Implement CodedError system with NATA-XXXX error codes

Add platform-specific error codes (NATA prefix) for user-facing error
messages. Error types in common/errors/ package.

- Add CodedError interface, AppError, NfcError, SubscriptionError
- Make ApiException implement CodedError (NATA-2001, NATA-2002)
- Move error types to common/errors/ package
- Add Throwable.codedDescription extension
- Update all ViewModels to use codedDescription
- Add unit tests for all error types

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dadachi

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/MainActivityViewModel.kt

@@ -5,6 +5,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.nativeapptemplate.nativeapptemplatefree.MainActivityUiState.Loading
 import com.nativeapptemplate.nativeapptemplatefree.MainActivityUiState.Success
+import com.nativeapptemplate.nativeapptemplatefree.common.errors.codedDescription
 import com.nativeapptemplate.nativeapptemplatefree.data.login.LoginRepository
 import com.nativeapptemplate.nativeapptemplatefree.model.CompleteScanResult
 import com.nativeapptemplate.nativeapptemplatefree.model.CompleteScanResultType
@@ -125,8 +126,8 @@ class MainActivityViewModel @Inject constructor(
       try {
         loginRepository.setCompleteScanResult(completeScanResult)
       } catch (exception: Exception) {
-        val message = exception.message
-        completeScanResult.message = message ?: "Unknown Error"
+        val message = exception.codedDescription
+        completeScanResult.message = message
         completeScanResult.completeScanResultType = CompleteScanResultType.Failed
 
         loginRepository.setCompleteScanResult(completeScanResult)

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/common/errors/ApiException.kt

@@ -0,0 +1,21 @@
+package com.nativeapptemplate.nativeapptemplatefree.common.errors
+
+sealed class ApiException(message: String, cause: Throwable? = null) :
+  Exception(message, cause), CodedError {
+
+  class ApiError(
+    val code: Int,
+    val apiMessage: String,
+  ) : ApiException("$apiMessage [Status: $code]") {
+    override val errorCode: String = "NATA-2001"
+    override val errorDescription: String = "$apiMessage [Status: $code]"
+  }
+
+  class UnprocessableError(
+    val rawMessage: String,
+    cause: Throwable? = null,
+  ) : ApiException("Not processable error($rawMessage).", cause) {
+    override val errorCode: String = "NATA-2002"
+    override val errorDescription: String = "Processing error: $rawMessage"
+  }
+}

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/common/errors/AppError.kt

@@ -0,0 +1,12 @@
+package com.nativeapptemplate.nativeapptemplatefree.common.errors
+
+sealed class AppError(
+  override val errorCode: String,
+  override val errorDescription: String,
+) : Exception(errorDescription), CodedError {
+
+  class Unexpected(detail: String? = null) : AppError(
+    errorCode = "NATA-1001",
+    errorDescription = "Unexpected error" + if (detail != null) ": $detail" else "",
+  )
+}

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/common/errors/CodedError.kt

@@ -0,0 +1,11 @@
+package com.nativeapptemplate.nativeapptemplatefree.common.errors
+
+interface CodedError {
+  val errorCode: String
+  val errorDescription: String
+  val formattedDescription: String
+    get() = "[$errorCode] $errorDescription"
+}
+
+val Throwable.codedDescription: String
+  get() = (this as? CodedError)?.formattedDescription ?: message ?: "Unknown Error"

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/common/errors/NfcError.kt

@@ -0,0 +1,12 @@
+package com.nativeapptemplate.nativeapptemplatefree.common.errors
+
+sealed class NfcError(
+  override val errorCode: String,
+  override val errorDescription: String,
+) : Exception(errorDescription), CodedError {
+
+  class ScanFailed(detail: String? = null) : NfcError(
+    errorCode = "NATA-3001",
+    errorDescription = "NFC scan operation failed" + if (detail != null) ": $detail" else "",
+  )
+}

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/common/errors/SubscriptionError.kt

@@ -0,0 +1,17 @@
+package com.nativeapptemplate.nativeapptemplatefree.common.errors
+
+sealed class SubscriptionError(
+  override val errorCode: String,
+  override val errorDescription: String,
+) : Exception(errorDescription), CodedError {
+
+  class RestoreFailed(detail: String? = null) : SubscriptionError(
+    errorCode = "NATA-6001",
+    errorDescription = "Failed to restore purchases" + if (detail != null) ": $detail" else "",
+  )
+
+  class SubscriptionRequired : SubscriptionError(
+    errorCode = "NATA-6002",
+    errorDescription = "User needs an active subscription",
+  )
+}

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/data/login/LoginRepositoryImpl.kt

@@ -1,11 +1,11 @@
 package com.nativeapptemplate.nativeapptemplatefree.data.login
 
 import androidx.annotation.VisibleForTesting
+import com.nativeapptemplate.nativeapptemplatefree.common.errors.ApiException
 import com.nativeapptemplate.nativeapptemplatefree.datastore.NatPreferencesDataSource
 import com.nativeapptemplate.nativeapptemplatefree.model.*
 import com.nativeapptemplate.nativeapptemplatefree.model.LoggedInShopkeeper
 import com.nativeapptemplate.nativeapptemplatefree.model.Login
-import com.nativeapptemplate.nativeapptemplatefree.network.ApiException
 import com.nativeapptemplate.nativeapptemplatefree.network.Dispatcher
 import com.nativeapptemplate.nativeapptemplatefree.network.NatDispatchers
 import com.nativeapptemplate.nativeapptemplatefree.network.emitApiResponse

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/network/ApiException.kt

@@ -1,5 +1,6 @@
 package com.nativeapptemplate.nativeapptemplatefree.network
 
+import com.nativeapptemplate.nativeapptemplatefree.common.errors.ApiException
 import com.nativeapptemplate.nativeapptemplatefree.model.NativeAppTemplateApiError
 import com.skydoves.sandwich.ApiResponse
 import com.skydoves.sandwich.message

app/src/main/kotlin/com/nativeapptemplate/nativeapptemplatefree/network/ApiResponseExtensions.kt

@@ -2,6 +2,7 @@ package com.nativeapptemplate.nativeapptemplatefree.ui.app_root
 
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
+import com.nativeapptemplate.nativeapptemplatefree.common.errors.codedDescription
 import com.nativeapptemplate.nativeapptemplatefree.data.login.LoginRepository
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.flow.MutableStateFlow
@@ -41,10 +42,10 @@ class AcceptPrivacyViewModel @Inject constructor(
 
       booleanFlow
         .catch { exception ->
-          val message = exception.message
+          val message = exception.codedDescription
           _uiState.update {
             it.copy(
-              message = message ?: "Unknown Error",
+              message = message,
               isLoading = false,
             )
           }