New: Provide checksum warning to user.

If the user enters an invalid seed phrase, let them know immediately, per #120.

app/src/main/java/cash/z/ecc/android/ext/Dialogs.kt

@@ -46,6 +46,18 @@ fun Context.showUninitializedError(error: Throwable? = null, onDismiss: () -> Un
         .show()
 }
 
+fun Context.showInvalidSeedPhraseError(error: Throwable? = null, onDismiss: () -> Unit = {}): Dialog {
+    return MaterialAlertDialogBuilder(this)
+        .setTitle("Oops! Invalid Seed Phrase")
+        .setMessage("That seed phrase appears to be invalid! Please double-check it and try again.\n\n${error?.message ?: ""}")
+        .setCancelable(false)
+        .setPositiveButton("Retry") { dialog, _ ->
+            dialog.dismiss()
+            onDismiss()
+        }
+        .show()
+}
+
 fun Context.showScanFailure(error: Throwable?, onCancel: () -> Unit = {}, onDismiss: () -> Unit = {}): Dialog {
     val message = if (error == null) {
         "Unknown error"

app/src/main/java/cash/z/ecc/android/ui/setup/RestoreFragment.kt

@@ -17,6 +17,7 @@ import cash.z.ecc.android.R
 import cash.z.ecc.android.databinding.FragmentRestoreBinding
 import cash.z.ecc.android.di.viewmodel.activityViewModel
 import cash.z.ecc.android.ext.goneIf
+import cash.z.ecc.android.ext.showInvalidSeedPhraseError
 import cash.z.ecc.android.feedback.Report
 import cash.z.ecc.android.feedback.Report.Funnel.Restore
 import cash.z.ecc.android.feedback.Report.Tap.*
@@ -118,7 +119,12 @@ class RestoreFragment : BaseFragment<FragmentRestoreBinding>(), View.OnKeyListen
                 if (birthdateString.isNullOrEmpty()) ZcashSdk.SAPLING_ACTIVATION_HEIGHT else birthdateString.toInt()
             }.coerceAtLeast(ZcashSdk.SAPLING_ACTIVATION_HEIGHT)
 
-        importWallet(seedPhrase, birthday)
+        try {
+            walletSetup.validatePhrase(seedPhrase)
+            importWallet(seedPhrase, birthday)
+        } catch (t: Throwable) {
+            mainActivity?.showInvalidSeedPhraseError(t)
+        }
     }
 
     private fun importWallet(seedPhrase: String, birthday: Int) {

app/src/main/java/cash/z/ecc/android/ui/setup/WalletSetupViewModel.kt

@@ -142,6 +142,13 @@ class WalletSetupViewModel @Inject constructor() : ViewModel() {
        }
    }
 
+    /**
+     * Throw an exception if the seed phrase is bad.
+     */
+    fun validatePhrase(seedPhrase: String) {
+        mnemonics.validate(seedPhrase.toCharArray())
+    }
+
     object LockBoxKey {
         const val SEED = "cash.z.ecc.android.SEED"
         const val SEED_PHRASE = "cash.z.ecc.android.SEED_PHRASE"

mnemonic/src/main/java/cash/z/ecc/kotlin/mnemonic/Mnemonics.kt

@@ -19,4 +19,8 @@ class Mnemonics @Inject constructor() : MnemonicPlugin {
     override fun nextMnemonicList(entropy: ByteArray): List<CharArray> = MnemonicCode(entropy).words
     override fun toSeed(mnemonic: CharArray): ByteArray = MnemonicCode(mnemonic).toSeed()
     override fun toWordList(mnemonic: CharArray): List<CharArray> = MnemonicCode(mnemonic).words
+
+    fun validate(mnemonic: CharArray) {
+        MnemonicCode(mnemonic).validate()
+    }
 }