexes
     * @param _prevIndex uint256 the starting index. starting from 0, ending at the last. (putting 0,2 will return 1,2.)
     * @param _limit uint256 the number of non zero buckets to fetch after the start index
     * @return (uint256, uint256[], uint256[], uint256[], uint256[], bytes, address[])
     *  count, index array, stakeStartTime array, duration array, decay array, stakedAmount array, concat stakedFor, ownerAddress array
     */
    function getActiveBuckets(uint256 _prevIndex, uint256 _limit) external view returns(uint256 count,
            uint256[] indexes, uint256[] stakeStartTimes, uint256[] stakeDurations, bool[] decays, uint256[] stakedAmounts, bytes12[] canNames, address[] owners) {

        (count, indexes) = getActiveBucketIdxImpl(_prevIndex, _limit);
        stakeStartTimes = new uint256[](count);
        stakeDurations = new uint256[](count);
        decays = new bool[](count);
        stakedAmounts = new uint256[](count);
        canNames = new bytes12[](count);
        owners = new address[](count);

        for (uint256 i = 0; i < count; i++) {
            Bucket memory bucket = buckets[indexes[i]];
            stakeStartTimes[i] = bucket.stakeStartTime;
            stakeDurations[i] = bucket.stakeDuration;
            decays[i] = !bucket.nonDecay;
            stakedAmounts[i] = bucket.stakedAmount;
            canNames[i] = bucket.canName;
            owners[i] = bucket.bucketOwner;

        }

        return (count, indexes, stakeStartTimes, stakeDurations, decays, stakedAmounts, canNames, owners);
    }


    function getActiveBucketCreateTimes(uint256 _prevIndex, uint256 _limit) external view returns(uint256 count,
            uint256[] indexes, uint256[] createTimes) {
        (count, indexes) = getActiveBucketIdxImpl(_prevIndex, _limit);
        createTimes = new uint256[](count);
        for (uint256 i = 0; i < count; i++) {
            createTimes[i] = buckets[indexes[i]].createTime;
        }
        return (count, indexes, createTimes);
    }

    /**
     * @dev Get bucket indexes from a given address
     * @param _owner address onwer of the buckets
     * @return (uint256[])
     */
    function getBucketIndexesByAddress(address _owner) external view returns(uint256[]) {
        return stakeholders[_owner];
    }

    /**
     * @notice Extend the stake to stakeDuration from current time and/or set nonDecay.
     * @notice MUST trigger BucketUpdated event
     * @param _bucketIndex uint256 the index of the bucket
     * @param _stakeDuration uint256 the desired duration of staking.
     * @param _nonDecay bool if auto restake
     * @param _data bytes optional data to include in the emitted event
     */
    function restake(uint256 _bucketIndex, uint256 _stakeDuration, bool _nonDecay, bytes _data)
            external whenNotPaused canTouchBucket(msg.sender, _bucketIndex) checkStakeDuration(_stakeDuration) {
        require(block.timestamp.add(_stakeDuration * secondsPerEpoch) >=
                buckets[_bucketIndex].stakeStartTime.add(buckets[_bucketIndex].stakeDuration * secondsPerEpoch),
                "current stake duration not finished.");
        if (buckets[_bucketIndex].nonDecay) {
          require(_stakeDuration >= buckets[_bucketIndex].stakeDuration, "cannot reduce the stake duration.");
        }
        buckets[_bucketIndex].stakeDuration = _stakeDuration;
        buckets[_bucketIndex].stakeStartTime = block.timestamp;
        buckets[_bucketIndex].nonDecay = _nonDecay;
        buckets[_bucketIndex].unstakeStartTime = 0;
        emitBucketUpdated(_bucketIndex, _data);
    }

    /*
     * @notice Vote for another candidate with the tokens that are already staked in the given bucket
     * @notice MUST trigger BucketUpdated event
     * @param _bucketIndex uint256 the index of the bucket
     * @param canName bytes the IoTeX address of the candidate the tokens are staked for
     * @param _data bytes optional data to include in the emitted event
     */
    function revote(uint256 _bucketIndex, bytes12 _canName, bytes _data)
            external whenNotPaused canTouchBucket(msg.sender, _bucketIndex) {
        require(buckets[_bucketIndex].unstakeStartTime == 0, "cannot revote during unstaking.");
        buckets[_bucketIndex].canName = _canName;
        emitBucketUpdated(_bucketIndex, _data);
    }

