feat: floor price set to the 0.06 USDFC/month (#320)

_Edit: This got switched to having 0.06 USDFC as the floor, not the
bytes; so now the bytes works out as ~24.576 GiB and we get to talk
about it in terms of cents per month._

(PR on top of #316, that should be merged first)

Amounts below this pay as if they are storing 24 GiB, which is
0.05859375 USDFC / month.

Closes: #319

---

*  24 GiB = 24/1024 TiB = 0.0234375 TiB
* At 2.5 USDFC/TiB/month, price = 0.0234375 * 2.5 = 0.05859375
USDFC/month

Are we OK with 0.05859375? I have an option here of either setting 24GiB
as the floor _size_ or 0.06 as the floor _price_.

If we go with 0.06 as the floor then we're working with 24.576 GiB floor
size.

---

I also had to change the mock token from 6 decimal places to 18, cause
there's already a floor rounding bit of code in here and it was getting
stuck on a higher floor due to not enough decimal places, so everything
came out wrong.

Author: rvagg

service_contracts/abi/FilecoinWarmStorageService.abi.json

@@ -101,7 +101,7 @@
   },
   {
     "type": "function",
-    "name": "calculateRatesPerEpoch",
+    "name": "calculateRatePerEpoch",
     "inputs": [
       {
         "name": "totalBytes",
@@ -357,6 +357,11 @@
             "name": "epochsPerMonth",
             "type": "uint256",
             "internalType": "uint256"
+          },
+          {
+            "name": "minimumPricePerMonth",
+            "type": "uint256",
+            "internalType": "uint256"
           }
         ]
       }
@@ -1681,6 +1686,115 @@
       }
     ]
   },
+  {
+    "type": "error",
+    "name": "InsufficientFundsForMinimumRate",
+    "inputs": [
+      {
+        "name": "payer",
+        "type": "address",
+        "internalType": "address"
+      },
+      {
+        "name": "minimumRequired",
+        "type": "uint256",
+        "internalType": "uint256"
+      },
+      {
+        "name": "available",
+        "type": "uint256",
+        "internalType": "uint256"
+      }
+    ]
+  },
+  {
+    "type": "error",
+    "name": "InsufficientLockupAllowance",
+    "inputs": [
+      {
+        "name": "payer",
+        "type": "address",
+        "internalType": "address"
+      },
+      {
+        "name": "operator",
+        "type": "address",
+        "internalType": "address"
+      },
+      {
+        "name": "lockupAllowance",
+        "type": "uint256",
+        "internalType": "uint256"
+      },
+      {
+        "name": "lockupUsage",
+        "type": "uint256",
+        "internalType": "uint256"
+      },
+      {
+        "name": "minimumLockupRequired",
+        "type": "uint256",
+        "internalType": "uint256"
+      }
+    ]
+  },
+  {
+    "type": "error",
+    "name": "InsufficientMaxLockupPeriod",
+    "inputs": [
+      {
+        "name": "payer",
+        "type": "address",
+        "internalType": "address"
+      },
+      {
+        "name": "operator",
+        "type": "address",
+        "internalType": "address"
+      },
+      {
+        "name": "maxLockupPeriod",
+        "type": "uint256",
+        "internalType": "uint256"
+      },
+      {
+        "name": "requiredLockupPeriod",
+        "type": "uint256",
+        "internalType": "uint256"
+      }
+    ]
+  },
+  {
+    "type": "error",
+    "name": "InsufficientRateAllowance",
+    "inputs": [
+      {
+        "name": "payer",
+        "type": "address",
+        "internalType": "address"
+      },
+      {
+        "name": "operator",
+        "type": "address",
+        "internalType": "address"
+      },
+      {
+        "name": "rateAllowance",
+        "type": "uint256",
+        "internalType": "uint256"
+      },
+      {
+        "name": "rateUsage",
+        "type": "uint256",
+        "internalType": "uint256"
+      },
+      {
+        "name": "minimumRateRequired",
+        "type": "uint256",
+        "internalType": "uint256"
+      }
+    ]
+  },
   {
     "type": "error",
     "name": "InvalidChallengeCount",
@@ -1957,6 +2071,22 @@
       }
     ]
   },
+  {
+    "type": "error",
+    "name": "OperatorNotApproved",
+    "inputs": [
+      {
+        "name": "payer",
+        "type": "address",
+        "internalType": "address"
+      },
+      {
+        "name": "operator",
+        "type": "address",
+        "internalType": "address"
+      }
+    ]
+  },
   {
     "type": "error",
     "name": "OwnableInvalidOwner",

