Compute lp_token_value in USD

[AngelaKTE]

lp_token_value in USD
refers to the value of a liquiditiy provider's pool share at any point in time.

How to calculate:
a) ((total_token_value in USD = TVL)/total_pool_balance)*lp_pool_balance
b) (((total_pool_balance/lp_pool_balance)*token_a_balance)*USD)+((total_pool_balance /lp_pool_balance)*token_b_balance)*USD)+...
....
check logic and options for implementation

[VasilySumanov]

Algorithm of lp_token_value function:

1. Retrieve total_token_balance - current token balances in the pool
2. Calculate total_pool_value - the TVL of the pool by multiplying token balances on their USD prices
3. Calculate lp_pool_value - the value of some number of BPT tokens based on share in underlying basket

Step 1: Function for calculation total_token_balance

The function should return the array containing token balances

The sample of solidity code is below. Input argument: address of balancer pool.
It calls the getCurrentTokens function of the pool and after that getBalance in the cycle, retrieving actual balances of tokens inside the pool. Finally, the array containing token balances is returned.

function getBalancerTokensAndBalances(address _balancerPool)
    public
    view
    returns (address[] memory tokens, uint256[] memory balances)
  {
    tokens = BPoolInterface(_balancerPool).getCurrentTokens();
    uint256 len = tokens.length;

    balances = new uint256[](len);
    for (uint256 i = 0; i < len; i++) {
      balances[i] = BPoolInterface(_balancerPool).getBalance(tokens[i]);
    }
  }

Step 2: Function for calculation total_pool_value
Function uses total_token_balances to calculate the pool_value (TVL in the pool).

Solidity code sample:

 function balancerPoolUsdTokensSum(address _balancerPool) public view returns (uint256) {
    (address[] memory tokens, uint256[] memory balances) = getBalancerTokensAndBalances(_balancerPool);
    return usdcTokensSum(tokens, balances);
  }

We need to create our own usdcTokensSum that uses input data (price feeds). It can be artificial data set or the Uniswap token prices data set.

Step 3: Function for calculation lp_pool_value
The sample of solidity code is below. The total supply of LP shares can be calculated by calling total_pool_balance function as this token is basically ERC20 token

function totalSupply() public view returns (uint) {
     return _totalSupply;
 }

After the total supply of LP share is received, we find a ratio: [number of given LP shares]/[totalSupply] and multiply it on TVL

References for code samples:
Step 1,2: https://github.com/powerpool-finance/power-oracle-contracts/blob/master/contracts/InstantUniswapPrice.sol
Step 3: https://github.com/balancer-labs/balancer-core/blob/master/contracts/BToken.sol

[AngelaKTE]

@raul pls check for
C1 - analyse LP pool share value over time