Reduce coupon barcode CPU while preserving recognition

Directory.Packages.props

@@ -56,6 +56,7 @@
     <PackageVersion Include="SixLabors.ImageSharp" Version="3.1.12" />
     <PackageVersion Include="ZXing.Net" Version="0.16.11" />
     <PackageVersion Include="ZXing.Net.Bindings.ImageSharp.V3" Version="0.16.18" />
+    <PackageVersion Include="ZXingCpp" Version="0.5.3" />
 
     <!-- Testing -->
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />

src/CouponHubBot/CouponHubBot.fsproj

@@ -27,6 +27,7 @@
     <PackageReference Include="SixLabors.ImageSharp" />
     <PackageReference Include="ZXing.Net" />
     <PackageReference Include="ZXing.Net.Bindings.ImageSharp.V3" />
+    <PackageReference Include="ZXingCpp" />
     <!-- FakeTimeProvider for the test-only /test/clock/advance endpoint. Stable, ~30KB. -->
     <PackageReference Include="Microsoft.Extensions.TimeProvider.Testing" />
   </ItemGroup>

src/CouponHubBot/Services/CouponOcrEngine.fs

@@ -210,8 +210,71 @@ type CouponOcrEngine(azureTextOcr: IBotOcr, logger: ILogger<CouponOcrEngine>, ti
     let someMoney (v: decimal) : Nullable<decimal> = Nullable(v)
     let someDate (v: DateTime) : Nullable<DateTime> = Nullable(v)
 
-    let tryDecodeBarcode (imageBytes: ReadOnlyMemory<byte>) =
-        use activity = botActivity.StartActivity("couponOcr.barcode")
+    let tryDecodeNative (imageBytes: ReadOnlyMemory<byte>) =
+        use activity = botActivity.StartActivity("couponOcr.barcode.native")
+        try
+            // Resolve the library before constructing objects with native finalizers.
+            let format = ZXingCpp.BarcodeFormat.Parse("EAN13")
+            use ms = new MemoryStream(imageBytes.ToArray())
+            use image = Image.Load<L8>(ms)
+            let pixels = Array.zeroCreate<byte> (image.Width * image.Height)
+            image.CopyPixelDataTo(pixels)
+            use reader = new ZXingCpp.BarcodeReader()
+            reader.Formats <- ZXingCpp.BarcodeFormats(format)
+            reader.TryHarder <- true
+            reader.TryRotate <- true
+            reader.TryInvert <- false
+            reader.TryDownscale <- true
+            reader.MaxNumberOfSymbols <- 1
+            reader.MinLineCount <- 2
+            reader.ReturnErrors <- false
+            // ImageView borrows the pixel buffer throughout native decoding.
+            use _pin = Memory<byte>(pixels).Pin()
+            let decode x y width height =
+                let offset = y * image.Width + x
+                let length = (height - 1) * image.Width + width
+                let region = ReadOnlySpan<byte>(pixels, offset, length)
+                let view = ZXingCpp.ImageView(region, width, height, ZXingCpp.ImageFormat.Lum, image.Width)
+                let results =
+                    try reader.From(view)
+                    finally GC.KeepAlive(view)
+                try
+                    results
+                    |> Array.tryPick (fun barcode ->
+                        if barcode.IsValid && not (String.IsNullOrWhiteSpace barcode.Text) then
+                            Some barcode.Text
+                        else
+                            None)
+                finally
+                    for barcode in results do
+                        barcode.Dispose()
+
+            let result =
+                match decode 0 0 image.Width image.Height with
+                | Some text -> Some text
+                | None ->
+                    let bands = [| 0.0, 0.50; 0.0, 0.60; 0.20, 0.70; 0.30, 0.80; 0.45, 1.0; 0.55, 1.0; 0.65, 1.0 |]
+                    [| 0.0; 0.10; 0.20 |]
+                    |> Array.tryPick (fun margin ->
+                        bands
+                        |> Array.tryPick (fun (top, bottom) ->
+                            let x = int (Math.Round(float image.Width * margin))
+                            let y = min (image.Height - 1) (int (Math.Round(float image.Height * top)))
+                            let width = image.Width - 2 * x
+                            let height = max 1 (int (Math.Round(float image.Height * bottom)) - y)
+                            decode x y width height))
+            if not (isNull activity) then
+                %activity.SetTag("barcode.found", result.IsSome)
+            result
+        with ex ->
+            if not (isNull activity) then
+                %activity.SetTag("error.type", ex.GetType().FullName)
+                %activity.SetStatus(ActivityStatusCode.Error)
+            logger.LogWarning(ex, "Native barcode decode failed; trying managed decoder")
+            None
+
+    let tryDecodeManaged (imageBytes: ReadOnlyMemory<byte>) =
+        use activity = botActivity.StartActivity("couponOcr.barcode.managed")
         let mutable attempts = 0
         try
             use original =
@@ -224,12 +287,12 @@ type CouponOcrEngine(azureTextOcr: IBotOcr, logger: ILogger<CouponOcrEngine>, ti
             let opts = DecodingOptions()
             opts.TryHarder <- true
             opts.PossibleFormats <- [| BarcodeFormat.EAN_13 |]
-            opts.TryInverted <- true
+            opts.TryInverted <- false
             let reader = BarcodeReader<Rgba32>()
             reader.Options <- opts
             reader.AutoRotate <- true
 
