owner address
phb token address
phb token address

 function setInflationSpeed(uint256 speed) external;
 // reward amount per second

 function stake(uint256 amount) external;

 function withdrawableAmount(address account)external view returns(uint256);

function applyWithdraw(uint256 amount) external nonReentrant; //apply withdraw
function withdraw(uint256 amount) external; //can withdraw token after the locking time

function getUserRewards(address account) external view returns(uint256);

function claimReward() external;

we maintains 2 (kinds) index:
globalIndex: means how many rewards per staking token,has 2 fields: index and last updated timestamp
userIndex: user share from the total staking
every time the total staking amount changed ,user claimed rewards and inflation speed changed, we need to update the globalIndex
initial status: we ignore the decimals of tokens 
globalindex = 1, total staking = 0, speed = 0, we do the operation every 10 seconds

1) admin set speed to 100 (100 phb per seconds), since still now staking, we only update the globalindex timestamp to now.
2) user A stakes 10000 phb, previous total staking  = 0, globalindex = 1, previous balance(A) = 0,distributed reward = 0, then set user A's index = 1
3) user B stakes 10000 phb, previous total staking = 10000 , globalindex = 1 + delta(time) * speed/ 10000 = 1.1, set user B's index = 1 ,previous balance(b) = 0,distributed reward = 0, then set user B's index = 1.1
4) query/claim user A's reward now(also 10 seconds past) ,the new globalindex = 1.1 + 10 * 100/20000 = 1.15
    (if for the getUserReward function, the globalindex is not saved to storage since it's a 'view' function)   
    so the rewards is delta(index) * balance(A) = (1.15-1)*10000 = 1500 phb    
5) at the same time user B's reward is delta(index) * balance(B) = (1.15-1.1) * 10000 = 500 phb
now let's check the result(***NOTE since no one staked in the 1st 10 seconds, so the 1st 1000 phb is wasted!!!!!)

for refresh speed is the same
6) admin change speed to 200, then global index = 1.1(assume step 5 is query operation, didn't change the storage) + delta(time) * oldspeed / 20000 = 1.1+20 *100/20000 = 1.2
7) user A query reward: current global index = 1.2+ delta(time) * newspeed / 20000 = 1.2 + 10 * 200/20000 = 1.3, so the reward should be (1.3 - 1)* 10000 = 3000
user B query reward: so the reward should be (1.3 - 1.1)* 10000 = 2000