get_maximal_no_swap_lp_amount.go

package types

import (
	sdk "github.com/cosmos/cosmos-sdk/types"
	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
)

// getMaximalNoSwapLPAmount returns the coins(lp liquidity) needed to get the specified amount of shares in the pool.
// Steps to getting the needed lp liquidity coins needed for the share of the pools are
// 1. calculate how much percent of the pool does given share account for(# of input shares / # of current total shares)
// 2. since we know how much % of the pool we want, iterate through all pool liquidity to calculate how much coins we need for
// each pool asset.
func GetMaximalNoSwapLPAmount(pool Pool, shareOutAmount sdk.Int) (neededLpLiquidity sdk.Coins, err error) {
	totalSharesAmount := pool.GetTotalShares()
	// shareRatio is the desired number of shares, divided by the total number of
	// shares currently in the pool. It is intended to be used in scenarios where you want
	shareRatio := sdk.NewDecFromBigInt(shareOutAmount.BigInt()).QuoInt(totalSharesAmount.Amount)
	if shareRatio.LTE(sdk.ZeroDec()) {
		return sdk.Coins{}, sdkerrors.Wrapf(ErrInvalidMathApprox, "Too few shares out wanted. "+
			"(debug: getMaximalNoSwapLPAmount share ratio is zero or negative)")
	}

	poolLiquidity := pool.GetTotalPoolLiquidity()
	neededLpLiquidity = sdk.Coins{}

	for _, coin := range poolLiquidity {
		// (coin.Amt * shareRatio).Ceil()
		neededAmt := sdk.NewDecFromBigInt(coin.Amount.BigInt()).Mul(shareRatio).Ceil().RoundInt()
		if neededAmt.LTE(sdk.ZeroInt()) {
			return sdk.Coins{}, sdkerrors.Wrapf(ErrInvalidMathApprox, "Too few shares out wanted")
		}
		neededCoin := sdk.Coin{Denom: coin.Denom, Amount: neededAmt}
		neededLpLiquidity = neededLpLiquidity.Add(neededCoin)
	}
	return neededLpLiquidity, nil
}