2 files changed, 119 insertions, 0 deletions
diff --git a/src/FundLab.Domain/CashLedger.fs b/src/FundLab.Domain/CashLedger.fs
new file mode 100644
index 0000000..d9d8b32
--- /dev/null
+++ b/src/FundLab.Domain/CashLedger.fs
@@ -0,0 +1,118 @@
+namespace FundLab.Domain
+
+open System
+
+/// Cash-ledger event sourcing and reconciliation for a fund. The ledger records every
+/// movement of the fund's cash (available plus reserved) with a source category so the
+/// statement can be grouped and checked against the actual cash balance. Amounts are
+/// signed: positive is an inflow, negative an outflow.
+module CashLedger =
+    /// Source category of a cash movement. The set is the vocabulary surfaced by the
+    /// reconciliation API/UI; not every category is reachable until the corresponding
+    /// operation actually moves cash.
+    type CashEventSource =
+        | Subscription
+        | Redemption
+        | Dividend
+        | Sip
+        | StockBuy
+        | StockSell
+        | BondBuy
+        | BondSell
+        | BondCoupon
+        | BondMaturity
+        | CapitalDeposit
+
+    let sourceText (source: CashEventSource) : string =
+        match source with
+        | Subscription -> "subscription"
+        | Redemption -> "redemption"
+        | Dividend -> "dividend"
+        | Sip -> "sip"
+        | StockBuy -> "stock_buy"
+        | StockSell -> "stock_sell"
+        | BondBuy -> "bond_buy"
+        | BondSell -> "bond_sell"
+        | BondCoupon -> "bond_coupon"
+        | BondMaturity -> "bond_maturity"
+        | CapitalDeposit -> "capital_deposit"
+
+    let parseSource (text: string) : CashEventSource option =
+        match (if isNull text then "" else text.Trim().ToLowerInvariant()) with
+        | "subscription" -> Some Subscription
+        | "redemption" -> Some Redemption
+        | "dividend" -> Some Dividend
+        | "sip" -> Some Sip
+        | "stock_buy" -> Some StockBuy
+        | "stock_sell" -> Some StockSell
+        | "bond_buy" -> Some BondBuy
+        | "bond_sell" -> Some BondSell
+        | "bond_coupon" -> Some BondCoupon
+        | "bond_maturity" -> Some BondMaturity
+        | "capital_deposit" -> Some CapitalDeposit
+        | _ -> None
+
+    /// A scheduled/automated contribution is tagged as SIP; any other subscription key
+    /// is a manual subscription. The key prefix is the only origin signal carried by the
+    /// order pipeline, and it is set by the callers that own the schedule.
+    let subscriptionSourceForKey (key: string) : CashEventSource =
+        let text = if isNull key then "" else key
+
+        if text.StartsWith("sip:", StringComparison.Ordinal)
+           || text.StartsWith("investment-plan:", StringComparison.Ordinal) then
+            Sip
+        else
+            Subscription
+
+    type CashLedgerEvent =
+        {
+            Source: CashEventSource
+            EventDate: DateOnly
+            Amount: decimal
+            ReferenceType: string
+            ReferenceId: string
+            Note: string option
+        }
+
+    type SourceTotal =
+        {
+            Source: CashEventSource
+            NetAmount: decimal
+            EventCount: int
+        }
+
+    type CashReconciliation =
+        {
+            OpeningCash: decimal
+            NetInflow: decimal
+            ClosingCash: decimal
+            LedgerBalance: decimal
+            Difference: decimal
+            Sources: SourceTotal list
+        }
+
+    /// Opening cash plus the net of every ledger event must equal the fund's actual cash
+    /// balance. `Difference` is zero exactly when the ledger fully explains the balance.
+    let reconcile (openingCash: decimal) (ledgerBalance: decimal) (events: CashLedgerEvent list) : CashReconciliation =
+        let netInflow = events |> List.sumBy (fun event -> event.Amount)
+        let closingCash = openingCash + netInflow
+
+        let sources =
+            events
+            |> List.groupBy (fun event -> event.Source)
+            |> List.map (fun (source, group) ->
+                {
+                    Source = source
+                    NetAmount = group |> List.sumBy (fun event -> event.Amount)
+                    EventCount = group.Length
+                })
+            |> List.sortBy (fun total -> sourceText total.Source)
+
+        {
+            OpeningCash = openingCash
+            NetInflow = netInflow
+            ClosingCash = closingCash
+            LedgerBalance = ledgerBalance
+            Difference = closingCash - ledgerBalance
+            Sources = sources
+        }
diff --git a/src/FundLab.Domain/FundLab.Domain.fsproj b/src/FundLab.Domain/FundLab.Domain.fsproj
index 6d6a8ac..7c6db3f 100644
--- a/src/FundLab.Domain/FundLab.Domain.fsproj
+++ b/src/FundLab.Domain/FundLab.Domain.fsproj
@@ -14,6 +14,7 @@
     <Compile Include="InvestmentPlan.fs" />
     <Compile Include="Rebalance.fs" />
     <Compile Include="Dividend.fs" />
+    <Compile Include="CashLedger.fs" />
     <Compile Include="BondRules.fs" />
     <Compile Include="StockRules.fs" />
     <Compile Include="Performance.fs" />