    /*
     * @notice Set the new owner of a given bucket, the sender must be whitelisted to do so to avoid spam
     * @notice MUST trigger BucketUpdated event
     * @param _name bytes12 the name of the candidate the tokens are staked for
     * @param _bucketIndex uint256 optional data to include in the Stake event
     * @param _data bytes optional data to include in the emitted event
     */
    function setBucketOwner(uint256 _bucketIndex, address _newOwner, bytes _data)
            external whenNotPaused onlyWhitelisted canTouchBucket(msg.sender, _bucketIndex) {
        removeBucketIndex(_bucketIndex);
        buckets[_bucketIndex].bucketOwner = _newOwner;
        stakeholders[_newOwner].push(_bucketIndex);
        // TODO split event.
        emitBucketUpdated(_bucketIndex, _data);
    }

    /**
     * @notice Unstake a certain amount of tokens from a given bucket.
     * @notice MUST trigger BucketUnstake event
     * @param _bucketIndex uint256 the index of the bucket
     * @param _data bytes optional data to include in the emitted event
     */
    function unstake(uint256 _bucketIndex, bytes _data)
            external whenNotPaused canTouchBucket(msg.sender, _bucketIndex) {
        require(_bucketIndex > 0, "bucket 0 cannot be unstaked and withdrawn.");
        require(!buckets[_bucketIndex].nonDecay, "Cannot unstake with nonDecay flag. Need to disable non-decay mode first.");
        require(buckets[_bucketIndex].stakeStartTime.add(buckets[_bucketIndex].stakeDuration * secondsPerEpoch) <= block.timestamp,
            "Staking time does not expire yet. Please wait until staking expires.");
        require(buckets[_bucketIndex].unstakeStartTime == 0, "Unstaked already. No need to unstake again.");
        buckets[_bucketIndex].unstakeStartTime = block.timestamp;
        emit BucketUnstake(_bucketIndex, buckets[_bucketIndex].canName, buckets[_bucketIndex].stakedAmount, _data);
    }

    /**
     * @notice this SHOULD return the given amount of tokens to the user, if unstaking is currently not possible the function MUST revert
     * @notice MUST trigger BucketWithdraw event
     * @param _bucketIndex uint256 the index of the bucket
     * @param _data bytes optional data to include in the emitted event
     */
    function withdraw(uint256 _bucketIndex, bytes _data)
            external whenNotPaused canTouchBucket(msg.sender, _bucketIndex) {
        require(buckets[_bucketIndex].unstakeStartTime > 0, "Please unstake first before withdraw.");
        require(
            buckets[_bucketIndex].unstakeStartTime.add(unStakeDuration * secondsPerEpoch) <= block.timestamp,
            "Stakeholder needs to wait for 3 days before withdrawing tokens.");

        // fix double linked list
        uint256 prev = buckets[_bucketIndex].prev;
        uint256 next = buckets[_bucketIndex].next;
        buckets[prev].next = next;
        buckets[next].prev = prev;

        uint256 amount = buckets[_bucketIndex].stakedAmount;
        bytes12 canName = buckets[_bucketIndex].canName;
        address bucketowner = buckets[_bucketIndex].bucketOwner;
        buckets[_bucketIndex].stakedAmount = 0;
        removeBucketIndex(_bucketIndex);
        delete buckets[_bucketIndex];

        require(stakingToken.transfer(bucketowner, amount), "Unable to withdraw stake");
        emit BucketWithdraw(_bucketIndex, canName, amount, _data);
    }

    /**
     * @notice Returns the total of tokens staked from all addresses
     * @return uint256 The number of tokens staked from all addresses
     */
    function totalStaked() public view returns (uint256) {
        return stakingToken.balanceOf(this);
    }

    /**
     * @notice Address of the token being used by the staking interface
     * @return address The address of the ERC20 token used for staking
     */
    function token() public view returns(address) {
        return stakingToken;
    }