service_contracts/src/Errors.sol

@@ -286,4 +286,44 @@ library Errors {
     /// @param dataSetId The data set ID
     /// @param pdpEndEpoch The end epoch when the PDP payment rail will finalize
     error PaymentRailsNotFinalized(uint256 dataSetId, uint256 pdpEndEpoch);
+
+    /// @notice Payer has insufficient available funds to cover the minimum storage rate
+    /// @param payer The payer address
+    /// @param minimumRequired The minimum lockup required to cover the minimum storage rate
+    /// @param available The available funds in the payer's account
+    error InsufficientFundsForMinimumRate(address payer, uint256 minimumRequired, uint256 available);
+
+    /// @notice Operator is not approved for the payer
+    /// @param payer The payer address
+    /// @param operator The operator address (warm storage service)
+    error OperatorNotApproved(address payer, address operator);
+
+    /// @notice Operator has insufficient rate allowance for the minimum storage rate
+    /// @param payer The payer address
+    /// @param operator The operator address (warm storage service)
+    /// @param rateAllowance The total rate allowance approved
+    /// @param rateUsage The current rate usage
+    /// @param minimumRateRequired The minimum rate required per epoch
+    error InsufficientRateAllowance(
+        address payer, address operator, uint256 rateAllowance, uint256 rateUsage, uint256 minimumRateRequired
+    );
+
+    /// @notice Operator has insufficient lockup allowance for the minimum lockup
+    /// @param payer The payer address
+    /// @param operator The operator address (warm storage service)
+    /// @param lockupAllowance The total lockup allowance approved
+    /// @param lockupUsage The current lockup usage
+    /// @param minimumLockupRequired The minimum lockup required
+    error InsufficientLockupAllowance(
+        address payer, address operator, uint256 lockupAllowance, uint256 lockupUsage, uint256 minimumLockupRequired
+    );
+
+    /// @notice Operator's max lockup period is insufficient for the default lockup period
+    /// @param payer The payer address
+    /// @param operator The operator address (warm storage service)
+    /// @param maxLockupPeriod The maximum lockup period approved
+    /// @param requiredLockupPeriod The required lockup period
+    error InsufficientMaxLockupPeriod(
+        address payer, address operator, uint256 maxLockupPeriod, uint256 requiredLockupPeriod
+    );
 }

service_contracts/src/FilecoinWarmStorageService.sol

@@ -159,6 +159,7 @@ contract FilecoinWarmStorageService is
         uint256 pricePerTiBCacheMissEgress; // Cache miss egress price per TiB (usage-based)
         IERC20 tokenAddress; // Address of the USDFC token
         uint256 epochsPerMonth; // Number of epochs in a month
+        uint256 minimumPricePerMonth; // Minimum monthly charge for any dataset size (0.06 USDFC)
     }
 
     // Used for announcing upgrades, packed into one slot
@@ -197,6 +198,7 @@ contract FilecoinWarmStorageService is
     uint256 private immutable STORAGE_PRICE_PER_TIB_PER_MONTH; // 2.5 USDFC per TiB per month without CDN with correct decimals
     uint256 private immutable CDN_EGRESS_PRICE_PER_TIB; // 7 USDFC per TiB of CDN egress
     uint256 private immutable CACHE_MISS_EGRESS_PRICE_PER_TIB; // 7 USDFC per TiB of cache miss egress
+    uint256 private immutable MINIMUM_STORAGE_RATE_PER_MONTH; // 0.06 USDFC per month minimum pricing floor
 
