2 files changed, 111 insertions, 0 deletions
diff --git a/src/FundLab.Domain/FundLab.Domain.fsproj b/src/FundLab.Domain/FundLab.Domain.fsproj
index 9417a4c..6d6a8ac 100644
--- a/src/FundLab.Domain/FundLab.Domain.fsproj
+++ b/src/FundLab.Domain/FundLab.Domain.fsproj
@@ -15,6 +15,7 @@
     <Compile Include="Rebalance.fs" />
     <Compile Include="Dividend.fs" />
     <Compile Include="BondRules.fs" />
+    <Compile Include="StockRules.fs" />
     <Compile Include="Performance.fs" />
   </ItemGroup>
 </Project>
diff --git a/src/FundLab.Domain/StockRules.fs b/src/FundLab.Domain/StockRules.fs
new file mode 100644
index 0000000..0102e5b
--- /dev/null
+++ b/src/FundLab.Domain/StockRules.fs
@@ -0,0 +1,110 @@
+namespace FundLab.Domain
+
+open System
+
+/// Stock trading terms. Every rate/limit is supplied by the caller (config),
+/// nothing about a specific regime is hardcoded into the functions below.
+///
+/// A-share conventions the caller typically supplies: 100-share lot, commission
+/// rate with a per-order minimum, sell-side stamp duty, transfer fee, a 15:00
+/// same-day cutoff and T+1 settlement.
+type StockTerms =
+    {
+        /// Minimum tradable unit in shares (A shares: 100).
+        MinUnit: decimal
+        /// Brokerage commission rate applied to the gross amount.
+        CommissionRate: decimal
+        /// Minimum commission per order (e.g. 5.00).
+        CommissionMin: decimal
+        /// Stamp duty rate, charged on sells only (e.g. 0.0005).
+        StampDutyRate: decimal
+        /// Transfer fee rate applied to the gross amount (both sides).
+        TransferFeeRate: decimal
+        /// Latest same-day order time; at/after this the order is next-day.
+        CutoffTime: TimeOnly
+        /// Settlement lag in trading days (T+1 => 1).
+        SettlementDays: int
+    }
+
+module StockTerms =
+    let create
+        (minUnit: decimal)
+        (commissionRate: decimal)
+        (commissionMin: decimal)
+        (stampDutyRate: decimal)
+        (transferFeeRate: decimal)
+        (cutoffTime: TimeOnly)
+        (settlementDays: int)
+        : StockTerms =
+        {
+            MinUnit = minUnit
+            CommissionRate = commissionRate
+            CommissionMin = commissionMin
+            StampDutyRate = stampDutyRate
+            TransferFeeRate = transferFeeRate
+            CutoffTime = cutoffTime
+            SettlementDays = settlementDays
+        }
+
+    /// Common A-share defaults; callers may override any field.
+    let aShareDefault: StockTerms =
+        create 100m 0.00025m 5.00m 0.0005m 0.00001m (TimeOnly(15, 0)) 1
+
+/// Pure stock trading rules: cutoff handling, T+1 settlement, fee bounds and
+/// lot-size validation.
+module StockRules =
+    let private nextTradingDay (date: DateOnly) =
+        let next = date.AddDays 1
+
+        match next.DayOfWeek with
+        | DayOfWeek.Saturday -> next.AddDays 2
+        | DayOfWeek.Sunday -> next.AddDays 1
+        | _ -> next
+
+    /// Order date after applying the same-day cutoff: an order at/after the
+    /// cutoff is treated as placed on the next trading day.
+    let effectiveTradeDate (terms: StockTerms) (tradeDate: DateOnly) (at: TimeOnly) : DateOnly =
+        if at >= terms.CutoffTime then nextTradingDay tradeDate else tradeDate
+
+    /// Settlement date for a trade, skipping weekends. A real exchange trading
+    /// calendar would extend this; weekends are the minimum correctness bar.
+    let settlementDate (terms: StockTerms) (tradeDate: DateOnly) (at: TimeOnly) : DateOnly =
+        let rec advance (date: DateOnly) (remaining: int) =
+            if remaining <= 0 then date else advance (nextTradingDay date) (remaining - 1)
+
+        advance (effectiveTradeDate terms tradeDate at) terms.SettlementDays
+
+    let private commission (terms: StockTerms) (gross: decimal) =
+        let raw = Decimal.Round(gross * terms.CommissionRate, 2, MidpointRounding.AwayFromZero)
+        if gross > 0m && raw < terms.CommissionMin then terms.CommissionMin else raw
+
+    let private transferFee (terms: StockTerms) (gross: decimal) =
+        Decimal.Round(gross * terms.TransferFeeRate, 2, MidpointRounding.AwayFromZero)
+
+    /// Cash cost of buying `quantity` shares: gross plus commission and
+    /// transfer fee (no stamp duty on buys).
+    let buyCost (terms: StockTerms) (quantity: decimal) (price: decimal) : decimal =
+        let gross = Decimal.Round(quantity * price, 2, MidpointRounding.AwayFromZero)
+        let fees = commission terms gross + transferFee terms gross
+        gross + fees
+
+    /// Cash proceeds of selling `quantity` shares: gross minus commission,
+    /// stamp duty and transfer fee.
+    let sellProceeds (terms: StockTerms) (quantity: decimal) (price: decimal) : decimal =
+        let gross = Decimal.Round(quantity * price, 2, MidpointRounding.AwayFromZero)
+        let fees = commission terms gross + transferFee terms gross + Decimal.Round(gross * terms.StampDutyRate, 2, MidpointRounding.AwayFromZero)
+        gross - fees
+
+    /// Quantity must be positive and a whole multiple of the minimum unit.
+    let validateQuantity (terms: StockTerms) (quantity: decimal) : Result<decimal, string> =
+        if quantity <= 0m then
+            Error "quantity must be positive"
+        elif terms.MinUnit > 0m && (quantity % terms.MinUnit) <> 0m then
+            Error(sprintf "quantity must be a multiple of %O shares" terms.MinUnit)
+        else
+            Ok quantity
+
+    /// A stock cannot be sold on the same day it was bought (T+1): given a buy
+    /// date and a sell date, returns true only once settlement has elapsed.
+    let isSellAllowed (terms: StockTerms) (buyDate: DateOnly) (sellDate: DateOnly) : bool =
+        sellDate >= settlementDate terms buyDate (TimeOnly(0, 0))