    /**
     * @notice Emit BucketUpdated event
     */
    function emitBucketUpdated(uint256 _bucketIndex, bytes _data) internal {
        Bucket memory b = buckets[_bucketIndex];
        emit BucketUpdated(_bucketIndex, b.canName, b.stakeDuration, b.stakeStartTime, b.nonDecay, b.bucketOwner, _data);
    }

    /**
     * @dev  Create a bucket and vote for a given canName.
     * @param _canName bytes The IoTeX address of the candidate the stake is being created for
     * @param _amount uint256 The duration to lock the tokens for
     * @param _stakeDuration bytes the desired duration of the staking
     * @param _nonDecay bool if auto restake
     * @param _data bytes optional data to include in the emitted event
     * @return uint236 the index of new bucket
     */
    function createBucket(bytes12 _canName, uint256 _amount, uint256 _stakeDuration, bool _nonDecay, bytes _data)
            external whenNotPaused checkStakeDuration(_stakeDuration) returns (uint256) {
        require(_amount >= minStakeAmount, "amount should >= 100.");
        require(stakeholders[msg.sender].length <= maxBucketsPerAddr, "One address can have up limited buckets");
        require(stakingToken.transferFrom(msg.sender, this, _amount), "Stake required"); // transfer token to contract
        // add a new bucket to the end of buckets array and fix the double linked list.
        buckets[bucketCount] = Bucket(_canName, _amount, _stakeDuration, block.timestamp, _nonDecay, 0, msg.sender, block.timestamp, buckets[0].prev, 0);
        buckets[buckets[0].prev].next = bucketCount;
        buckets[0].prev = bucketCount;
        stakeholders[msg.sender].push(bucketCount);
        bucketCount++;
        emit BucketCreated(bucketCount-1, _canName, _amount, _stakeDuration, _nonDecay, _data);
        return bucketCount-1;
    }

    /**
     * @dev Remove the bucket index from stakeholders map
     * @param _bucketidx uint256 the bucket index
     */
    function removeBucketIndex(uint256 _bucketidx) internal {
        address owner = buckets[_bucketidx].bucketOwner;
        require(stakeholders[owner].length > 0, "Expect the owner has at least one bucket index");

        uint256 i = 0;
        for (; i < stakeholders[owner].length; i++) {
          if(stakeholders[owner][i] == _bucketidx) {
                break;
          }
        }
        for (; i < stakeholders[owner].length - 1; i++) {
          stakeholders[owner][i] = stakeholders[owner][i + 1];
        }
        stakeholders[owner].length--;
    }
}

pragma solidity ^0.4.21;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */

  /*@CTK SafeMath_mul
    @tag spec
    @post __reverted == __has_assertion_failure
    @post __has_assertion_failure == __has_overflow
    @post __reverted == false -> c == a * b
    @post msg == msg__post
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
    if (a == 0) {
      return 0;
    }
    c = a * b;
    assert(c / a == b);
    return c;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  /*@CTK SafeMath_div
    @tag spec
    @pre b != 0
    @post __reverted == __has_assertion_failure
    @post __has_overflow == true -> __has_assertion_failure == true
    @post __reverted == false -> __return == a / b
    @post msg == msg__post
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    // uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return a / b;
  }

  /**
  * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  /*@CTK SafeMath_sub
    @tag spec
    @post __reverted == __has_assertion_failure
    @post __has_overflow == true -> __has_assertion_failure == true
    @post __reverted == false -> __return == a - b
    @post msg == msg__post
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  /*@CTK SafeMath_add
    @tag spec
    @post __reverted == __has_assertion_failure
    @post __has_assertion_failure == __has_overflow
    @post __reverted == false -> c == a + b
    @post msg == msg__post
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
    c = a + b;
    assert(c >= a);
    return c;
  }
}

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
  address public owner;


  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  /*@CTK owner_set_on_success
    @pre __reverted == false -> __post.owner == owner
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function Ownable() public {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  /*@CTK transferOwnership
    @post __reverted == false -> (msg.sender == owner -> __post.owner == newOwner)
    @post (owner != msg.sender) -> (__reverted == true)
    @post (newOwner == address(0)) -> (__reverted == true)
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}

/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is Ownable {
  event Pause();
  event Unpause();

  bool public paused = false;