-            let decode (label: string) (img: Image<Rgba32>) =
+            let decode (label: string) (img: LuminanceSource) =
                 use attempt = botActivity.StartActivity("couponOcr.barcode.decode")
                 attempts <- attempts + 1
                 if not (isNull attempt) then
@@ -248,12 +311,12 @@ type CouponOcrEngine(azureTextOcr: IBotOcr, logger: ILogger<CouponOcrEngine>, ti
 
             let clamp (v: int) (minv: int) (maxv: int) = max minv (min maxv v)
 
-            let cropTry (baseLabel: string) (img: Image<Rgba32>) (rect: Rectangle) =
+            let cropTry (baseLabel: string) (img: LuminanceSource) (rect: Rectangle) =
                 let x = clamp rect.X 0 (img.Width - 1)
                 let y = clamp rect.Y 0 (img.Height - 1)
                 let w = clamp rect.Width 1 (img.Width - x)
                 let h = clamp rect.Height 1 (img.Height - y)
-                use cropped = img.Clone(fun ctx -> ctx.Crop(Rectangle(x, y, w, h)) |> ignore)
+                let cropped = img.crop(x, y, w, h)
                 decode baseLabel cropped
 
             let tryOnImage (labelPrefix: string) (img: Image<Rgba32>) =
@@ -263,7 +326,8 @@ type CouponOcrEngine(azureTextOcr: IBotOcr, logger: ILogger<CouponOcrEngine>, ti
                 // - Middle band crops (covers centre region)
                 // - Bottom crops (useful for app screenshots)
                 // - Center-narrowed variants of the above (avoid noise on sides)
-                match decode (labelPrefix + ":full") img with
+                let luminance = ImageSharpLuminanceSource<Rgba32>(img)
+                match decode (labelPrefix + ":full") luminance with
                 | Some t -> Some t
                 | None ->
                     let w = img.Width
@@ -312,7 +376,7 @@ type CouponOcrEngine(azureTextOcr: IBotOcr, logger: ILogger<CouponOcrEngine>, ti
 
                     allRects
                     |> Array.mapi (fun i r -> (i, r))
-                    |> Array.tryPick (fun (i, r) -> cropTry $"{labelPrefix}:crop{i}" img r)
+                    |> Array.tryPick (fun (i, r) -> cropTry $"{labelPrefix}:crop{i}" luminance r)
 
             let tryAll () =
                 match tryOnImage "orig" original with
@@ -369,6 +433,16 @@ type CouponOcrEngine(azureTextOcr: IBotOcr, logger: ILogger<CouponOcrEngine>, ti
             logger.LogWarning(ex, "Barcode decode failed")
             noneBarcode
 
+    let tryDecodeBarcode (imageBytes: ReadOnlyMemory<byte>) =
+        use activity = botActivity.StartActivity("couponOcr.barcode")
+        let result =
+            match tryDecodeNative imageBytes with
+            | Some text -> text
+            | None -> tryDecodeManaged imageBytes
+        if not (isNull activity) then
+            %activity.SetTag("barcode.found", not (String.IsNullOrWhiteSpace result))
+        result
+
     let parseFromText (nowUtc: DateTime) (ocrText: string) =
         let amounts = CouponOcrParsing.findEuroAmounts ocrText
         let dates = CouponOcrParsing.findDates nowUtc ocrText

