@jakmro/classification android (#55)

## Description
Image classification for android

### Type of change
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] Documentation update (improves or adds clarity to existing
documentation)

### Tested on
- [ ] iOS
- [x] Android

### Checklist
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have updated the documentation accordingly
- [x] My changes generate no new warnings

Author: jakmro

android/src/main/java/com/swmansion/rnexecutorch/Classification.kt

@@ -0,0 +1,59 @@
+package com.swmansion.rnexecutorch
+
+import android.util.Log
+import com.facebook.react.bridge.Promise
+import com.facebook.react.bridge.ReactApplicationContext
+import com.swmansion.rnexecutorch.models.classification.ClassificationModel
+import com.swmansion.rnexecutorch.utils.ETError
+import com.swmansion.rnexecutorch.utils.ImageProcessor
+import org.opencv.android.OpenCVLoader
+import com.facebook.react.bridge.Arguments
+import com.facebook.react.bridge.WritableMap
+
+class Classification(reactContext: ReactApplicationContext) :
+  NativeClassificationSpec(reactContext) {
+
+  private lateinit var classificationModel: ClassificationModel
+
+  companion object {
+    const val NAME = "Classification"
+    init {
+      if(!OpenCVLoader.initLocal()){
+        Log.d("rn_executorch", "OpenCV not loaded")
+      } else {
+        Log.d("rn_executorch", "OpenCV loaded")
+      }
+    }
+  }
+
+  override fun loadModule(modelSource: String, promise: Promise) {
+    try {
+      classificationModel = ClassificationModel(reactApplicationContext)
+      classificationModel.loadModel(modelSource)
+      promise.resolve(0)
+    } catch (e: Exception) {
+      promise.reject(e.message!!, ETError.InvalidModelPath.toString())
+    }
+  }
+
+  override fun forward(input: String, promise: Promise) {
+    try {
+      val image = ImageProcessor.readImage(input)
+      val output = classificationModel.runModel(image)
+
+      val writableMap: WritableMap = Arguments.createMap()
+      
+      for ((key, value) in output) {
+        writableMap.putDouble(key, value.toDouble())
+      }
+
+      promise.resolve(writableMap)
+    }catch(e: Exception){
+      promise.reject(e.message!!, e.message)
+    }
+  }
+
+  override fun getName(): String {
+    return NAME
+  }
+}

android/src/main/java/com/swmansion/rnexecutorch/RnExecutorchPackage.kt

@@ -19,7 +19,10 @@ class RnExecutorchPackage : TurboReactPackage() {
       ETModule(reactContext)
     } else if (name == StyleTransfer.NAME) {
       StyleTransfer(reactContext)
-    } else {
+    } else if (name == Classification.NAME) {
+      Classification(reactContext)
+    } 
+    else {
       null
     }
 
@@ -51,6 +54,15 @@ class RnExecutorchPackage : TurboReactPackage() {
         false,  // isCxxModule
         true
       )
+
+      moduleInfos[Classification.NAME] = ReactModuleInfo(
+        Classification.NAME,
+        Classification.NAME,
+        false,  // canOverrideExistingModule
+        false,  // needsEagerInit
+        false,  // isCxxModule
+        true
+      )
       moduleInfos
     }
   }

android/src/main/java/com/swmansion/rnexecutorch/models/BaseModel.kt

@@ -38,7 +38,7 @@ abstract class BaseModel<Input, Output>(val context: Context) {
 
   abstract fun runModel(input: Input): Output
 
-  protected abstract fun preprocess(input: Input): Input
+  protected abstract fun preprocess(input: Input): EValue
 
-  protected abstract fun postprocess(input: Tensor): Output
+  protected abstract fun postprocess(output: Array<EValue>): Output
 }

android/src/main/java/com/swmansion/rnexecutorch/models/StyleTransferModel.kt

@@ -6,6 +6,7 @@ import org.opencv.core.Mat
 import org.opencv.core.Size
 import org.opencv.imgproc.Imgproc
 import org.pytorch.executorch.Tensor
+import org.pytorch.executorch.EValue
 
 
 class StyleTransferModel(reactApplicationContext: ReactApplicationContext) : BaseModel<Mat, Mat>(reactApplicationContext) {
@@ -19,22 +20,23 @@ class StyleTransferModel(reactApplicationContext: ReactApplicationContext) : Bas
     return Size(height.toDouble(), width.toDouble())
   }
 
-  override fun preprocess(input: Mat): Mat {
+  override fun preprocess(input: Mat): EValue {
     originalSize = input.size()
     Imgproc.resize(input, input, getModelImageSize())
-    return input
+    return ImageProcessor.matToEValue(input, module.getInputShape(0))
   }
 
-  override fun postprocess(input: Tensor): Mat {
+  override fun postprocess(output: Array<EValue>): Mat {
+    val tensor = output[0].toTensor()
     val modelShape = getModelImageSize()
-    val result = ImageProcessor.EValueToMat(input.dataAsFloatArray, modelShape.width.toInt(), modelShape.height.toInt())
+    val result = ImageProcessor.EValueToMat(tensor.dataAsFloatArray, modelShape.width.toInt(), modelShape.height.toInt())
     Imgproc.resize(result, result, originalSize)
     return result
   }
 
   override fun runModel(input: Mat): Mat {
-      val inputTensor = ImageProcessor.matToEValue(preprocess(input), module.getInputShape(0))
-      val outputTensor = forward(inputTensor)
-      return postprocess(outputTensor[0].toTensor())
+      val modelInput = preprocess(input)
+      val modelOutput = forward(modelInput)
+      return postprocess(modelOutput)
   }
 }

android/src/main/java/com/swmansion/rnexecutorch/models/classification/ClassificationModel.kt

@@ -0,0 +1,45 @@
+package com.swmansion.rnexecutorch.models.classification
+
+import com.facebook.react.bridge.ReactApplicationContext
+import com.swmansion.rnexecutorch.utils.ImageProcessor
+import org.opencv.core.Mat
+import org.opencv.core.Size
+import org.opencv.imgproc.Imgproc
+import org.pytorch.executorch.Tensor
+import org.pytorch.executorch.EValue
+import com.swmansion.rnexecutorch.models.BaseModel
+
+
+class ClassificationModel(reactApplicationContext: ReactApplicationContext) : BaseModel<Mat, Map<String, Float>>(reactApplicationContext) {
+  private fun getModelImageSize(): Size {
+    val inputShape = module.getInputShape(0)
+    val width = inputShape[inputShape.lastIndex]
+    val height = inputShape[inputShape.lastIndex - 1]
+
+    return Size(height.toDouble(), width.toDouble())
+  }
+
+  override fun preprocess(input: Mat): EValue {
+    Imgproc.resize(input, input, getModelImageSize())
+    return ImageProcessor.matToEValue(input, module.getInputShape(0))
+  }
+
+  override fun postprocess(output: Array<EValue>): Map<String, Float> {
+    val tensor = output[0].toTensor()
+    val probabilities = softmax(tensor.dataAsFloatArray.toTypedArray())
+
+    val result = mutableMapOf<String, Float>()
+
+    for (i in probabilities.indices) {
+      result[imagenet1k_v1_labels[i]] = probabilities[i]
+    }
+
+    return result
+  }
+
+  override fun runModel(input: Mat): Map<String, Float> {
+      val modelInput = preprocess(input)
+      val modelOutput = forward(modelInput)
+      return postprocess(modelOutput)
+  }
+}