feat: allow profile deletion

Introduce deleteProfile() for removing a single user profile.
Deletion removes both the registry entry (SharedPreferences) and
the on-disk data directory. The only guard is: the currently active
profile cannot be deleted, all other profiles including default
are deletable.

Author: criticalAY

AnkiDroid/src/main/java/com/ichi2/anki/multiprofile/ProfileManager.kt

@@ -26,15 +26,14 @@ import android.webkit.WebView
 import androidx.annotation.VisibleForTesting
 import androidx.core.content.ContextCompat
 import androidx.core.content.edit
+import com.ichi2.anki.CollectionHelper.PREF_COLLECTION_PATH
 import com.ichi2.anki.IntentHandler
 import com.ichi2.anki.common.crashreporting.CrashReportService
 import com.ichi2.anki.common.time.TimeManager
 import com.ichi2.anki.common.time.getTimestamp
-import org.acra.ACRA
 import org.json.JSONObject
 import timber.log.Timber
 import java.io.File
-import java.util.UUID
 
 /**
  * Manages the creation, loading, and switching of user profiles.
@@ -266,6 +265,191 @@ class ProfileManager private constructor(
         Timber.d("Renamed profile $profileId to '$newDisplayName'")
     }
 
+    /**
+     * Permanently deletes a profile, removing its registry entry and associated data
+     * across both internal and external storage.
+     *
+     * - Internal storage: app-private. We own these directories, so bulk deletion is safe.
+     *   For non-default profiles: the profile's data directory and every
+     *   `profile_<id>_*.xml` SharedPreferences file. For the default profile:
+     *   the legacy root folders (`files`, `cache`, `databases`, ...).
+     * - Collection directory: user-visible under `Android/data/.../files/` and
+     *   relocatable by the user to any path via [PREF_COLLECTION_PATH] (e.g. `/Pictures/`).
+     *   We therefore resolve the stored path, and only delete known AnkiDroid artifacts
+     *   inside it - never `deleteRecursively()`.
+     */
+    fun deleteProfile(profileId: ProfileId) {
+        /*
+         * File-system data is removed before the registry entry. If deletion fails
+         * or is interrupted, the registry entry remains so the user can retry.
+         */
+        require(profileRegistry.getLastActiveProfileId() != profileId) {
+            "Cannot delete the currently active profile ($profileId). Switch first."
+        }
+
+        val appDataRoot = ContextCompat.getDataDir(appContext)
+
+        if (profileId.isDefault()) {
+            deleteDefaultProfileDataOnly(appDataRoot)
+        } else {
+            val profileDir = resolveProfileDirectory(profileId).file
+            if (profileDir.exists()) {
+                profileDir.deleteRecursively()
+            }
+            deleteNamespacedSharedPreferences(appDataRoot, profileId)
+        }
+
+        resolveStoredCollectionDir(profileId)?.let { deleteCollectionArtifactsSafely(it) }
+
+        profileRegistry.removeProfile(profileId)
+        Timber.i("Deleted profile: $profileId")
+    }
+
+    /**
+     * Deletes every `profile_<id>_*.xml` file inside the app's `shared_prefs` directory.
+     * No-op if [appDataRoot] is null or the `shared_prefs` dir doesn't exist.
+     */
+    private fun deleteNamespacedSharedPreferences(
+        appDataRoot: File?,
+        profileId: ProfileId,
+    ) {
+        if (appDataRoot == null) return
+        val sharedPrefsDir = File(appDataRoot, "shared_prefs")
+        if (!sharedPrefsDir.exists() || !sharedPrefsDir.isDirectory) return
+
+        val prefix = "profile_${profileId.value}_"
+        sharedPrefsDir
+            .listFiles()
+            ?.filter { it.name.startsWith(prefix) }
+            ?.forEach { it.delete() }
+    }
+
+    /**
+     * Returns the collection directory for [profileId], see any user relocation via
+     * [PREF_COLLECTION_PATH]. Falls back to the default location if the preference is unset.
+     * Returns null if no candidate directory can be resolved.
+     *
+     * Default profile: `<external>/AnkiDroid/` (the historical layout).
+     * Non-default profile: `<external>/<profileId>/`
+     */
+    private fun resolveStoredCollectionDir(profileId: ProfileId): File? {
+        val candidate: File =
+            readStoredCollectionPath(profileId)?.let(::File)
+                ?: defaultCollectionDirFor(profileId)
+                ?: return null
+
+        return candidate.takeIf { it.exists() && it.isDirectory }
+    }
+
+    /** The default-location fallback used when the profile has never written `PREF_COLLECTION_PATH`. */
+    private fun defaultCollectionDirFor(profileId: ProfileId): File? {
+        val externalFilesDir = appContext.getExternalFilesDir(null) ?: return null
+        return if (profileId.isDefault()) {
+            File(externalFilesDir, "AnkiDroid")
+        } else {
+            File(externalFilesDir, profileId.value)
+        }
+    }
+
+    /**
+     * Reads [PREF_COLLECTION_PATH] from the profile's namespaced default SharedPreferences
+     * by filename, so we don't need to instantiate a [ProfileContextWrapper] (which has
+     * mkdir side effects we don't want in the delete flow).
+     *
+     * The filename format must stay in sync with [ProfileContextWrapper.getSharedPreferences].
+     */
+    private fun readStoredCollectionPath(profileId: ProfileId): String? {
+        val defaultPrefsName = "${appContext.packageName}_preferences"
+        val prefsName =
+            if (profileId.isDefault()) defaultPrefsName else "profile_${profileId.value}_$defaultPrefsName"
+        return appContext
+            .getSharedPreferences(prefsName, Context.MODE_PRIVATE)
+            .getString(PREF_COLLECTION_PATH, null)
+    }
+
+    /**
+     * Deletes only known AnkiDroid collection artifacts inside [collectionDir].
+     *
+     * AnkiDroid lets the user point the collection path at any directory — including ones
+     * they also use for unrelated data, e.g. `/Pictures/`. We therefore never
+     * `deleteRecursively()` this directory. Files and subdirectories we don't recognize are
+     * left untouched.
+     *
+     * If [collectionDir] is empty after the sweep, it is also removed. If anything remains,
+     * we send a silent crash report
+     */
+    private fun deleteCollectionArtifactsSafely(collectionDir: File) {
+        if (!collectionDir.exists() || !collectionDir.isDirectory) return
+
+        collectionDir.listFiles()?.forEach { entry ->
+            when {
+                entry.isFile && entry.name in COLLECTION_ARTIFACT_FILES -> entry.delete()
+                entry.isDirectory && entry.name in COLLECTION_ARTIFACT_DIRS -> entry.deleteRecursively()
+                else -> {
+                    val entryType = if (entry.isDirectory) "Directory" else "File"
+                    Timber.w("deleteProfile: leaving unknown entry untouched: <$entryType>")
+                }
+            }
+        }
+
+        val remaining = collectionDir.listFiles()
+        if (remaining.isNullOrEmpty()) {
+            collectionDir.delete()
+            return
+        }
+
+        val fileCount = remaining.count { it.isFile }
+        val dirCount = remaining.count { it.isDirectory }
+
+        val message =
+            "deleteCollectionArtifactsSafely left ${remaining.size} unknown entries in collection dir (Files: $fileCount, Dirs: $dirCount)"
+
+        val silent = IllegalStateException(message)
+        CrashReportService.sendExceptionReport(
+            silent,
+            "ProfileManager::deleteCollectionArtifactsSafely",
+        )
+        Timber.w(silent, message)
+    }
+
+    /**
+     * Wipes the Default profile's legacy data from the root directories
+     * while protecting the subdirectories belonging to other profiles.
+     */
+    private fun deleteDefaultProfileDataOnly(appDataRoot: File?) {
+        if (appDataRoot == null) return
+
+        val defaultFolders =
+            listOf(
+                "app_webview",
+                "databases",
+                "files",
+                "cache",
+                "code_cache",
+                "no_backup",
+            )
+
+        defaultFolders.forEach { folderName ->
+            val folder = File(appDataRoot, folderName)
+            if (folder.exists()) {
+                folder.deleteRecursively()
+            }
+        }
+
+        val sharedPrefsDir = File(appDataRoot, "shared_prefs")
+        if (sharedPrefsDir.exists() && sharedPrefsDir.isDirectory) {
+            sharedPrefsDir.listFiles()?.forEach { file ->
+                val fileName = file.name
+                val isRegistry = fileName == "$PROFILE_REGISTRY_FILENAME.xml"
+                val isOtherProfile = fileName.startsWith("profile_")
+
+                if (!isRegistry && !isOtherProfile) {
+                    file.delete()
+                }
+            }
+        }
+    }
+
     /**
      * Holds the meta-data for a profile.
      * Converted to JSON for storage to allow future extensibility (e.g. avatars, themes).
@@ -364,6 +548,18 @@ class ProfileManager private constructor(
             return result
         }
 
