1 files changed, 57 insertions, 0 deletions
diff --git a/src/FundLab.Api/NavDateProbe.fs b/src/FundLab.Api/NavDateProbe.fs
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+++ b/src/FundLab.Api/NavDateProbe.fs
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+namespace FundLab.Api
+
+open System
+open System.Collections.Concurrent
+open System.Threading
+
+/// Read-only probe that returns the most recent NAV dates for a fund code.
+///
+/// This is the "real data first" seam for the market NAV-date endpoint: the only
+/// implementation talks to the AKShare collector, and there is deliberately no
+/// synthetic fallback. A failed probe surfaces as a MarketDataFailure so the API
+/// can answer 503 with the underlying reason instead of inventing dates.
+type INavDateProbe =
+    abstract RecentNavDates: code: string * limit: int * CancellationToken -> Result<DateOnly list, MarketDataFailure>
+
+/// AKShare-backed probe. Successful lookups are memoised per fund code
+/// (the F# equivalent of functools.lru_cache) so repeated UI reads during one
+/// process do not re-spawn the collector; failures are never cached.
+type AkshareNavDateProbe(collector: IMarketDataCollector) =
+    let cache = ConcurrentDictionary<string, DateOnly list>(StringComparer.Ordinal)
+
+    let isFundCode (value: string) =
+        not (String.IsNullOrWhiteSpace value)
+        && value.Length = 6
+        && value |> Seq.forall Char.IsDigit
+
+    let clip limit =
+        if limit < 1 then 1
+        elif limit > 60 then 60
+        else limit
+
+    member _.Clear() = cache.Clear()
+
+    interface INavDateProbe with
+        member _.RecentNavDates(code, limit, token) =
+            let normalized = if isNull code then "" else code.Trim()
+
+            if not (isFundCode normalized) then
+                Error(InvalidMarketDataRequest "fund code must contain exactly six digits")
+            else
+                match cache.TryGetValue normalized with
+                | true, cached -> Ok(cached |> List.truncate (clip limit))
+                | _ ->
+                    match collector.FetchNav(normalized, token) with
+                    | Error message -> Error(MarketDataCollectorUnavailable message)
+                    | Ok json ->
+                        match MarketData.parseNavPayload json with
+                        | Error message -> Error(InvalidMarketDataPayload message)
+                        | Ok payload ->
+                            let dates =
+                                payload.Observations
+                                |> List.map (fun observation -> observation.NavDate)
+                                |> List.distinct
+                                |> List.sortDescending
+
+                            cache.[normalized] <- dates
+                            Ok(dates |> List.truncate (clip limit))