Phase 2: biometric app lock

app/src/main/java/io/github/abrarul/modularai/security/Lock.kt

@@ -0,0 +1,27 @@
+package io.github.abrarul.modularai.security
+
+import android.content.Context
+import androidx.biometric.BiometricManager
+import androidx.biometric.BiometricManager.Authenticators.BIOMETRIC_WEAK
+import androidx.biometric.BiometricPrompt
+import androidx.core.content.ContextCompat
+import androidx.fragment.app.FragmentActivity
+
+object Lock {
+    fun available(ctx: Context): Boolean =
+        BiometricManager.from(ctx).canAuthenticate(BIOMETRIC_WEAK) == BiometricManager.BIOMETRIC_SUCCESS
+
+    /** Calls [onOk] after a successful biometric check. Stays locked on cancel or failure. */
+    fun prompt(a: FragmentActivity, onOk: () -> Unit) {
+        if (!available(a)) return // caller only enables the lock when biometrics exist
+        val cb = object : BiometricPrompt.AuthenticationCallback() {
+            override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult) = onOk()
+        }
+        val info = BiometricPrompt.PromptInfo.Builder()
+            .setTitle("Unlock ModularAI")
+            .setNegativeButtonText("Cancel")
+            .setAllowedAuthenticators(BIOMETRIC_WEAK)
+            .build()
+        BiometricPrompt(a, ContextCompat.getMainExecutor(a), cb).authenticate(info)
+    }
+}