src/CouponHubBot/docs/OCR.md

@@ -1,27 +1,30 @@
-# OCR Pipeline
-
-## Overview
-
-`CouponOcrEngine` combines barcode scanning (ZXing) with Azure Computer Vision text OCR to extract coupon data from photos.
-
-## Components
-
-- **ZXing.Net** + ImageSharp bindings — barcode/QR code scanning
-- **AzureOcrService** — calls Azure Computer Vision `imageanalysis:analyze` endpoint
-- **CouponOcrEngine** — orchestrates both, returns `CouponOCR` record
-
-## OCR Result
-
-`CouponOCR` contains optional fields: `value`, `min_check`, `expires_at`, `barcode_text`. Any combination may be present. The result is **always a pre-fill suggestion** — the user confirms final values in the wizard.
-
-## Caching (for tests)
-
-`tests/CouponHubBot.Ocr.Tests/AzureCache/` stores Azure OCR responses as `*.azure.json` files. These are git-tracked so tests can run without Azure API keys (cache-only mode).
-
-## Configuration
-
-Env vars:
-- `OCR_ENABLED` — enable/disable OCR (default: false)
-- `OCR_MAX_FILE_SIZE_BYTES` — max photo size for OCR processing
-- `AZURE_OCR_ENDPOINT` — Azure Computer Vision endpoint URL
-- `AZURE_OCR_KEY` — Azure API key
+# OCR Pipeline
+
+## Overview
+
+`CouponOcrEngine` combines barcode scanning (ZXing) with Azure Computer Vision text OCR to extract coupon data from photos.
+
+## Components
+
+- **ZXingCpp** + ImageSharp — EAN-13 scanning on grayscale images, followed by horizontal crops
+- **ZXing.Net** + ImageSharp bindings — fallback with rotation, contrast and resizing; luminance is shared across crops
+- **AzureOcrService** — calls Azure Computer Vision `imageanalysis:analyze` endpoint
+- **CouponOcrEngine** — orchestrates both, returns `CouponOCR` record
+
+Native library load or decode failures fall back to the managed decoder. The Linux native binaries require glibc 2.38 and libstdc++ with GLIBCXX_3.4.31; the Noble runtime image provides both.
+
+## OCR Result
+
+`CouponOCR` contains optional fields: `value`, `min_check`, `expires_at`, `barcode_text`. Any combination may be present. The result is **always a pre-fill suggestion** — the user confirms final values in the wizard.
+
+## Caching (for tests)
+
+`tests/CouponHubBot.Ocr.Tests/AzureCache/` stores Azure OCR responses as `*.azure.json` files. These are git-tracked so tests can run without Azure API keys (cache-only mode).
+
+## Configuration
+
+Env vars:
+- `OCR_ENABLED` — enable/disable OCR (default: false)
+- `OCR_MAX_FILE_SIZE_BYTES` — max photo size for OCR processing
+- `AZURE_OCR_ENDPOINT` — Azure Computer Vision endpoint URL
+- `AZURE_OCR_KEY` — Azure API key

tests/BotInfra.Tests/EventStoreSnapshotTests.fs

@@ -59,16 +59,16 @@ let private hasEvent (name: string) (a: Activity) = a.Events |> Seq.exists (fun
 
 /// A fold that parks its first call until released — holds a load between its query and its cache put.
 let private parkedFold () =
-    let entered = new SemaphoreSlim(0)
+    let entered = TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously)
     let release = new SemaphoreSlim(0)
     let mutable first = true
     let f s e =
         if first then
             first <- false
-            %entered.Release()
-            release.Wait()
+            entered.SetResult()
+            Assert.True(release.Wait(TimeSpan.FromSeconds 30.0), "The concurrent operation did not release the parked fold")
         fold s e
-    f, entered, release
+    f, entered.Task, release
 