  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {
    require(!paused);
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {
    require(paused);
    _;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() onlyOwner whenNotPaused public {
    paused = true;
    emit Pause();
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() onlyOwner whenPaused public {
    paused = false;
    emit Unpause();
  }
}


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender) public view returns (uint256);
  function transferFrom(address from, address to, uint256 value) public returns (bool);
  function approve(address spender, uint256 value) public returns (bool);
  event Approval(address indexed owner, address indexed spender, uint256 value);
}

/**
 * @title Basic token
 * @dev Basic version of StandardToken, with no allowances.
 */
contract BasicToken is ERC20Basic {
  using SafeMath for uint256;

  mapping(address => uint256) balances;

  uint256 totalSupply_;

  /**
  * @dev total number of tokens in existence
  */
  function totalSupply() public view returns (uint256) {
    return totalSupply_;
  }

  /**
  * @dev transfer token for a specified address
  * @param _to The address to transfer to.
  * @param _value The amount to be transferred.
  */
  /*@CTK transfer_success
    @pre _to != address(0)
    @pre balances[msg.sender] >= _value
    @pre __reverted == false
    @post __reverted == false
    @post __return == true
   */
  /*@CTK transfer_same_address
    @tag no_overflow
    @pre _to == msg.sender
    @post this == __post
   */
  /*@CTK transfer_conditions
    @tag assume_completion
    @pre _to != msg.sender
    @post __post.balances[_to] == balances[_to] + _value
    @post __post.balances[msg.sender] == balances[msg.sender] - _value
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function transfer(address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[msg.sender]);

    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    emit Transfer(msg.sender, _to, _value);
    return true;
  }

  /**
  * @dev Gets the balance of the specified address.
  * @param _owner The address to query the the balance of.
  * @return An uint256 representing the amount owned by the passed address.
  */
  /*@CTK balanceOf
    @post __reverted == false
    @post __return == balances[_owner]
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function balanceOf(address _owner) public view returns (uint256) {
    return balances[_owner];
  }

}

/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * @dev https://github.com/ethereum/EIPs/issues/20
 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
contract StandardToken is ERC20, BasicToken {

  mapping (address => mapping (address => uint256)) internal allowed;


  /**
   * @dev Transfer tokens from one address to another
   * @param _from address The address which you want to send tokens from
   * @param _to address The address which you want to transfer to
   * @param _value uint256 the amount of tokens to be transferred
   */
  /*@CTK transferFrom
    @tag assume_completion
    @pre _from != _to
    @post __return == true
    @post __post.balances[_to] == balances[_to] + _value
    @post __post.balances[_from] == balances[_from] - _value
    @post __has_overflow == false
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);

    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    emit Transfer(_from, _to, _value);
    return true;
  }

  /**
   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   *
   * Beware that changing an allowance with this method brings the risk that someone may use both the old
   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   * @param _spender The address which will spend the funds.
   * @param _value The amount of tokens to be spent.
   */
  /*@CTK approve_success
    @post _value == 0 -> __reverted == false
    @post allowed[msg.sender][_spender] == 0 -> __reverted == false
   */
  /*@CTK approve
    @tag assume_completion
    @post __post.allowed[msg.sender][_spender] == _value
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
  }

  /**
   * @dev Function to check the amount of tokens that an owner allowed to a spender.
   * @param _owner address The address which owns the funds.
   * @param _spender address The address which will spend the funds.
   * @return A uint256 specifying the amount of tokens still available for the spender.
   */
  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];
  }

  /**
   * @dev Increase the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To increment
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _addedValue The amount of tokens to increase the allowance by.
   */
  /*@CTK CtkIncreaseApprovalEffect
    @tag assume_completion
    @post __post.allowed[msg.sender][_spender] == allowed[msg.sender][_spender] + _addedValue
    @post __has_overflow == false
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

