feat: use osm in destination oracle

Signed-off-by: Reinis Martinsons <reinis@umaproject.org>

src/OevOracle.sol

@@ -27,6 +27,8 @@ abstract contract OevOracle is IOevOracle {
         cachedLatestTimestamp = _latestTimestamp;
     }
 
+    // TODO: Decide how to handle negative values. Since not all source oracles support negative values we may need to
+    // limit the support only to positive values.
     function rawLatestAnswer() public view override returns (int256) {
         if (canReturnCachedValue(cachedLatestTimestamp)) return cachedLatestAnswer;
         return sourceAdapter.latestAnswer();

src/adapters/makerdao/ChronicleDestinationOracleAdapter.sol

@@ -2,31 +2,28 @@
 pragma solidity 0.8.17;
 
 import "../../controllers/BaseController.sol";
-import "../../interfaces/chronicle/IMedian.sol";
+import "../../interfaces/chronicle/IOSM.sol";
 
-contract ChronicleDestinationOracleAdapter is BaseController, IMedian {
-    uint8 public decimals;
+contract ChronicleDestinationOracleAdapter is BaseController, IOSM {
+    constructor(address _sourceAdapter) BaseController(_sourceAdapter) {}
 
-    constructor(uint8 _decimals, address _sourceAdapter) BaseController(_sourceAdapter) {
-        decimals = _decimals;
-    }
-
-    function read() public view override returns (uint256) {
-        // TODO: if we never have more than 18 decimals on the output oracle then we can subtract decimals and divide.
-        return (uint256(rawLatestAnswer()) * (10 ** decimals)) / (10 ** 18);
+    function read() public view override returns (bytes32) {
+    // MakerDAO performs decimal conversion in collateral adapter contracts, so all oracle prices are expected to have
+    // 18 decimals, the same as returned by the rawLatestAnswer().
+        return bytes32(uint256(rawLatestAnswer()));
     }
 
     // TODO: might need to add toll functionality to replicate consumer authorization as in MakerDao.
-    function peek() public view override returns (uint256, bool) {
-        uint256 val = read();
-        return (val, val > 0);
-    }
-
-    function age() public view override returns (uint32) {
-        return uint32(rawLatestTimestamp());
+    function peek() public view override returns (bytes32, bool) {
+        uint256 val = uint256(rawLatestAnswer());
+        // TODO: In current design we cannot pass through invalid 0 values and fetching them from source OSM would revert.
+        // This might be required for MakerDAO when voiding Oracle sources.
+        return (bytes32(val), val > 0);
     }
 
-    function bar() public view override returns (uint256) {
-        return uint256(decimals);
+    // This is only implemented to satisfy the interface, but should not be consumed, especially when mixing with other
+    // source Oracle adapters than OSM.
+    function zzz() public view override returns (uint64) {
+        return uint64(rawLatestTimestamp());
     }
 }

src/adapters/makerdao/ChronicleSourceOracleAdapter.sol

@@ -16,6 +16,7 @@ contract ChronicleSourceOracleAdapter is IBaseOracleAdapter {
     }
 
     function latestAnswer() public view override returns (int256) {
+        // This will revert if the price has been voided.
         return int256((uint(source.read()) * (10 ** 18)) / (10 ** decimals));
     }
 

src/interfaces/chronicle/IOSM.sol

@@ -11,7 +11,7 @@ interface IOSM {
     // function src() external view returns (address); // Address of source oracle.
 
     // function hop() external view returns (uint16); // Oracle delay in seconds.
-    function zzz() external view returns (uint64); // Start of period timestamp when the price was last updated.
+    function zzz() external view returns (uint64); // Time of last update (rounded down to nearest multiple of hop).
 
     // function bud(address _addr) external view returns (uint256); // Whitelisted contracts, set by an auth