Use expo-file-system and expo-asset to fetch files (#97)

## Description
1. Use expo-file-system and expo-asset to fetch files.
2. Enable background model downloads.
3. Add downloadProgress functionality to useClassification,
useObjectDetection, useStyleTransfer, useExecutorchModule and its
corresponding hookless implementations ClassificationModule,
ObjectDetectionModule, StyleTransferModule, ExecutorchModule.
4. Add functionality allowing for listing downloaded files and models.

### Type of change
- [x] 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
- [x] iOS
- [x] Android

### Related issues
- #77 

### 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/ETModule.kt

@@ -6,9 +6,9 @@ import com.facebook.react.bridge.ReactApplicationContext
 import com.facebook.react.bridge.ReadableArray
 import com.swmansion.rnexecutorch.utils.ArrayUtils
 import com.swmansion.rnexecutorch.utils.ETError
-import com.swmansion.rnexecutorch.utils.Fetcher
 import com.swmansion.rnexecutorch.utils.TensorUtils
 import org.pytorch.executorch.Module
+import java.net.URL
 
 class ETModule(reactContext: ReactApplicationContext) : NativeETModuleSpec(reactContext) {
   private lateinit var module: Module
@@ -18,19 +18,8 @@ class ETModule(reactContext: ReactApplicationContext) : NativeETModuleSpec(react
   }
 
   override fun loadModule(modelSource: String, promise: Promise) {
-    Fetcher.downloadModel(
-      reactApplicationContext,
-      modelSource,
-    ) { path, error ->
-      if (error != null) {
-        promise.reject(error.message!!, ETError.InvalidModelSource.toString())
-        return@downloadModel
-      }
-
-      module = Module.load(path)
-      promise.resolve(0)
-      return@downloadModel
-    }
+    module = Module.load(URL(modelSource).path)
+    promise.resolve(0)
   }
 
   override fun loadMethod(methodName: String, promise: Promise) {

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

@@ -3,22 +3,19 @@ package com.swmansion.rnexecutorch
 import android.util.Log
 import com.facebook.react.bridge.Promise
 import com.facebook.react.bridge.ReactApplicationContext
-import com.swmansion.rnexecutorch.utils.Fetcher
-import com.swmansion.rnexecutorch.utils.ProgressResponseBody
-import com.swmansion.rnexecutorch.utils.ResourceType
 import com.swmansion.rnexecutorch.utils.llms.ChatRole
 import com.swmansion.rnexecutorch.utils.llms.ConversationManager
 import com.swmansion.rnexecutorch.utils.llms.END_OF_TEXT_TOKEN
 import org.pytorch.executorch.LlamaCallback
 import org.pytorch.executorch.LlamaModule
+import java.net.URL
 
 class LLM(reactContext: ReactApplicationContext) :
   NativeLLMSpec(reactContext), LlamaCallback {
 
   private var llamaModule: LlamaModule? = null
   private var tempLlamaResponse = StringBuilder()
   private lateinit var conversationManager: ConversationManager
-  private var isFetching = false
 
   override fun getName(): String {
     return NAME
@@ -37,84 +34,20 @@ class LLM(reactContext: ReactApplicationContext) :
     Log.d("rn_executorch", "TPS: $tps")
   }
 
-  private fun updateDownloadProgress(progress: Float) {
-    emitOnDownloadProgress((progress / 100).toDouble())
-  }
-
-  private fun downloadResource(
-    url: String,
-    resourceType: ResourceType,
-    isLargeFile: Boolean = false,
-    callback: (path: String?, error: Exception?) -> Unit,
-  ) {
-    Fetcher.downloadResource(
-      reactApplicationContext, url, resourceType, isLargeFile,
-      { path, error -> callback(path, error) },
-      object : ProgressResponseBody.ProgressListener {
-        override fun onProgress(bytesRead: Long, contentLength: Long, done: Boolean) {
-          val progress = (bytesRead * 100 / contentLength).toFloat()
-          updateDownloadProgress(progress)
-          if (done) {
-            isFetching = false
-          }
-        }
-      })
-  }
-
-  private fun initializeLlamaModule(modelPath: String, tokenizerPath: String, promise: Promise) {
-    llamaModule = LlamaModule(1, modelPath, tokenizerPath, 0.7f)
-    isFetching = false
-    this.tempLlamaResponse.clear()
-    promise.resolve("Model loaded successfully")
-  }
-
   override fun loadLLM(
     modelSource: String,
     tokenizerSource: String,
     systemPrompt: String,
     contextWindowLength: Double,
     promise: Promise
   ) {
-    if (isFetching) {
-      promise.reject("Model is fetching", "Model is fetching")
-      return
-    }
-
     try {
       this.conversationManager = ConversationManager(contextWindowLength.toInt(), systemPrompt)
-
-      isFetching = true
-
-      downloadResource(
-        tokenizerSource,
-        ResourceType.TOKENIZER
-      ) tokenizerDownload@{ tokenizerPath, error ->
-        if (error != null) {
-          promise.reject("Download Error", "Tokenizer download failed: ${error.message}")
-          isFetching = false
-          return@tokenizerDownload
-        }
-
-        downloadResource(
-          modelSource,
-          ResourceType.MODEL,
-          isLargeFile = true
-        ) modelDownload@{ modelPath, modelError ->
-          if (modelError != null) {
-            promise.reject(
-              "Download Error",
-              "Model download failed: ${modelError.message}"
-            )
-            isFetching = false
-            return@modelDownload
-          }
-
-          initializeLlamaModule(modelPath!!, tokenizerPath!!, promise)
-        }
-      }
+      llamaModule = LlamaModule(1, URL(modelSource).path, URL(tokenizerSource).path, 0.7f)
+      this.tempLlamaResponse.clear()
+      promise.resolve("Model loaded successfully")
     } catch (e: Exception) {
-      promise.reject("Download Error", e.message)
-      isFetching = false
+      promise.reject("Model loading failed", e.message)
     }
   }
 

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

@@ -2,26 +2,16 @@ package com.swmansion.rnexecutorch.models
 
 import android.content.Context
 import com.swmansion.rnexecutorch.utils.ETError
-import com.swmansion.rnexecutorch.utils.Fetcher
 import org.pytorch.executorch.EValue
 import org.pytorch.executorch.Module
-import org.pytorch.executorch.Tensor
+import java.net.URL
 
 
 abstract class BaseModel<Input, Output>(val context: Context) {
   protected lateinit var module: Module
 
   fun loadModel(modelSource: String) {
-    Fetcher.downloadModel(
-      context,
-      modelSource
-    ) { path, error ->
-      if (error != null) {
-        throw Error(error.message!!)
-      }
-
-      module = Module.load(path)
-    }
+    module = Module.load(URL(modelSource).path)
   }
 
   protected fun forward(input: EValue): Array<EValue> {