     // Fixed lockup amounts for CDN rails
     uint256 private immutable DEFAULT_CDN_LOCKUP_AMOUNT; // 0.7 USDFC
@@ -331,6 +333,7 @@ contract FilecoinWarmStorageService is
         STORAGE_PRICE_PER_TIB_PER_MONTH = (5 * 10 ** TOKEN_DECIMALS) / 2; // 2.5 USDFC
         CDN_EGRESS_PRICE_PER_TIB = 7 * 10 ** TOKEN_DECIMALS; // 7 USDFC per TiB
         CACHE_MISS_EGRESS_PRICE_PER_TIB = 7 * 10 ** TOKEN_DECIMALS; // 7 USDFC per TiB
+        MINIMUM_STORAGE_RATE_PER_MONTH = (6 * 10 ** TOKEN_DECIMALS) / 100; // 0.06 USDFC minimum
 
         // Initialize the lockup constants based on the actual token decimals
         DEFAULT_CDN_LOCKUP_AMOUNT = (7 * 10 ** TOKEN_DECIMALS) / 10; // 0.7 USDFC
@@ -584,6 +587,10 @@ contract FilecoinWarmStorageService is
 
         // Create the payment rails using the FilecoinPayV1 contract
         FilecoinPayV1 payments = FilecoinPayV1(paymentsContractAddress);
+
+        // Validate payer has sufficient funds and operator approvals for minimum pricing
+        validatePayerOperatorApprovalAndFunds(payments, createData.payer);
+
         uint256 pdpRailId = payments.createRail(
             usdfcTokenAddress, // token address
             createData.payer, // from (payer)
@@ -1096,15 +1103,65 @@ contract FilecoinWarmStorageService is
         }
     }
 
+    /// @notice Validates that the payer has sufficient funds and operator approvals for minimum pricing
+    /// @param payments The FilecoinPayV1 contract instance
+    /// @param payer The address of the payer
+    function validatePayerOperatorApprovalAndFunds(FilecoinPayV1 payments, address payer) internal view {
+        // Calculate required lockup for minimum pricing
+        uint256 minimumLockupRequired = (MINIMUM_STORAGE_RATE_PER_MONTH * DEFAULT_LOCKUP_PERIOD) / EPOCHS_PER_MONTH;
+
+        // Check that payer has sufficient available funds
+        (,, uint256 availableFunds,) = payments.getAccountInfoIfSettled(usdfcTokenAddress, payer);
+        require(
+            availableFunds >= minimumLockupRequired,
+            Errors.InsufficientFundsForMinimumRate(payer, minimumLockupRequired, availableFunds)
+        );
+
+        // Check operator approval settings
+        (
+            bool isApproved,
+            uint256 rateAllowance,
+            uint256 lockupAllowance,
+            uint256 rateUsage,
+            uint256 lockupUsage,
+            uint256 maxLockupPeriod
+        ) = payments.operatorApprovals(usdfcTokenAddress, payer, address(this));
+
+        // Verify operator is approved
+        require(isApproved, Errors.OperatorNotApproved(payer, address(this)));
+
+        // Calculate minimum rate per epoch
+        uint256 minimumRatePerEpoch = MINIMUM_STORAGE_RATE_PER_MONTH / EPOCHS_PER_MONTH;
+
+        // Verify rate allowance is sufficient
+        require(
+            rateAllowance >= rateUsage + minimumRatePerEpoch,
+            Errors.InsufficientRateAllowance(payer, address(this), rateAllowance, rateUsage, minimumRatePerEpoch)
+        );
+
+        // Verify lockup allowance is sufficient
+        require(
+            lockupAllowance >= lockupUsage + minimumLockupRequired,
+            Errors.InsufficientLockupAllowance(
+                payer, address(this), lockupAllowance, lockupUsage, minimumLockupRequired
+            )
+        );
+
+        // Verify max lockup period is sufficient
+        require(
+            maxLockupPeriod >= DEFAULT_LOCKUP_PERIOD,
+            Errors.InsufficientMaxLockupPeriod(payer, address(this), maxLockupPeriod, DEFAULT_LOCKUP_PERIOD)
+        );
+    }
+
     function updatePaymentRates(uint256 dataSetId, uint256 leafCount) internal {
         // Revert if no payment rail is configured for this data set
         require(dataSetInfo[dataSetId].pdpRailId != 0, Errors.NoPDPPaymentRail(dataSetId));
 