  /**
   * @dev Decrease the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To decrement
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _subtractedValue The amount of tokens to decrease the allowance by.
   */
  /*@CTK CtkDecreaseApprovalEffect_1
    @pre allowed[msg.sender][_spender] >= _subtractedValue
    @tag assume_completion
    @post __post.allowed[msg.sender][_spender] == allowed[msg.sender][_spender] - _subtractedValue
    @post __has_overflow == false
   */
   /*@CTK CtkDecreaseApprovalEffect_2
    @pre allowed[msg.sender][_spender] < _subtractedValue
    @tag assume_completion
    @post __post.allowed[msg.sender][_spender] == 0
    @post __has_overflow == false
   */
  /* CertiK Smart Labelling, for more details visit: https://certik.org */
  function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
    uint oldValue = allowed[msg.sender][_spender];
    if (_subtractedValue > oldValue) {
      allowed[msg.sender][_spender] = 0;
    } else {
      allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    }
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

}

contract IoTeXNetwork is StandardToken, Pausable {
    string public constant name = "IoTeX Network";
    string public constant symbol = "IOTX";
    uint8 public constant decimals = 18;

    modifier validDestination(address to) {
        require(to != address(0x0));
        require(to != address(this) );
        _;
    }

    function IoTeXNetwork(uint tokenTotalAmount) {
        totalSupply_ = tokenTotalAmount;
        balances[msg.sender] = tokenTotalAmount;
        emit Transfer(address(0x0), msg.sender, tokenTotalAmount);
    }

    /*@CTK CtkTransferNoEffect
      @post (_to == address(0)) \/ (paused == true) -> __reverted == true
     */
    /*@CTK CtkTransferEffect
      @pre __reverted == false
      @pre balances[msg.sender] >= _value
      @pre paused == false
      @pre __return == true
      @pre msg.sender != _to
      @post __post.balances[_to] == balances[_to] + _value
      @post __has_overflow == false
     */
    /* CertiK Smart Labelling, for more details visit: https://certik.org */
    function transfer(address _to, uint _value) whenNotPaused
        validDestination(_to)
        returns (bool) {
        return super.transfer(_to, _value);
    }

    /*@CTK CtkTransferFromNoEffect
      @post (_to == address(0)) \/ (paused == true) -> __reverted == true
     */
    /*@CTK CtkTransferFromEffect
      @tag assume_completion
      @pre _from != _to
      @post __post.balances[_to] == balances[_to] + _value
      @post __post.balances[_from] == balances[_from] - _value
      @post __has_overflow == false
     */
    /* CertiK Smart Labelling, for more details visit: https://certik.org */
    function transferFrom(address _from, address _to, uint _value) whenNotPaused
        validDestination(_to)
        returns (bool) {
        return super.transferFrom(_from, _to, _value);
    }

    /*@CTK CtkApproveNoEffect
      @post (paused == true) -> __post == this
     */
    /*@CTK CtkApprove
      @tag assume_completion
      @post __post.allowed[msg.sender][_spender] == _value
     */
    /* CertiK Smart Labelling, for more details visit: https://certik.org */
    function approve(address _spender, uint256 _value) public whenNotPaused
      returns (bool) {
      return super.approve(_spender, _value);
    }

    /*@CTK CtkIncreaseApprovalNoEffect
      @post (paused == true) -> __reverted == true
     */
    /*@CTK CtkIncreaseApprovalEffect
      @pre paused == false
      @tag assume_completion
      @post __post.allowed[msg.sender][_spender] == allowed[msg.sender][_spender] + _addedValue
      @post __has_overflow == false
     */
    /* CertiK Smart Labelling, for more details visit: https://certik.org */
    function increaseApproval(address _spender, uint _addedValue) public whenNotPaused
      returns (bool success) {
      return super.increaseApproval(_spender, _addedValue);
    }

    /*@CTK CtkDecreaseApprovalNoEffect
      @post (paused == true) -> __reverted == true
     */
    /*@CTK CtkDecreaseApprovalEffect
      @pre allowed[msg.sender][_spender] >= _subtractedValue
      @tag assume_completion
      @post __post.allowed[msg.sender][_spender] == allowed[msg.sender][_spender] - _subtractedValue
      @post __has_overflow == false
     */
    /* CertiK Smart Labelling, for more details visit: https://certik.org */
    function decreaseApproval(address _spender, uint _subtractedValue) public whenNotPaused
      returns (bool success) {
      return super.decreaseApproval(_spender, _subtractedValue);
    }
}