+        /**
+         * Removes a profile entry from the registry.
+         *
+         * Does **not** delete the profile's data directory on disk.
+         * Callers are responsible for cleaning up file-system resources.
+         *
+         * @param id The [ProfileId] of the profile to remove.
+         */
+        fun removeProfile(id: ProfileId) {
+            globalPrefs.edit { remove(id.value) }
+        }
+
         fun contains(id: ProfileId): Boolean = globalPrefs.contains(id.value)
     }
 
@@ -385,6 +581,29 @@ class ProfileManager private constructor(
 
         const val DEFAULT_PROFILE_DISPLAY_NAME = "Default"
 
+        /** Files AnkiDroid creates directly inside the collection directory. */
+        private val COLLECTION_ARTIFACT_FILES =
+            setOf(
+                "collection.anki2",
+                "collection.anki2-journal",
+                "collection.anki2-wal",
+                "collection.anki2-shm",
+                "collection.media.db",
+                "collection.media.db-journal",
+                "collection.media.db-wal",
+                "collection.media.db-shm",
+                ".nomedia",
+            )
+
+        /** Subdirectories AnkiDroid creates inside the collection directory. */
+        private val COLLECTION_ARTIFACT_DIRS =
+            setOf(
+                "collection.media",
+                "media.trash",
+                "backup",
+                "broken",
+            )
+
         /**
          * Factory method to safely create and initialize the ProfileManager.
          * Guaranteed to return a ProfileManager with a valid [activeProfileContext].