 type SnapshotRow = { schema_version: int; stream_version: int; state: string }
 
@@ -448,10 +448,13 @@ type EventStoreSnapshotTests(db: PostgresFixture) =
         do! appendRaw sid (added 2)
         use _scope = store.BeginRequestScope()
         let parked, entered, release = parkedFold ()
-        let slowLoad = store.LoadState(parked, Tally.Zero, policy 100, sid)
-        do! entered.WaitAsync()
-        let! _ = increment (policy 100) sid 10
-        %release.Release()
+        let slowLoad = Task.Run<Tally * int>(fun () -> store.LoadState(parked, Tally.Zero, policy 100, sid))
+        try
+            do! entered.WaitAsync(TimeSpan.FromSeconds 30.0)
+            let! _ = increment (policy 100) sid 10
+            ()
+        finally
+            %release.Release()
         let! (_, slowVersion) = slowLoad
         Assert.Equal(2, slowVersion)
         let! (state, version) = load (policy 100) sid
@@ -465,10 +468,13 @@ type EventStoreSnapshotTests(db: PostgresFixture) =
         do! appendRaw sid (added 2)
         use _scope = store.BeginRequestScope()
         let parked, entered, release = parkedFold ()
-        let slowLoad = store.LoadState(parked, Tally.Zero, policy 100, sid)
-        do! entered.WaitAsync()
-        let! _ = store.Transact(fold, Tally.Zero, (fun _ -> [ Added {| amount = 10 |} ]), sid)
-        %release.Release()
+        let slowLoad = Task.Run<Tally * int>(fun () -> store.LoadState(parked, Tally.Zero, policy 100, sid))
+        try
+            do! entered.WaitAsync(TimeSpan.FromSeconds 30.0)
+            let! _ = store.Transact(fold, Tally.Zero, (fun _ -> [ Added {| amount = 10 |} ]), sid)
+            ()
+        finally
+            %release.Release()
         let! _ = slowLoad
         let! (state, version) = load (policy 100) sid
         let! (_, rawVersion) = store.GetRawEventsForStream sid
@@ -504,11 +510,14 @@ type EventStoreSnapshotTests(db: PostgresFixture) =
         let otherPod = EventStore(db.ConnectionString, "event", jsonOpts, "event_snapshot")
         use spans = new LoadSpans()
         let parked, entered, release = parkedFold ()
-        let slowLoad = store.LoadState(parked, Tally.Zero, policy 1, sid)
-        do! entered.WaitAsync()
-        do! appendRaw sid (added 3)
-        let! _ = otherPod.LoadState(fold, Tally.Zero, policy 1, sid)
-        %release.Release()
+        let slowLoad = Task.Run<Tally * int>(fun () -> store.LoadState(parked, Tally.Zero, policy 1, sid))
+        try
+            do! entered.WaitAsync(TimeSpan.FromSeconds 30.0)
+            do! appendRaw sid (added 3)
+            let! _ = otherPod.LoadState(fold, Tally.Zero, policy 1, sid)
+            ()
+        finally
+            %release.Release()
         let! (_, slowVersion) = slowLoad
         Assert.Equal(2, slowVersion)
 

tests/CouponHubBot.Ocr.Tests/OcrTests.fs

@@ -8,10 +8,14 @@ open System.Net.Http
 open System.Text
 open Microsoft.Extensions.Logging
 open Microsoft.Extensions.Options
+open SixLabors.ImageSharp
+open SixLabors.ImageSharp.PixelFormats
+open SixLabors.ImageSharp.Processing
 open Xunit
 
 open CouponHubBot
 open CouponHubBot.Services
+open CouponHubBot.Utils
 open BotInfra
 
 module private XUnitLogging =
@@ -179,6 +183,12 @@ module private Parsing =
 
 type OcrTests(output: ITestOutputHelper) =
 
+    let buildCpuOnlyEngine () =
+        let azure =
+            { new IBotOcr with
+                member _.AnalyzeImageBytes _ = task { return null } }
+        CouponOcrEngine(azure, Microsoft.Extensions.Logging.Abstractions.NullLogger<CouponOcrEngine>.Instance, TimeProvider.System)
+
     let buildEngine (imageFileName: string) =
         let logs = ResizeArray<string>()
         let endpoint = Environment.GetEnvironmentVariable("AZURE_OCR_ENDPOINT")
@@ -213,6 +223,34 @@ type OcrTests(output: ITestOutputHelper) =
             CouponOcrEngine(azure, XUnitLogging.XUnitLogger<CouponOcrEngine>(output, logs), timeProvider)
         engine, http, logs
 
+    [<Theory>]
+    [<InlineData(0)>]
+    [<InlineData(90)>]
+    [<InlineData(180)>]
+    [<InlineData(270)>]
+    member _.``Coupon barcode is recognized without OCR at any right angle``(angle: int) =
+        task {
+            let path = Path.Combine(AppContext.BaseDirectory, "Images", "10_50_01-04_01-13_2706602781191.jpg")
+            use image = Image.Load<Rgba32>(path)
+            image.Mutate(fun ctx -> %ctx.Rotate(float32 angle))
+            use stream = new MemoryStream()
+            image.SaveAsPng(stream)
+            let! result = (buildCpuOnlyEngine ()).Recognize(ReadOnlyMemory<byte>(stream.ToArray()))
+            Assert.Equal("2706602781191", result.barcode)
+        }
+
+    [<Theory>]
+    [<InlineData(1, 1)>]
+    [<InlineData(120, 80)>]
+    member _.``Blank image does not invent a barcode``(width: int, height: int) =
+        task {
+            use image = new Image<L8>(width, height, L8(255uy))
+            use stream = new MemoryStream()
+            image.SaveAsPng(stream)
+            let! result = (buildCpuOnlyEngine ()).Recognize(ReadOnlyMemory<byte>(stream.ToArray()))
+            Assert.Null(result.barcode)
+        }
+
     [<Theory>]
     [<InlineData("10_50_01-04_01-13_2706602781191.jpg")>]
     [<InlineData("10_50_01-06_01-15_2706643333717.jpg")>]