         uint256 totalBytes = leafCount * BYTES_PER_LEAF;
         FilecoinPayV1 payments = FilecoinPayV1(paymentsContractAddress);
 
-        // Update the PDP rail payment rate with the new rate and no one-time
-        // payment
+        // Update the PDP rail payment rate with the new rate and no one-time payment
         uint256 pdpRailId = dataSetInfo[dataSetId].pdpRailId;
         uint256 newStorageRatePerEpoch = _calculateStorageRate(totalBytes);
         payments.modifyRailPayment(
@@ -1177,21 +1234,29 @@ contract FilecoinWarmStorageService is
 
     /**
      * @notice Calculate storage rate per epoch based on total storage size
-     * @dev Returns storage rate per TiB per month
+     * @dev Returns storage rate per TiB per month with minimum pricing floor applied
      * @param totalBytes Total size of the stored data in bytes
      * @return storageRate The PDP storage rate per epoch
      */
-    function calculateRatesPerEpoch(uint256 totalBytes) external view returns (uint256 storageRate) {
-        storageRate = calculateStorageSizeBasedRatePerEpoch(totalBytes, STORAGE_PRICE_PER_TIB_PER_MONTH);
+    function calculateRatePerEpoch(uint256 totalBytes) external view returns (uint256 storageRate) {
+        storageRate = _calculateStorageRate(totalBytes);
     }
 
     /**
      * @notice Calculate the storage rate per epoch (internal use)
+     * @dev Implements minimum pricing floor and returns the higher of the natural size-based rate or the minimum rate.
      * @param totalBytes Total size of the stored data in bytes
      * @return The storage rate per epoch
      */
     function _calculateStorageRate(uint256 totalBytes) internal view returns (uint256) {
-        return calculateStorageSizeBasedRatePerEpoch(totalBytes, STORAGE_PRICE_PER_TIB_PER_MONTH);
+        // Calculate natural size-based rate
+        uint256 naturalRate = calculateStorageSizeBasedRatePerEpoch(totalBytes, STORAGE_PRICE_PER_TIB_PER_MONTH);
+
+        // Calculate minimum rate (floor price converted to per-epoch)
+        uint256 minimumRate = MINIMUM_STORAGE_RATE_PER_MONTH / EPOCHS_PER_MONTH;
+
+        // Return whichever is higher: natural rate or minimum rate
+        return naturalRate > minimumRate ? naturalRate : minimumRate;
     }
 
     /**
@@ -1289,7 +1354,8 @@ contract FilecoinWarmStorageService is
             pricePerTiBCdnEgress: CDN_EGRESS_PRICE_PER_TIB,
             pricePerTiBCacheMissEgress: CACHE_MISS_EGRESS_PRICE_PER_TIB,
             tokenAddress: usdfcTokenAddress,
-            epochsPerMonth: EPOCHS_PER_MONTH
+            epochsPerMonth: EPOCHS_PER_MONTH,
+            minimumPricePerMonth: MINIMUM_STORAGE_RATE_PER_MONTH
         });
     }