add spec (#1910)

content/sips/sip-2059.md

@@ -1,41 +1,92 @@
 ---
 sip: 2059
 title: Legacy Spot Synth Migration
-network:  Ethereum
+network: Ethereum
 status: Draft
 type: Governance
-author: Kaleb (@kaleb-keny)
+author: Kaleb (@kaleb-keny), MEB (@barrasso)
+implementor: MEB (@barrasso)
+release: Acrab
 ---
 
 ## Simple Summary
 
-The sip proposes to deprecate classic exchanges (and atomic exchanges) of `sETHBTC`, `sETH` and `sBTC` with a new redeemer contract that redeems users at the chainlink price multiplied by a `discountRate`. This `discountRate` would start at 1 and can be decrease gradually as per a pre-approved schedule that can be voted on by governance with an SCCP.
+The SIP proposes deprecating classic exchanges (and atomic exchanges) of sETHBTC, sETH, and sBTC in favor of a new redeemer contract that redeems users at the Chainlink price multiplied by a discountRate. This discountRate would start at 1 and could decrease gradually according to a pre-approved schedule that can be voted on by governance with an SCCP.
 
 ## Abstract
 
 <!--A short (~200 word) description of the proposed change, the abstract should clearly describe the proposed change. This is what *will* be done if the SIP is implemented, not *why* it should be done or *how* it will be done. If the SIP proposes deploying a new contract, write, "we propose to deploy a new contract that will do x".-->
 
-After this sip is implemented, users holding `sETH`, `sBTC`   or `sETHBTC` can only redeem their synths to `sUSD` at the chainlink price multiplied by the specified discount factor.
+After this SIP is implemented, users holding sETH, sBTC, or sETHBTC will only be able to redeem their synths for sUSD at the Chainlink price multiplied by the specified discount factor.
 
 ## Motivation
 
-The legacy spot synths are overutilsed relative to their value to stakers, they produce minimal revenue and incur significant hedging costs for stakers. Spot synths in V3 have been redesigned to be more aligned with the interests of stakers, this proposal will immediately begin to reduce the debt pool skew, and the costs associated with stakers managing their debt hedging due to changes in the composition of outstanding synths. It also prepares for the migration of debt to V3 later in the year as new products are launched, including the upcoming L1 ETH perp.
+The legacy spot synths are overutilized relative to their value to stakers; they generate minimal revenue and incur significant hedging costs for stakers. Spot synths in V3 have been redesigned to be more aligned with the interests of stakers. This proposal will immediately begin to reduce the debt pool skew and the costs associated with stakers managing their debt hedging due to changes in the composition of outstanding synths. It also prepares for the migration of debt to V3 later in the year as new products are launched, including the upcoming L1 ETH perp.
 
 ## Specification
 
-Pending
+- Suspend existing exchange functionality via `SystemStatus.suspendSynthsExchange`.
+
+- Create a new redeemer contract `DynamicSynthRedeemer` that allows users to redeem synths for `chainlink price * discountRate`. The contract adjusts redemption prices based on Chainlink price data at the time of execution (as opposed to [SIP-174: Synth Redeemer](https://sips.synthetix.io/sips/sip-174/), which does so at a fixed rate).
+
+- Update `DebtCache` to take the discountRate into account for its issued synth reporting:
+
+```
+    function _issuedSynthValues(
+        bytes32[] memory currencyKeys,
+        uint[] memory rates
+    ) internal view returns (uint[] memory values) {
+        uint numValues = currencyKeys.length;
+        values = new uint[](numValues);
+        ISynth[] memory synths = issuer().getSynths(currencyKeys);
+
+        for (uint i = 0; i < numValues; i++) {
+            address synthAddress = address(synths[i]);
+            require(synthAddress != address(0), "Synth does not exist");
+            uint supply = IERC20(synthAddress).totalSupply();
+            uint value = supply.multiplyDecimalRound(rates[i]);
+            values[i] = value.multiplyDecimalRound(dynamicSynthRedeemer().discountRate());
+        }
+
+        return (values);
+    }
+```
 
 ### Test Cases
 
-Pending
+#### Unit Tests
+
+For `DynamicSynthRedeemer`:
+
+- It only allows owner to update discountRate.
+- It reverts if synth is not up for redemption.
+- It reverts if the sender does not have enough synth balance.
+- It applies the expected discountRate to the redemption price.
+- It correctly updates synth balances.
+
+#### Integration Tests
+
+A integration test to cover the dynamic redemptions.
+
+- Verify synth exchanging is suspended.
+- Verify the caller has enough synth balance.
+- Verify it burns the correct amount of synths from the caller.
+- Verify it returns the correct amount of sUSD to the caller.
+- Verify the total issued synth values are correctly reported.
+- Verify it emits a `SynthRedeemed` event with the expected values.
+
+#### Manual Tests
+
+- Deploy and test on sepolia and sepolia-ovm.
+- Confirm discountRate is applied to the aggregator price on redemption.
+- Confirm debt value is reported as expected by debt oracle.
 
 ### Configurable Values (Via SCCP)
 
 <!--Please list all values configurable via SCCP under this implementation.-->
 
 The `discountRate` that allows configuration of the funding rate imposed on holding volatile synths on L1.
 
-
 ## Copyright
 
 Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).