wip: add platform channels

mobile-v2/android/app/src/main/kotlin/com/alextran/immich/MainActivity.kt

@@ -1,5 +1,15 @@
 package com.alextran.immich
 
+import ImmichHostService
+import com.alextran.immich.platform.ImmichHostServiceImpl
 import io.flutter.embedding.android.FlutterActivity
+import io.flutter.embedding.engine.FlutterEngine
 
-class MainActivity: FlutterActivity()
+class MainActivity: FlutterActivity() {
+  override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
+    super.configureFlutterEngine(flutterEngine)
+
+    // Register piegon handler
+    ImmichHostService.setUp(flutterEngine.dartExecutor.binaryMessenger, ImmichHostServiceImpl())
+  }
+}

mobile-v2/android/app/src/main/kotlin/com/alextran/immich/platform/MessagesImpl.kt

@@ -0,0 +1,47 @@
+package com.alextran.immich.platform
+
+import ImmichHostService
+import android.util.Log
+import kotlinx.coroutines.DelicateCoroutinesApi
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.launch
+import java.io.FileInputStream
+import java.security.MessageDigest
+
+class ImmichHostServiceImpl: ImmichHostService {
+
+  @OptIn(DelicateCoroutinesApi::class)
+  override fun digestFiles(paths: List<String>, callback: (Result<List<ByteArray?>?>) -> Unit) {
+    GlobalScope.launch(Dispatchers.IO) {
+      val buf = ByteArray(Companion.BUFFER_SIZE)
+      val digest: MessageDigest = MessageDigest.getInstance("SHA-1")
+      val hashes = arrayOfNulls<ByteArray>(paths.size)
+      for (i in paths.indices) {
+        val path = paths[i]
+        var len = 0
+        try {
+          val file = FileInputStream(path)
+          file.use { assetFile ->
+            while (true) {
+              len = assetFile.read(buf)
+              if (len != Companion.BUFFER_SIZE) break
+              digest.update(buf)
+            }
+          }
+          digest.update(buf, 0, len)
+          hashes[i] = digest.digest()
+        } catch (e: Exception) {
+          // skip this file
+          Log.w(TAG, "Failed to hash file ${paths[i]}: $e")
+        }
+      }
+      callback(Result.success(hashes.asList()))
+    }
+  }
+
+  companion object {
+    private const val BUFFER_SIZE = 2 * 1024 * 1024;
+    private const val TAG = "ImmichHostServiceImpl"
+  }
+}