Add proper pricing to My Positions

[grod220]

The current state:

We need to properly calculate the pricing to fill in accurate values for:

• Effective Price
• Base Price
• Current Value

Math behind the values

=== Quoted from @erwanor ===

• buy/sell
  • the logic that decides whether an LP is buy/sell is sound, but there's one caveat: it's ultimately a user experience decision based on which asset is the "numeraire" (in another word, which asset is the unit of account for the trades)
    • a somewhat under-advertised in the dex is that trading pairs have a canonical (unambiguous) ordering based on asset ids (asset_id_1 < asset_id_2 ), and asset ids are random. this means that for a pair like UM/USDX, it's totally possible that asset_1 is USDX and asset_2 is UM. yet, you would want to render a position that provisions UM to acquire USDX as a Sell and vice-versa.
  • not sure how to best articulate that in the code, but you could keep this logic and have a layer with more context "flip the sign" when necessary, or just fuse it together there. it's possible for a position to be neither a sell/buy, though it should be relatively uncommon once the DEX has fully bootstrapped.
• Fees
  • a Position is a trading function (defining prices + fee) and a tuple of reserves, the trading function is immutable but the reserves can change.
  • the fee is expressed in basis points:
    • 0bps -> 0u32
    • 10bps -> 10u32
    • 5% -> 500u32
    • 100% -> 10_000u32
  • its practical meaning is that every time inventory is routed through the position, it will confiscate some of the input to go into its own reserves. this means that there's a slight difference between a position "nominal price" (the price defined by its price coefficients) and it's "effective price" (the price people actually get inclusive of fees).
  • in the dex internals, there's another parameter called gamma, it is a fee percentage that is computed as follow: gamma = (10_000 - fee)/10_000
  • for example:
    • 0bps -> 1
    • 10bps -> 0.999
    • 5% -> 0.95
    • 100% -> 0
  • gamma is useful to compute the effective price, it lets you compute a discount/premium on the position quoted price to obtain the effective price. we will see how next:
• nominal price vs. effective price
  • a Position is:
    • a trading function (immutable)
    • a tuple of reserves
  • a trading function defines a price and a custom fee tier, this is how:
    • it defines two coefficients p_1 and p_2
    • it defines a fee parameter f
  • the nominal exchange rate between asset 1 and asset 2 is given by: p_1/p_2 (how much asset_1 you get per asset_2)
  • the nominal exchange rate between asset 2 and asset 1 is given by: p_2/p_1 (vice-versa)
  • but clearly, this measure of price is insufficient because if two positions have the same coefficients but one quote a 100% fee and the other a 0% fee, they have in fact very different prices. how do we get a measure of price that includes this information?
  • this is what the effective price is for:
    • effective exchange rate between asset 1 and asset 2: (p_1/p_2)*gamma
    • asset 2 to asset 1: (p_2 * gamma)/p_1

• Now to map onto the figma design:
  • base price is what i call the "nominal price" so p1/p2
  • fee (percentage): this is the fee parameter of the trading function, recall that it's expressed in bps so to turn it into a percentage you will have to do (fee/100), e.g, applying f/100 to our example values:
    • 0 bps -> 0%
    • 10 bps -> 0.01%
    • 500 bps -> 5%
    • 10000 bps -> 100%
  • fee (USDC): this is (f/100) * (p_1/p_2)
  • effective price: (p_1/p_2)*gamma like we explained above